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Friday, December 31, 2010

Contents: January 1, 2011

In this issue of the Yard and Garden News:

What Is Biting Me?

Jeffrey Hahn, Asst. Extension Entomologist

bed bugs - Jeff Hahn.jpg

Photo 1: Bed bugs. Jeff Hahn.

A common call that has been received recently has been from people that have been experiencing bites of an unknown source. It is challenging to correctly diagnose these problems. It is important to know that unknown bites can be the result of insects as well as non-insect causes. If it is an insect infestation, the most common causes are bed bugs and fleas.

Bed bugs have been on the increase over the last 10 or so years. Adult bed bugs are about 1/4 inch long, brown, and similar in size and shape to wood ticks; newly hatched bed bug nymphs are about 1/16th inch long or about the size of a pinhead. Bed bugs like to hide during the day and generally prefer to bite at night so it's possible to be bitten and not realize it. When looking for bed bugs, first check out bed rooms and other places where people sleep or rest. Other good areas to look are places where luggage is stored.

Bed bugs like to hide in cracks and behind or under objects so examine closely around mattresses, boxsprings, bed frames, as well as dressers, desks, chairs, and other furniture, the edges along carpeting and behind clocks, pictures, and baseboards. Also be aware of signs of bed bugs in your home. In addition to bites, watch for cast skins (empty shells of insects) as well as dark (but not red) spots. These spots are fecal droppings, composed of digested blood. Look for these spots on sheets, bedding, or other places where bed bugs feed or around their hiding places.

You can also try to determine whether bed bugs are present by using a bed bug interceptor. They are small plastic trays with an inner and outer ring. Put them under each leg of your bed. Bed bugs that attempt to climb up from the floor to the bed become trapped in the outer well. Any bed bugs that try to climb down will become trapped in the inner well. You can purchase Bed bug Interceptors online (type "bed bug interceptor" into a search engine for sources).

Fleas have been an increasing problem in the last few years. They may be present in homesfleas.jpg

Photo 2: Fleas. Nancy Hinkle, Univ. of Georgia.

regardless of whether you have pets or not. An adult flea is small, about 1/8th inch long and dark colored. It's body is flattened from side to side and it has long back legs for jumping. Because of their size and shape, they can easily hide in cracks and crevices and not be seen.

To determine whether you have fleas infesting your home, try the white socks test. Walk slowly through a room where you suspect fleas wearing a pair of white socks. Fleas are attracted to the vibrations from the walking and the warmth of the person and will jump towards the ankle. Their dark colored bodies show up plainly against the white background of the socks. Particularly check areas where pets spend a lot of time (if they are present).

While bed bugs and fleas are the most common biting insects there are other possible causes. Head lice, mosquitoes, as well as insect relatives, such as bird mites, like northern fowl mites, chiggers, and rodent mites, such as tropical rat mites, can potentially be problems. During winter however, mosquitoes, bird mites and chiggers are not active and are not possible causes. Head lice are most common on children and are restricted to the head (it is possible to find body lice which are located on the body as well as clothing and bedding. However, they are rarely a problem). Rodent mites can be encountered, although this rare. In one case, a tropical rodent mite problem was infesting a pet guinea pig and was biting the people in the house. Dust mites do not bite people; they are problem because of the allergic reactions to them by individuals.

If you are not clear whether you have an insect or mite problem in your home, consider having an experienced pest control company inspect your home. You could also submit any suspicious insects to your local county extension office for identification. Under no circumstances should you use insecticides in your homes if you can not confirm a biting insect or mite problem.

However, if you do not find any evidence of biting insects or mites, it is very important to consider non-insect explanations. There are a variety of causes that can explain insect-like bites or irritations that are unrelated to insects or mites. Some of these possibilities can include dry air, allergic reactions to personal or household products (e.g., detergents, soaps, cosmetics, clothes, jewelry), environmental contaminants, microscopic fibers (e.g. insulation or paper fibers), certain health conditions (e.g. diabetes, neurological, liver, or kidney disorders), or even stress.

Copy of DSC_0052.JPG

Photo 3: Fibers and blood thought to be biting insects. Jeff Hahn.

There is also a condition known as delusory (or delusional) parasitosis, also called Ekbom's syndrome. This is a very real condition where sufferers have the mistaken belief that they are being invaded by parasites even when presented with evidence to the contrary. Typically, people suffering from delusory parasitosis have been battling this problems for months, sometimes even years. Commonly they have had pest control technicians search their homes for pests but without find anything that would be biting. They often have tried a variety of solutions, including pesticide applications, but if there is any relief it is short-lived. Some sufferers have even thrown out their furniture, even moved, to tried to escape this problem. Of course this action is not successful.

People that are experiencing unknown bites that can not confirm an insect or mite problem should see a family physician for help in diagnosing their problem. They should work with an entomologist to verify or rule out insects. For more information on unknown bites and delusory parasitosis see the following web pages, and

Does climate affect the taste of apples? - Minnesota vs. Washington grown Honeycrisp Apples

Thaddeus McCamant

In November, the stores were running low on Minnesota Honeycrisp and started replenishing the shelves with Honeycrisp shipped from Washington. For a while, my local grocery store had Minnesota and Washington Honeycrisp in the same bin. At the time, a friend complained to me about some apples he had recently bought. "I don't even think they are Honeycrisp," he told me, "the store must be selling red Delicious."

Even before he brought me an apple, I told him that they were Honeycrisp, but they were raised in a low elevation area of Washington.

I always get a little defensive when people use Delicious as the ultimate example of a bad tasting apple. Some of the best apples I have ever eaten were Washington Delicious. Twenty years, ago, I worked with about thirty apple orchards along the Washington-Oregon border. Some orchards were planted in the true desert near the Columbia River, while others were high in the foothills of nearby mountains. While testing the quality of the different apples, I quickly noticed that red Delicious and Golden Delicious grown in the desert were large and soft, while those grown in the mountains were smaller, crisper and had better overall flavor. When buying apples for myself or as gifts, I often bought Delicious grown near the mountains.

Certain varieties, like Granny Smith and Fuji, taste great when raised in areas with hot, dry summers. Other varieties taste better when grown in areas with cooler summers, like the foothills of the mountains. For cool season varieties like Delicious and Golden Delicious, elevation influences firmness, sugar content and the sugar acid balance. Granny Smith from the desert are firm and have a mouth-puckering supply of acid. The sugar/acid balance of cool season varieties can be adversely affected by climate.

Honeycrisp was developed in Minnesota and became very popular because it stays crisp long, has a high sugar content, and a moderate acid content. Honeycrisp has a little more acid than Delicious or Fuji, but less than Granny Smith. The sugar/acid balance of Honeycrisp is critical, because a Honeycrisp with no acid tastes just like a bland red Delicious.

My friend gave me one of his apples. It was a Honeycrisp, with the characteristic round shape and red/yellow color pattern, but the apple tasted as bad as Delicious apples that had been stored for a year and were being sold for $0.75 a pound. The apple was soft. I measured its sugar content at 11 % (11°Brix). The Honeycrisp I have measured in Minnesota usually have a sugar content greater than 15%. The acid content was low, making an apple with a dismal sugar content taste even blander.

Studying the influence of climate on apple quality was easy along the Washington-Oregon border, because nearly all the variability was due to elevation. High elevations have cooler nights. Where nights are cool, fruit is smaller and firmer. When we compare fruit quality of apples grown in Washington with those grown in Minnesota, there are a host of factors that could influence flavor: soil, daytime temperatures, humidity, sunlight intensity as well as nighttime temperatures.

With so many factors influencing the quality of apples, we cannot say for sure why Honeycrisp grown in Minnesota taste better than those grown in other climates. I can, however, go to a grocery store where Minnesota and Washington Honeycrisp are displayed together and pick out the Minnesota apples. The color pattern is slightly different on the Minnesota apples. When buying fruit for my family, I am very picky. I have no problem paying good money for good fruit, but I would not pay $0.75 a pound for the Honeycrisp my friend gave me.

Wine makers and wine consumers have known for centuries that wine tastes different depending on where the grapes were grown. Apple quality also appears to vary depending on where the apples were grown, and apples are grown over a much broader range of climates and soils than grapes. Apple consumers should also start becoming as particular about where their fruit was grown as the wine drinkers.

Thaddeus McCamant has been a Specialty Crops Management Instructor at Northland Community and Technical College in Thief River Falls Minnesota, and has fifteen years of experience in the fruit industry.

Hosta Virus X: New Information

Grace Anderson, MAg, UM Department of Plant Pathology
Hennepin County Master Gardener


Photo 1: Hosta 'Sum and Substance' infected with Hosta Virus X. Note the crinkled tissue between the leaf veins. Grace Anderson.

HVX is a plant virus in the Potexvirus group first identified in 1996 by Dr. Ben Lockhart: Plant Virologist, Department of Plant Pathology, University of Minnesota. It is thought to be host specific and is not transmitted by traditional insect fungi or nematode vectors, or via seed or pollen. It is transmitted mechanically through wounds created during propagation or transplanting, or any time sap to sap contact is made through dividing or trimming plants. Vegetative propagation of infected plants, whether by tissue culture or division, will produce infected plants. Once a plant has HVX, there is no cure and it must be destroyed.

HVX reduces plant vigor and destroys foliage appearance through leaf distortion, color bleeding, and necrosis. Symptoms vary among cultivars and may take years to surface, however the likely result is an unattractive and unacceptable foliage plant (Photos 1 - 3). See for additional pictures of these symptoms.

The disease appeared to be widespread and yet little was known about procedures to identify the virus, its methods of transfer, or the existence of resistant varieties. In order to address these issues The American Hosta Society under the leadership of Cynthia Wilhoite (VP Genus Hosta, Indianapolis, Indiana) initiated an effort to obtain research-based, empirical data on the nature and transmission of the virus. Funds were obtained and the research effort was led by Dr. Ben Lockhart.


Photo 2: Note the dark green discoloration on the leaf margin Grace Anderson.

Experiments were designed to replicate the actions taken by gardeners and growers in maintaining and propagating Hosta. The goals of the experiment were to answer the following questions. Results of the experiment follow each question.

Can HVX be transmitted during normal cultivation?

Virus transmission was accomplished through the use of contaminated tools and by planting in soil containing pieces of infected plant material.

If it can be transmitted in this way, how long is it infective on tools and soil?

Infected plant material kept in the refrigerator remained infective for more than nine weeks. Fresh infected plant material was always infective. Soil with HVX infected plant debris and root material was infective for more than two years.

What practical measure can be taken to eliminate the virus if it can be transmitted by my tools or via infected soil?

All three tested methods of decontamination including, household detergent (Dawn), 70% alcohol solution, and 10% household bleach solution were effective at eliminating infectivity of the virus. The decontamination process required intense scrubbing and cleaning of tools, hands, and pots to remove plant material, soil and sap. It is not enough to simply dip tools in cleaning solution. Tools must be scrubbed free of all dirt and debris.


Photo 3: Hosta 'Sum and Substance' - Note the lack of crinkling and the uniform color in a healthy leaf. Enter Caption Description Here Karl Foord.

Is HVX transmission dose dependent?
No difference in infectivity or speed of infectivity was related to dosage of the virus isolate. A significant difference in the rate of infectivity was dependent on the stage of plant growth. The virus was most easily transmitted prior to flowering and when the plant was rapidly growing the spring. We were not able to transmit the virus while the plants were flowering in late summer/fall or dormant.

Are all isolates of the virus transmissible?

Yes, we collected and mechanically transmitted 15 isolates of HVX. The success of transmission was not only dependent on mechanical injury but also on the season in which the contact occurred.

Are there resistant varieties of HVX?
This warrants further study. We were able to infect all Hosta tested under the proper conditions in the field, home garden or greenhouse. At this time, we believe all hosta are susceptible to the virus.


Photo 4: Author Grace Anderson working in the greenhouse.

What is the best way to test for the virus?

ELISA testing through Plant Disease Clinics and certified labs is the most reliable method of testing. The new rapid test strips are accurate, reliable, and portable. The strips can be used in the field or greenhouse and will work with leaf or root material.

Strips can be obtained from Agdia, Inc.

What is the best protection against HVX?

Know whether the original sources of plants you buy tests for HVX. Don't be afraid to ask your retail or wholesale source for this information.

For further information on this topic please visit the American Hosta Society.

Grace Anderson recently completed her 23rd year as a Master Gardener in Hennepin County. She is a scientist in the Soybean Pathology Project at UMN and recently received the Master of Agriculture degree in Horticulture at the University of Minnesota. Conducting this research was one of the requirements for receiving this degree.

What are your woody plants doing right now?

Karl Foord, UMN Extension Educator

Well, here we are in Minnesota where most parts of the state are sitting under several feet of snow. This led me to think about what was the state of my apple and maple trees.
The plants in our state are adapted to northern climates with harsh winters that are unfavorable to plant growth. One mechanism that these plants have adopted to survive involves a suspension of growth termed dormancy.

The bud that overwinters in an apple tree is a miniature shoot with apical meristem, leaf and perhaps flower primordial, and axillary buds enclosed by modified leaves termed bud scales. Bud scales protect the bud from mechanical injury, restrict gas exchange and prevent desiccation.

Preparation for winter and true dormancy
KFTbl.jpgThe buds are the photoperiod receptors and in preparation for winter undergo a series of physical and physiological changes triggered primarily by the shorter days of late summer. These short days (actually long nights) trigger the production of abscisic acid (ABA) which acts as a growth inhibitor. ABA has been found to build up to high levels in the fall. Although cool temperatures are not the primary trigger they facilitate dormancy of the buds. There is a point at which the bud cannot be induced to grow even given under optimum environmental conditions. At this point the bud is said to be in true dormancy. The only way the bud can be induced to grow is by experiencing a chilling period. Temperatures need to be below 45° F (7.2° C) and last for between 800 and 1,000 hours for northern adapted apples (Table 1). It may be the presence of ABA that inhibits growth and only after this inhibitor decays over time that the plant has the ability to respond to favorable environmental conditions. This removes the internal block to growth, but external factors such as low temperature can also inhibit growth in the early spring.

Dormancy can be distinguished from quiescence where the bud is in a resting state in response to adverse environmental conditions, but will resume when the environmental conditions become favorable again. Fascinatingly enough, roots overwinter in a in a quiescent state.

When the soil begins to warm, promoters of growth such as gibberellin and cytokinins build up, signaling the bud to resume growth.

Intracellular water management for plants in cold climates

Another aspect to surviving harsh winters other than the dormancy state is the management of cellular water either through deep supercooling or intracellular dehydration. Temperate woody plants utilize one of these two mechanisms.

Supercooled water is water below 32° F (0° C) that remains in a liquid state. Supercooled water can remain in the liquid state down to -36.6° F (- 38.1° C) and in the presence of dissolved solutes to -43.6° F (-42° C). This temperature is called the Homogeneous Nucleation Point. Without nucleating points no ice crystals will form above this temperature, and plants avoid cold damage by not allowing nucleating points. At temperatures below -43.6° F (-42° C) ice will form and the plant cells will be damaged or killed. Most temperate plants in North America utilize this mechanism.

Plants growing in parts of the world where temperatures fall below -43.6° F (-42° C) utilize a different mechanism. These plants avoid injury by preventing intracellular (within the cell) ice formation. Water freezes in the extracellular spaces which pulls liquid water out of the living cells leaving them dehydrated. These plants avoid damage by freezing but can be injured by dehydration. This mechanism permits plants to survive in areas where the temperatures drop below -43.6° F (-42° C).

Calendar: January 1, 2011

Happy new year from the Yard and Garden News team!

Start the new gardening year by familiarizing yourself with the University of Minnesota Extension's source of reliable, localized information on the web. Visit Garden Info to learn about growing plants indoors, in flower or vegetable gardens, and in landscapes.

Keep holiday poinsettias in tip-top condition for months by placing them near a sunny window and rotating the pots a quarter-turn every few weeks. water the soil thoroughly whenever its surface feels slightly dry; don't wait until the leaves begin to wilt. Fertilize monthly at first, then every two or three weeks as the days grow longer in March. Always mix your fertilizer half strength to avoid problems.

Bring pots of amaryllis up from the basement to force them into bloom. Water them thoroughly, then put them in a sunny window. They usually bloom in six to eight weeks, depending on how warm you keep your home. Often, flower stems appear first, but don't be alarmed if you only see leaves. If the plant received sufficient light last year, flower stems should follow. Continue to water your amaryllis whenever the soil surface feels dry, but wait until late February or March to resume fertilizing.

Tuesday, November 30, 2010

Contents: December 1, 2010

In this issue of the Yard and Garden News:

Yard and Garden News Editor: Karl Foord
Technical Editor: Bridget Barton

What Can I do About Bed Bugs?

Jeffrey Hahn, Asst. UMN Extension Entomologist

Bed bugs are often a very challenging and costly problem with which to deal. The best long-term control is to hire an experienced professional pest control company to treat your home. They have the expertise, experience and effective products to properly control bed bugs. These insects are too difficult for a homeowner to eliminate themselves. However, while you cannot eradicate bed bugs are your own, there are some steps you can take to help reduce their numbers.

Make Sure You Have Bed Bugs

Not every insect you see is necessarily a bed bug. Especially with all of the media attention recently, it is easy to think that you see bed bugs in every crack and crevice in your home so be sure you know what they look like. Despite what some people believe, bed bugs are not microscopic. Adults are similar in size and shape to a wood tick. They measure about ¼ - 3/8 inches long and are oval, flattened, brown, and wingless.. Young bed bugs are much smaller; when they first hatch, about 1/16 inches long and are nearly colorless except after feeding, but are oval like adults. If you have any doubts, let an expert identify your insects to be sure they are bed bugs.

Photo 1: Bed bug adult
Jeff Hahn
The best places to look for bed bugs are the bedroom or other rooms where you may rest or sleep or where you set down or store your luggage. Bed bugs like to hide in cracks and behind or under objects so examine behind baseboards, mattresses, boxsprings, bed frames, as well as dressers, desks, chairs, and other furniture, the edges along carpeting, and behind clocks and pictures. Consider having an inspection done by an experienced pest control company.

Be aware of signs of bed bugs in your home. One of the first indications some people experience is bites. However, be careful because reaction to bites varies considerably from no reaction to mild (small red bumps) to severe (rash- or hive-like lesions). Also, not all unknown bites turn out to be bed bugs. When you are inspecting for bed bugs, also look for cast skins (empty shells of insects). You may also find dark (not red) spots. These spots are fecal droppings which are composed of digested blood. They are on sheets, bedding, or other places where bed bugs feed or around their hiding places.

Using Temperature to Kill Bed Bugs

Using Heat

You can use your washing machine and dryer to kill bed bugs that may be infesting clothes. Clothes laundered in hot water and dried in temperatures hotter than 122o F for 20 minutes will kill all stages of bed bugs. This is typically the medium-high setting. You can also sterilize curtains and other fabrics, rugs, shoes, backpacks, stuffed animals, toys, and similar objects by drying them for about 30 minutes (for a full load).

Using Cold

Cold temperatures can kill bed bugs if they are exposed to it long enough and at temperatures that are cold enough. If you place objects into a freezer, at 0o F all stages of bed bugs will be killed when they are left in it for 7 - 10 days.

Photo 2: Mattress encasement
Credit: Protect-a-bed

It is believed (or hoped) that if you put infested furniture outdoors during winter, that the temperatures are sufficient to kill bed bugs. While you will undoubtedly kill some bed bugs, there is no guarantee that you will kill all of them. It is generally believed that if you expose furniture to 0o F or less for four days or more, that may be sufficient.

Even if you put furniture outdoors at 0o F, consider that the temperature where the bed bugs are hiding may not be as cold as the air temperature. Also, any sun shining on the furniture can raise the temperature in localized areas. Although it may seem cold, the odds of the temperature remaining consistently at 0o F or less for four consecutive days are unlikely.

Although you cannot guarantee that freezing temperatures will kill all of the bed bugs infesting an object, you can use the cold to immobilize any bed bugs that are present until you decide what to do with the object.


Mattress Encasements

An encasement is a fabric covering that completely encloses a mattress or box springs. It creates a barrier to prevent bed bugs from infesting or escaping mattresses or box springs. Although the encasement can become infested themselves, the infestation is easier to detect. They are useful when you want to protect a mattress you know is free of bed bugs (it has been heat treated or you have purchased a new mattress). You can also use encasements on infested mattresses and box springs trapping the bed bugs inside them and allowing you to continue to use them as long as they are not ripped or torn. Make sure you buy encasements that are specifically designed for protecting against bed bugs. You can purchase encasements from professional pest control services or retail stores.

Bed Bug Interceptors

Thumbnail image for Thumbnail image for Climbup intercept trap.jpg
Photo 3: Bed bug interceptor
Stephen Kells
These are small plastic trays with an inner and outer ring. They are intended to be placed under the bed legs. Bed bugs that attempt to climb up from the floor to the bed become trapped in the outer well. Any bed bugs that try to climb down will become trapped in the center well. Bed bug Interceptors not only help to reduce the number of bed bugs that can reach the bed but also acts as a monitoring tool to help determine whether bed bugs are present (if that is an issue). You can purchase Bed bug Interceptors online (type bed bug interceptor into a search engine for sources).

Bug Bombs

One of the first products some people reach for when they know they have bed bugs are bug bombs also known as total release foggers. These products throw insecticide into air of which very little, if any, comes in contact with bed bugs which are hiding in cracks and behind and under objects. Its use will not have any impact on a bed bug infestation. Unfortunately, it is too easy for people to misuse or over use bug bombs which can result in unnecessary pesticide exposure. Bug bombs are also potentially flammable if used incorrectly.

What's Happening at the Plant Disease Clinic

Karl Foord, UMN Extension Educator
Dimitre Mollov - Director of Diagnostic Services, UMN Plant Disease Clinic

Dimitre Mollov Plant Disease Clinic_pptx [Read-Only]_2.jpg
Dimitre Mollov at his dissecting scope. Karl Foord.
Every year brings its unique weather but 2010, with its unseasonably warm April and our cool and wet late May and June, presented some ideal conditions for disease. To explore this further I visited with Dimitre Mollov, the Director of Diagnostic Services of the Plant Disease Clinic of the University of Minnesota. Dimitre took over leadership of the lab some three years ago and to date has analyzed some 6,500 samples from 22 states. These samples have included some 1000 pathogens on some 300 hosts. Eighty plus percent of the samples come from commercial entities where control decisions have greater financial impact, but there may be times when it might be worth it for a homeowner to send a sample to the clinic. How are samples processed and how are the results analyzed at the clinic?

The challenge in diagnosis

You can see the challenge in diagnosis when someone hands you three leaves and asks what is wrong. Sometimes this can be easy with clearly diagnostic insect chewing or piercing damage or pathogens with characteristic necrotic lesions. However there are times when the evidence is asymptomatic, or confounded by more than one organism, or saprophytes who have followed wounds created by other means or organisms. This is why the information sheets submitted with the sample are so important; the more that is known about the specific situation the more information there is to work with in complicated situations.

The importance of information beyond the sample
A well supported sample has information about the plant's symptoms and what parts of the plant were affected. Is there a pattern observed such as the problems began at the top of the plant and worked their way down or started at the bottom and worked their way up. Were other plants in the area affected? When were the symptoms first observed? Other information about the site such as slope, or predominant compass direction of exposure is helpful. The soil type and drainage of the site as well as other chemical inputs to the situation are useful to the diagnostician.

Dimitre Mollov Plant Disease Clinic_pptx [Read-Only]_3.jpg
Karl Foord.
The importance of soil analysis

As an example, a sample that had just been received was a three year old Fir tree sent in by a Christmas tree grower. The small tree was about two feet tall and the length of annual growth nodes had been decreasing for the last two years (Exhibit 1). In this case there was no evidence of the presence of an insect or disease pathogen. Given this one would have to expect abiotic factors. Also this stunted growth was not uniformly distributed throughout the field. It is possible that the tree is experiencing problems associated with a high pH soil. See the Climate and Site Requirements section of the publication entitled Choosing Landscape Evergreens. However, in this case a soil analysis had not been performed and the diagnosis could not be definitive. Dimitre recommends having a soil test done before sending in samples for pathological analysis. Having such basic information is a good base from which to continue diagnosis. But what if the sample does show other symptoms?

A systematic approach to diagnosis

The approach I learned from Jeff Hahn and Michelle Grabowski is to first look for insect damage which is typically at a macro level and can be viewed with the naked eye. The next step is to look for signs of fungal or bacterial pathogens. Dimitre begins this at a macro level with a dissecting scope (picture) and confirms identification with a microscope (picture). He will look for characteristic fungal structures such as spores or mycelia or evidence of the presence of bacteria from cell breakdown or lysis. Should these forms of identification not be present Dimitre has the ability to perform laboratory tests for viruses. Correct diagnosis of viral diseases normally requires laboratory tests because symptoms induced by viruses can also occur due to adverse environmental conditions. Common laboratory tests include identification of specific proteins of the virus by ELISA (enzyme-linked immunosorbent assay) or DNA of the virus by PCR (polymerase chain reaction).

Some of these tests for viruses are now available to the commercial grower or passionate homeowner. One supplier is Biobest who make Flashkits for viral detection.

The lesson I took from my visit to Dimitre is as follows: Understand your limitations as a diagnostician and the environmental impacts of your decision. If you cannot identify the pathogen with certainty, avoid application of environmentally potentially harmful chemicals that may have little impact on the problem. To help in diagnosis you can use the diagnostics section of the extension website.

If you want more information about the clinic or to obtain sample submission instructions and forms, please go to the UMN Plant Disease Clinic website.

The Uncertain Future of the Butternut Tree

Michelle Grabowski, UMN Extension Educator


Photo 1: Nuts from a butternut tree B.Cook Michigan State University,

Once commonly planted near farmstead houses for the nuts it produces, many Minnesotans would not recognize a butternut tree today. Butternut (Juglans cinerea), also known as white walnut, is a native tree in Minnesota and a close relative of black walnut (Juglans nigra). This nut bearing tree provides food for squirrels and other rodents and is used for wood carving and furniture building. Butternut is hardy to zone 3 and is therefore a valuable tree in northern Minnesota, where black walnut will not grow.

Although butternut is naturally found in small numbers in native forests of the United States, these populations have decreased due to a lethal disease known as butternut canker. Butternut canker is caused by the fungus Sirococcus clavigignenti-juglandacearum and is responsible for the near extinction of butternut in some eastern forests. Populations of butternut still grow in Minnesota, but many of these trees are already infected with butternut canker.


Photo 2: Butternut tree suffering from canker MNDNR

Infected trees can be recognized by dead branches in the trees canopy and elliptical cankers on trunks and branches. The fungus infects through wounds or natural openings like leaf scars, bark cracks or stomata. The first year of infection, dark sunken oval cankers can be seen on infected branches. These often ooze sticky dark liquid in the spring and may have a sooty black center with a white border later in the season. The fungus infects and kills bark and the sapwood beneath it. Black staining of the sapwood can be seen if the bark is peeled back.

Infections on small branches quickly girdle and kill the branch, resulting in dieback within the tree's canopy. On large branches or the main trunk of the tree, cankers do not grow quickly enough to girdle the tree in one season. Rather the bark over the canker cracks open and ridges of wound wood develop around the canker. With time, multiple cankers accumulate on the main trunk of the tree and it succumbs to the disease.


Photo 3: Sooty discoloration on bark from butternut canker J.OBrien, USDA FS,

The butternut canker fungus produces spores during wet weather throughout the growing season. These spores are washed down the trunk or splashed onto nearby trees, starting new infections where they find an entry point. It is unknown how the fungus moves long distance. Seed can carry the pathogen, and it is suspected that insects or birds may play a role. People can also move the pathogen by moving infected wood from place to place. The fungus survives in wood infected with butternut canker for two years after the tree has been killed.

Unfortunately there is no strategy to prevent infection with butternut canker. Infected butternut trees often survive many years however. During this time the trees provide shade and nuts. Large branches and trees that have been killed by the disease should be removed. Butternut is not as rot resistant as black walnut. Dead trees and limbs can be a hazard if located in areas near people or valuable property.


Photo 4: Black staining of infected sapwood J.OBrien, USDA Forest Service,

The US Department of Agriculture Forest Service has an active butternut breeding program, working to identify canker resistant butternut trees. If you know of a mature butternut tree that is thriving despite having a few cankers or a tree that is healthy despite many neighboring butternut trees succumbing to the disease, contact Dr. Ostry at the USDA North Central Forest Service ( 651-649-5113). These trees are a valuable natural resource that may provide disease resistance to butternut canker.

For more information on butternut canker visit the USDA Forest Service website.

Calendar and Contributors: December 1, 2010

Make cleaning your houseplant foliage part of sprucing up your home for the holidays. Clean leaves look best-- and they capture more light for photosynthesis. Wash both the surface and underside of each leaf with lukewarm water that's had a drop or two of dishwashing liquid added. For more information, see the wide range of houseplant care publications on the University of Minnesota Extension Garden Info site.

Poinsettia's are among the easiest holiday plants to grow. But first you must choose a plant and get it home without suffering cold damage. It must be wrapped well, then transported in a heated vehicle. Cut the bottom of the pot so excess water will drain out, and place the poinsettia in a bright- even sunny- location. water thoroughly when the soil surface begins to dry, and fertilize monthly after four to six weeks.

Want to see more poinsettias? Spend some time at the Marjorie McNeely Conservatory in St. Paul's Como Park. The annual holiday display will help you forget December's snow and cold!

The Minnesota Landscape Arboretum also has many winter offerings. This month, the Arboretum will be hosting Hot Chocolate Walks, guided walks with a naturalist through the quiet of winter, with a cup of hot chocolate to warm up at the end. Visit the Arboretum website for this and other opportunities to take advantage of the snowy Minnesota landscape.


This month the Yard and Garden News will feature Julie Weisenhorn, Director of the Master Gardener Program and Assistant Extension Professor. We have asked Julie two questions: "What do you like most about your job?" and "What are you passionate about outside of work?"

I have always loved teaching landscaping and plant selection to my Master Gardeners - my three areas of focus! They are the greatest students - full of energy and the desire to learn. They also ask really good questions - they keep me on my toes - and draw excellent conclusions. I love to hear from them how they used the information they learned in my class to help citizens with their gardening questions.

Photography of plants, landscapes and architecture: I love waiting for the right light, the right subject, the right combination of elements and then getting that perfect shot. I love coming upon a unique plant or combination of plants and getting the shot. It's very satisfying to go back over the day's work and say "wow!"

Dogs and landscaping: I love dogs and will always have a dog in my life, my home - and my garden! That means landscaping with the notion that a dog will be a participant and use the landscape as their territory. Keeping expectations realistic when creating spaces, selecting plants and designing for specific needs of the dog are key to having a landscape that is functional, maintainable and looks great.

Music and friends who play music: My personal time is often spent playing music with friends. My husband is a musician and I come from a musical family. I have always loved to sing and am playing better guitar thanks to hanging out and jamming at a local music store on Saturdays. While I don't count on music as a career, I love to perform in groups and play at weddings, benefits, and parties for the pure bliss of the rush you feel when an ordinary song turns out great.

Julie Weisenhorn wormclass09.jpg
Julie Weisenhorn teaching vermicomposting at a Somali school in Inver Grove Heights.

Sunday, October 31, 2010

Contents: November 1, 2010

In this issue of the Yard and Garden News:

The Plight of Bees

Marla Spivak (University of Minnesota); Eric Mader and Mace Vaughan (Xerces Society for Invertebrate Conservation); Ned Euliss (USGS)
Excerpted from feature article to appear in upcoming issue of Environmental Science and Technology.

Bee Declines

Colony collapse disorder (CCD), the name for the syndrome causing honey bees to suddenly and mysteriously disappear from their hives--thousands of individual worker bees literally flying off to die--captured public consciousness when it was first named in 2007. Since then, the story of vanishing honey bees has become ubiquitous in popular consciousness--driving everything from ice cream marketing campaigns to plots for The Simpsons. The untold story is that these hive losses are simply a capstone to more than a half-century of more prosaic day-to-day losses that beekeepers already faced from parasites, diseases, poor nutrition, and pesticide poisoning.

The larger story still is that while honey bees are charismatic and important to agriculture, other important bees are also suffering, and in some cases their fates are far worse. These other bees are a subset of the roughly 4,000 species of wild bumble bees (Bombus), leafcutter bees (Megachile), and others that are native to North America. While the honey bee was originally imported from Europe by colonists in the early 17th century, these native bees have evolved with our local ecosystems, and along with honey bees, are valuable crop pollinators.

People want to know why bees are dying and how to help them. This concern provides a good opportunity to more closely examine pollinators and our dependence upon them. Bees are reaching their tipping point because they are expected to perform in an increasingly inhospitable world.

Bee declines can be attributed to three factors:

1. Bees have their own diseases and parasites that weaken and kill them. Sick bees are more susceptible to the effects of poor nutrition and pesticide poisoning, and vice versa.
2. Many flowers, nest sites, and nesting materials are contaminated with pesticides. Bees pick up the insecticides, herbicides and fungicides applied to home gardens and lawns, golf courses, roadsides, and crops. These pesticides, alone and in combination, can be toxic.
3. There are not enough blooming flowers over the length of the growing season in our agricultural and urban landscapes to support bees.

Emerging Responses to Declines in Bee Health

To study CCD and other pollinator health issues, the 2008 Farm Bill approved more than $17 million in funding annually for five years for the U.S. Department of Agriculture (USDA) and for university research grants. The Farm Bill also approved another annual $2.75 million for five years to increase honey bee health inspections. Since the Farm Bill became law this funding has never been fully appropriated.

The 2008 Farm Bill also dictated that current USDA competitive grant programs should include pollinators - honey bees and native bees - as research priorities. As a result, research programs funded by the USDA under the National Institute of Food and Agriculture (NIFA), such as the Specialty Crops Research Initiative (SCRI) and the Agriculture and Food Research Initiative (AFRI), made pollinators a research priority in 2010.

Protection from Pesticides

A factor that can be addressed at multiple levels is the use of pesticides. In particular, while extensive literature exists on the sublethal effects of insecticides on bees in the laboratory, little exists on sublethal effects to colonies under natural conditions. Common insecticides such as neonicotinoids and pyrethroids have been shown to affect learning, foraging activities, and nest site orientation by honey bees at sublethal doses.

Individual farmers and homeowners have the ability to mitigate harm to pollinators through simple changes in application methods such as avoiding treatments around blooming plants or to areas where bees are nesting. Evening spraying when bees are less active is another simple, underutilized way to reduce harm. The best course of action, and the one most accessible to gardeners, for whom insect damage is cosmetic rather than economic, is to eliminate the use of pesticides entirely.

The Need for Habitat

The third major challenge facing bees is a lack of season-long food sources, especially in agricultural landscapes where, if bee-pollinated plants even exist, they typically consist of large monocultures like cranberries, canola, or almonds, which provide only a few weeks of abundant food followed by a season-long dearth. Roughly 360 million hectares, or more than one-third, of the lower 48 states are managed as private cropland, pasture, or rangeland. This makes agriculture the largest land use activity in the country and thus one with the most potential impact on bees.

Specific habitat guidelines for all of these landscapes (rural, urban, roadside) vary across regions. Baseline habitat guidelines encourage the inclusion of at least 3 different plant species that bloom at any given time during the growing season (spring, summer, fall), with more being even better. For planting recommendations, visit:

Concluding Remarks

Pollinators are receiving more conservation attention today than at any other time in history. Scientists, conservationists, and farmers are working harder than ever - in partnership - to understand how pesticides, diseases, and habitat loss impact pollinator populations. They are also working to understand the most successful strategies for creating landscapes that support the greatest abundance of these important insects.

At the same time, the public and policy-makers are increasingly aware of the problems afflicting bees and the critical role they play in food production and natural systems. But there is no reason to wait for research and policy to mitigate the plight of the bees. Individuals can modify their immediate landscapes to make them healthier for bees, whether that landscape is a public rangeland in Wyoming or a flower box in Brooklyn. It is also possible to reduce agricultural and urban pesticide use to mitigate bee poisonings. We can engage in the sustainable management of honey bees and native bees. Promoting the health of bee pollinators can begin as an individual or local endeavor, but collectively has the far-reaching potential to beautify and benefit our environment in vital and tangible ways.

Editor's note: Imidacloprid we have been talking about is a neonicotinoid.

Help Your Woody Ornamentals Survive the Coming Winter

Kathy Zuzek, UMN Extension Educator

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Photo 1: Winter burn symptoms. Kathy Zuzek, UMN Extension.

The effects of winter sun, wind, temperature fluctuations, snow, and ice can all combine to make winter a high-hazard time for tree and shrub health. Animal browsing is an additional challenge in our winter landscapes. Here's a checklist for gardeners who want to minimize injury to woody ornamentals in the coming winter.

Apply tree wraps and tree guards to prevent sunscald. Sunscald occurs when winter sun heats up bark on the south or west side of a tree enough to stimulate cambial activity. When shading or sunset causes the air temperature to drop quickly, the activated cambium is killed resulting in dead bark on the south or west side of a tree in the form of sunken, dried, or cracked areas. To prevent sunscald, tree wraps and guards should be applied in fall. They should be light-colored to reflect sun and to keep bark at a lower temperature on sunny winter days. Pay special attention to trees that have bark newly exposed to sun from recent pruning to raise tree canopies, trees that have been recently transplanted from shady sites to sunny sites, and young trees and other thin-barked trees such as cherries, crabapples, plums, maples, mountain ash, basswood, and honey locust. You will need to protect newly planted and thin-barked trees for several years but remember to remove tree wraps each spring and reapply them in autumn.

Avoid over watering and late season fertilizing that can encourage late season succulent growth. Late season growth is vulnerable to winter injury.

Avoid under watering of your trees and shrubs. Remember to water trees and shrubs in your landscape until the ground freezes. As temperatures drop in autumn and plants are acclimating for winter, it is easy to forget that they still need water. Inadequate watering stresses plants. Avoid this stress by watering until the ground freezes. The average freeze date of soils in Minnesota ranges from mid-November through mid-December; the average date for Minneapolis and St. Paul is December 6.

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Photo 2: A burlap barrier to prevent winter burn. Kathy Zuzek, UMN Extension.

Roots are less hardy than stems of woody plants and can be injured when soil temperatures reach 10-15 ° F. Thankfully, soil temperatures are much higher than air temperatures in winter. A moist soil holds more heat than dry soil and helps to prevent deep frost penetration.

Evergreen foliage that turns brown during winter due to desiccation and injury is called winter burn (Photo 1). One way this damage occurs is when winter sun and wind trigger transpiration in evergreen foliage. During transpiration stomata (the openings on foliage that allow gas and water exchange with the atmosphere) open and water is lost from the foliage. Because the soil is frozen, the plant cannot replace the lost water and foliage desiccates and turns brown. Damage often occurs on the south, southwest, or windward side of evergreens but in severe cases, an entire plant can be affected. Winter burn can affect all evergreens but yew, arborvitae, and hemlocks are particularly susceptible. Minimize winter burn by watering evergreens until the ground freezes in late autumn or early winter.

Construct a barrier around plants susceptible to winter burn to protect them from winter sun and wind. A second way that winter burn occurs is similar to sunscald damage on tree trunks. Cellular activity in evergreen foliage can be stimulated by sunny winter days that increase tissue temperature in evergreen foliage. When shading or sunset occurs, foliage temperature drops, resulting in foliage injury or mortality. Whether it is caused by transpiration and water loss or by sun's activation of foliage tissue, winter burn is an indication that evergreens were not sited properly in a landscape. A short term and aesthetically unappealing solution to this problem is to construct a barrier of burlap or cut evergreen branches around plants to protect them from winter sun and wind (Photo 2).

Don't apply antitranspirant sprays to prevent winter burn. Most research shows that antitranspirant sprays do not protect evergreens from winter burn.

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Photo 3: Narrow branch angle. J. O'Brien, USDA Forest Service,

Apply several inches of mulch around your trees and shrubs to buffer soil temperatures. Mulch is especially important at preventing cold injury to roots during snowless winters. Snow is a great insulator and moderator of soil temperatures. In its absence, several inches of mulch will help to moderate soil temperature.

Protect your trees and shrubs from animal damage. Rodents, rabbits, and deer feed on twigs, bark, and foliage during winter. In severe cases, their feeding can girdle and kill stems or entire plants. Deer rubbing their antlers on trees can also cause damage. Protect tree trunks and shrubs from rodent and rabbit feeding damage by using tree guards or a hardware cloth wrap. Start your protection a few inches below the ground for mice and extend it 24 inches above the average snow line for rabbit protection. Or protect entire beds from rodents, rabbits and deer with wire fencing, repellent sprays, or by hanging repellant-drenched rags.

Prune to prevent snow and ice damage. Prune to eliminate multiple leaders and narrow branch angles (Photo 3) between branches or branches and trunks of trees. Removing these weak branch attachments makes trees less susceptible to snow and ice damage.

Pollinator Blues: Part II

Karl Foord, UMN Extension Educator

Pollinator Blues - Part II

To approach the problem of creating a bee friendly garden,I first researched the plants that are pollinator friendly and created a table of pollinator friendly plants from the Xerces site (Exhibit 1).

Second, I used the following recommendations from the Urban Bee Garden site as criteria for selecting plants; the goal being to insure that continual bee floral food will be available for the complete growing season.

1. Plant a minimum of three plant species that bloom at any given time during the growing season i.e. spring, summer and fall.

2. Each species of flower should be planted to a minimum patch size of approximately 5 ft. x 5 ft. Patch size is important because smaller patch sizes will often be ignored, even if the plant is quite attractive to the bees.

3. Higher bee diversity and abundance occurs when gardens have a rich assortment of bee plants. It also appears that bees remain longer in a garden if plant diversity is high.

Third, I then took an inventory of my present plants and estimated their flowering periods (shown in yellow on Exhibit 2). Fourth, I considered the areas available for planting shown in my property. Given the patch size and species diversity recommendations, I chose six plants to fortify my local bee garden, as follows: Milkweed (Asclepias), Single flowering Roses (Rosa), Catmint (Nepeta), Russian sage (Perovskia), Cosmos (Cosmos), and Lavender (Lavandula). These plants were chosen for attractiveness to bees and longer flowering periods.

I hope that you will consider increasing the attractiveness of your plantings to bees, if appropriate. Taking an inventory of the flowering periods and bee appeal of the plants that you presently have is a good first step. Then choosing plants from the table to supplement, if necessary, should enable you to increase the appeal of your bee garden.



Beware of Bed Bug Internet Hoax

Jeffrey Hahn, Asst. Extension Entomologist

There is a story making the rounds on the internet these days. It goes like this:

Hi All: A bit of information that you might like to know about. We have friends here in our community and one of their sons is an entomologist (insect expert), and has been telling them that there is an epidemic of bed bugs now occurring in America. Recently I have heard on the news that several stores in NYC have had to close due to bed bug problems, as well as a complete mall in New Jersey.

Bed bug
Jeff Hahn
He says that since much of our clothing, sheets, towels, etc. now comes from companies outside of America, (sad but true), even the most expensive stores sell foreign clothing from China, Indonesia, etc. The bed bugs are coming in on the clothing as these countries do not consider them a problem. He recommends that if you buy any new clothing, even underwear and socks, sheets, towels, etc. that you bring them into the house and put them in your clothes dryer for at least 20 minutes. The heat will kill them and their eggs. DO NOT PURCHASE CLOTHES AND HANG THEM IN THE CLOSET FIRST. It does not matter what the price range is of the clothing, or if the outfit comes from the most expensive store known in the U.S. They still get shipments from these countries and the bugs can come in a box of scarves or anything else for that matter That is the reason why so many stores, many of them clothing stores have had to shut down in NYC and other places. All you need is to bring one item into the house that has bugs or eggs and you will go to hell and back trying to get rid of them. He travels all over the country as an adviser to many of these stores, as prevention and after they have the problem.

It is true that we are experiencing a significant increase in bed bug problems that has reached epidemic proportions. It is also true that a few retail stores have had bed bug problems and have had to temporarily close. However the rest of the story is unnecessarily alarmist and untrue.

While some clothing stores have found bed bugs, it is not because they were brought into the store on new clothes but rather they hitchhiked into stores on individuals that entered them. Fortunately, the incidence of bed bugs in clothing stores has been rare and owners have taken steps to prevent and better deal with bed bug problems. Because bed bugs would have a hard time finding a person resting for a period of time in clothing store, it is difficult for them to establish a reproducing colony which greatly reduces the risk of someone accidentally bringing bed bugs homes with them.

The idea that you need to worry about clothes you buy, especially those made in Asia, is an unfounded and false statement. The chances of bed bugs inadvertently hitching a ride in new clothes is extremely remote and there are not any known cases of this actually happening. If this was true, we would be routinely seeing bed bugs associated with clothing stores, instead of rarely.

This letter looks like it was meant to alarm and frighten people. Ignore it and continue to buy new clothes as you normally would. We have enough in things in our lives that gives us stress without unnecessarily adding to the list.

Rust Diseases of Lawn Grasses Very Common this Fall

Bob Mugaas, UMN Extension Educator

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Photo 1: Areas of rust infection on Kentucky bluegrass lawn. Bob Mugaas.
Rust diseases of our lawn grasses have been on the increase throughout much of this fall period but became especially evident during the drier conditions of October. Rust infestations usually show up as areas of yellow to orange-yellow grass blades, see Picture 1.

Upon closer examination of the grass blade, one will usually see orange colored, tiny tuft-like pustules breaking through the grass leaf surface, see Picture 2. It is these pustules that produce massive numbers of individual spores. These are the same spores that can become air-borne and cover our shoes or lawn mowers in an orange 'powder' as we walk through rust infected areas of the lawn. They can also re-infect other grass plants that in turn can produce more of the same spore producing rust pustules thus carrying on the infection cycle.

What is a rust disease?

Rust diseases have very complex life cycles that include as many as five different stages during a single year. In addition, it is often necessary for various species of rust to spend a portion of their life cycle on one plant species and the other portion on an entirely different plant, often referred to as an alternate host. Such is the case with the specific rust disease known as crown rust (Puccinia coronata) of grass. This disease completes part of its lifecycle on its alternate host, common buckthorn (Rhamnus cathartica) or glossy buckthorn (Frangula alnus, formerly Rhamnus frangula), and the second portion of its lifecycle on some of our lawn grasses, especially perennial ryegrass and tall fescue. Other rust species including Puccinia graminis (Stem Rust) and Puccinia striiformis (Stripe Rust) can also affect Kentucky bluegrass, along with many other grass species.

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Photo 2: Spore producing rust pustules pushing through grass leaf surface. Bob Mugaas.
Rust on turfgrass can overwinter in plant debris but it will need to infect its alternate host before returning to the grass plant. It should also be noted that the disease causing spores can develop in warmer climates to our south and be blown up here during the summer and serve as a source of infection from summer into the middle of fall. This can be an important source of rust infection in this area. In a typical year and under favorable conditions, crown rust will usually start to show up toward the end of June while stem rust can be a bit later. Once begun, the rust infection cycle can continue throughout much of the growing season so long as favorable rust infection conditions persist.

Why rust and why now?

Slow growing lawn grasses are a prime target for rust disease attack. It is usually the combination of warm daytime temperatures, dry weather and heavy amounts of overnight dew production on the grass foliage that creates a favorable environment for rust spores to germinate and infect the foliage. When these common weather conditions are combined with low levels of available nitrogen, an element responsible for active, vigorous growth of our grasses, you have very favorable conditions for a rust outbreak. Shadier areas often experience greater incidence of rust. Note the lighter yellow to orange areas scattered around the lawn underneath the spruce trees in Picture 3.

Rust disease started showing up more frequently around the Twin Cities during late August to early September. However, it wasn't until the very dry conditions lasting nearly the entire month of October that significantly increased the occurrence of rust in our lawns and other turfgrass areas. Frequent enough rainfall combined with an occasional supplemental watering kept our lawn grasses actively growing and utilizing available nitrogen throughout much of the summer period.

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Photo 3: Rust infection on a partially shaded lawn area. Bob Mugaas.
Nitrogen can also be lost when it is carried with water down through the soil and beyond the reach of grass roots, a process known as leaching. Thus, due to relatively continuous grass growth during the summer and nitrogen losses due to leaching, it is quite likely that the amount of available soil nitrogen was in short supply by late summer, a time of year when our lawn grasses naturally resume active shoot and root growth. That condition along with the prevailing weather conditions during late September and much of October has contributed to a much higher than usual amount of rust disease on our lawns and other turfgrass areas.

So, what should I do now?

With the rains of the last few days of October, we have improved our previously dry soil conditions. That will be a big help in improving the growing conditions for lawn grasses. While it's late to be putting down nitrogen for this year, it would be a good idea to plan on applying some next spring as our lawns are beginning to show active growth. For the most part, we try to manage rust diseases by changes in our cultural practices. There are fungicides that can be applied in severe cases. However, at this late date in the season, both the rust fungi and the turfgrasses are preparing for winter survival and dormancy. Thus, fungicide applications at this time of year will be of no benefit. Use of protective fungicides can be reevaluated next year should serious rust problems begin to develop.

Where disease levels were quite high and there was some thinning of the lawn, one should be prepared to do some reseeding of those areas as needed. Some overseeding could be done yet this fall in a process known as dormant seeding. Normally this would be done once the ground is cold enough to prohibit germination with the seed remaining in the ground until next spring when it will sprout and grow. One could also wait until early next spring to do some seeding.

For some additional information on rust diseases of lawns, check out the following link to our Gardening Information page, What's Wrong with My Plant?

The author would like to gratefully acknowledge the input and review of Dr. Eric Watkins, Assistant Professor-Turfgrass Science, University of Minnesota Department of Horticultural Science and Michelle Grabowski, Extension Educator - Horticulture & Plant Pathology, University of Minnesota Extension, in the preparation of this article.

Prevent Snow Mold on Lawns Now

Michelle Grabowski, UMN Extension Educator

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Photo 1: Snow mold damage on a lawn in spring 2010 Photo by T. Burnes.
In the spring of 2010 snow melted away from yards and landscapes to reveal round dinner plate sized patches of tan or gray matted turf. Two fungi, known as snow molds, were responsible for the damage. Many gardeners were dismayed to learn that little could be done in the spring to cure snow mold. Rather they had to wait for the weather to change and the grass to recover. This is because the time to prevent snow mold is not in the spring. The time is now.

Snow mold is caused by two different fungi, Microdochium nivale and Typhula sp. Both of these fungi thrive at temperatures just above or below freezing with high levels of moisture. Although snow cover is not a requirement for the growth for snow mold, snow cover provides ideal conditions for the fungi. Of course, gardeners cannot control how much snow Minnesota will receive this winter or how long that snow will stay. Gardeners can prepare their lawns for winter in a way that provides the best chance of a healthy spring.

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Photo 2: Fluffy white mycelia of snow mold can often be seen in moist conditions Photo by T. Burnes.
Several factors can increase the chances of snow mold the following spring. Long turf that is bent over by snow creates a canopy that traps humidity at the base of the turf plant. Piles of leaves or other debris on the lawn have a similar effect. Snow mold thrives in these humid microclimates. Fertilizing lawns in late September or early October can cause the grass to produce a flush of young succulent growth. This new succulent turf often does not have time to harden off before winter comes and is an easy meal for the snow mold fungi.

Several simple steps can be followed to prepare turf for the winter and reduce the risk of snow mold the following spring.

1. Rake up leaves and any other debris on the lawn.
2. Continue mowing until the grass goes dormant. A height of 2 inches will help the turf remain upright and facilitate air movement and drying of the turf.
3. Do not fertilize lawns until next year. A late season application of fertilizer can be done around Labor Day, but there is little benefit of fertilizing beyond that date.

Calendar and Contributors: November 1, 2010

Garden Calendar

Check out more fall tips to reduce snow mold next spring from UMN Extension Educator Bob Mugaas, as featured with Bobby and Belinda on Kare11.

Be a responsible gardener and remove any buckthorn shrubs still growing on your property. They're easy to spot late in autumn when most other shrubs have lost their leaves. Buckthorn has green leaves and small clusters of black berries, with sharp barbs sparsely placed. Unfortunately, they're difficult to dig out. Larger plants will require brush killer next spring or summer. Do you have buckthorn in your yard? Learn more about buckthorn from the Minnesota DNR.

Buckthorn (R. Frangula) and all cultivars are considered to be restricted noxious weeds, according to the DNR. Check this list of Minnesota and Federal Prohibited and Noxious Plants by Scientific Name if you are ever uncertain about something in your yard.


The Yard and Garden News will now feature brief profiles of the contributors! We've asked UMN Extension Educator, Kathy Zuzek "What do you like most about your job?" and "What are you passionate about outside of work?"

Kathy Zuzek, UMN Extension Educator, Horticulture
The best parts of my job are being able to teach horticulture to invested students and working with other extension educators who enjoy helping others to learn as much as I do. During my 20 years as a research scientist I often commented on how much I enjoyed presenting to Master Gardeners, so becoming an Extension Educator and part of the Master Gardener education team was and continues to be a thrill.

I am passionate about plant hybridizing and developing attractive & adapted landscape cultivars for northern climates, parenthood, Minnesota's Arrowhead region, camping, hiking, kayaking, and my dogs (That's Max in the photo. Kirby, my golden retriever, missed that camping trip.)


Yard and Garden News Editor: Karl Foord
Technical Editor: Bridget Barton

Thursday, October 14, 2010

Contents: October 15, 2010

In this special mid-month issue of the Yard and Garden News:

Bringing tropical plants into the house for the winter, or a short biochemistry lesson

Karl Foord, UMN Extension Educator

Jeff Hahn.
Each fall brings the challenge of not only what tropical plants to keep over the winter, but also how to keep them healthy in the Minnesota winter home environment. Invariably despite all efforts I will provide winter refuge for aphids and mites. It seems like this is the perfect time to use imidacloprid. As a systemic it will control the aphids and has no chance of impacting natural populations of insect predators or pollinators in this environment. However, Imidacloprid will not control spider mites. Why not?

The fact that an effective insecticide will usually not harm a mite seems counter intuitive. After all they are both Arthropods i.e. small creatures with exoskeletons and jointed appendages. Although following this basic pattern, the body structure differences between mites and insects are dramatic. On closer inspection the mite has no antennae, no wings, 4 pairs of legs, an unsegmented abdomen, and simple eyes. Whereas an insect such as a bee will have 3 body parts, 2 compound eyes, 2 antennae, 4 wings, 3 pairs legs, and a 2kf.jpg
Karl Foord.
segmented abdomen. These physical differences reflect a very ancient common ancestor.

The first arthropod fossils date to the Cambrian @ 555 million years ago (mya). From this common ancestor five groups emerged, 1.Trilobites - extinct, 2. Arachnids (spiders & mites), 3. Centipedes and millipedes, 4. Crustaceans, and 5. Insects. The Arachnids and centipedes are more closely related to each other than to the crustaceans and insects. So a lobster is more closely related to a bee than to a spider. Who would have thought? The oldest arachnid fossil dates to the Silurian period 420 mya, while the oldest insect fossil dates to the early Devonian 407 mya. Sometime in the Cambrian period 542 - 488 mya or Ordovician 488 - 433 mya the insect and arachnid lines diverged. During this time the animals diverged physically as well as metabolically. Imidacloprid capitalizes on the metabolic differences.

Insecticides vary in their mode of action, one of which is to interfere with the nervous system. Imidacloprid mimics the action of acetylcholine (a neurotransmitter). The normal functioning system calls for rapid degradation of acetylcholine to maintain control of neural 3kf.jpg
Karl Foord.
transmission; a little like an on off switch. Imidacloprid is not degraded by normal enzymatic control and thus leaves the switch on which overexcites the nervous system and removes control from the insect. Imidacloprid is specific for insect nervous tissue and doesn't affect mites or mammals in the same manner.

I plan to drench the soil in the pots containing tropical hibiscus, dwarf olive, dwarf Cavendish banana, Australian tree fern, two palms, and the climbing fig. I'll not drench the dwarf Meyer lemon or the star jasmine as I expect them to flower next year and know that the imidacloprid is persistent and could harm pollinators. I have read that bees are attracted to tropical hibiscus, but I have never observed bees visiting these flowers.

My only regret in bringing in the house plants is that I know they suffer from low light intensity. Wouldn't it be great if we could all afford a winter greenhouse for tropical like the one at the Minnesota Landscape Arboretum?

Download a copy of the geologic time scale and access Jeff Hahn's article on mite control.

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