- What is biting me?
- Hosta Virus X: New Information
- Does climate affect the taste of apples? - Minnesota vs. Washington grown Honeycrisp Apples
- What are your woody plants doing right now?
Friday, December 31, 2010
Jeffrey Hahn, Asst. Extension Entomologist
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).
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.
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, http://www.ca.uky.edu/agc/pubs/ent/ent58/ent58.pdf http://delusion.ucdavis.edu/delusional.html and http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7443.html
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.
Hennepin County Master Gardener
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 http://www.americanhostasociety.org/Education/HostaViruses.pdf 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.
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.
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.
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.
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
The 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).
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.