University of Minnesota Extension
Menu Menu

Extension > Yard and Garden News > 2016

Tuesday, December 27, 2016

Caring for Your Norfolk Island Pine

By Beth Berlin, University of Minnesota Extension

Many people will receive a Norfolk Island Pine for the holidays. These beautiful evergreen trees can become a wonderful houseplant with the right care for many years to come.

Norfolk Island Pines, Araucaria heterophylla, is not actually a pine tree. It is a coniferous evergreen native to Norfolk Island in the South Pacific near Australia.  They have short dark green needle-like leaves with broad spanning branches that give it a tiered appearance.  In its native climate they can reach 200 feet tall with a ten foot diameter trunk.  As a houseplant it is very slow growing, only growing about 3-6 inches per year, but can reach a height of 5-8 feet.

To care for a Norfolk Island Pine, place it in a bright, sunny location. Be sure to spin your plant each week so that it doesn’t start to lean or grow towards the window and light. In general Norfolk Island Pines can be kept at 65-72°F, but it is important not to expose them to extremes, both hot and cold.  The minimum night time temperature this plant will tolerate is 50-55°F. The plant will perform best where night time temperatures are about 10°F cooler than the day temperatures.

Humidity is important for nearly all houseplants. The Norfolk Island Pines prefer higher humidity than what most of our homes are in the winter time, preferably around 50% humidity.  Placing a humidifier nearby may help alleviate dry air. Fertilize when plants begin to put on new growth, typically March through September. However the plant will tolerate very little fertilizer which will minimize growth and keep the plant shorter and grow slower. The plant prefers moist roots but doesn’t like to be wet so be sure to have a well drained soil and container.  Water thoroughly once the top one-inch of the soil is dry.

Norfolk Island Pines that experience wet soil and low light conditions may have lower limbs drop off. Some may experience needle drop which could be caused by dry conditions, including soil moisture, lack of humidity, or either cold or hot drafts or airflow. However in general this is a fairly pest free plant and can be enjoyed for decades if well kept.

Thursday, December 1, 2016

Weeds in the Turf Lawn: Invasive Nuisances or Sources of Forage?

By James Wolfin, Graduate Research Assistant

The turf lawn accounts for nearly 2% of the continental United States land cover, and has become engrained in the architecture of many United States neighborhoods and landscapes.  As urban and suburban areas continue to expand, we can expect this number to increase as many yards, store fronts, and commercial buildings are installed to accompany properties.

While the planting of turf lawns alongside most properties is a standard practice, the management practices and personal perceptions of those managing lawns are variable.  Lawns differ in the level of input that is imparted by the landowner.  Input generally refers to the effort that is directed towards maintaining the aesthetics of the lawn, normally in the form of mowing, watering, weeding, and fertilizing.  While each of these practices are generally required to ensure proper turf health, how frequently inputs are applied can vary greatly.  Practicing responsible lawn maintenance practices may be obvious in certain situations.  For example, mowing too frequently can be hazardous due to the fossil fuel emissions let off from a motorized lawn mower and excessive watering or fertilizing can cause harm in the form of runoff, leading to algal blooms in bodies of water.  What may be less obvious are the impacts of weed management practices.  Many land managers differ in the way they perceive weeds, which can have a great impact on the biodiversity that is supported by a lawn.

A weed is generally considered a plant that is undesirable in a lawn for any reason, often due to aesthetics.  Many land managers place a premium on maintaining a uniform, green turf, and believe weeds are a disruption or a nuisance.  What may go unnoticed, however, is the benefit that weedy flowers can have in terms of supporting biodiversity, especially for pollinators.  Weedy flowers often produce nectar and pollen which are collected by pollinators, including honey bees and wild (native) bees.  These floral rewards are essential to the diet of bees, as nectar serves as the main source of carbohydrates in a bee’s diet, while pollen serves as the main source of protein.  While it is impossible to discuss every weedy flower that may exist in a lawn, specific flowers that are popular in lawns or are especially beneficial to pollinators are important to consider.

White CloverWhite Clover
White clover (Trifolium repens) is one of the most common lawn weeds that land managers may encounter.  White clover is often indicative of soils that have low fertility or a situation where lawns are mowed to a very low height.  This plant spreads through a stoloniferous growth habit, where lateral stems grow at or just above the soil surface.   White clover is easily recognizable due to its distinctive leaves, which appear in the form of a three-leaf trifoliate.  Once established in a lawn, white clover will bloom from mid-spring through the fall, generally peaking in May and June.  The blooms of white clover appear in the form of a white flower head that is attractive to a great diversity of bees.   The medium sized blooms provide an adequate landing pad for larger bees, including bumble bees and honey bees, but are also visited by smaller bees.  White clover is a significant source of both nectar and pollen for bees, making it a great addition to a home lawn or garden in terms of supporting biodiversity.  White clover can also benefit overall lawn health due to its ability to fix and add nitrogen to the soil, supporting healthy plant growth.  White clover will bloom at low heights, which will allow a landowner to maintain a normal lawn height (~3.0”) while still supporting bees.

Self-heal (Prunella vulgaris) is a forb from the mint family, Lamiaceae, that receives its name from its history in folk medicine.  A sub-species of this flower, Prunella vulgaris ssp. Lanceolata, is native to Minnesota, making self-heal a useful addition for landowners that want to attract native pollinators.  This flower will grow in home lawns, especially moist areas that receive partial shade.  The central stem of a self-heal flower is distinctive due to its spiked, hairy vegetation that stands upright.  The striking flowers have a violet color and a whorled bloom, giving a tubular shape to the flower.  The tubular shape of self-heal flowers make the nectaries difficult to reach for short-tongued bees.  As a result, self-heal is most frequently visited by long tongued bees, like bumble bees and honey bees (tongue size is strongly correlated with body size).  Self-heal is able to withstand regular mowing, blooming at heights as low as two inches.

Creeping thyme
Creeping thyme (Thymus serpyllum) is another flower from the mint family (Lamiaceae) that is most commonly found in sandy soil areas, but has the ability to establish in a variety of habitats.  Creeping thyme grows by spreading lateral stems in the form of above ground stems (stolons) or below ground stems (rhizomes).  Closely related to the culinary species of thyme, Thymus vulgaris, this species also retains a strong, herbal scent.  The leaves of this plant grow low to the ground in opposite pairs, with flowers that will bloom at heights as low as one inch.  The flowers are pink-purple in color, and form small, open blooms.  The size of these blooms makes the rewards accessible to smaller bees, like mining bees, but may also be visited by honey bees.  In addition to supporting bees, this plant also serves as important habitat for butterflies.  Two species of butterflies, the small blue butterfly and the large blue butterfly, will lay eggs on the vegetation of creeping thyme.  Their larvae will then feed on the leaves before maturing into adult butterflies.  Creeping thyme is also useful as a border plant for gardens, as it acts as a natural deer deterrent.  

Dandelion (Taraxacum officinale) is a common perennial lawn weed not only throughout the Unites states, where it is present in every state, but globally.  Dandelion is native to Europe and Asia, but is now present on all continents except Antarctica.  This herbaceous forb is able to establish in a wide variety of conditions and will bloom in full sun, part sun, or full shade.  Dandelion is found frequently in disturbed soils, especially those that are high in potassium content.  The leaves of dandelion vary in size based on the age of the plant, but are easily recognized by their unique, lobed shape.  Dandelion has conspicuous yellow flower heads, containing many individual ray flowers.  This species spreads easily once established in the soil due to dandelion’s prolific seed production and the ability of these seeds to be distributed widely by the wind.  Dandelion does not require pollination and is able to reproduce via apomixes, a form of asexual reproduction in plants.  Despite this, dandelion still produces nutritious pollen that is moderately high in crude protein content.  Although it is often considered a nuisance in residential and recreational lawns, a wide range of insects use dandelion as a source of forage, including many types of bees.  Honey bees, bumble bees, and a variety of solitary bee species will use this plant as a source of both nectar and pollen.  Dandelion can survive and bloom despite mowing at low heights, making it an ideal candidate for a bee-friendly lawn.

Creeping CharlieCreeping Charlie
Creeping Charlie (Glechoma hederacea, aka ground ivy) is an aggressive lawn weed species that is found in every state in the United States, except for certain parts of the Southwest (NV, AZ, NM).  This plant is considered an invasive species in some habitats, and tends to thrive in disturbed sites that are shady and poorly drained.  Once established in a soil, creeping Charlie will spread quickly through aggressive stolons, forming mats that provide dense ground cover.  The flowers of creeping Charlie are easily recognizable, with small, purple, tubular flowers arising from upright, square stems.  Creeping Charlie has been the subject of heavy debate as to whether or not it should be used as a forage source for bees and other pollinators.  While it has many desirable qualities, including ease of establishment and a low-growing nature, recent research suggests that creeping Charlie is not an ideal forage source due to its unique pattern of nectar production.  Creeping Charlie exhibits wide ranges in both the quantity of nectar that it produces, and in the quality of the nectar (sugar concentration).  While some flowers of creeping Charlie will produce great amounts of nectar high in sugar concentration, the average flower from this plant produces less than half the nectar quantity seen in comparable flowers like white clover.  On average, nectar from creeping Charlie is higher in sugar concentration than that of white clover; however the range in sugar concentration is much more extreme.  Because of this, creeping Charlie is considered an inconsistent source of nectar for visiting pollinators, and should be omitted for more reliable alternatives like dandelion and white clover. 

Thursday, November 10, 2016

Preparing your trees for winter

By Gary Wyatt, Extension Educator - Agroforestry and Bioenergy

It may not seem like it with the unseasonably warm temperatures we’ve been experiencing this fall,
but winter is on its way. Are your trees and perennials prepared for the changes ahead?
Perennial shrubs and trees, especially conifers, should be watered generously until the soil freezes. Mulching trees will help reduce winter root damage.

Young maples and thin barked trees may benefit from some kind of sunscald protection to prevent the bark from cracking this winter and spring. This protection is usually in the form of a plastic tube or tree wrap which is removed in spring. These practices can also help in reducing winter animal damage. Read more ....

Thursday, October 27, 2016

What to do about fruit flies

Jeffrey Hahn, Extension Entomologist

Fruit flies, Drosophila spp., can be a common insect in homes during fall. Also called vinegar or pomace flies, they are small, about 1/8th inch long with a brownish body and a dark colored abdomen. Fruit flies typically have red eyes which are a good feature to help distinguish them
Fruit flies are about 1/8th inch long and usually have red eyes.
Photo: Jeff Hahn, U of M Extension
between other indoors flies (however this color fades once the flies are dead).

Be careful as there are other small-sized flies, such as fungus gnats, moth flies, and humpbacked flies, that could be confused with fruit flies. There is even a couple of species of fruit flies with dark colored eyes that are a little larger than an average fruit fly. The control varies depending on what the type of fly is found so it is important to verify the insect you are finding in your home.

Fruit flies are associated with fermenting, moist, relatively undisturbed organic material. This is often due to overripe and decaying fruits and vegetables but can also be in a variety of other sources, such as soft drink, wine, and beer residue in unclean containers (and have been sitting around for a while) and trash containers with wet garbage that are not cleaned regularly.

These flies can also be found in unusual, unexpected sites. In one case they were found infesting an osage orange that had been set out to control spiders (which by the way does not work) and forgotten about. As it became soft and started to decay, it attracted fruit flies which infested it.

The best control of these flies is to find the source of the infestation and remove it. While this is straight forward, it can be easier said than done. You often have to be a detective to locate the problem as it may not be immediately obvious what they are infesting. Particularly examine areas where fruit flies are found but keep in mind that the infestation source may not always be near where fruit flies are found; it could even be in a different room. Keep inspecting after you find the breeding site as there may be more than one infestation source.

It may be tempting to kill the adults by spraying, swatting or trapping them but this rarely eliminates them. As long as a food sources remains, fruit flies can reproduce faster than you kill the adults. It is very difficult, if not impossible, to get ahead of the problem and eliminate all of the flies by directing control at the adults.

Friday, October 14, 2016

2017 Minnesota Gardening Calendar available

2017 Minnesota Gardening Calendar
30 pages of tips, photos, guidelines for MN gardeners
The 2017 Minnesota Gardening Calendar is a great resource for the gardeners in your life! It is a terrific holiday gift, housewarming gift (especially new homeowners who have never owned a yard), host gift, or just a thanks-for-watching-my-plants gift. Whatever your reason, this is the time to get your copies. Buy online or in person from selected University of Minnesota bookstores and the Minnesota Landscape Arboretum gift shop. Written by Extension Horticulturists. the 2017 Minnesota Gardening Calendar features monthly lawn care and gardening. Featured writer and turf extension Educator Sam Bauer contributes an informative article called Water Saving Strategies for Home Lawns and provides guidance on reducing our water use without sacrificing a great looking lawn. And then there are the photos! Each month features a timely photo that reminds us Minnesota landscapes are beautiful at any time of the year!
Timely photos each month
Timely gardening tips each month

Articles by Extension experts
Important guides for successful gardens

There's still time for dormant seeding - a good option for good lawn next spring

“I know I missed the best time for seeding my lawn which is mid-August to mid-September. Can I still seed even though it’s October and temperatures have been mild?” According to turfgrass Extension educator, Sam Bauer, “Just wait, dormant seeding in November will be your best option." True temperatures are warm during the month of October, and a homeowner could get some seed germination before winter snows, but this is touch-and-go. Bauer recommends saving your time and money and wait dormant seed in mid- to end-November. Read more.

Thursday, September 29, 2016

Temperature Control in a Bumble Bee Nest

Karl Foord - Extension Educator, Horticulture

The previous post linked to a video showing a new born bumble bee. The following video is of the same nest but involves a different observation.

To view and photograph the nest I had to pull away the straw covering the nest. This exposed the nest to the direct sun and evidently increased the temperature of the nest beyond the acceptable range of the worker bees. In this video a worker bumble bee uses her wings to fan and cool the nest. The wings are moving so fast that they practically disappear, a little like airplane propellers.

To give a sense of perspective, the engine on a propeller driven airplane rotates some 43 times in one second. I timed the wing speed of bumble bees in one of my videos to 172 beats per second. No wonder the wings are impossible to see when filmed at regular speed. In the second half of the video I have slowed the speed of the action by a factor of 4 and it is still difficult to see the wings moving. You can see the wings just when they begin to move and when they stop moving. Enjoy the blur as another one of the fascinating things one can find in the garden.

Observe a Newborn Bumble Bee

Karl Foord Extension Educator, Horticulture

Some of the folks maintaining the Display Garden located on the St. Paul Campus discovered a Two Spotted Bumble Bee nest (Bombus bimaculatus). On June 5th I found the nest with the help of Julie Weisenhorn and took some video.

This is a young nest and relatively early in the season, so the worker bumble bees are significantly smaller than the Queen. This bee is identified in the video.

In addition a new born bumble bee appears from under the top end of the nest. This individual can be recognized by the white hair covering its body. Later the hair in some places will turn golden and in other places black. Other evidence that this is a new born come from the shape of its wings. Notice that the wings on this bee are flat and curve around the base of the abdomen. The bee will proceed to pump hemolymph (the fluid of their circulatory system) into the veins of the wings. This will will expand and straighten the wings after which they will dry and become hardened. Only after this will the wings become functional and enable the bee to fly.

Tuesday, September 20, 2016

Remove white mold infected annuals

M. Grabowski, UMN Extension Educator
Zinnias killed by white mold. M. Grabowski, UMN Extension

 White mold is a plant disease caused by the fungus, Sclerotinia sclerotiorum. This pathogen is capable of infecting over 400 plant species. Flower garden favorites like zinnia, petunia, salvia, and snap dragon are highly susceptible to white mold. In the vegetable garden, tomatoes, green beans, lettuce and cabbage can all be infected. Removal of infected plants is a critical management strategy for white mold. The pathogen can survive up to 8 years in specialized resting structures produced on infected plant material. 

Tomato stem with fluffy white fungal growth on the outside and
black sclerotia on the inside.  M. Grabowski, UMN Extension

Plants infected with white mold often wilt and die. The lower stems of these plants will be tan and dry. If the humidity is high, white fluffy clumps of fungal growth may be seen on the stems. Gardeners may also see small, rough, black structures that look like seeds or peppercorns forming along stems or inside of them. These are special resting structures, called sclerotia that are created by the fungus. Sclerotia can survive in the soil for up to 8 years. Each year the sclerotia produce tiny mushroom like structures that releases spores and starts new infections. 

Gardeners that are seeing white mold in their gardens now, need to remove infected plants before sclerotia are dropped into the soil. The entire plant should be removed as soon as possible. Infected plants can be composted if the pile heats up to a minimum temperature of 148 F. Alternatively infected plants can be deeply buried (6-12 inches below ground) in an area of the yard that will not be used for flowers or vegetables in the future like a mulched are around trees or shrubs. 

Petunia bed with multiple plants killed by
white mold.  M. Grabowski, UMN Extension

Lower stems of white mold infected petunias are clearly tan and dry.
M. Grabowski, UMN Extension 

Friday, September 16, 2016

Orb weaving spiders

Jeffrey Hahn, Extension Entomologist

Spiders are particularly common around homes and gardens during late summer and fall. Undoubtedly the most common types are the orb weaving spiders (family Araneidae). These spiders can be recognized from the large, circular, flat webs that they construct. They vary in size although many are moderate to large sized.  Some species are very colorful. They typically have round, plump abdomens with relatively short stout legs.
Black and yellow argiope spider, a
common spider during late summer and
fall.  Photo: Jeff Hahn, U of M Extension

There are two common groups of orb weaving spiders that people commonly encountered, spiders in the genus Argiope and those belonging to the genus Araneus.

Argiope spiders, also referred to garden spiders are large with a body length up to one inch long, and conspicuously colored yellow and black or silver, yellow and black. Their abdomen is more oval compared to most orb weavers.

Araneus species are typically moderate sized.  They can be either brownish or colored brightly, especially orange or yellow.  Their abdomens are generally more round, sometimes even somewhat triangular.  Common species include barn (orbweaver) spider, cross orbweaver, shamrock orbweaver, and marbled orbweaver. Click here to learn about other Araneus orb weaving spiders.

Fortunately despite their appearance, orb weaving spiders are not aggressive or dangerous to people and no control is necessary. In fact, orb weaving spiders are fascinating to observe and people should consider themselves fortunate to have an orb weaving spider in their garden or yard to watch.

Wednesday, September 14, 2016

EAB found in Duluth again

Jeffrey Hahn, Extension Entomologist

(The following information is modified from a Minnesota Department of Agriculture news release).

The Minnesota Department of Agriculture (MDA) is issuing an emergency quarantine for the southeastern portion of St. Louis County (see below map) after confirming a second emerald ash borer (EAB) detection within the city of Duluth. EAB was found in Superior, Wisconsin across Lake Superior from Duluth in August, 2013. It was first found in Duluth in October, 2015 on Park Pointe; the quarantine at that time was restricted to only this island.

New quarantine area in southeast St. Louis
county due to new EAB discovery in Duluth. 
Map courtesy of MDA.
The emergency EAB quarantine limits the movement of firewood and ash material out of the quarantined area of the county. The quarantined area now runs from MN Highway 33/US Highway 53 on the west to the Lake County border on the east. The northern border of the quarantine runs from US Highway 53 along Three Lakes Road (County Highway 49) east to the intersection of Vermilion Trail. It then continues along the northern edge of Gnesen, North Star, and Alden townships. This extends south to the Carlton County/State of Wisconsin border.

To see the original MDA news release, go here.  For  more information on EAB, see Emerald ash borer in Minnesota.

Wednesday, September 7, 2016

EAB is found in Dodge County

Jeffrey Hahn, Extension

(The following information is modified from a Minnesota Department of Agriculture news release).

The Minnesota Department of Agriculture (MDA) has placed Dodge County under an emergency quarantine after emerald ash borer (EAB) was found in the city of Kasson last week. Kasson is about 13 miles west of the nearest known EAB infestation in Rochester (Olmstead County). The EAB was found in a United States Department of Agriculture (USDA) trap. MDA staff has since conducted a search of the area and discovered an EAB infested tree.
Emerald ash borer was found for the first time in Dodge
county, caught on a trap.  Photo: Jeff Hahn, U of M Extension

Because this is the first time EAB has been identified in Dodge County, the MDA is enacting an emergency quarantine to limit the movement of firewood and ash material out of the county. This will reduce the risk of further spreading the tree-killing insect. Currently 12 other Minnesota counties and Park Point in the city of Duluth are under quarantine to prevent the spread of the emerald ash borer.

The biggest risk of spreading EAB comes from people unknowingly moving firewood or other ash products harboring larvae. Take these three easy steps to keep EAB from spreading:

• Don’t transport firewood. Buy firewood locally from approved vendors, and burn it where you buy it;

• Be aware of the quarantine restrictions. If you live in a quarantined county, be aware of the restrictions on movement of products such as ash trees, wood chips, and firewood; and,

• Watch your ash trees for infestation. If you think your ash tree is infested, go to and use the “Do I Have Emerald Ash Borer?” guide.

Emerald ash borer larvae kill ash trees by tunneling under the bark and feeding on the part of the tree that moves nutrients up and down the trunk. Since its accidental introduction into North America, EAB has killed tens of millions of ash trees in 24 states. The invasive insect was first discovered in Minnesota in 2009. Minnesota is highly susceptible to EAB as the state has nearly one billion ash trees.

For more information on EAB, see Emerald ash borer in Minnesota. Go here for the original MDA news release.

Thursday, September 1, 2016

Turf War: Overwatering our lawns is sucking up our water supply (Star Tribune)

Sam Bauer, Extension Educator

Over the weekend the Star Tribune ran an article discussing lawn watering and its impacts on our pocketbooks and our water supply.  The author, Hannah Covington, spent a day with our Extension Turfgrass Science Team as we conducted irrigation audits for several homeowners in Apple Valley.  This study is sponsored by the Metropolitan Council with the ultimate goal of reducing the amount of water being applied to our home landscapes, much of which is wasted water.  With this study, we are conducting a survey (which many of you filled out- thank you!) and we are also selecting residents in the 7-county Metro Area to have their home irrigation systems being audited.  The audits entail checking irrigation system components, conducting performance testing and making recommendations on how to save water through basic irrigation system adjustments.  You can read more about how to properly conduct an audit of your irrigation system in the previous Yard and Garden News article titled "Water Wisely: Auditing Home Lawn Irrigation Systems."  To see just how strongly people feel about lawn watering, either for or against the practice, have a look at the 170 comments following the article below on the Star Tribune website.  Click the image below to be directed to the original article.  Thank you for your support of our water saving initiatives!  

Water Wisely: Auditing Home Lawn Irrigation Systems

Sam Bauer, Extension Educator

A broken sprinkler can waste thousands
of gallons of water in a single year
Auditing irrigation systems is an important practice for maximizing water use efficiency in the home landscape.  Audits entail checking for irrigation uniformity and converting minutes of irrigation to a depth in inches of water applied.   A full irrigation audit should be conducted at least every three years, although proper irrigation requires more frequent monitoring of irrigation system components to ensure that everything is working properly.  Broken sprinkler heads and irrigation of impervious surfaces are very common issues that we observe and these must be repaired in a timely manner. 

Basic Irrigation Auditing Procedure

Step 1: System inspection
Irrigation of impervious surfaces is
bad practice and will cost you money
Run each irrigation zone.  Look for broken sprinklers, low water pressure and arcs or angles of water spray that are distributing water where it is not needed (i.e. on streets or driveways).  Replace sprinklers, correct water pressure issues, and make adjustments to the water distribution so your system is supplying water where it is needed.  

Step 2: Performance testing
Performance testing involves placing catch cans on the lawn in an evenly spaced grid pattern throughout an individual irrigation zone.  Cans should be placed 5 to 8 feet apart for small area spray-sprinklers and 10 to 20 feet apart for large area rotor-type sprinklers.  A minimum of 20 cans should be used for each irrigation zone- more cans allow for greater accuracy.  Tuna or coffee cans work great for this, or you can purchase special catch cans designed for irrigation audits from big box stores for less than $1/each (be sure to use cans that have straight sides). 
Catch cans will allow you to measure
uniformity and rate of irrigation

After the catch cans are placed throughout an irrigation zone, run the zone for a set amount of time; minimum run time should be 30 minutes, but longer run times such as 60 minutes will be more accurate.  Next, measure and record the depth in inches of water in each can.  Repeat this procedure for each individual zone of your irrigation system.

Step 3: Uniformity calculations and scheduling zones
To calculate the precipitation rate of each irrigation zone, calculate the average depth of water in the catch cans for one hour of run time.  For example, if the average depth of our 20 cans was 0.75 inches and we ran the zone for 30 minutes, our precipitation rate would be 1.5 inches per hour.  For uniformity calculations, take the average depth of the lowest 25% of cans (in this case the 5 lowest cans) divided by the overall average of all cans.  For example, if the average of our 5 lowest measuring cans is 0.5 inches, divide 0.5 by 0.75 = 0.67 or 67%.  Irrigation systems with lower than 60% uniformity should be adjusted for better uniformity.
Special cans for auditing
make measurements easy

Once you have calculated the precipitation rate for each zone, you can set the run times.  If your goal is to apply 0.5 inches in one irrigation cycle and the precipitation rate is 1.5 inches per hour, set the zone for 20 minutes.    

For more information on auditing irrigation systems, visit the Irrigation Association website.

Wednesday, August 31, 2016

Bacterial diseases of vegetables

M. Grabowski, UMN Extension Educator

The bacteria that cause black rot in cabbage spread through the
plant's veins in the field and in storage.
M. Grabowski, UMN Extension
The high heat and humidity this summer, combined with multiple heavy rain events have created ideal conditions for many bacterial plant pathogens to multiply and spread. This is especially evident in the vegetable garden, where black rot can be easily found on cabbage, kale, and broccoli, beans bear spots and browning from bacterial leaf blights, and tomato and peppers are spotted by bacterial spot.

Bacterial plant pathogens have several unique features that make them good plant pathogens. Many are able to infect seed and can be introduced into the garden unseen on infected seed or transplants.

Bacterial diseases of bean often result in spots on leaves and
 bean pods. M. Grabowski, UMN Extension
Bacteria are covered in a sticky coating and are easily spread through the garden on hands, tools, and insects. Many bacterial plant pathogens are also easily spread by splashing rain or sprinkler irrigation. Bacteria infect the plant through natural openings or wounds. They multiply within infected plant tissue and can survive from one growing season to the next in infected plant debris in the soil.

Many management strategies for bacterial plant diseases are designed to prevent the introduction and spread of the pathogen. For example, gardeners should buy healthy seeds and transplants from a reputable source and use drip irrigation instead of sprinklers to keep leaves dry.

At this time of year, there are still a few things that gardeners can do to manage bacterial diseases. 
  • Avoid working in plants when they are wet. 
  • When working in the garden, take care of healthy plants before working in infected plants. 
  • Clean tools with solution of 1 part household bleach and 9 parts of water after working in infected plants. Clean hands with soap and water. 
  • Up to 1/3rd of infected leaves can be removed from an infected plant to reduce disease spread. (At this time of year, this is practical for crops like Brussels sprouts and kale that are still developing a crop, but is not necessary for tomatoes, peppers, and beans, which are near the end of their natural production cycle.)
  • Remove infected plants that are no longer producing a crop. 
  • Do not save seed from infected plants. 
Seed saved from tomato fruit infected by a bacterial plant
pathogen may be infected with the bacteria.
M. Grabowski, UMN Extension 

Diseased plant material can be composted if the compost pile heats up to 148 F and all plant material becomes broken down. Many counties offer municipal compost sites that accept yard waste. If composting is not an option, infected plants should be buried in the soil soon after harvest. The soil microorganisms will begin to break down the infected plant material. The pathogen would be expected to survive in the soil and plant debris for 1 to 2 years. As a result, the same crop and related plants should not be planted at that site for the next 1 to 2 years.

Springtails in homes

Jeffrey Hahn, Extension Entomologist

A consequence of the abundant rainfall that most of Minnesota has received has been an increase of springtails found in homes and other buildings. Springtails are small insects that are associated with moisture. They range in size from 1/16 - 1/8 inch in length. Most are slender, although some are round and stout. They are typically dark colored, gray, black or brown, but some are white and some even iridescent and brightly colored. Springtails lack wings but do have the ability to jump.

Springtails as a group are very numerous, living in a variety of moist habitats including in soil, leaf litter, mulch, decaying wood, and around bark where they feed on fungi, pollen, algae, and decaying plant matter. They can live inside buildings when high moisture exits, e.g. around plumbing leaks. They can also seek shelter indoors when areas around the outside of the home become excessively wet. Fortunately, regardless of the number that are seen, they do not harm people or damage property. But they can be annoying when conspicuous numbers are present.
They may be small but springtails can occur in large
numbers and be a nuisance in homes. Photo: Unknown

They key to controlling springtails is reducing moisture; they cannot survive if sufficient moisture is not present. However, the reason springtails are present will influence how easy it is to get rid of them. If springtails entered structures to escape excessive damp outdoor areas, they are expected to go away on their own as the rain lessens and the humidity goes down. Use a fan or dehumidifier to reduce indoor humidity to help reduce springtail numbers until they are gone.

However, if there is some sort of ongoing moisture problem, springtails will continue to be an issue. Check indoors for sources of moisture and areas of high humidity. The moisture source could also originate outdoors, e.g. rainspouts that do not carry the water far enough away from the foundation or landscapes that slope towards buildings. Correcting existing moisture conditions is a long-term solution in springtail control.

Although it may be tempting for some to treat springtails with an insecticide, the products available to residents are not very effective against these insects. Moisture control is the most effective strategy.

For more information, see the University of Minnesota Extension fact sheet Springtails

A bad year for bur oak blight

M. Grabowski, UMN Extension Educator

Bur oak blight, M. Grabowski, UMN Extension
This summer many bur oak trees are suffering significant leaf browning and death due to bur oak blight. Frequent rain events at the time new leaves were reaching their mature size created highly favorable conditions for infection by the fungus that causes bur oak blight. For property owners with affected bur oak trees, now is the time to submit a sample for diagnosis. If disease is severe, contact an arborist now to schedule treatment for bur oak blight in spring of 2017.

Bur oak blight, often referred to as BOB, is a plant disease caused by the fungus Tubakia iowensis. The BOB fungus survives the winter on infected leaves that remain attached within the tree canopy.  In wet spring weather, the fungus releases spores that start infections on new leaves. Although the infections occur in spring, the most obvious symptoms do not appear until the end of July or early August. Initially, dark discolored lines can be seen forming along major leaf veins. As the disease progresses the discoloration expands into brown wedge shaped areas. Leaves may remain partially brown and green or may turn completely brown and withered. When autumn leaf drop occurs, many leaves infected with bur oak blight remain attached to the tree.

Wedge shaped brown areas and completely
brown leaves are both symptoms of bur oak
blight. M. Grabowski, UMN Extension 
Bur oak blight is a slow moving disease. The leaves in the lower canopy are usually first to be infected. Some of these leaves remain attached until the following growing season and will allow the disease to move up to higher branches. Each year, the disease infects a greater portion of the tree canopy. This slow progression of disease eventually stresses the tree and allows secondary pests and pathogens, like two lined chestnut borer and Armillaria root rot to infect and further injure the tree. The combination of these infections can lead to tree decline and death.

Many pests and pathogens can cause leaf browning in oak trees. Oak wilt, another fungal disease of oak trees, can cause similar symptoms to bur oak blight. It is important to identify exactly what pest or pathogen is causing the problem, so the appropriate management strategy can be applied. Property owners with bur oak trees in poor condition should submit a sample to the UMN Plant Disease Clinic for diagnosis.  

Browning begins on major leaf veins and expands into large
wedge shaped areas. M. Grabowski, UMN Extension 
Once bur oak blight has been confirmed, a management plan can be created. Trees can tolerate BOB for multiple years and do not require treatment if less than 50-60% of the leaves in the canopy are infected. Trees with low levels of infection should be examined each year in August to determine if severity has increased to the point that intervention is needed.

In high-value, landscape trees, once 50-60% or more of the canopy is infected with BOB, treatment of bur oak blight with a fungicidal injection is recommended to prevent tree decline. A trunk injection of propiconazole fungicide in spring when new leaves have just reached their mature size has been shown to significantly reduce bur oak blight in most cases.  This treatment must be applied by an arborist and timing of the treatment is critical. Property owners wishing to have their trees treated in 2017 should contact an arborist now to schedule the treatment.

Bur oaks are sensitive to propiconazole fungicides. As a result, the fungicide must be applied at the rate of 10 ml per inch of trunk diameter at breast height. This is half the maximum rate labeled for oak wilt. Applying the fungicide at a lower rate will help to reduce phytotoxicity, but even at low rates, gardeners may notice some leaf browning and other leaf damage the year the application is made. Unfortunately no other fungicides have proven effective in protecting bur oaks from BOB. Once an application has been made, disease should be significantly reduced and the tree will not need to be treated again until bur oak blight once again affects 50-60% of the canopy.

Tuesday, August 30, 2016

Useful Tools to Determine Soil Moisture Status II: Gypsum blocks and others

Karl Foord, Extension Educator - Horticulture

Another tool for measuring soil moisture are gypsum blocks. Gypsum is a porous material that equilibrates with soil water similar to the ceramic tips of the tensiometers. In this case two electrodes are embedding in the gypsum block in a cylindrical or parallel mode (Figure 1). The commercial product often has a perforated metal covering to protect the gypsum (Figure 2).
Figure 1

Figure 2

This system functions by connecting to a meter that measures the resistance between the two electrodes embedded in the gypsum. Water is a good conductor of electricity. As soil water decreases due to plant draw down resistance increases and visa versa when soil water increases resistance decreases. The electrodes can be permanently connected to a box (Figure 3) or temporarily connected to a portable meter (Figure 4).

Figure 3

Figure 4

Placement of gypsum blocks follows the same strategy that is used with tensiometers. One block is placed in the middle of the fibrous root zone and another below this zone. The upper block indicates when irrigation is needed, and the lower block determines when to turn the irrigation off.

Other systems

There are other types of soil moisture sensors. The principles behind these sensors range from simple to sophisticated.

The most inexpensive type of moisture sensor follows the principles of a galvanic cell e.g. a battery. The shaft of the instrument is made of one metal and the tip of another, often copper and lead respectively. The soil water functions as the electrolyte facilitating the movement of electrons from one metal to the other. High meter readings are associated with high soil moisture and low readings with low soil moisture (Figure 5). One note of caution about these meters. They are designed to take a soil moisture reading and be removed from the soil. If left in the soil the "battery" will continue to discharge and the meter will quickly become nonfunctional. What can you expect from a meter that might cost $8? There are more robust meters with greater capacity due to more metal but they are significantly more expensive.

Figure 5

Other soil moisture sensors utilize other principles of physics to measure soil water content. These principles are beyond the scope of this blog. Suffice it to say that they all use water as part of their "circuitry" and respond differently to different amounts of soil moisture.

The information given herein is supplied with the understanding that no endorsement of named products is intended, nor is discrimination or criticism implied of products mentioned or not mentioned.

Monday, August 29, 2016

Useful Tools to Determine Soil Moisture I: Tensiometers

Karl Foord, Extension Educator - Horticulture

Generally the most limiting element in maintaining uniform plant growth and high quality produce is water. A plant can be experiencing water deficit prior to our observation of wilting. Such deficits can lead to slower growth rates, pollen mortality and loss of flowers, lighter fruit weight, and blossom end rot, among others. It is best to avoid having the plant experience any water deficit.

However, how can you know that the plant is in water deficit? The truth is that you can only know this indirectly. One can estimate soil water content by taking a soil surface sample and feeling the water content with your hand; this will of course vary with soil type and again extrapolates the soil water content within the root zone. This method will require consistent attention to growing conditions including temperature humidity and rainfall.

What  other options might allow a more direct sampling of soil water content within the rooting zone of the plant?

Soil Water Potential

Soil water potential is a measure of the amount of energy required by the plant to absorb or extract water from the soil matrix. A soil water potential value of 0 (Zero) means that the soil is saturated, water moves freely, and the plant need not expend energy to absorb water at this potential. However as water is removed from the soil by the plant, more energy will be required by the plant to extract water overcoming the forces holding water molecules to soil particles. The soil water potential is measured in centibars and as the values become more negative the difficulty in obtaining water becomes greater. One tool to measure water potential is a tensiometer.


A tensiometer is a hollow tube with a porous ceramic tip at one end (Figure 1).
Figure 1

The tube is filled with water and sealed with a cap, and has an attached vacuum gauge. The porous tip allows the water in the tube to be connected to the soil water matrix. As plants use water and the soil dries out, water is also drawn out of the tensiometer. Because the tube is sealed, a vacuum is created and measured by the gauge. Plants can easily extract soil water when the soil water potential value is 10 centibars (CB). At higher values such as 35 CB it is more difficult for the plant to extract water. Figure 2 shows the face of the pressure gauge.
Figure 2

Figure 3 shows the cycling of tensiometer readings over a period of time. The plants use water and the pressure increases into a range between 20 and 38. The sloped lines indicate the water draw down and the straight lines indicate a watering event. The gauge reading returns to near zero following the watering event .
Figure 3

By placing tensiometers at two depths, we have a way of knowing when to turn the water on and when to turn it off. A short tensiometer (6") is place in the middle of the active root zone, and a longer tensiometer (12") is placed below the active root zone. When the short tensiometer reads between 30 and 35 CB begin irrigation. As irrigation begins the 6" gauge will begin to move to zero. But when should you stop irrigating because the 6" gauge is in the middle of the root zone? When the 12" gauge begins to move to zero it means that the water is beginning to exit the active root zone. At this point the irrigation should be turned off (Figure 4).
Figure 4
 We will take a look at some other tools used to measure soil moisture in the second part of this blog.

Friday, August 19, 2016

Bugs on milkweed

Jeffrey Hahn, Extension Entomologist

Home gardeners have been finding orange and black insects on their milkweed and related plants. Although some people think they are boxelder bugs, they are actually insects called large milkweed bugs, Oncopeltus fasciatus.
Large milkweed bugs are colorful and conspicuous and
fortunately harmless.  Photo: Jeff Hahn, U of M Extension

Adults grow as large as ¾ inch long. They are mostly orange and black including a black horizontal band across the center of the body and black on the end of the wings (the membranous section). A portion of the head is reddish orange. The immature nymphs are mostly orange with black wing pads and smaller than the adults.

Large milkweed bugs prefer to feed on common milkweed but will also feed on other related species. They often feed in large groups making them conspicuous on the plants. Despite their appearance, they do not harm milkweed nor any insects, like monarchs, they may also be on the plants. No action is necessary if large milkweed bugs are found in your garden.

Thursday, August 18, 2016

Sap beetles in gardens

Jeffrey Hahn, Extension Entomologist

Some home gardeners have been finding sap beetles in some of their fruits and vegetables. These beetles are generally small, between 1/8 – ¼ inch long, oval, and dark colored. Some sap beetles have orange spots on their wing covers.
A picnic beetle, a common type of sap beetle.
Photo: Tom Murray
Sap beetles are attracted to fermenting smells and will attack fruits and vegetables, such as tomatoes, sweet corn, raspberries, strawberries, and muskmelons, that are damaged, overripe, or rotting. They often are just a nuisance, although it is possible for them to move to and damage ripening fruit.

The best management for sap beetles is to pick fruits and vegetables regularly as they ripen and remove any damaged or overripe produce in your garden and dispose of by burying or bagging them. This helps eliminate smells that could attract them to your garden. However, once sap beetle find your garden, they can be challenging to eliminate.

Insecticides, such as carbaryl or permethrin, can kill sap
Pick up fallen and damaged fruit to prevent
attracting sap beetles to your garden.
Photo: Jeff Hahn, U of M Extension
beetles and reduce their numbers. However, the challenge is that there is an interval of time between when a product is applied and when the fruits or vegetables can be safely harvested. You can find this information by looking for the Days to Wait to Harvest number on the pesticide label.

Depending on the product, this can take days or even weeks. By then the sap beetles have likely returned. If that is the case, try to use a product with as short of a time interval as possible.

See also Sap beetles in home gardens

Friday, August 12, 2016

Extension publications: New & Revised in 2016

The following list is updated with links to new and revised online Extension publications as they become available. The publications are new unless otherwise indicated.


Monday, August 1, 2016

Lawn Irrigation Survey and Water Saving Strategies

The Metropolitan Council and University of Minnesota Extension are conducting a survey to assess irrigation practices throughout the 7-county Twin Cities Metropolitan Area.  This survey is part of a larger project with the ultimate goal of reducing water use in the home landscape.  You can help us by taking 10-15 minutes to answer a 30 question survey regarding your irrigation practices.  All survey participants will be entered into a drawing for 1 of 10 Visa Gift Cards ($50 value).  Additionally, we are conducting irrigation audits for many properties throughout the Twin Cities.  To have your home irrigation system audited, please complete the survey and indicate that you would like to receive a free audit.  To access the survey, please follow click the hyperlink below: 


Basic water saving strategies for home lawns      
Pay attention to the weather
During a Minnesota summer we may see heavy periods of rainfall followed by extended periods of drought. Homeowners with lawns should adjust irrigation practices accordingly. Operating irrigation controllers in manual mode is one way to monitor and cut down on water use, rather than using an automated schedule.
Select turfgrass species that use less water and can tolerate drought
Choice of grass species will impact irrigation requirements. Traditional turfgrass species for Minnesota include Kentucky bluegrass, perennial ryegrass, fine fescue, and tall fescue. The fescue species offer the best drought tolerance potential. 
Adjust irrigation programs to conserve water
To encourage rooting and drought tolerance, lawns should be irrigated infrequently (one time or less per week) with a sufficient volume of water (up to 0.5 inches). Set irrigation programs or sprinklers to water during the morning hours, because daytime irrigation is often lost through evaporation or wind deflection.    
Implement water saving technologies
Rain sensors connected to irrigation controllers are vital to conserving water. There’s no need for an automatic sprinkler system to be used when it’s raining.
Conduct an audit on your irrigation system
Irrigation auditing is one great way to conserve water.  Irrigation contractors will often perform this service for you if you have a contract with them.  Auditing an irrigation system includes three basic steps: 1) checking system components including sprinklers, valves and controllers, 2) conducting a performance test, and 3) programming the controller.  Visit the Irrigation Association website for more information on conducting an irrigation audit

Friday, July 29, 2016

Ground-nesting solitary wasps

Jeff Hahn, Extension Entomologist

There have been a lot of questions about solitary wasps lately. The most common questions have been about cicada killers (Sphecius speciosus) but residents have also seen great golden digger wasps (Sphex ichneumoneus), steel-blue cricket hunters (Chlorion aerarium), and sand wasps (Bembicini).
Cicada killer returning to its nest with a paralyzed cicada. 
Photo: Jeff Hahn, UMN Extension

These wasps are generally large insects. Cicada killers range in size from 1 – 1 ½ inches with a stout body, black and reddish brown thorax, amber colored wings, reddish brown legs, and a black abdomen with yellow bands. Great golden digger wasps are about one inch in length, a more slender body with a black head and thorax covered with short golden hair with a reddish-orange and black abdomen and reddish-orange legs. They have smoky, dark colored wings. Steel-blue cricket hunters are also about one inch in size and relatively slender with iridescent dark blue bodies and wings. Sand wasps are smaller, most are close to ½ inch in length and are typically black and yellow.

Great golden digger wasp with a captured katydid.
Photo: Jeff Hahn, UMN Extension
Their biology is similar to each other. They nest individually in burrows but are gregarious, i.e. there are many nests in a small area. They hunt specific insect prey, paralyze them, and bring them back to their nest to feed to their young. Cicada killers seek out cicadas; great golden digger wasps hunt katydids, steel-blue cricket hunters capture field crickets and sand wasps, depending on the species, look for a variety of different insects, especially flies.

These wasps can be common in lawns, gardens, areas adjacent to sidewalks and driveways, and areas with patio stones. Typically they are found nesting in well drained, light textured or sandy soils. The females are not aggressive and while they are capable of stinging will only do so to defend themselves. Males can aggressively guard a territory and will challenge other males (even people) but they lack a stinger cannot harm us.
Aggregation of dozens of great golden digger wasp nests (with
dozens more to the right).  Photo: Jeff Hahn, UMN Extension

They do not injure turf, nesting in areas where the lawn has thinned or existing bare spots. There can be a large quantity of dirt that is dug up which can be unsightly. It is possible that their tunneling can undermine patio bricks but nothing worse than that. Some people are frightened by them because of their size and perceived threat.

There are a couple of options for dealing with ground nesting solitary wasps. The first is to ignore them. They are not causing any real harm and are not dangerous to people. They will go away eventually on their own sometime during August. However, if they were present this year, they will probably nest in the same area next year.

Sand wasp with paralyzed leaf-footed bug prey.
Photo: Jeff Hahn, UMN Extension
If control is desired, it will be necessary to treat the nests with an insecticide. Generally spraying the nests is not very effective. Instead, apply an insecticide directly into each individual nest entrance. Dusts are most effective; granules and sprays can also help reduce numbers. Effective active ingredients include permethrin and carbaryl. If you rather, you can also contact a lawn service to treat the cicada killers for you.
  • © Regents of the University of Minnesota. All rights reserved.
  • The University of Minnesota is an equal opportunity educator and employer. Privacy