University of Minnesota Extension
Menu Menu

Extension > Yard and Garden News > November 2010

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.

  • © Regents of the University of Minnesota. All rights reserved.
  • The University of Minnesota is an equal opportunity educator and employer. Privacy