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Extension > Yard and Garden News > Archives > June 2013 Archives

June 2013 Archives

Stag Beetles in Yards

Jeffrey Hahn, Asst. Extension Entomologist

Jeff Hahn

Photo 1: Stag beetles. Note the large mandibles.

People have been finding stag beetles in their yards and gardens recently, sometimes in large numbers. Also known as pinching bugs, these beetles typically measure a little more than one inch in size and are reddish brown to dark brown in color. Stag beetles resemble June beetles but have more prominent heads. The mandibles (jaws) of both sexes are also large and conspicuous, especially those of males. Stag beetles have short antennae with conspicuous asymmetrical plates (lobes) at the end of them which they are not able to close together. One of the most common species in Minnesota is Lucanus placidus.

All stag beetle larvae feed in dead or decaying wood, such as logs and stumps. Most adults emerge in May or June and feed on sap that exudes from plants. Stag beetles are active at night and are often attracted to lights. They can fly into a yard, land on the ground and remain there until the following morning. Some people have observed stag beetles emerging from the ground. This indicates that there are some old roots or other buried decaying wood where the larvae were feeding and developing.

Although a lot of stag beetles in a yard is annoying, they are harmless to people and property. Do not spray stag beetles, their control isn't necessary. Just ignore them until they go away on their own.

M. Grabowski

Photo 1: Impatiens showing symptoms of downy mildew

Michelle Grabowski, UMN Extension Educator


The extended cool wet weather present throughout much of Minnesota has brought out the symptoms of impatiens downy mildew early this year. Plants infected with impatiens downy mildew drop their blossoms and have yellow stippled leaves that curl under at the edges. As the disease progresses, infected leaves fall off, leaving barren green stalks, which flop to the soil like cooked spaghetti noodles with time. Plants that are infected very young often remain small and yellow, dropping leaves and collapsing before they can ever grow to maturity.

The pathogen responsible for impatiens downy mildew is Plasmopara obducens, a water mold that thrives in cool wet conditions. Spores of the pathogen can be seen as fluffy white growth on the lower surface of infected leaves. These spores are easily spread on wind and splashing rain.

M.Grabowski, UMN Extension

Photo 2: Sporulation of downy mildew on the lower surface of an infected leaf

Gardeners observing symptoms of downy mildew on impatiens should remove plants immediately. Once spores of the pathogen have been found on the plant, there is no way to prevent its eventual decline from disease. Impatiens downy mildew only infects some species of impatiens. All varieties of Impatiens walleriana, standard impatiens, are highly susceptible to the disease. In gardens where the disease has been found, other shade annuals like begonia, coleus, and caladium are good choices for replacement plants. New Guinea impatiens, Impatiens hawkeri, are resistant to the disease and can also be planted in beds with a history of disease.

Some fungicides can protect healthy impatiens from infection with downy mildew but most are unavailable to home gardeners. Gardeners interested in protecting impatiens from downy mildew should contact a landscape professional with a pesticide applicators license to treat plants. More information about impatiens downy mildew can be found at the UMN Extension Garden webpage.

Protect Yourself from Mosquitoes

Jeffrey Hahn, Asst. Extension Entomologist

A benefit of our cold, late spring has been that the primary biting mosquito in Minnesota, Aedes vexans, was delayed in its emergence until early June. However, they are out now and if you spend any time outside, they will find you sooner or later. Mosquitoes have been particularly abundant this year because of the frequent rainfalls we have received. As long as we received regular rain, we can expect to continue to battle mosquitoes. In addition to the annoyance of their bites, mosquitoes are capable of transmitting diseases to people, especially west Nile virus (there were 70 cases in 34 counties in Minnesota last year including one death) and Lacrosse encephalitis. 

Jeff Hahn

Photo 1: Mosquitoes are abundant when we have a lot of rain.

It is challenging to completely avoid mosquito bites but there are some steps you can take to minimize your exposure to them. It is important to remove or drain potential breeding sites for mosquitoes. Any kind of standing water, with a little bit of organic material, is a suitable place for mosquito larvae to live and develop. This can include, but not limited to, buckets, tires, cans, and children's' swimming pools. Even clogged gutters can be source for mosquitoes. The key is that the site contains shallow water and is left undisturbed. While this step helps to reduce mosquitoes that can be produced on your property, this does not impact mosquitoes that can fly into your yard from adjacent areas.


Try to avoid, when possible, being outside when mosquitoes are most common. Mosquitoes typically are most active and bite during the morning and evening, although they will take a blood meal from us anytime during the day if we are close enough to their resting sites around grassy and brushy areas, shrubs, and trees.
Also use personal protection to help prevent mosquitoes from biting you. Consider wearing protective clothes to cover bare skin including sleeves shirts, long pants, and socks and shoes. Ultimately, the best personal protection against mosquitoes is the application of repellents. 

doubleoakmountainpharmacy.blogspot.com

Photo 2: Using a repellent, like DEET, is the best defense against mosquitoes.

The most effective and long lasting repellent is DEET (N,N diethyl m toluamide). This product has an excellent track record of safety for the last six decades. It comes in different concentrations, ranging from 4% to 100%, offering protection from 90 minutes up to 10 hours. However, there appears to be a limit to how much protection increasing concentrations of DEET can provide. There is evidence that suggests that there may not be much difference between concentrations of 35% and 100%. Applications of no more than 30% DEET can be used on children and infants at least two years old.


There are several alternatives that are effective repellents. One is option is picaridin. Picaridin has long been used as a mosquito repellent in Europe and Australia. It sold in the U.S. as a 7% or 15% concentration (Cutter Advanced and Cutter Advanced Sport). It is comparable to lower concentrations of DEET in effectiveness. Picaridin is generally less irritating to skin and lacks a chemical odor and sticky feel. Do not treat children younger than two years old with this product.

There are a couple of botanically based repellents available. Oil of lemon eucalyptus (p-menthane 3,8-diol), Repel brand, is a plant-based repellent sold as a 40% concentration. It is comparable to products containing low concentrations of DEET. Bite Blocker containing 2% soybean oil is also option. Research has shown that this repellent can offer protect for about 90 minutes or about the same protection as a very low concentration (4.75%) of DEET.

Whatever repellent you choose to use, be sure to always follow all label directions so the product is used most effectively while minimizing potential hazard to safety.

People's frustration with mosquitoes often leads them to put their faith in a variety of dubious methods to combat these blood-sucking insects. However, people are typically disappointed in the results of these tactics. Caveat emptor (buyer beware) -- what sounds too good to be true usually is.

Insect electrocuters, also known as bug zappers, attract large numbers of insects. However, research has shown that mosquitoes makes up less than 5% of all the flying insects killed. The number of mosquito bites remained the same regardless of whether or not you used a bug zapper. Research has even showed that insect electrocuters do more harm by killing beneficial insects.

Mosquito traps use carbon dioxide to attract mosquitoes, but it is unlikely that they can remove enough mosquitos to reduce the incidence of mosquito bites in a given area. While they sometimes can trap an impressive number of mosquitoes, this is a percentage of the overall mosquito population around the traps. Under the right circumstances, these traps can actually draw more mosquitoes into a yard than what they actually collect. These devices are also usually expensive.

Jeff Hahn

Photo 3: Beware of gimmicks that promise to get rid of your mosquitoes; they are unlikely to prevent mosquitoes from biting.

There are a variety of devices that use sound to repel mosquitoes. They may claim to imitate the sound of male mosquitoes or predators like bats or dragonflies, insects or animals that female mosquitoes are supposed to avoid. Unfortunately this doesn't repel them in practice. Research has tested many of these products; none reduce the number of mosquito bites. A female mosquitoes' urge to find a blood meal outweighs potential threats to them.

The Citrosa 'Mosquito Fighter' plant is genetically created by crossing an African geranium with the Grass of China (which contains some citronella, a mild repellent). These plants are pleasant smelling and will grow to a height of 12 feet if left unpruned. But despite their claims, research has demonstrated that these plants do not repel mosquitoes. Citronella candles can help to some degree but its effectiveness is limited to small, calm areas. Any wind will disperse the smoke, negating any effect the candles could have.

Purple martins and bats have been reputed to consume large numbers of mosquitoes. While there is generally nothing wrong with encouraging these animals, mosquitoes actually made up less than 3% of purple martins' diets and less than 1% of bats' diets. Larger-sized, flying insects, such as dragonflies, butterflies, crane flies, beetles, and moths are the most common meals for these animals. The presence of purple martins and bats does not diminish the number of mosquito bites.

Something "bugging" you????? Join Julie Weisenhorn and special guest extension entomologist, P1150490.JPGJeff Hahn, this Saturday, 8-9am, on WCCO Radio's "Smart Gardens" (830 AM on the dial). This is your opportunity to get Jeff's help in solving those pesky pest questions. Listeners can call or text in questions for Jeff and Julie.

About the show: WCCO Radio has teamed up with U of M Extension to bring you "Smart Gardens" which airs every Saturday from 8-9 a.m. If you have something to say, call-in at 651-989-9226 or text 81807. For more info and podcasts: WCCO Smart Gardens

What the Heck is a Hellgrammite?

Jeffrey Hahn, Asst. Extension Entomologist

Andrew Williams

Photo 1: Hellgrammite, the larva of a dobsofly

Some residents have been recently encountering a large (and to some people a scary) insect larva. This dark colored insect, a hellgrammite (Corydalus cornutus), has an elongate and somewhat flattened body. It has six conspicuous legs as well as a series of filaments on the sides of its abdomen with small finger-like gills clustered at the base. A hellgrammite also has very prominent, strong mandibles (jaws). It reaches about two to three inches in length when fully grown. Despite its appearance, hellgrammites are not aggressive or dangerous to people, although it is possible that they can bite if they are handled carelessly.

A hellgrammite lives in running fresh water, such as streams or rivers, often hiding around rocks or debris. They are predaceous, feeding on insects and other aquatic invertebrates. They have the interesting ability of being able to swim backwards as well as forward. It is generally believed that they take one to three years before crawling out onto dry land to finish their development. They will usually create a cell in the soil near the water to pupate. They are sometimes used by fishermen as bait.

John Fogal

Photo 2: Male dobsonfly. Note the large mandibles.

As an adult, a hellgrammite becomes a dobsonfly. A dobsonfly is brown up to two inches long with long slender antennae and long wings with conspicuous mandibles. You can distinguish between the sexes as males possess mandibles up to 3/4 inch long, making them look quite fierce and dangerous. Fortunately they are not able to bite people, using their mandibles only for fighting other male dobsonflies. Females have smaller mandibles but could bite people if given a chance. Although adults are usually found near water, they are attracted to lights and can be found a fair distance away. Dobsonflies are harmless and are just a curiosity.



Pine Sawfly Larvae are out and about

Karl Foord - Extension Educator, Horticulture

Keep and eye out for Pine Sawfly Larvae. Please refer to the following two articles for details.


European Pine Sawfly is Active Now

Sawflies of trees and shrubs

Karl Foord - Extension Educator, Horticulture

Apple maggots are predicted to emerge in the beginning of July so this is a good time to consider protective strategies.

Karl Foord

Photo 1: Apple fruit prior to thinning


Apple maggot flies recognize and identify apples through a series of visual and chemical clues. The red sphere traps and the yellow square traps both covered with a sticky substance as well as scented lures aid in capture of apple maggot flies and will indicate their presence. However, it is unlikely that such traps will effectively protect your apples.




Karl Foord


Photo 2: Apple fruit after thinning



I have tried plastic bags which can work although they make the tree look phantasmagorical (i.e. nightmarish - please forgive - I always wanted to use that word in a sentence). I have also found that they can collect water and if faced toward the south can heat up and cause damage to the apple skin.

Karl Foord

Photo 3: Apple fruit with maggot barrier I

So this year I am trying Maggot Barriers that I purchased from the Seattle Tree Fruit Society although there are other suppliers of this product that can be found on the web. The Seattle Tree Fruit Society web site does show pictures of their recommendations for attaching the barrier. The maggot barriers are the so called "footies" which serve as single use protective socks that can be used to try on shoes if you have no socks.

Karl Foord

Photo 4: Apple fruit with maggot barrier II

The maggot barriers may confuse the flies who no longer recognize the apples because of the different color and texture of the footie covering the apple. The barriers may physically inhibit the maggots from depositing their eggs under the skin of the apple. However, mosquitoes don't seem to have any problem getting their proboscis through our woven shirts, so I wonder if apple maggot flies would really have a problem getting their ovipositor through the mesh of the footie.

Karl Foord

Photo 5: Apple fruit with maggot barrier III


This is the procedure that I am using. First thin the flower to one fruit per cluster (Photos 1 & 2). Then slip the sock/barrier over the apple and secure with a rubber band. I have three examples: the first with the apple at the end of the sock (photo 3), the second with the apple in the middle of the sock (photo 4), and finally the apple with most of the sock above the apple (photo 5). (note the last photo was taken with a flash which is why the color is so different)

I will let you know how this works for me.

For more information on apple maggot including other methods of control please use the following link. apple maggot

Bright orange slimy fungus in junipers

M. Grabowski, UMN Extension

Photo 1: Cedar Apple Rust Gall on Juniper

M. Grabowski, UMN Extension Educator

There is nothing that catches the eye so much as a bright orange slimy tentacle-like fungus hanging from a landscape juniper tree. What is that thing? you might ask. The answer is cedar apple rust, one of several Gymnosporangium rust fungi that infect junipers in the state of Minnesota. Gymnosporangium rust fungi are unique in that they spend part of their life infecting juniper trees, causing unusual brightly colored galls, and the other part of their life infecting leaves, fruits, and green stems of trees or shrubs in the Rosaceae family. The Rosaceae family includes crabapples, hawthorns and serviceberry. Different Gymnosporangium rusts infect different trees and shrubs.

On junipers, the cedar apple rust results in brown woody galls that can grow to over an inch in diameter. With wet weather, the galls produce bright orange tentacle like spore producing structures. These release spores that are carried to nearby crabapple or apple trees, later to become bright orange and red leaf spots. Cedar apple rust galls on juniper can dry down and rehydrate multiple times in one spring. With repeat rain events in Minnesota this year, the cedar apple rusts have been putting on a colorful show. The good news is the galls will dry up and die when warm dry weather arrives. Juniper trees are rarely harmed by cedar apple rust galls although gardeners might notice some dieback on branch tips girdled by large galls.

More information about cedar apple rust and other Gymnosporangium rusts can be found on the UMN Extension webpage, including information on how to identify and manage the different diseases on different host plants.

Anthracnose of shade trees thrives in cool wet spring

M. Grabowski, UMN Extension

Photo 1: Anthracnose on Maple

M. Grabowski, UMN Extension Educator


As cool wet weather persists in Minnesota this year, a common leaf blight disease of shade trees known as anthracnose thrives and spreads. Anthracnose is a fungal disease that causes leaf blotches, leaf distortion, shoot blight, and leaf drop. This disease is caused by several related fungi that thrive in cool wet conditions. Ash, maple and oak trees are all commonly infected with anthracnose and symptoms of the disease have been seen on all of these trees this spring. Despite blackening of leaves and shoots, anthracnose actually only results in a minor stress on the health of the tree. Only young growing leaves and shoots are susceptible to infection. Mature leaves are relatively resistant to the disease. Once warm dry weather arrives in Minnesota, leaves will mature and trees will replace lost leaves with a new flush of growth. As long as cool wet weather persists, however, expect this fungal disease to spread throughout the trees canopy. More information can be found about this disease at the UMN Extension publication on anthracnose in shade trees.

June 1 Issue of Yard and Garden News

Karl Foord - Extension Educator, Horticulture

This spring I noticed the black color on the branches of my Taylor's Sunburst Pine (Pinus contorta 'Taylor's Sunburst'). I remember seeing the same thing on my Uncle Fogy Jack Pine (Pinus banksiana) last year. The cause was the same in both cases Sooty Mold that has formed on the honeydew secretions of the Pine tortoise scale (Toumeyella parvicornis). To confirm this I went to the What's Wrong with My Plant Diagnostic Tool via the Extension Garden web page/Pest Management/Diagnose a Problem link. I tracked through "Evergreen Trees and Shrubs" to "Pine" to Black powdery coating on "needles" and "shoots". This confirmed the Sooty Mold. I also tracked through "Sticky substance coating needles" to confirm the Pine tortoise scale as the culprit.

Karl Foord

Photo 1: Uncle Fogy Pine (Pinus banksiana 'Uncle Fogy'

The scale organism put such stress on my Uncle Fogy Pine that the needles it produced were half the size of the normal needles. Upon removal of the scale the needles returned to normal size (photo 1). I had learned my lesson about the impact of Pine tortoise scale on my trees.

I knew that Imidacloprid had worked on Uncle Fogy so I grabbed the bottle and reread the label - not trusting my memory. I confirmed that yes this product is labeled for soft scales. I also reviewed the precautions about letting the chemical get into aquatic environments - no lakes, streams, or ponds nearby. I agreed with the label that whatever I used to measure the chemical should not be followed by using the same utensil for soup.

There was nothing on the label regarding protective equipment, however the label warned that this chemical can be harmful if absorbed through the skin so I followed my previous procedures of long sleeve shirt, long pants and plastic gloves for handling.

Because this was an evergreen ornamental tree I was not concerned about the potential effects of a systemic pesticide on pollinators because there would be no flowers to pollinate. Also because the product is used as a drench around the plant, I didn't have to worry about airborne spray drifting onto other plants, people, or pets. In addition there were no wet leaf surfaces so there was no issue of reentry to the area or drying time of the product.

The directions called for the tree trunk circumference in inches at a height of 4.5 ft. and that this length in inches should equal the number of ounces of product to be applied to the plant. But there were too many needles to measure the circumference so I estimated the diameter and multiplied by Pi. How often do you get to use the trigonometry you learned in high school? The amount came to @ 5 oz. I added this to a gallon of water as instructed and applied the solution evenly in a circle 2 ft. from the tree trunk. Put the container away and washed up.

I checked the tree every other day or so and several days later the scales were starting to look ill. In approximately two weeks all the scales were dead. My Taylor's Sunburst Pine is looking and growing nicely without having hundreds of Pine tortoise scale stylets sucking its "life's blood" plant sap.

Reading the label wasn't all that painful. Reading size 6 font text definitely required glasses for "mature" eyes. However, I did not skim the label or skip parts. I read carefully and made sure that I understood all parts and the risks involved. Yes following the label is the law. Following the label is also the responsible and intelligent thing to do. By proceeding in this manner I felt in command of the situation and understood that the action I was taking was going to solve the problem with minimal impact to the environment and all the other actors in our theater of life.

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