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Extension > Yard and Garden News > June 2015

Monday, June 29, 2015

Eight-legged friends or foes?

Lindsey Christianson, Recent M.S. Entomology Graduate

Spiders are common in and around homes this time of year. And while many may be fuzzy, not many people would consider spiders a warm and friendly type of fuzzy. However, in most cases, these creatures fall into the friendly category. Spiders eat insects and other arthropod pests and are considered beneficial. Some spiders inadvertently end up indoors and can be a nuisance by their presence. Two spiders in particular that have been noticeable have been the dark fishing spider and the bold jumper.

The most common species of fishing spider in Minnesota is the dark fishing spider Dolomedes tenebrosus. Fishing spiders are some of Minnesota’s largest and most conspicuous spiders, with bodies that can be up to an inch long. Fishing spiders have two rows of four eyes, and long “sprawling” legs. Dark fishing spiders tend to have brown and black banded legs and chevron markings on the abdomen. They are often found on tree trunks, building walls, fence posts, and near docks. Instead of spinning webs to catch prey, they ambush larger insects that pass by. Fishing spiders are not aggressive towards humans and rarely bite, but they may bite if mishandled or if they feel threatened. The bite is described as feeling similar to a bee sting, but it not harmful. BugGuide has more information and comparison photos for this species.
Dark fishing spider.  Photo: Jeffrey Hahn, UMN Extension
Bold jumpers (Phidippus audax) are often called white-spotted jumping spiders because of the distinct white spot on their abdomen. Bold jumpers are large bodied jumping spiders, ranging from ¼” to ¾” in size. While they are mostly black, they may also be mottled with white on their abdomen and legs.  To identify a bold jumper, look for eight eyes of which two are particularly large.  Bold jumper's chelicerae (fangs) are typically an iridescent green or blue. They are not web-spinners, and hunt small insect prey. Bold jumpers rarely bite but like fishing spiders can if mishandled. Any bites do not produce any lasting effects.
Bold jumper (note the two large eyes facing forward).
Photo: Jeffrey Hahn, UMN Extension

If you occasionally find a spider indoors, regardless of which one you discover, tolerate it as much as possible. If convenient, capture it in a container and release it outdoors. See also the University of Minnesota Extension publication: Common spiders in and around homes.

Friday, June 26, 2015

Spotted wing Drosophila is now active

The following was slightly edited from an article recently written by Eric Burkness and Suzanne Burkness of the University of Minnesota, Department of Entomology.

The first adult spotted wing Drosophila (SWD) fly of the 2015 growing season was detected in a trap collected on June 23, 2015, in Rosemount, MN (Dakota Co.). Based on this detection, home gardeners with soft-skinned fruit such as June bearing strawberries, summer bearing (floricane) raspberries, and blueberries should begin monitoring their fields, if they haven’t already.

Most June bearing strawberries in Minnesota should be nearing the end of fruiting but summer bearing raspberries and most blueberry varieties should have green fruit and potentially low levels of ripening fruit. Fall bearing (primocane) raspberries and blackberries should not be flowering yet, but these crops will be at increased risk later in the season as the populations of SWD should continue to increase.
Spotted wing Drosophila attacks many types of soft-skinned
fruit, including raspberries, blueberries, and strawberries.
Photo: Jeffrey Hahn, UMN Extension
The first detection of SWD consisted of a single female fly, collected from a Trece Pherocon® SWD trap, baited with apple cider vinegar and a Trece SWD lure (these traps and lures are available through Great Lakes IPM). This detection coincides with previous years where SWD was first found during the last week of June in both 2013 and 2014. It is still unknown if SWD can overwinter in Minnesota or if populations migrate into the state but because this pest reproduces rapidly, monitoring should begin now in all parts of the state.

SWD flies resemble common fruit flies found near overripe fruit, but unlike the common fruit fly, female SWD have the potential to damage otherwise healthy, intact fruit. They will also exploit fruit that has previous damage such as splitting or wounds from birds or disease.

Home gardeners with susceptible fruit are encouraged to monitor their fields regularly to confirm the presence of SWD before considering chemical management options. Although cultural management options are limited, they have been shown to help minimize rapid buildup of SWD populations.

The Department of Entomology and the UMN Extension-IPM Program, in collaboration with the MDA, are monitoring multiple farm locations in the greater metro area and will be posting regular updates regarding SWD phenology and activity on the UMN FruitEdge website.

For more information, see Spotted wing Drosophila in home gardens.

Thursday, June 25, 2015

Say blister beetle

Jeffrey Hahn, Extension Entomologist

There have been a number of reports of green beetles with orange legs in flower gardens. These beetles are ant-like, have soft wing covers and are about ¾ inch in length. This is the Say blister beetle Lytta sayi. They have been found feeding on a variety of flower blossoms, including roses, peonies, irises, and lupines. When they are abundant, they can cause serious damage to plants.

Say blister beetle close up.  Photo: Jeffrey Hahn, UMN Extension
All blister beetles secrete a defensive oil called cantharidin which can be very irritating and can raise blisters when skin is exposed to it. Fortunately, the Say blister beetle generally does not have a high enough concentration of cantharidin to cause severe problems to people.

If Say blister beetles are in your garden, there are several options for their management. Physical removal is a good management method. If there is concern about exposure to cantharidin and blisters, wear gloves to be on the safe side. If you are interested in a low impact insecticide, try spinosad or neem oil. You can also apply pyrethrins; to be effective this insecticide has to directly contact the insects. There is also no residual and it may need to be reapplied.
Say blister beetles on Addie Tischler peony. 
Photo: Jeffrey Hahn, UMN Extension
There are a variety of residual garden insecticides that can kill blister beetles, such as permethrin, bifenthrin, lambda cyhalothrin, and carbaryl. Take care when using these insecticides as they are toxic to pollinators (although spinosad is considered a low impact insecticide to beneficial insects, it is also toxic to bees). Do not treat plants when pollinators are active around them. Instead, treat plants during late evening or nighttime when pollinators are no longer active to minimize exposure to insecticides.

Friday, June 12, 2015

Euonymus caterpillars: Are they in your yard?

Jeffrey Hahn, Extension Entomologist

Unknown caterpillars were found defoliating a euonymus shrub in Ramsey County recently. They were identified as Euonymus caterpillars, Yponomeuta cagnagella. The larvae were up to ¾ inch long, cream to yellowish colored with rows of black spots. These caterpillars also produce silk and can envelop branches, even entire plants, with their webbing. They should not be confused with the feeding and webbing of eastern tent caterpillars. Eastern tent caterpillars primarily attack flowering fruit trees, such as crab apples, cherries, and plums and create their tents in the forks of branches.

Euonymus caterpillars are European in origin. They were first found in North America in 1967. They have been reported sporadically in the Midwest, e.g. in Wisconsin, Illinois, Iowa, and Michigan. This appears to be the first time euonymus caterpillars have been reported in Minnesota, although it is possible that they have been seen before, but not reported to the University of Minnesota.

We would be interested to learn of any other incidences of euonymus caterpillar in Minnesota. If you believe you have seen it (and live in Minnesota), please report it to the author at Please include any photographs of the insects or their damage. For more information see: Euonymus caterpillar (U of WI publication.
Have you seen euonymus caterpillars?  Photo: Linda Treeful RCMG

Ants in turf

Jeffrey Hahn, Extension Entomologist

Ants are one of the most common insects we encounter. Many species nest in the soil and can cause problems in lawns and other turf areas. There are two common types of ants that residents may encounter: field ants and cornfield ants.

Field ants are about 1/4 inch long and black or red and black. Their nests are mound-like and can cover a fairly large area in the ground, up to two feet in diameter. Field ant can be found in healthy, vigorously growing turf.
Field ant nest.  Photo: Jeffrey Hahn, UMN Extension

Residents can confuse field ants with carpenter ants. While these two ants are somewhat similar in size and color, carpenter ants do not nest in the soil but prefer to nest in moisture-damaged wood. The mounds created by field ants can also lead some people to believe that they are fire ants. However, fire ants only occur in the southeastern area of the U.S.; the closest fire ants to Minnesota are in southern Tennessee. While field ants can bite, it is not as painful as the stings of fire ants which create a burning,very intense pain

Cornfield ants can also be found in home lawns. They are smaller than field ants, about 1/8th inch long and range in color from light to dark brown. They construct small, conical mounds, particularly in areas where bare or thinning areas of lawns are present.
Cornfield ant nests.  They take advantage of sparse, thinning
grass.  Photo: Jeffrey Hahn, UMN Extension

Fortunately, ants do not injure or kill grass, despite the circumstantial evidence. Even the excavated soil on top of the grass caused by field ant nests does not typically cause any lasting damage to the grass (just rake the soil periodically to prevent it from mounding up). It is possible to dull lawn mower blades when they hit ant mounds. Ant activity may also make the turf look like it is being undermined by the tunneling but this is unlikely - a very large nest would need to be present to cause that kind of damage.

Management of ant nests can be challenging. It is not possible or practical to try to control all of the nests on a property. Tolerate ant nests when possible. Treat particularly troublesome nests with a granular insecticide labeled for ants in turf (follow all label direction carefully). Common active ingredients include bifenthrin, B-cyfluthrin, and permethrin. The products typically need to be watered in after application.

Monday, June 8, 2015

Imported cabbageworms are active now

Jeffrey Hahn, Extension Entomologist

There have been sightings recently of imported cabbageworms on crucifer (cole) crops.  This includes cabbage, broccoli, cauliflower, radish,  kale, and turnips.  Watch for holes in the leaves to indicate that they are feeding.  Also watch for medium sized white butterflies in your garden.  This in the adult stage of this pest.  If they are present, watch your crucifers closely for evidence of the caterpillars.

Imported cabbageworm.  Photo: Jeffrey Hahn, UMN Extension

Early detection is important; the sooner you can find imported cabbageworms, the sooner you can take steps to minimize their damage.  Be sure to look on both sides of the leaves when inspecting plants.  Handpicking can be effective management, especially if your garden is not too large.  Bacillus thuringiensis and spinosad are low impact insecticides effective against these caterpillars.  Effective, residual insecticides include permethrin and lambda cyhalothrin.

For more information, see Caterpillar pests of cole crops in home gardens.

Thursday, June 4, 2015

Check your garden for Colorado potato beetles

Jeffrey Hahn, Extension Entomologist

Are you growing potatoes, eggplants, peppers, or tomatoes in your garden.  If so, now is a good time to check for the presence of Colorado potato beetles.  Both the adults and larvae feed on these plants.  Feeding can be severe and can impact production of your vegetables.  These beetles have one to two generations a year and are seen from spring until harvest.
Colorado potato beetle larvae on eggplant. 
Photo Jeffrey Hahn, UMN Ext

There are several options for managing Colorado potato beetles.  Handpicking is an option as long as your garden is not too large and you have the time to remove them on a regularly basis.  Spinosad is a low impact insecticide that is effective against Colorado potato beetles and importantly there is no known resistance by these beetles to it.

Traditional insecticides such as carbaryl (Sevin) and permethrin are generally not effective as most populations of Colorado potato beetles have developed resistance to it.  It is possible that some relatively newer pyrethroids, such as lambda cyhalothrin or cyfluthrin can help to manage these beetles.  However, if sprays don't seem to be affecting them, discontinue their use and switch to another management method.

For more information see Colorado potato beetles in home gardens.

Wednesday, June 3, 2015

Four-lined plant bugs are out!

Jeffrey Hahn, Extension Entomologist

Many gardeners have been encountering four-lined plant bugs on a wide variety of plants, especially perennials, such as chrysanthemums, Chinese lantern, Russian sage, mint, and wild geranium.  They can also feed on shrubs, fruits, and vegetables.  Immature four-lined plant bugs are bright red when they first hatch and gradually become darker as the black wing pads become larger.  They eventually turn into yellowish greenish adults with four black stripes.

These insects use their piercing-sucking mouthparts to create small, sunken, dark-colored spots on the leaves.  Heavily damaged leaves can become browned and misshapen.  Despite the appearance, the injury is primarily cosmetic and the health of the plants is not typically impacted.  It is possible that when plants are severely attacked a few years in a row, that their health can be affected.
Fourlined plant bug nymphs on wild geranium. Note the
dark colored necrotic spots on the leaves from their feeding.
Photo: Jeffrey Hahn, UMN Extension

There are several options for treating four-lined plant bugs.  Insecticidal soap can be effective on nymphs but you have directly contact the insects to kill them.  Insecticidal soap  is not very effective on adults.  Contact insecticides, such as permethrin, give good control; one application should be sufficient.  When trying to treat these insects on basil and mint, try pyrethrins as they are usually broadly labeled to include herbs.  However, like insecticidal soap, the spray has to directly contact the insects to be effective.

Four-lined plant bugs are active until early July so treating them now will still minimize feeding injury.  For more information see Fourlined plant bugs in home gardens.

Monday, June 1, 2015

Anthracnose arrives with spring rains

 M. Grabowski, UMN Extension

Fall leaves, brown leaf spots, and twisted distorted leaves are all symptoms that gardeners may be seeing on shade trees like oak, ash and maple. These symptoms are caused by anthracnose, a fungal disease that affects young growing leaves during wet weather. No management is needed as anthracnose is not a major threat to the health of the tree. As leaves mature they become resistant to the fungal pathogens that cause anthracnose. Warm dry summer weather will help to further reduce disease problems.
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