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Hort Update for July 21, 2015

Lawns Major Symptom:
1. Summer patch Circular or S-shaped tan patches; may be green in the center
2. Brown patch Brown patches; tan lesions with red margins on grass blades
3. Dollar spot Small, tan patches in lawns; tan lesions with red margins on blades
4. Bermuda grass and other weedy grass control Identify before controlling
5. Surfactants Used correctly, can improve herbicide effectiveness for weed control
6. Grub control timing Late for preventives; consider waiting and using rescue treatment if grub population is high enough in August or September
   
Trees & Shrubs  
7. Cytospora canker on multiple tree species Browning of leaves on individual branches
8. Crabapple issues Browning, yellowing or reddening of leaves and branch dieback
9. Woolly bark or pine adelgid White woolly material on white pine bark
10. Hackberry decline Yellowing of leaves on entire full branches
   
Landscape Ornamentals  
11. Powdery mildew Grayish white powder on leaf surfaces
12. Daylily leaf streak & rust Leaves yellow and die from the tip downward
13. Aster yellows Flowers with stiff, bushy growth that remains green
14. Fasciation Peculiarly broad and flattened growth of flowers or vegetative stems
   
Fruits & Vegetables  
15. Flea beetle Being found on potato; small jumping beetles cause shot holes in leaves
16. Raspberry canes wilting & dying Brown to black stems, wilt and die
17. Powdery & downy mildew in cucurbits Leaf diseases appearing in the vegetable garden now
18. Tomato leaf spots Yellow, brown, tan leaf spots on lower leaf surfaces
19. Poor fruit set & flower drop Weather conditions may affect flower pollination and fruit set
20. Blossom end rot Leathery to soft brown rot on the blossom end of tomatoes and other vegetables
21. Wireworms Holes, feeding damage in carrots, potato; may be accompanied by rot
22. Spotted wing drosophila Monitor for insect presence; male fruit fly with red eyes and one dark spot on wing tip
23. Weed identification Identification critical to good control
   
Miscellaneous  
24. Wasp vs. honeybee identification Identify insects before using control measures to preserve beneficial pollinators
25. Grasshoppers Control while grasshoppers are small

 

1. Summer patch is a challenging disease to control in Nebraska lawns. Summer patch symptoms are one to two foot, tan colored, circular, crescent, or serpentine shaped patches that usually appear during summer in full sun areas. Tufts of healthy green grass may remain in patch centers. No leaf spots will be found on grass blades. The fungus attacks turfgrass roots in spring. Infected plants may have dark brown to black roots. Control includes proper lawn care practices to reduce stress, over-seeding with resistant cultivars, and fungicide applications made in April and May. For a listing of these fungicides, see the following resources.

Necrotic Ring Spot and Summer Patch Disease, Nebraska Extension

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2. Brown patch disease is typically seen from July to September and infects tall fescue or perennial ryegrass on lawns or athletic fields. It is problematic during periods with extended high humidity and night temperatures greater than 75F.  It causes roughly circular patches of blighted grass with a reddish-tan color. On close inspection, long, irregularly shaped tan or brown leaf lesions surrounded by a dark brown or reddish margin will be found on grass blades. Most lawns recover from brown patch without treatment.

Recommended cultural maintenance includes avoiding high nitrogen fertilizer applications during summer; using low rates of nitrogen to maintain moderate growth and good recovery from disease; improving air circulation across the turf; avoiding evening and night irrigation; and reseeding or overseeding the turf with resistant species or cultivars.

Although we rarely recommend a fungicide on home lawns, high label rates of propiconazole or thiophanate methyl could provide three to four weeks of protection when applied prior to onset of symptoms. If a history of brown patch exists in a lawn, irrigation and fertility should be reduced.  With high fertility and irrigation on athletic fields, fungicides may be justified.

Brown Patch Disease of Turfgrass, Nebraska Extension

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3.  Dollar spot causes small (three to six inch diameter), roughly circular patches in lawns. Spots may coalesce into a large patch. Grass blades have tan, band-like lesions with red margins. Damage is usually most severe where there is a nitrogen deficiency. With fall fertilization, most lawns recover well. Fungicide treatments are available, but typically not needed on home lawns.

Dollar Spot Disease of Turfgrass, Nebraska Extension

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4. Bermudagrass and other weedy grass control - Perennial grasses, such as Bermudagrass, nimblewill, quackgrass, and windmillgrass are some of the most difficult to control weeds in the lawn.

Bermudagrass, a warm season grass, is a creeping, wiry grass that forms dense mats from rhizomes and stolons. Leaf blades are flat and smooth. It is often planted as a desirable turf on golf courses and athletic fields south of Nebraska.

Nimblewill is a warm season grass that forms circular patches in the lawn. It is a thin, wiry, pale green grass. The leaf blades are short and emerge at 45 degrees angles from the stems, which are slender, smooth and tend to lie flat on the ground. It spreads by short stolons, or above ground stems, that root at the nodes.

Quackgrass is a cool-season grass that has naturalized throughout Nebraska. It grows in moist areas of the lawn, but can survive well in dry areas once established. It spreads through an aggressive rhizomatous root system, choking out more desirable grasses. The leaf blades are flat and thin, with few hairs, and no noticeable ridges or folds.

Windmill grass is a native, warm-season bunchgrass that is most common in the eastern and southern parts of the state. As a warm-season grass it begins growth late in spring, but grows and seeds quickly from May through September, spreading primarily by seed. Plants have coarse, light green leaves and produce seedheads at a short height, becoming unsightly in a mowed lawn. The seedheads consist of 6-20 spike-like branches attached to a central axis, which resemble small tumbleweeds and can roll across the lawn in fall dispersing seeds.

Nimblewill and windmillgrass can be controlled selectively with the herbicide Tenacity (mesotrione). Several applications should be made on 3-4 week intervals for the best control. Tenacity can be applied by commercial pesticide applicators, or purchased online by homeowners.

Quackgrass and Bermudagrass is more difficult to control since there are no herbicides to selectively kill these without damaging the lawn. Also, pulling or digging is often unsuccessful as only a small portion of a rhizome remaining in the soil will generate a new plant. The best way to control quackgrass, is to spot treat weed-infested areas with glyphosate (Roundup, Kleenup, etc.).

The establishment of a thick, healthy lawn and its proper maintenance will help prevent future weed infestations.

Control of Perennial Weedy Grasses, Nebraska Extension

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5. Surfactants, also known as spreader-stickers, are materials that facilitate and accentuate the emulsifying, dispersing, spreading, wetting, or other surface modifying properties of liquids. Postemergence liquid herbicides are generally foliar applied and absorbed, so they must remain on the leaf surface for 24 to 48 hours following application for adequate absorption. Along with not mowing a few days prior to or after herbicide application to ensure satisfactory leaf surface area, the addition of surfactants to spray solutions of herbicides that do not already contain them, will aid in the herbicide covering and adhering to the foliage.

Activity of most postemergence herbicides is enhanced with addition of an adjuvant (or surfactant). Some herbicides require the use of surfactant. Adjuvants facilitate herbicide movement into the leaf. Many types of adjuvants are available, and the concentration of active ingredient varies among brands. For most turf herbicide applications, a nonionic surfactant with at least 85 percent active ingredient is sufficient. The adjuvant rate to add to the tank is stated on the herbicide label

Some individuals suggest household detergents can be substituted for surfactant. This is not recommended for several reasons. Household detergents do not contain as much surface active ingredient per unit volume as do agricultural surfactants. The amount of surface active ingredient per unit volume varies among brands of detergents. Hence, their use is more costly than use of agricultural surfactant. Detergents foam excessively, can form scums that affect sprayer performance, and can interfere with herbicide activity. Remember to purchase a good agricultural surfactant, if the label recommends its use, to save money.

Source: Mississippi State University

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6. White grub control timing - On turfgrass with a history of white grub damage, preventive insecticides, such as Merit, Mach 2, Acelepryn and Arena, are recommended for application by mid-July. While it is after mid-July, these preventive products could still provide some control if applied very soon.  The alternative is to wait and see if grub populations hit a threshold of 8 grubs per square foot in August or September and then apply a rescue treatment of Dylox or carbaryl (Sevin).  For all products, correct irrigation is important to effectiveness. Read and follow label directions.

White Grub Management 2015, Turf iNfo Nebraska Extension

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7. Cytospora canker on multiple tree species. While most common on Spruce trees, Cytospora is believed to be causing branch dieback in a number of tree species; in part due to environmental stress and mechanical injury from hail storms or high winds setting trees up for infection. Cytospora commonly causes branches near the base of trees to die or the tops of trees to dieback. Resin often oozes from branch or trunk cankers. There are no fungicide controls. Prune and destroy dead and dying branches during winter. The fungus of often spread during spring rains. Disinfect all pruning tools such as knives and saws by wiping them with rubbing alcohol. Avoid stress by spacing trees correctly, then mulching and watering correctly. Avoid wounds, such as from pruning, when trees are stressed.

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8. Crabapple dieback issues - Numerous crabapples are showing a variety of symptoms from leaf yellowing and reddening to sudden browning of leaves on entire branches to entire tree death. Again, weather related stresses and wounding have likely set crabapples up for various issues. In some cases, the cause could be bacterial fire blight which causes branch cankers.  Fungal cankers may also be infecting crabapples.  Last years' cold spell in November may have injured the cambium layer of crabapples that were not fully dormant at the time. For the most part, we are making educated guesses as to the actual cause. As with Cytospora canker, prune and destroy dead and dying branches during winter.  Disinfect all pruning tools such as knives and saws by wiping them with rubbing alcohol.  Avoid stress by spacing trees correctly, then mulching and watering correctly and by not over-fertilizing with nitrogen.

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9. Pine bark adelgid is being found now on pine, particularly white pine. The insects are very small and dark, but covered with a cottony white material.  Infested trees have woolly white material covering the bark of the trunk or branches, where the insects are feeding and reproducing. Adelgids insert needle-like mouthparts into tree bark to feed on sap. Healthy, vigorous mature trees suffer little damage from this feeding, but young trees can become stunted and weakened. Stressed trees may suffer heavy infestations.

Monitor trees for infestations from April through early autumn. Use a dormant oil spray in early spring to smother overwintering aphids hiding in bark crevices. Spray active infestations during the growing season with an insecticide, using enough water pressure to penetrate their woolly covering.

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10. Hackberry yellowing and branch decline are some signs of hackberry decline. The cause of decline is suspected to be the result of a combination of stresses such as herbicide injury, drought, poorly drained soils and weather extremes.

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11. Powdery mildew causes grayish white powder-like patches on upper leaf surfaces. It is promoted by warm temperatures and high humidity. Extended wet conditions this spring and early summer have caused early infections on many garden plants.  Many types of plants are susceptible, such as Phlox, Monarda and Zinnia. Recently reports of powdery mildew on peony foliage and monarda have been received.  If plants are heavily infected consider replacing them with resistant varieties.  Place susceptible plants in areas with good air circulation.  Avoiding overhead irrigation and excess nitrogen fertilizer. Fungicides will provide some protection as new healthy foliage emerges. Refer to the publication below for recommended fungicides.

Powdery Mildew on Landscape Plants, Nebraska Extension

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12. Daylily leaf streak and daylily rust are two diseases causing daylily leaves to yellow and die from the tip back. With leaf streak, symptoms begin as small, reddish-brown flecks and brown lesions on leaves and a yellow streak along the mid-vein that begins at the leaf tip. Rust begins as leaf yellowing from the tip back and reddish brown leaf lesion. With both diseases, entire leaf yellow and die. Run fingers along an infected leaf. If an orangish powdery residue remains on fingers, this confirms rust disease. Overcrowding and warm, wet conditions result in a fungal leaf infections. Control by dividing and increasing the spacing of plantings so leaves dry quickly after rain or heavy dew. Prune out affected plant tissue and maintain good sanitation practices in the garden. Avoid overhead irrigation. Plant healthy, disease-free stock.

Daylily Leaf Streak, University of Wisconsin Extension
Daylily Rust, Cornell University
Daylily, Nebraska Extension

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13. Aster yellows is a common disease that affects many ornamental flowers. Susceptible plants include asters, Chrysanthemum, Coreopsis, cosmos, Echinacea (coneflowers), Dianthus, Gladiola, marigold and petunias. Vein clearing, or loss of green pigment within the veins, is often the first symptom. Stunting; stiff, bushy yellow growth and deformed or poorly developed flowers that remain green are symptoms. There is no cure for infected plants. Remove and discard them to reduce further spread.

Aster Yellows, Iowa State University

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14. Fasciation is an abnormal type of plant growth, resulting in the development of peculiarly flattened, broad stems with many vegetative and flower buds arranged randomly. It may appear as if several stems have fused together, with stems having short, swollen clumps of distorted shoots. One theory is fasciation occurs in plant stems due to a hormone imbalance.  This imbalance may be caused by random genetic cell mutation; bacteria, fungi or virus infection; environmental factors such as frost; or insect, slug, or physical damage to plant growing tips. Anything that damages the growing point of a stem may cause fasciation to occur. Unless it is caused by a disease, such as Aster yellows, fasciation is not contagious. It is simply a garden oddity and can be pruned out of affected plants.

Fasciated Plants, University of Arkansas

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15. Flea beetles are small, dark beetles that jump when disturbed. Their feeding causes shot-holes in leaves on some vegetables. Feeding is damaging to seedlings or young plants, but late season feeding affects potato tuber quality and may lead to tuber rots. Watch for these beetles on fall planted vegetables.

Damage is being reported now of flea beetle activity on potatoes. Floating row covers are an organic control. Control weeds around the garden to minimize flea beetle populations. Minor foliage damage to established plants is usually a minor issue and control is not recommended. Carbaryl (Sevin) or permethrin insecticides can be applied as a foliar spray to kill adult beetles, if populations are high late in the season and tuber quality is affected.

Flea Beetles, Colorado State University
Potato and Tuber Flea Beetles, Nebraska Extension

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16. Raspberry canes wilting & dying may be caused by raspberry cane borer, anthracnose, root rot for fireblight.  The raspberry cane borer damages raspberry plants from early June to late August. Females puncture two rows of holes in raspberry stem tips and lay their eggs between them. The punctures restrict sap flow resulting in wilting, blackening and finally death of the tip.

Raspberries with root rot have similar symptoms. Roots are rotted and lack fibrous roots. After hot, dry periods, older leaves may wither or become bronzed and scorched. Affected leaves flag. Fruit stems usually are shortened and berries, if formed, remain small and often wither before ripening

Anthracnose causes slightly raised spots with gray centers and purplish margins on raspberry canes. These eventually girdle and kill canes. Infection can occur throughout the season during wet periods. If needed, apply labeled fungicides to susceptible raspberries. Sanitation is important for control. After harvest, remove and destroy all old fruited canes (floricanes) and any new primocanes that are infected. It is best to remove old canes during the dormant season before new growth begins in spring.

Fireblight is also being reported this year. Symptoms include dead branches, water-soaked blossoms, light brown to blackened leaves, discolored bark, black "shepherd's crook" twigs, and dried fruits. Examine raspberry canes for Remove each infected branch eight to 12 inches below the canker to be sure all infected growth is removed. Fireblight is a bacterial disease that kills branches and entire plants in the rose family, including apple, pear and crabapple. Management includes resistant varieties, cultural practices, pruning and preventive chemical sprays. Chemical controls are best applied during blooming.

Raspberry Cane Borer, University of New Hampshire
Anthracnose of Raspberry and Blackberry, The Ohio State University
Raspberry Root Rot, The Ohio State University
Fireblight on Raspberries and Blackberries, Michigan State University Extension

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17. Powdery & downy mildew are common diseases in Cucurbits, such as summer squash, zucchini, cucumber and pumpkin.  Powdery mildew appears as a white flour-like dusting growing on leaf surfaces. Downy mildew first appears as pale green areas on upper leaf surfaces which change to yellow irregular shaped spots. A fine white-to-grayish downy growth soon appears on lower leaf surfaces. Infected leaves generally die but may remain erect while the edges of the leaf blades curl inward. Usually, the leaves near the center of a hill or row are infected first. The infected area spreads outward, causing defoliation, stunted growth, and poor fruit development. The entire plant may eventually be killed. Spores are carried by wind so crop rotation is not as effective.

Plant resistant cultivars. Avoid overhead irrigation. Space plants correctly. Improve air circulation. Remove over-mature or heavily infected plants from the garden quickly. Copper based fungicides are recommended for mildew in cucurbits, but can damage plants. Read and follow label directions.

Managing Downy Mildew in Cucurbits, Cornell University
Powdery Mildew of Vine Crops, Ohio State University

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18. Tomato leaf spots, such as early blight and septoria leaf spot, are fungal diseases that begin as leaf spots on lower leaves, then work their way up the plant causing leaves to die; often leading to fruit sunscald. Both can be reduced with fungicides labeled for use on tomatoes. For best results, applications need to begin as soon as symptoms first appear on lower leaves and applications made about every 7 to 10 days. Avoid overhead irrigation and increase air circulation around plants with proper spacing and caging. Mulch the soil around tomatoes to reduce soil splash of fungus onto lower leaves. Plant resistant varieties and avoid planting tomatoes in the same area each year. Severely infected plants are best pulled and destroyed. Use fall sanitation to reduce the amount of overwintering fungus.

Common Vegetable Diseases, Backyard Farmer on YouTube
Tomato Leaf and Fruit Diseases & Disorders, Kansas State University

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19. Poor fruit set and flower drop (peppers, zucchini, tomatoes, etc.) – may soon be happening in the vegetable garden on tomatoes, peppers and zucchini, and is likely weather related. Vegetable garden plants had a slow start this spring, with late freezes and cool temperatures.  This delayed plant growth, development and blooming.

More recently daytime temperatures above 90 degrees, and/or nighttime temperatures above 70 degrees interfere with pollination.  Ideal conditions for pollination are moderate temperatures, 59-68 degrees. Plants receiving excessive fertilization and abundant moisture often produce excessive foliage growth that inhibits flower formation.  However, very low fertility levels, substantial damage from insects or diseases, and inadequate moisture can also inhibit flower development.

Provide plants with good basic growing requirements, without over or under fertilizing, so that flower clusters are produced.  In small gardens, hand pollination can be done to encourage fruit formation.  If the lack of fruit set was due to high temperature conditions, plants should begin to set fruits again now that temperatures have cooled.

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20. Blossom end rot is a common problem of tomatoes, but also affects peppers, eggplant, summer squash, zucchini and watermelon. It appears as a flat, dry, sunken, brown rot on the blossom end of tomato and pepper fruits. On squash and watermelon tissue at the blossom end may first turn yellow, then brown, feeling wilted or shriveled. Blossom end rot is caused by a calcium deficiency in the fruit. In Nebraska, rarely is there a lack of calcium in the soil. Blossom end rot occurs when plants cannot pull calcium up quickly enough for developing tissues. Calcium must be dissolved in water to move within a plant, so dry soils can increase the problem.

Drought stress, low daytime humidity, high temperatures, and rapid vine growth favor blossom end rot. Applying calcium to the soil or to the plant is not beneficial. Plants do not take foliar applied calcium in through leaf tissues. Instead, maintain a consistently moist but not saturated soil; use organic mulch near the base of plants; and avoid excess nitrogen fertilization with ammoniacal nitrogen sources.

Often the first ripe fruits are affected.  Remove them and later ripening fruits will usually be normal. 

Blossom End Rot of Tomato, Eggplant and Pepper, Ohio State University
Special Tomato Problems, University of Nebraska - Lincoln Extension

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21. Wireworms, the immature stage of click beetles, can cause damage in the vegetable garden to root crops like carrots and potatoes. Wireworms are most common in new gardens that have recently been covered by grass.  However, adult click beetles may also lay eggs in gardens where grassy weeds are a problem. Immature wireworms may stay in the soil for 2 to 6 years, depending on the exact species present. Wireworm feeding on root crops appears as straight, round holes with smooth walls. Feeding damage also opens potato or carrot roots up for invasion by secondary rots.

No chemical control methods are available or effective in home gardens.  Avoid planting potatoes or carrots in gardens with a history of wireworm infestation for several years, or in new gardens recently taken out of grass.

Wireworms, University of Minnesota
Click Beetle/ Wireworm, University of Maine

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22. Spotted wing drosophila (SWD) is a new pest in Nebraska that attacks the soft fruits of brambles (raspberry, black berry), strawberry, blueberry, grape, cherry, plum, peach and many small wild berries. UNL Department of Entomology received their first 2015 positive sample last week, July 6, 2015.

Adult flies emerge in early July. Adult females make a slit through the fruit skin and insert eggs inside. Larval feeding inside the fruit causes fruits to become wrinkled and dimpled and they are prone to fungal infection causing decay and rot. In its native range in Japan roughly 13 generations occur each year.  Upwards of 10 generations are predicted in the United States depending on climate.

Monitor for SWD through trapping to distinguish it from native fruit flies. Fruit growers especially need to be monitoring frequently, but also to be checking for evidence of ovipositional or early larval damage. Traps do not always keep in real time sync with what is going on in the field.

Treatment is warranted immediately once one or more SWD flies are discovered, or if larvae are found in fruit. Remember to take notice of PHI's for whatever insecticide is used. Sanitation is also important as a means of helping to minimize fly numbers, and consequently, yield losses.

If SWD occurs, manage it through sanitation including prompt remove of infested fruits and insecticide applications.

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23. Weed identification is critical to successful control.  In mid to late summer weeds seem to grow by leaps and bounds, and landscape managers can get frustrated trying to keep up.  But mid-summer herbicide applications are usually not very effective.  First determine if the weed is a grassy or broadleaf plant, then whether it's an annual, perennial or biennial weed.  These two identification characteristics will help pinpoint the best time of year for herbicide applications and any cultural practices that can aid control.

Weed Identification Guide, Virginia Tech
Weed ID Guide, University of Missouri

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24. Grasshoppers are reaching mature size and becoming more difficult to control. As adults, they can severely defoliate garden and landscape plants if populations are high. Effective control includes treating egg-hatching areas (roadsides and weedy areas) at egg hatch while grasshoppers are still small, since adult grasshoppers are very difficult to control.

Grashoppers in the Field and Garden, Nebraska Extension
Grasshopper Control, Backyard Farmer on YouTube
Grasshoppers of Nebraska, Nebraska Extension

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25. Wasp vs. honeybee identification – Yellow jackets are one of the most common stinging insects we can encounter. These are social wasps that build their nests underground in abandoned rodent burrows, under compost piles, or in voids of wood. They can also build aerial nests in trees or shrubs. They construct a paper nest in these areas where the queen and her workers raise their young. Yellow jacket colonies are annual and die out at the first hard freeze of the year. A yellow jacket worker is about ½ inch long with alternating yellow and black bands on the abdomen. They will look different than honey or bumble bees as these pollinating insects have hairy bodies, while the yellow jacket is smooth and glossy in appearance.

These wasps are carnivorous and feed on a variety of insects and spiders, but also enjoy finding sweet treats such as soda pop or fruit lying on the ground. While they are not important pollinators they do help control pest populations and also move plant seeds around. However, they are an important health pest as they can be aggressive when disturbed and individuals will sting multiple times. Encounters with humans often occur during mowing or when working with outdoor trash cans. If a colony has been disturbed, cover your face with your hands and slowly retreat from the area towards a building, car, or dense vegetation. Do not run as the swift motion may attract more yellowjackets.

Control of a yellowjacket colony should be done at dusk or after dark when the insects are the least active. Care should also be taken to wear long sleeves, a hat, and pants to try and ensure protection from possible stings. Chemical control options include aerosols cypermethrin (Raid Wasp and Hornet Killer), lambda cyhalothrin (Spectracide Wasp and Hornet Killer) as well as insecticide dusts like carbaryl (Sevin) or permethrin (Eight). Locate the entrance to the nest and then spray or sprinkle the insecticide into the entrance and leave the area. Wait 24 hours and return to see if the job has been finished. If not, repeat the previous steps. Non-chemical control of yellowjackets includes solid waste receptacles (no wire mesh, etc.) that have wasp-tight lids to prevent workers from entering the can.

Two common species of yellowjackets in Nebraska, German yellowjackets (right) and the Eastern yellowjacket (left). Both photos from Jim Kalisch; University of Nebraska, Entomology

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