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Horticulture Pest Update - Summer Pests (June and July)

submitted by Mary Jane Frogge, Extension Associate

Insect/Mites Pests:

Aphids

Aphids (June):

Aphids attack such a wide variety of plant material that it is not practical to list individual species. Aphids are small (about 1/8 of and inch long), soft-bodied, pear-shaped insects of many colors such as green, black, gray, yellow or red. Some are winged during certain times of the year.

Aphids feed by sucking sap from buds, leaves, twigs and developing fruit. Leaves may be stunted and distorted and fruit may become misshapen. Aphids can also carry a number of plant viruses.

Aphids are usually controlled effectively by nature. Adverse weather conditions such as rains and low temperatures, as well as fungus diseases, insect predators and parasites keep the aphids in check. Aphid enemies include lady beetles, syrphid fly larvae and small wasp parasites known as braconids.

Insecticide applications destroy beneficial insects as well as pests. Since beneficial insects play an important role in natural aphid control, try washing aphids away with a forceful stream of water before using insecticide sprays.

If control measures are warranted, use malathion, carbaryl or permethrin. Reapplication is often needed.

Wooly Aphid Damage

Damage from Wooly Aphids

Wooly Aphid (June):

If your ash tree leaves are twisted and curled, this is the result of the feeding of ash leaf curl aphids, a type of woolly aphid. If you uncurl the disfigured leaves, you will see aphids as well as white, waxy material that the aphids produce. Ash leaf curl aphids also produce large amounts of honeydew which covers leaves, branches, and other nearby objects. Honeydew is a waste product that aphids produce while they are feeding which is also attractive to ants.

Despite the appearance of the misshapen leaves, these woolly aphids do little actual harm to ash tree. Relatively few leaves are likely to be affected and those that are curled are still able to photosynthesize.

An application of a systemic insecticide, such as acephate (Orthene) or dimethoate (Cygon) would effectively manage these woolly aphids. Insecticides, however, do not affect leaves already disfigured; they remain curled for the rest of the season. Be careful not to over apply insecticides to avoid negatively affecting natural insect enemies.

Photo Credit: The Bugwood Network - http://www.bugwood.org/ - College of Agricultural and Environmental Sciences/Warnell School of Forest Resources-The University of Georgia

Bean Leaf Beetle (June):

Bean Leaf BeetleThe bean leaf beetles love to feed on bush and pole beans. They damage seedlings by eating the stems and emerging leaves. Heavily damaged plants can be severely set back in development and may never fully recover. Damage to older plants appears as numerous holes chewed into the leaves, giving them a lace like appearance.

The beetles hibernate in the adult stage in the soil or under crop residue. In the spring the beetles emerge and begin feeding and depositing eggs. The orange eggs are deposited in groups at the soil surface, near the stem of the host plant. The eggs hatch in about eleven days. The complete life cycle requires 35 to 55 days. Bean leaf beetles are difficult to see because the usually fall off the plants when disturbed. Adults are about fourth inch long and vary in color from yellow to reddish-tan. They have variable black markings on the back, usually consisting of four large spots.

Crop rotation is an effective management strategy. Plant beans in a new location each year. If you had a heavy infestation the previous year, consider not planting this crop for one or two years. The tachinid fly, (Celatoria diabroticae), often parasitizes the adult. Adjusting the planting date so that young seedlings get started between the periods of high beetle populations is helpful in control.

Applications of carbaryl (Sevin 5D, 50 WP) or permethrin (Eight) or malathion 50EC, 57EC will give good control. If beetles remain active you may need to repeat treatment to keep the insects from destroying the crop. Be sure to follow label directions and observe harvest waiting periods.

Blister BeetlesBlister Beetles (June):

Blister beetles have long, slender bodies with a relatively large head. These insects release a caustic substance when crushed that can raise blisters on the skin. The adult stage causes the damage, not the larvae.

The beetles tend to move in swarms and can cause a great deal of defoliation, but may not stay in one area for very long. Often beetles will move on in a day or two. If beetles are handpicked, be sure to wear gloves.

The beetles will feed on beans, peas, potatoes and other vegetables.

Galls:

Galls are abnormal plant growths caused by various organisms (insects, mites, nematodes, fungi, bacteria, and viruses). Because of their unusual forms and colors, galls often cause homeowners to become concerned. However, galls seldom threaten plant health and their numbers are highly variable from season to season. For those reasons, control is generally not suggested.

Galls are formed by insect/mite feeding or egg-laying activity. Either mechanical damage or salivary secretions (introduced by insects and/or mites) initiate increased production of normal plant growth hormones. These plant hormones cause localized plant growth that can result in increases in cell size and/or cell number. The outcome is an abnormal plant structure called a gall.

Gall formation generally occurs during the accelerated growth period (late spring) of new leaves, shoots, flowers, etc. Mature plant tissues are usually unaffected by gall-inducing organisms. The gall-making organism develops inside the gall and the gall continues to grow as the insect/mite feeds and matures. Once gall formation is initiated, many galls will continue to form even if the insect dies. In addition, most galls are usually not noticed until they are fully formed and remain on plants for extended periods of time. During heavy infestations of leaf galls, leaves may drop prematurely from the tree. Most galls do not adversely affect plant health. Therefore, management is generally not suggested to protect plant vitality. Chemical applications are often ineffective since the precise timing of sprays is critical. To be effective, sprays must be timed to coincide with initial insect/mite activity before gall formation begins. Once galls start to form, they conceal the causal organism and it is too late for treatment.

Grasshoppers (June):

Small grasshoppers are very plentiful now, especially on acreages or in rural areas. Insecticides work best when the grasshoppers are still small. In vegetable garden use Sevin or Eight. In lawn, shrubs, flower and ornamental beds you can use Sevin, Eight or Malathion. Be sure to read the label directions before using any pesticide.

Harlequin BugHarlequin Bug (July):

Both the adults and nymphs feed on many vegetable garden plants, such as cabbage, potatoes, tomatoes, okra, callards and turnips. Severe infestations can cause plants to wilt, turn brown and die. Often populations peak and fall quickly. The adult is a flat, shield-shaped stink bug about 3/8 of an inch long with red and black markings on its back. The nymph, though smaller and more round, has the same markings.

Recommendations: Carbaryl (Sevin) can be used for control. Note waiting period before spraying.

Hollyhock WeevilHollyhock Weevil (July):

Tiny long gray weevils with a snout as long as the body itself. They feed on hollyhock leaves and buds, chewing small, irregular holes. Females deposit individual eggs in holes in buds and each larva attacks and feeds in a maturing hollyhock seed, destroying it from the inside.

Recommendation: Dust with carbaryl (Sevin) or spray with acephate (Orthene) to prevent serious damage. This insect is the primary reason that hollyhocks do not seem to reseed very well after initial establishment. Photo Credit: University of Maryland

Spider Mite Damage

Damage on Tomato Plant from Spider Mites

Spider Mites (Summer):

Spider MitesSpider mites and hot, dry weather seem to go together. Mites are tiny creatures that feed primarily on the undersides of leaves, sucking juices from the plant. They can be found on tomatoes, peppers, beans, potatoes and many other vegetable crops. They do not eat holes in the leaves but the first symptom is a pale, tiny spot on the leaf. Multiple mites feeding on individual spots results in a white speckling on the leaf. Mites are held in check by several natural predators, but in hot dry weather the mites seem to get out ahead of the predators rapidly. Sevin insecticide has no effect on spider mites, but kills predators causing mite populations to explode, literally overnight. Mites usually develop on the younger, newer leaves at or near the top of the plant. Mites are sometimes 'spotty' in that they develop on plants here and there but not necessarily evenly over a large area. Controlling spider mites can be a difficult process since they are small and located on the bottom sides of leaves.

Use a fine mist spray directed at the bottom side of the leaf. Take your time and spray from several different angles to make sure you are covering the area. A pesticide that is available in many garden centers is Kelthane. Malathion can work, but not as reliable as Kelthane and has a wide label for many vegetable crops and a short waiting interval from application to harvest. Insecticidal soaps work well in controlling mites if they are applied frequently. It takes several applications of insecticidal soap every two to three days to get control of spider mite populations. If mites are not controlled, you may see some tiny webbing near the mites. Leaves will turn a bronze-brown color and shrivel up. Many gardeners confuse this symptom with hot, dry weather. The key to spider mite control is recognize the symptom early, use a fine mist spray directed at the undersides of leaves, and repeat several times.

(This resource was updated January 18, 2006. For information on reproducing this resource or using any photographs or graphics, read the Terms of Use statement)

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