Insects and Diseases on Shrubs and Trees
Blotchminer Beetle

Lives on cottonwood and other poplars. Young larvae are white or cream-colored and very flat, while older larvae are more cylindrical and 4 to 5 mm long. Moths have a wingspread of 6 to 17 mm and have elongated yellowish forewings with white cross bars and diagonal markings. Larvae appear in spring and pupate within the mines during July and August; adults emerge during August.

During early summer, larvae of blotchminers feed and construct irregularly shaped mines between upper and lower surfaces of leaves. By mid-summer these mines appear as blotches on leaves. Infested trees usually shed damaged leaves prematurely.

Control:

Spray leaves with chlorpyrifos or oxydemeton-methyl at first sign of mining.

Elm Leaf Beetle

Lives on American and Siberian (Chinese) elms.

Small larvae are black and hairy; large larvae are yellow with two longitudinal dark stripes. Adults are 5 to 7 mm long, yellowish-green, and have a black stripe on the outer margin of each wing cover. Three black spots are present behind the head.

Elm leaf beetles overwinter as adults in sheltered dry areas, especially in and around buildings and in litter and bark crevices. They emerge when buds begin to expand in the spring and feed on leaves before laying clusters of yellow eggs on foliage in late spring.

Larvae skeletonize leaves for 2 to 3 weeks before pupating. There are two or three generations per year. Shade trees are often heavily defoliated, making them weak and unsightly.

Control:

Spray elm leaves with carbaryl or methoxychlor to kill larvae and adults. Do not spray when the weather is hot and dry. Inject systemics recommended by your extension service (see our Links section) into the trunk or apply them to the soil. Spray pupae larvae clustered at the base of the tree with carbaryl or methoxychlor, or pour boiling water or a light oil on them.

Honeysuckle Witches’ Broom

The aphids are pale green to cream and less than 2 mm long. They overwinter as eggs or adults on infested shrubs. Eggs hatch in early spring when new leaves appear, and aphids feed on the new growth throughout the summer. Many overlapping generations of wingless aphids may be produced asexually each year. Winged adults develop in the fall, mate, and lay eggs.

Damaged branches form unsightly witches’ brooms and have folded and dwarfed leaves.

Control:

Spray new foliage with acephate, or dimethoate every three weeks throughout the growing season.

Locust Borer

Lives on black locust. Mature larvae are 25 mm long and white with dark heads. Adult beetles are about 18mm long and black with bright yellow bands across the thorax and wing covers. The third band on the wings forms a “w” design.

Beetles emerge in late summer and early fall and are commonly seen on goldenrod flowers. In the fall they deposit eggs in cracks, crevices, and bark wounds. Newly hatched larvae immediately bore into the tree and overwinter in the inner bark. Larvae tunnel in the sapwood and heartwood throughout the following spring and summer. There is one generation per year.

By spring, entrances to the larval tunnels are marked by sap oozing from the tree and granular exudate pushed out by the larvae. Larval mines can literally honeycomb both sapwood and heartwood, weakening the tree and making it subject to windthrow. Borer damage also provides an opening for infection by heart rot fungus. This fungus weakens and can kill black locust.

Control:

Spray trees with lindane either in late summer or early fall or when buds expand in spring to kill young larvae. Stressed trees and trees growing on poor sites are most susceptible to attack. Avoid planting this shallow rooted tree where soil conditions are unfavorable, or where the roots will be moisture stressed.

Pine Needle Scale

Lives on pine and spruce. Mature scales are tiny insects that are covered by a white, oblong, waxy protective covering that is 2.5 to 3 mm in length.

Scales overwinter as eggs beneath female scales on the needles. In May, crawlers hatch and migrate to new needles on the tree. The crawlers then molt to an immobile nymph stage that feeds on the sap and secretes the scale covering. In the fall the scales mature and lay eggs for a second generation.

By August needles become spotted with white elongated scales. Damaged needles are discolored and may fall prematurely. Severely infested trees are less vigorous and occasionally may be killed.

Control:

Thoroughly spray foliage, branches, and trunk with a dormant oil in March or with malathion, diazinon, acephate, or chlorpyrifos in early June. Control is not effective after the insects have formed their protective waxy scales.

Sawfly

Lives on willow, cottonwood, and other poplars. Color of larvae depends on the species present, and may vary from black or greenish-black to light green with rows of yellow or dark colored spots along sides of the body. Adults resemble small bees.

Adult sawflies emerge during spring and lay eggs in pockets cut in leaf tissue. Larvae feed gregariously on leaves during the summer and then drop to the ground to overwinter and/or pupate. There may be more than one generation per year. When distrubed, larvae curl up in a characteristic “s” or “c” shape. Large infestations can cause substantial defoliation.

Control:

Spray larvae and leaves with malathion or carbaryl.

Tent Caterpillar

Live on chokecherry, plum, willow, ash, poplar and rose. Mature larvae are 50 mm long and can be quite variable in pattern. In general, most tent caterpillars are pale blue with an interrupted white stripe bordered by two reddish-orange stripes down the center of the back. Moths are reddish-brown, have two oblique whitish stripes on the forewings and have a wingspan of 37 to 50 mm.

Eggs hatch when the first new leaves appear. Larvae live in colonies and construct large silk tents around a fork or branches of trees. These tents are enlarged as the larvae grow, enclosing the entire branch or even the entire tree. Adults of tent caterpillars emerge in late summer and lay flat egg masses on twigs and branches. There is one generation per year.

Larvae skeletonize leaves outside tents. Infestations tend to be spotty and are often unrecognized until entire trees have been defoliated. Severely infested tress are less vigorous and unsightly, but are rarely killed.

Control:

Spray leaves with carbaryl, acephate, diazinon, malathion, or Bacillus thuringiensis (B.t.) when tents first appear and caterpillars are small. Caterpillars and tents on small trees can be picked off and destroyed.

Elm Bark Beetle

Lives on elm, especially American, Siberian, and Chinese elms. These beetles are vectors of the fungus that causes Dutch Elm Disease; they carry fungal spores from diseased to healthy trees.

Larvae are grub-like and white. Adults are brownish-black, thinly covered with short yellow hairs, and about 3 mm long.

In early summer adults females lay eggs in tunnels mined between the sapwood and bark. During summer, larvae extend these tunnels in the inner bark. There are two generations per year in the southern part of their range, but only one in the northern part.

Leaves of diseased branches turn yellow to yellow-brown and die. After the beetles emerge, the bark of infested branches and trunks is marked by numerous pin-head-size exit holes. Sawdust-like frass accumulates below infested tree parts in cracks and crevices, or at the bases of trees.

Control:

There is no practical chemical control. In the spring, kill adult beetles before they mine into high value trees to feed and breed by spraying methoxychlor or chlorpyrifos on the bark. Thiabendazole injection will arrest the Dutch Elm Disease fungus. A community-wide sanitation program is advised. AS soon as an infestation has been diagnosed, infested trees or portions of trees should be removed, debarked, and either burned or buried beneath .5 m of soil.

Fall Web Worm

Can live on elm, plum, chokecherry, poplar, willow, and other hardwoods.

Larvae are about 25 mm long, and are either pale yellow with red heads and reddish-brown spots or yellow-green with black heads, a broad dark dorsal stripe and black spots. Moths are white, with reddish-orange front legs and a wingspan of 30 to 42 mm.

Pupae overwinter in cocoons in soil or duff. Moths emerge in late spring or early summer and lay eggs in hair-covered masses on the undersides of leaves. Larvae emerge about 10 to 14 days later and feed in groups of webbed nests constructed around leaves at branch ends. By late summer the unsightly nests may be 1 m across and contain excrement, dried leaf fragments, and cast skins of larvae. There are one to two generations per year.

Ornamental trees may become severely defoliated and unsightly.

Control:

When webs first appear, spray foliage with Bacillus thuringiensis (B.t.), carbaryl, acephate, chlorpyrifos, methoxychlor, or diazinon. Except for B.t., these insecticides also will kill beneficial natural enemies of fall web worms. Remove and burn branches with webs.

Leaf Miner

Lives on aspen, cottonwood and other poplars.

Larvae and moths are similar in appearance to aspen blotch miners in which young larvae are white or cream- colored and very flat, while older larvae are more cylindrical and 4 to 5 mm long. moths have a wingspread of 6 to 17 mm and have elongated diagonal markings. Larvae appear in spring and pupate within the mines during July and August; adults emerge during August.

Leaf miners overwinter as adult moths. In spring eggs are laid near the tips of young leaves and larvae emerge a few days later. During summer larvae feed and construct winding tunnels within the leaves. There is one generation per year.

Severe infestation will reduce height growth and, if left unchecked for several years, can kill trees.

Control:

Spray leaves with chlorpyrifos.

Oystershell Scale

Lives on Ash, Maple, Lilac, Aspens, and many other species of hardwood trees and shrubs.

Crawlers are very small, flattened and pale yellow or orange. Scales resemble tiny oyster shells, are gray to purplish-brown, and are about 3 mm long at maturity.

Scales overwinter as eggs beneath female shells. Crawlers emerge in May or June, migrate to a feeding site, and molt to the immobile scale form. Nymph and adult oystershell scales feed on the sap of twigs, branches, and thin-barked stems.

Branch and tree mortality may result from large scale infestations.

Control:

Spray twigs, branches, and stems with superior oil in the spring before buds expand or with malathion or acephate when crawlers are present. During winter, scrape parent scales filled with overwintering eggs from infested tree parts by lightly rubbing with a plastic or TeflonĀ® dish pad.

Pine Tip Moth

Lives on ponderosa, Austrian, Scotch, and jack pines. Larvae vary from yellowish-white to pink to reddish-orange, with dark heads. Mature southwestern pine tip moth larvae are 12 to 15 mm long. Coloration and wingspan of the moths varies with the species; however, most are a mottled reddish-brown and gray.

They overwinter as pupae in the ground. Moths appear during spring and females lay eggs on new growth. They usually have only one generation per year.

Larvae mine needles, bud, and new shoots, killing shoots and stunting tree growth. Old infested tips crumble when squeezed. Shoots infested generally turn brown.

Control:

Spray acephate or dimethoate on foliage in spring when new shoots are elongating but before needles are more than 13 mm long. Repeat in late June or early July. Insecticide application should be timed to coincide with the appearance of young larvae. Synthetic attractants of the male pine tip moths are available commercially and can be used to monitor adult flight periods. Trees should be sprayed 10 to 14 days after moth flight begins.

Pine Sawfly

Lives on ponderosa, Scotch, Austrian and jack pines. Sawfly larvae have eight pairs of prolegs and vary in color from grayish- to yellowish-green. Some species have one or more longitudinal stripes. Mature larvae may reach 18 to 25 mm in length. Adult sawflies resemble small bees.

The life cycle and number of generations varies with the sawfly species. Most species overwinter as pupae or prepupae, a few as eggs. In spring larvae usually feed in groups on needles, starting at the needle tip. Older larvae feed singly or in pairs, but usually on the same branch as other larvae. The larvae of most species drop to the ground, spin cocoons, and pupate in the soil. All larvae rear up in a characteristic “s” shape when disturbed.

Some species characteristically feed on young needles, others on old needles, and still others on both young and old needles. Species that feed only on old or young needles weaken trees and slow their growth, while species that feed on both young and old needles may kill severely damaged trees.

Control:

Spray needles with carbaryl when sawfly larvae first appear in May, June, or July. Commercially formulated virus preparations can be used to kill some species. Natural enemies frequently are important in ending outbreaks.

Pine Bark Beetle

Lives on ponderosa, Scotch, eastern white, jack and other pines. Several species of bark beetles breed in pines in the Great Plains. Larvae are usually “c” shaped, legless, and white with brown heads. Adults range from 3 to 10 mm long and are brown or black.

If winters are not severe, most bark beetle species can overwinter as adults, larvae, or eggs. Eggs are laid in galleries constructed between the bark and wood, and larval feeding galleries radiate from these egg galleries. The number of generations per year can vary from one to three or more depending upon the species involved and the severity of winter.

Gallery patterns, vigor of trees attacked, and site of attack vary with the species. Small holes in the bark, pitch masses on the bark, and boring dust in crevices and at the base of the tree are the first signs of attack. Infested trees have a blue-gray sapwood, caused by blue stain fungi, which the beetles introduce. Feeding by larvae and the accompanying spread of flue stain fungi eventually girdle infested trees. Needles on girdled trees turn reddish-brown color. Group-killing of trees is characteristic of all species.

Control:

Avoid mechanical injuries to healthy trees. Prune only during dormant seasons. Cut and burn or debark infested materials. Thin overcrowded stands and remove weakened trees. Kill beetles in logging residue by burning slash or scattering slash so the sun can dry it quickly. High value trees can be protected from attack by late spring or early summer applications of carbaryl.

Hackberry Nipple Gall

Lives on hackberry. Adult psyllids are about 4 to 5 mm long, and look like miniature cicadas. The tiny, yellowish nymphs rapidly become enveloped by gall tissue and are rarely seen. Nipple galls are light green, nipple-shaped, and about 4 mm in diameter.

Psyllids overwinter as adults in bark cracks and crevices. After mating in spring, females lay eggs on new growth. Nymphs feed on new growth all summer, causing galls to form on the underside of leaves. In September, large numbers of adults emerge from galls and collect around doors and windows.

Insect injury occasionally causes premature leaf drop, but trees are not seriously damaged.

Control:

Control is not generally needed. Leaves can be sprayed with carbaryl in spring when leaves are expanding. Raking and burning infested dead leaves kills beneficial wasps that parasitize the psyllids and overwinter inside the galls.

Lilac (Ash) Borer

Mature larvae are about 25 mm long and creamy white with shining brown heads. The wasp-like moths vary from black and yellow to orange and brown, have clear wings, and have a wingspan of 26 to 28 mm.

Mature lilac borer larvae overwinter and pupate in tunnels under th ebark. Moths emerge and lay eggs on the bark during May, June and July. Larvae of banded ash clearwings pupate in August, and moths fly in late August or early September. Banded ash clearwings overwinter as young larvae in tunnels.

During the summer, larvae of both species mine the sapwood of young trees, causing leaves to turn reddish-brown and braches to die back and break. Entire trees are often killed. Entrances to the tunnels are frequently associated with sunken and cankered areas on stems and branches. Dark moist sawdust clings to the tunnel entrances and to the bases of trees. Empty pupal skins often protrude from exit holes.

Control:

Spray trunks and all branches below 3 m with chlorpyrifos. Trees should be sprayed two to three times at 2- week intervals during moth flight. Traps baited with a male attractant, (Z,Z)-3, 13-octadecadienyl acetate, can be used to monitor moth flight and determine the optimum times to spray. Trees should be sprayed 10 to 14 days after the first moth is captured. Cut and burn heavily infested trees and branches.

Pear Slug Sawfly

Can live on plum, cherry, cotoneaster, pear, and mountain ash.

Larvae are slug-like, dark olive green, and covered with slime. Adult sawflies are black and yellow, stout-bodied, adn approximately 5 to 8 mm long.

Larvae overwinter in protected places in soil and pupate in the spring. Adult sawflies emerge in June and July, and females lay eggs in slits cut in leaves. Eggs hatch after a few days and larvae feed on foliage for 2 to 3 weeks. A second generation is common in late summer of the Central Great Plains with adults emerging during late July and August and peak larval feeding occurring in September.

Larvae feed almost entirely on the upper leaf surface, consuming tissue and avoiding the main veins. Heavily infested leaves appear scorched and may drop prematurely. Severe defoliation reduces plant vigor and is unsightly.

Control:

Spray leaves with carbaryl, malathion, diazinon, or other commonly available insecticides when damage first appears.

Poplar Borer

Lives on cottonwood and other poplars. Larvae are legless and creamy-white with brown heads. Adults are elongate, robust, grayish beetles about 20 to 30 mm long with yellowish markings on the wings and body.

Adults emerge during the summer. They feed on the bark of young twigs and lay eggs in slits cut in the bark of the trunk and larger branches. Larvae tunnel inside the trunk and branches for 2 to 3 years.

Infested branches and trunks become swollen and scarred, and contain numerous holes marked by sawdust and sap. Wet areas around the holes eventually blacken and appear varnished. Large trees are often riddled with tunnels making them subject to wind breakage. Small trees may be girdled and killed.

Control:

Spray trunks and lower limbs of high value trees with chlorpyrifos when adult beetles begin to emerge in summer. Contact your local extension service for more information on proper treatment time.

Spider Mites

Lives on spruce, pine, honey locust, elm, linden, and other conifer and hardwood trees and shrubs. The tiny arthropods are less than 1 mm long and vary in color from yellow to red to green.

Mites overwinter as eggs on the tree. There are many generations per year. Mites feed on sap and spin a fine silk webbing among needles (or leaves).

The damaged needles (or leaves) become stippled, bleached, and brown, and may fall off. Severely infested trees are less vigorous and occasionally may be killed.

Control:

Spray trees thoroughly with diazinon, cyhexatin, malathion, chlorpyrifos, or tetradifon as soon as mite damage appears during April or May. Repeat every 10 to 14 days as needed.