Insect and Disease Management Guide 
for Woody Plants in North Dakota -- continued

Insect/Mite Management

Aphids

(general) family Aphididae

Host(s): Conifers and hardwoods. Many species of aphids are host specific, but more than one species can attack a given host. This makes species identification difficult, often requiring an aphid taxonomist.

Description/Biology: Small, soft-bodied insects with pear-shaped abdomens are typical. Aphids overwinter as eggs attached to foliage or twigs. Eggs hatch in early spring and the nymphs feed on twigs. The nymphs develop into asexual females that produce nymphs without mating. These nymphs develop into winged and wingless females that continue to reproduce asexually. There are as many as six generations annually. In late summer or early fall, a sexual generation is produced and these females deposit the overwintering eggs.

Damage/Symptoms: Aphids suck plant juices, causing discoloration on plant parts. Other symptoms include deformed plant parts (leaves and shoots) and reduced shoot growth. Damage is often minimal unless infestations are very severe and persistent for several years. Aphids secrete large amounts of honeydew, which can become overgrown with unsightly sooty mold. Honeydew causes problems when it lands on cars, picnic tables, and sidewalks, causing them to become sticky and overgrown with sooty mold. Ants often tend aphids for their honeydew secretions.

Comments: A few aphids will not substantially damage plants. There are often natural predators present that will keep aphid populations at low levels. If an aphid population is becoming unacceptable, look to see if there are predators (ladybird beetles, lace wings, etc.) present. If present, it may be better to hold off on chemicals and allow nature to take its course. In some cases, a strong jet of water from a hose may be effective in reducing aphids to insignificant levels. If compelled to use pesticides, use an alternative product such as insecticidal soap to reduce the impact on beneficial insects. Many conventional insecticides, such as acephate, carbaryl, malathion, and permethrin, are labeled for aphids on trees and shrubs. Acephate and other insecticides may be injected into the tree by professional applicators.

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Ash bark beetles

(Hylesinus spp.) family Scolytidae

Host(s): Ash

Description/Biology: Small (1/8 inch), cylindrical, hard-bodied bark beetles with dense scales common on the front wings. When viewed from above, the head is partly or completely hidden by the thorax. Adult beetles overwinter in hibernation chambers in the rough outer bark on the trunk of an ash tree. There is one generation per year. The adults emerge in the spring, usually late May or early June, and excavate egg galleries in twigs and branches. The eggs hatch into small, white, legless grubs with brown heads that form galleries parallel to the wood grain. Larvae pupate inside the galleries. Adults emerge from pupae in late summer and construct overwintering galleries. Some excavate egg galleries, but it is not known if the resultant larvae survive the winter.

Damage/Symptoms: Attacks and kills small twigs and branches. Only the western ash bark beetle, H. californicus, is capable of killing live trees by boring into the boles of the trees.

Comments: Remove dead branches and trees from the vicinity to prevent movement of the beetles to healthy trees. See "Maintaining Healthy Trees and Shrubs."

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Ash flower gall mite

(Aceria flainiflora) family Eriophyidae

Host(s): Ash

Description/Biology: The mites overwinter as fertile females beneath bud scales or in crevices of the bark. The females move to the male flowers in the spring, where they lay their eggs. Eriophyid mites are very tiny and difficult to see even with 10X magnification. Under magnification, these mites can be viewed when galls are forming. The mites are light colored and carrot shaped.

Damage/Symptoms: Male ash flowers are on different trees than female ash flowers. Male trees are widely used in ornamental plantings. Heavy infestations do not negatively affect tree health but may be considered unsightly. The galls are formed on the flowers, causing severe distortion and fusing of the flowers. The gall starts out green in color and matures to brown. Galls are persistent, remaining attached to the twigs for several seasons.

Comments: Sprays will not improve tree health but may be used when blossoms start to form for improved aesthetic value.

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Ash/lilac borer

(Podosesia syringae) family Sesiidae

Host(s): Ash, lilac

Description/Biology: The ash/lilac borer adult is a clearwing moth that resembles a paper wasp. The wings are narrow, dark brown and transparent and the bodies are dark brown/black with a yellow band on the abdomen. Adults emerge in May-June and lay their eggs on bark crevices. Larvae require three years to mature. During the first summer, larvae feed within the bark. Larvae then feed into the wood during the second year, and bore toward the surface just under a thin layer of bark during the third year. Fully grown larvae are 1 inch long with creamy-white bodies and brown heads. Pupae push their way to the surface just prior to adult emergence.

Damage/Symptoms: Feeding beneath the bark damages the plant's food and water-conducting tissue. Sawdust can be seen around tunnel entrances and at the bases of trees. Tunnel entrances are about 1/4 inch in diameter. The area around entrance holes may die, producing target-like sunken areas. Boring causes dieback of limbs and may kill young trees. Infestation often occurs at injury sites such as those caused by lawn mowers, weed trimmers, or previous attacks by Podosesia.

Comments: An Ichneumonid wasp, Phaeogenes ater, is a parasite of ash/lilac borer, but little is known about its effectiveness as a biocontrol agent. These borers often infest trees that are under considerable stress, but apparently healthy trees are also infested. See "Maintaining Healthy Trees and Shrubs." Insecticides can be used by spraying the trunk and lower branches with permethrin or lindane three times at three-week intervals beginning 10 to 14 days after the first adults emerge (mid-May to early June) and ending when adult flight stops (mid to late July). Pheromone traps are commercially available for monitoring and improving spray timing.

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Ash plant bug

(Tropidosteptes amoenus and other Tropidosteptes spp.) family Miridae

Host(s): Green ash

Description/Biology: There are two generations per season. They overwinter as eggs imbedded in bark. Green to tan nymphs emerge in the spring and feed on the undersides of the leaves. First-generation adults emerge in midsummer. Adults are tan colored with pinkish markings on the back and are about 1/2 inch long. Second-generation adults appear during late summer and remain active until a severe frost occurs.

Damage/Symptoms: Plant bugs pierce host tissues and suck plant sap, causing yellow spotting of leaves. Severe infestations cause leaf mottling, deformed leaves, and sometimes premature leaf drop. Trees usually tolerate ash plant bug damage well and it is normally not severe enough to cause defoliation or warrant control.

Comments: As numbers increase through the summer, damage to foliage can occasionally be significant. Control is justified when leaf injury is easily found throughout the canopy. Carbaryl and permethrin may be used to manage ash plant bug.

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Blister beetles

(Epicauta spp. or Lytta sp.) family Meloidea

Host(s): Caragana, green ash, honeysuckle

Description/Biology: Several species of blister beetles can feed on the foliage of shrubs and trees. Blister beetles have a similar body shape: long, narrow, first body segment narrower than head or remainder of body ("neck-like"). The most common blister beetles causing problems in ornamentals are the Ashgray (Epicauta fabricii) and Nuttall (Lytta nuttalli) - metallic green, red or purple. These beetles have body fluid containing cantharadin, a blistering agent. There is one generation per year. Adults emerge in late spring and early summer. Eggs are laid in moist soil. The larvae live in the soil, where they are predators on grasshopper egg pods and bee larvae. The larvae survive the winter and complete development in the spring.

Damage/Symptoms: The adults feed on plant foliage. The beetles are very mobile and tend to congregate in swarms to feed. Defoliation is localized due to the swarming behavior. When populations are large, young caragana shelterbelts may be damaged.

Comments: Blister beetle populations normally increase following outbreaks of grasshoppers within the region. Beetles may be sprayed with carbaryl or methoxychlor as large populations become evident, but before serious damage has occurred.

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Boxelder erineum gall mite

(Cosetacus negundi) family Eriophyidae

Host(s): Boxelder (Acer negundo)

Description/Biology: These mites are white, slender, and spindle-shaped. Mites remain in galls until the leaves mature.

Damage/Symptoms: Large, rounded, and pouch-like galls develop on the underside of the leaves as thick cavities with a dense mass of white hairs. Hairs protrude on the upper side of the leaf. The galls are solitary, do not occur on veins, and can be widespread on the leaves. These galls do not substantially damage the health of infested plants.

Comments: Earliest foliage is often affected, especially leaves nearest the trunk or on larger limbs. See "Mites (gall, rust, bud, and blister)." Treatments are not necessary.

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Boxelder twig borer

(Proteoteras willingana) family Tortricidae

Host(s): Boxelder

Description/Biology: The moths emerge in late June or early July. The moths are gray with dark brown markings and have a wingspan of 1/2 to 3/4 inch. Eggs are laid singly on the undersides of leaves. The larvae hatch in early July. Larvae feed on leaves first, then bore into shoots or buds by early August. These larvae hibernate for the winter, resuming feeding in the spring. New buds are attacked in the spring. Larvae are creamish to gray colored with dark spots at the base of hairs. The larval head capsule is black. Mature larvae are less than 1/2 inch long.

Damage/Symptoms: Newly hatched larvae skeletonize the undersides of leaves. By August, larvae bore into shoots. Entry holes are plugged by frass and silk. In the spring when larvae resume tunneling, the entrance hole and frass plug can be seen, along with swelling of the infested shoot. In ornamental plantings, the boring habits of the larvae result in a bushy growth that is unattractive.

Comments: If problems develop, insecticide treatments directed at leaf feeding caterpillars in July should provide effective protection.

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Bronze birch borer

(Agrilus anxius) family Buprestidae

Host(s): Birch

Description/Biology: The adult belongs to a group called metallic wood boring beetles. The beetles are bullet shaped, less than 1/2 inch long, and olive green with metallic bronze reflections. The larvae are known as flat-headed borers. The legless larvae have a flat, brown head, are creamy-white, and have a distinctly segmented body. They reach a length of 1 1/4 inches when fully grown. The life cycle may last from one to two years. Adults emerge from infested trees from late June until August. Eggs are laid in bark crevices of weak or dying trees. Limbs 1 inch in diameter or less are infested first, larger limbs and trunk later. Larvae hatch and tunnel beneath the bark. The larvae pupate in a chamber in the sapwood.

Damage/Symptoms: Young, transplanted birch trees and weakened or dying trees are at greatest risk for infestation. Infestations start on smaller branches, killing upper branches first. Larval feeding produces meandering tunnels beneath the bark. Infested branches may appear bumpy. The exit hole for the adult is "D" shaped. Bronze birch borer is the limiting problem for birch in North Dakota.

Comments: Insecticidal control is best directed at adults to prevent egg laying. Spray the bark surface of the trunk and limbs with permethrin in mid June and twice more at three week intervals until August. Insecticide injections, by trained professionals, have shown variable results. Heavily infested limbs and trees should be destroyed. The brown-barked river birch is resistant to bronze birch borers.

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Cankerworm, fall

(Alsophila pometaria) family Geometridae

Host(s): Variety of hardwoods, especially basswood, bur oak, elm, green ash, maple, white birch

Description/Biology: There is one generation per year and it overwinters in the egg stage. Eggs hatch into larvae that feed on the foliage beginning in the spring. Larvae are slender and about 3/4 to 1 1/2 inches long when mature. Color varies from light green with white lines to brownish green with dark bands down the back. Larvae have three pairs of prolegs with one pair being rudimentary. Larvae crawl using a looping behavior. In mid-summer, larvae pupate in cocoons in the soil. Adults emerge in the fall. Wingless females must crawl from the ground up the tree to lay masses of 100 eggs high up on the trunk and branches of trees. Females are about 3/4 inch long, brownish gray, and do not have spines. Males are also brownish gray with irregular light bands on the forewings.

Damage/Symptoms: Feeding by young larvae causes a shot hole appearance in the leaves. Older larvae consume leaves, defoliating entire trees or groups of trees when populations are high. Repeated defoliation for three or more consecutive years will stress trees, decrease the tree's aesthetic value, and may kill tree branches.

Comments: Placing a 3- to 4-inch band of sticky material, such as Tanglefoot®, in early September is a common technique used to prevent the wingless female moth from crawling up the tree to lay her eggs. It's recommended to apply the sticky material to a waterproof material wrapped around the tree. This prevents absorption and allows for removal of the sticky substance at the end of the pest season. Insecticidal treatments should be directed at the caterpillars in late spring or early summer. Acephate, Bt, carbaryl, and permethrin are registered for fall cankerworms.

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Cankerworm, spring

(Paleacrita vernata) family Geometridae

Host(s): Variety of hardwoods, especially basswood, bur oak, elm, green ash, maple, white birch

Description/Biology: There is one generation per year and they overwinter as larvae in earthen chambers. Larvae pupate and the spiny, wingless female emerges in early spring. Females lay masses of about 100 eggs in crevices of bark on the lower trunks of hosts. The difference between the spring and fall cankerworm is when the eggs are laid - spring cankerworm in early spring and fall cankerworm in September. Young larvae hatch from the eggs and feed on the buds and unfolded leaves. Larval feeding and development are similar to the fall cankerworm. Larvae range in color from yellow-green to almost black and have a yellow stripe along the side of the body. Another differentiating characteristic of spring cankerworm larvae is the two pairs of abdominal prolegs (fall cankerworm has three pairs) and a pair of tubercules on the dorsal surface of the abdomen. Larvae are slender and about 3/4 to 1 1/2 inches long when mature. Larvae crawl via a looping behavior and are often blown by the wind as they hang from their own strands of silk.

Damage/Symptoms: As with the fall cankerworm, defoliation is caused by larval feeding. Repeated defoliation for three or more consecutive years will stress trees, decrease aesthetic value, and may kill tree branches.

Comments: Banding of tree trunks with a sticky material such as Tanglefoot® is a common technique used for cultural control. A 3- to 4-inch band of sticky material applied in mid March is used to prevent the wingless female moth from crawling up the tree. It's recommended to apply the sticky material to a waterproof material wrapped around the tree. This prevents absorption and allows for removal of the sticky substance at the end of the pest season. Insecticidal treatments should be directed at the caterpillars in late spring or early summer. Bt, carbaryl, and permethrin are registered for spring cankerworms.

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Carpenterworm

(Prionoxystus robiniae) family Cossidae

Host(s): Variety of hardwoods.

Description/Biology: The moths are mottled gray with wingspans of 2 inches (males) to 3 inches (females). The wood boring caterpillars are greenish white with brown heads or spotted and pinkish with reddish brown heads. Fully grown larvae are 2 to 3 inches long. The life cycle of carpenterworms requires three years. Adults emerge in June. Females deposit eggs in bark crevices or wounds on the trunk or branches. The larvae tunnel through the cambium layer and into the wood, keeping the gallery clean of frass. Larvae pupate in May of their last year of development.

Damage/Symptoms: Carpenterworms are common pests of poplar and ash in windbreaks. The extensive tunnels often break through the surface of the bark. Though carpenterworms seldom kill trees, their feeding makes trees susceptible to breaking in strong winds. Wounds on the bark are very attractive egg laying sites. The exit holes are round and may be up to 5/8 inch in diameter.

Comments: Carpenterworms are often found in trees which are of low vigor, but apparently healthy trees may be affected if there is a bark opening. See "Maintaining Healthy Trees and Shrubs."

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Chokecherry midge

(Contarinia virginianiae) family Cecidomyiidae

Host(s): Chokecherry (Prunus virginiana)

Description/Biology: Gall midges are tiny, slender, fragile flies smaller than mosquitoes. Little information has been published on the chokecherry midge. It is likely that the adults are active during bloom or early fruit set. Their small orange maggots develop in the fruit. Larvae remain in infested fruit, which dry up and drop to the ground before harvest. Some fruit may remain attached to the plant. Other midge in the region overwinter as larvae in the soil, complete development in the spring, and emerge as adults.

Damage/Symptoms: Infested fruits are enlarged and pear shaped. The larvae destroy the seed and leave the fruit hollow.

Comments: Removing and destroying the infested fruit soon after they appear reduces the number of surviving midges for the next season. No chemical treatments have been proven effective for this pest.

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Chokecherry pocket gall mite

(Eriophyes emarginatae) family Eriophyidae

Host(s): Chokecherry (Prunus virginiana) and other Prunus spp.

Description/Biology: These mites are small, whitish, and wormlike. There is only one generation per year. Fertilized females overwinter in crevices of old buds near the base of branches. The females move to newly developing leaves in the spring.

Damage/Symptoms: Pouch-like galls are formed at random over the surface of the leaves. Galls are elongate, or finger-like, and erect. Galls become more visible when they turn yellowish to light brown. The galls cause little damage to trees but create an undesirable appearance in ornamental plantings.

Comments: See "Mites (gall, rust, bud, and blister)."

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Cottonwood leaf beetle

(Chrysomela scripta) family Chrysomelidae

Host(s): Poplars, willows

Description/Biology: Adult beetles are 1/4 to 1/3 inch long. The head is black and the pronotom is dark with reddish margins bearing a dark spot. The hard wing covers (elytra) are yellowish with a dark line on the inner edge and seven elongate dark spots. The eggs are yellow and laid in clusters on the leaves. The larvae have black heads, well developed legs and yellowish bodies with two rows of black spots along the back. The adult beetles overwinter in leaf litter, emerging when leaves first appear. Both adults and larvae feed on foliage. The larvae feed for about two weeks, skeletonizing the undersides of the leaves. Pupae hang from the leaves. From egg to adult requires about six weeks. Two generations occur annually.

Damage/Symptoms: Larvae skeletonize leaves. Young foliage is preferred. Large larval populations can kill leaders, resulting in deformed growth. Large numbers of adults can be found in the fall at the base of infested trees.

Comments: Can spray Bacillus thuringiensis (Bt) "San Diego" or pyrethrins on young larvae. Should use a synthetic insecticide, such as carbaryl, on adults and older larvae.

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Cottony maple scale

(Pulvinaria innumerabilis) family Coccidae

Host(s): Boxelder, elm, honeylocust, linden, maple, poplar, other hardwoods

Description/Biology: The brown, flat, inconspicuous immature female scales overwinter on twigs. In the spring, the females complete development and produce their large white cottony egg sac. The tiny, transparent crawlers hatch in late June to early July, moving to the undersides of leaves to feed. Males mate with immature females in late summer. Before leaves drop in the fall, the females move back to the twigs and attach themselves for overwintering. There is one generation per year.

Damage/Symptoms: Scale insects have piercing-sucking mouthparts that are inserted into leaf veins to draw out plant sap. Feeding can cause twig dieback. Severe infestation may kill major limbs. Honeydew, produced by the scales, coats the leaves and promotes the growth of black sooty mold fungi. In late spring, heavily infested branches with white egg sacs look like they have been strung with popcorn.

Comments: Dormant oils are directed at the overwintering scales on the twigs. Insecticides are used against the young crawlers and treatments are timed with hatching in late June.

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Eastern spruce gall adelgid

(Adelges abietis) family Adelgidae

Host(s): Spruce

Description/Biology: Adelgids are small aphid-like insects. There are two generations per year of A. abietis and both generations consist entirely of females that reproduce asexually. The adelgids overwinter as partly grown nymphs attached to the base of spruce buds. Females mature in April or May and lay between 100 and 200 eggs at the bases of needles. Eggs hatch in about a week, and the new nymphs feed at the bases of needles, causing twigs to swell. As the twig swells, a gall is formed, and the nymphs complete their development in the cavities of the gall. Later in the summer, winged females emerge from the galls and lay their eggs on the needles of nearby branches. These eggs hatch, and the nymphs overwinter.

Damage/Symptoms: Adelgids suck plant juices. A. abietis causes pineapple-shaped galls or swollen twigs that affect shoot growth. Galls become unsightly in heavily infested trees but are unlikely to seriously harm trees.

Comments: Can apply a summer spray of soap or oil or conventional insecticide such as carbaryl around bud break. Remove galls and destroy.

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Eastern tent caterpillar

(Malacosoma americanum) family Lasiocampidae

Host(s): Chokecherry, pin cherry, occasionally other hardwood species

Description/Biology: There is one generation annually and it overwinters as fully developed embryos within the eggs. Larvae are gregarious and construct tent-like nests of silk in the forks of trees. The tents are used as shelter or resting places. The larvae forage during the day for new foliage in nearby branches. Larvae feed for six to eight weeks and are about 2 inches long when mature. Larvae are black and somewhat hairy with a whitish-yellow stripe down the middle of the back, narrow broken orange-colored subdorsal stripes, and lateral white and blue markings. When mature, they disperse and spin cocoons in sheltered places. Adult moths appear during early summer (late June or early July) and lay their eggs in a bandlike cluster of 150 to 350 eggs around a small twig, covering them with a froth substance called spumaline. Adult moths are yellowish-brown, medium-sized (1 to 1 1/2 inch wingspans) and stout bodied, with hairy bodies, legs, and eyes. Two oblique whitish bands run across the forewings.

Damage/Symptoms: Larval feeding disfigures ornamental plants, but plants are usually not permanently damaged. Webs are unsightly.

Comments: When populations are high, usually at 10-year intervals, whole trees can become covered with webbing and defoliated. Egg masses should be destroyed when they are seen. Bt works well to control young larvae, while pyrethrins or synthetic insecticides are needed for older larvae.

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Elm leaf beetle

(Pyrrhalta luteola) family Chrysomelidae

Host(s): European species of elm are most susceptible to damage. Siberian and American elms are somewhat resistant.

Description/Biology: Adults are olive-green with black longitudinal stripes along the margin and center of the back. They overwinter as adults in protected places like sheds, bark crevices, or house shingles. Beetles occasionally become a nuisance inside homes when seeking overwintering sites. Adults emerge from overwintering sites in the spring and feed on elm leaves, chewing small, circular holes. Female beetles lay double row clusters of five to 25 eggs on the underside of leaves, with a total of 600 to 800 eggs in their life span. Tiny black, grub-like larvae hatch from the eggs and begin to feed on the leaves. As larvae mature, their color changes to green, then to yellow with dark tubercles that form two black lateral stripes. Larvae crawl down tree trunks to pupate on the ground at the base of trees, or in cracks or crevices on the trunk. A new generation of adults emerges from the pupae in about two weeks. New adults fly back to the foliage for feeding and egg laying. In late summer or fall, the adult beetles leave the host tree and seek an overwintering site. There are usually two generations per year.

Damage/Symptoms: Larval feeding skeletonizes foliage, while adult feeding causes a shothole pattern. Damage is most severe when beetles attack a tree for several consecutive years causing premature leaf drop, limb dieback or even tree death.

Comments: Boiling water, light oil, or insecticides may be applied to kill larvae congregating at the base of elms. Spray adults and larvae with carbaryl, permethrin, spinosad, or cyfluthrin when the weather is NOT hot and dry. Trunk injections have shown favorable results.

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Elm sawfly

(Cimbex americana) family Cimbicidae

Host(s): Aspen, basswood, elm, willow, other hardwoods.

Description/Biology: Mature larvae are 2 inches long and have wart-like bumps on their bodies. Elm sawflies overwinter as pupae in cocoons spun on the ground beneath plant litter. The adults emerge in mid June. The adults are heavy-bodied sawflies that are 1 inch long. Their wings are smoky colored. They have knobbed antennae and black heads. The abdomen of the female is black with yellow spots. The male's abdomen is reddish brown to purplish black. The larvae are gray when they first hatch but change to yellowish green with a blue and black line the length of their back as they grow older. The females lay eggs in pockets that they cut into the undersides of leaves. Eggs hatch in about seven to 10 days. Larvae feed until late August, when they drop from the tree and spin their cocoons. Mature larvae are 2 inches long and have wart-like bumps on their bodies. There is only one generation per year.

Damage/Symptoms: Elms and willows are the most commonly infested trees. The larvae defoliate trees. Larvae reach mature size and consume most of the foliage in late summer. The larvae are often found in large groups, particularly when they drop from trees and prepare to spin cocoons for the winter.

Comments: Elm sawfly outbreaks are rare. Treatment with conventional insecticides has proven effective, particularly if larvae are treated when damage is first observed.

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European elm bark beetle

(Scolytus multistriatus) family Scolytidae

Host(s): Elm

Description/Biology: The adult is shiny dark brown to black and about 1/8 inch long. Female beetles lay eggs in elm limbs, trunks, or recently cut elms. Adults feed in crotches of living elm twigs causing twigs to die and drop. If the adult is contaminated with the spores of the Dutch elm disease fungus, it can transmit the disease to healthy elms during feeding. After feeding, the female moves to recently cut elm logs or limbs or trunks of stressed trees and bores a 1- to 2-inch breeding gallery, where about 36 eggs are laid. Egg laying galleries are usually parallel to the wood grain. Larvae hatch from the eggs and bore larval galleries perpendicular to the egg laying galleries. There are usually two generations per year. The second generation of beetles overwinter as larvae, pupae, or adults beneath bark.

Damage/Symptoms: European elm bark beetles are a major vector of Dutch elm disease, causing devastating tree mortality.

Comments: This is an exotic pest that does not overwinter well in North Dakota and does so most often in protected sites. This is why elimination of elm firewood piles is so important in Dutch elm disease control.

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European elm scale

(Gossyparia spuria) family Eriococcidae

Host(s): Elm

European fruit lecanium scale

(Parthenolecanium corni) family Coccidae

Host(s): Ash, elm, boxelder, fruit trees, poplar, willow, other hardwoods

Description/Biology: The 1/4 inch in diameter, hemispherical in shape, and reddish brown protective cover of the female is the stage most often seen. Eggs are laid in June beneath the protective cover. The white crawlers, or nymphs, hatch from late-June to mid-July. Crawlers migrate to leaves, feeding on the undersides of leaves near the mid-vein. By late August, the crawlers move back to the bark to hibernate in bark crevices. In the spring, crawlers move to twigs where they complete development. There is only one generation per year.

Damage/Symptoms: Large clusters of the reddish brown mature scales can be seen on branches and twigs. Sticky honeydew is produced, making foliage appear wet. Large populations may weaken or kill twigs and branches.

Comments: Insecticide treatments, such as acephate are most effective when applied to the crawlers as they hatch in early July.

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Fall webworm

(Hyphantria cunea) family Arctiidae

Host(s): Alder, aspen, birch, chokecherry, cottonwood, elm, fruit trees, maple, pin cherry, poplar, willow, other hardwoods.

Description/Biology: There is one generation per year and it overwinters in the pupal stage. Adults emerge late June to mid July and are mostly white. Females lay large egg masses on the undersides of leaves. Eggs hatch into larvae after about 10 days. Larvae feed until late summer or early fall in silken nests located at the ends of tree branches. As the colony grows, more leaves are added to accommodate the food needs. Mature larvae (about 1 inch long) are whitish with a broad dark band, and have long white or black hairs arising from reddish-orange projections along the body.

Damage/Symptoms: Silken nests are very unsightly in nurseries, city parks, and yards. Fall webworms cause more of a nuisance than a threat to the health of the tree.

Comments: Nests may be pruned out and disposed of as soon as they appear. Caterpillars feed within the web, making control with insecticidal sprays difficult. Early sprays, with Bt, acephate, carbaryl, malathion, or permethrin, before nests appear are usually effective. When webs have formed, the nest should be opened up before any insecticides are applied.

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Fletcher scale

(Parthenolecanium fletcheri) family Coccidae

Host(s): Arborvitae, juniper, yew

Description/Biology: The female scales overwinter as reddish brown nymphs, completing development in the spring and laying eggs. The mature female is yellowish brown, hemispherical in shape, and about 1/6 inch in diameter. The oval, flat, yellow crawlers hatch in late June. There is one generation per year.

Damage/Symptoms: The crawlers do not migrate very far from their hatching site. This results in concentrated infestations on certain branches. Honeydew is produced by the scales, coating the plant. Black sooty mold grows on the honeydew, contributing to plant stress.

Comments: The eggs hatch over a short period of time. Summer sprays of soap or oil directed at the crawlers in early July can be very effective in reducing the population.

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Forest tent caterpillar

(Malacosoma disstria) family Lasiocampidae

Host(s): Ash, aspen, basswood, birch, cottonwood, elm, maple, oak, poplar, other hardwoods

Description/Biology: Similar to the eastern tent caterpillar. There is one generation annually, which overwinters as fully developed embryos in eggs. Larvae hatch in early spring, usually coinciding with flushing of aspen foliage. The fully mature larvae (2 inches long) are easily identified from other caterpillars by the keyhole shaped spots along their backs and broad bluish lateral bands. Larvae gather on their silken mat spun on branches and start their foraging. In five to six weeks, the larvae pass through five larval instars and form silken cocoons to pupate. The stout-bodied moth emerges from the cocoon after about 10 days. The adult moth is light yellow to buff brown in color with two oblique dark bands on the forewings and a wingspan of about 1 to 1 1/2 inch. A female deposits 150 to 200 eggs around small twigs and covers them in a frothy substance called spumaline. The embryos develop into larvae in about a month.

Damage/Symptoms: Defoliation is caused by larvae. Light defoliation has little effect on tree growth. Two or more years of moderate-to-severe defoliation is necessary to affect radial growth and cause branch and twig mortality. People also find the wandering masses of larvae to be extremely objectionable. Unlike other tent caterpillars, webs do not develop.

Comments: Outbreaks typically last for two to four years in North Dakota. Bt works well to control young caterpillars, while permethrin or pyrethrins or other insecticides are needed for older larvae.

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Honeylocust pod gall midge

(Dasineura gleditchiae) family Cecidomyiidae

Host(s): Honeylocust

Description/Biology: The small midges, 1/10 inch long, are black (males) or black with red abdomens (females). They become active when new growth appears in the spring. Eggs are laid on young leaflets. The cream colored larvae feed on the leaf, stimulating the growth of a pod. The larvae feed within the pod. There are three to five generations per year.

Damage/Symptoms: Infested leaflets develop into a pod-like gall. There may be one or more larvae within a gall. The galls dry up and fall from the tree after the adult midge emerges. With heavy infestations, twig dieback can occur. New shoots form at the base of dead twigs. Trees are not killed, but infested trees are reduced in ornamental value.

Comments: Insecticide treatments, with spinosad or carbaryl, timed to coincide with spring growth, with follow-up applications at two week intervals, can reduce infestations.

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Honeysuckle aphid

(Hyadaphis tataricae) family Aphididae

Host(s): Honeysuckle

Description/Biology: The aphids are pale green to cream colored with a fine powdery wax on their 1/16 inch long bodies. Females lay eggs on shoots and twigs in the fall. The eggs overwinter and hatch at the time buds break in the spring. These aphids are all females and bear live young. They feed on the undersides of leaves and new shoots. Later, the aphids feed on the top side of leaves.

Damage/Symptoms: Infested leaves cup upward. The aphid's saliva contains a toxin which stunts the growth of new shoots, creating an unsightly witches'-broom effect. Witches'-brooms may die over winter, and severe infestations can kill branches or whole plants.

Comments: Check with local nurseries for tolerant honeysuckle cultivars. Tolerant cultivars include Clavey's Dwarf, Dropmore Scarlet Trumpet, Emerald Mound, Miniglobe, and others. For susceptible cultivars, treatments with acephate or permethrin when aphids first appear in the spring may be helpful. Avoid actions that stimulate succulent growth (e.g., pruning, fertilizing), as such tissue is more prone to infestation.

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Introduced pine sawfly

(Diprion similis) family Diprionidae

Host(s): Austrian, jack, red, scotch, and white pines

Description/Biology: Female adults are black and yellow with threadlike antennae and average 1/3 inch long. The male sawflies are brown and black with broad feathery antennae and are slightly smaller. There are two generations per year. They overwinter as prepupae in leaf litter. Adults appear May to June, and females insert about 10 eggs in a row into a single pine needle. Females deposit an average of 70 eggs during their lives. Larvae hatch in 10 to 14 days. They feed on the outer portion of the needles early on and entire needles later. Sawfly larvae have more than five pairs of abdominal prolegs while caterpillars have less than six pairs of prolegs. The larva changes color as it matures, from dull gray to black with white and yellow spots, a shiny black head, and a dark, double stripe down the back. In late July, larvae spin cocoons among needles in bark crevices and at the bases of small branches. The second generation appears in early August. Eggs hatch in seven to eight days. Larvae feed until September and eventually spin cocoons for overwintering.

Damage/Symptoms: Defoliation is caused by larval feeding. Damage appears as missing needles or needle parts, with ragged, shredded edges on partly consumed needles. When defoliation is heavy late in the season, branches or entire trees may be killed.

Comments: Bt is NOT effective against sawflies. Insecticidal soap, carbaryl, methoxychlor, or permethrin may be used. Spray larvae when there are more than 10 larvae found on one- to four-year old trees. Treat trees before damage is severe.

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Maple bladdergall mite

(Vasates quadripedes) family Eriophyidae

Host(s): Red and silver maples

Description/Biology: This is a small, white, spindle-shaped mite. The mites overwinter as females that move onto the foliage in the spring. There is an in-season generation of males and females.

Damage/Symptoms: The pouch-type gall, known as a bladder gall, is visible on the upper leaf surface. The galls are variable in shape, ranging from rounded to elongate. The outside of the galls appear wrinkled. They change in color from yellowish green to pink to brown to black. The inside is hollow with an opening on the underside of the leaf. With heavy infestations, leaves become wrinkled and may drop prematurely. The galls cause little damage to the tree but appear unsightly on ornamental plantings.

Comments: See "Mites (gall, rust, bud, and blister)."

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Mites (Gall, Rust, Bud, and Blister)

Mites that cause plants to produce galls are extremely small and invisible to the naked eye. The Eriophyidae (er e ó fi de ) mites stimulate plants to produce bladder galls, spindle galls, or dense masses of hairy growths (erinea). The growths cause concern for tree owners, but their presence is rarely detrimental to the health of the tree. Sufficient foliage usually remains unaffected during the season to maintain a healthy plant.

These mites are soft bodied and spindle shaped. They are unique among mites in having only two pairs of legs.

The life cycles of these mites are similar and rather simple. Some eriophyid mites on deciduous trees have a more complex life cycle that has only females in the overwintering generation and both sexes during the growing season. These mites are very specialized, feeding on a very narrow range of host plants; in many cases, only a single species.

Gall formation results from a mite feeding on an individual plant cell. Symptoms of injuries may appear on buds, shoots, twigs, stems, flowers, and fruits. Symptoms are described as blisters, rosettes, scales, enlarged buds, witches'-brooms, and erinea (hairy growths). Symptoms are generally specific to host and mite and are useful for diagnosing the problem.

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Native elm bark beetle

(Hylurgopinus rufipes) family Scolytidae

Host(s): American and Siberian elms

Description/Biology: Adult beetles are about 1/8 inch long and dull brown to black. Their abdomens are rounded, unlike the concave rear with a spine of the European elm bark beetle. The larva is a white, legless, grub with a pale brown head. There is only one generation per year. They pass the winter as either larvae or adults. Adults that overwinter are in tunnels made in the thick bark at the base of elm trees. They emerge in May, burrow into bark and excavate their egg galleries. The egg gallery generally extends across the grain of the wood, not parallel like the European bark beetle. Larvae feed beneath bark, tunneling away from the egg gallery, creating a fan-like pattern.

Damage/Symptoms: The elm bark beetles transmit the fungus Ophiostoma ulmi, which causes Dutch elm disease (DED). The native elm bark beetle prefers branches 2 to 4 inches in diameter. This results in infections starting 10 to 20 feet inside the edge of the tree canopy. The resulting DED symptoms are wilting and browning of an entire branch or area of the crown. Infected sapwood develops brown streaks.

Comments: Insecticide treatments with permethrin applied in late summer and fall to the lower 9 feet of the trunk have been recommended to reduce successful boring of the overwintering native elm bark beetle adults. An early spring treatment may offer additional protection. This approach is beneficial near river corridors where beetle populations are high. The American elm is most seriously affected by DED. Siberian elm is more tolerant.

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Oak bullet gall wasp

(Disholcaspis quercusmamma) family Cynipidae

Host(s): Bur oak

Description/Biology: This tiny cynipid wasp causes persistent galls. The wasps are less than 1/4 inch long, black to brown in color, and antlike in appearance. The life cycle is not well understood. The larvae are white, legless, and without a distinct head. The larvae are found in the galls. Females emerge in the fall and lay eggs near bud scales. Eggs hatch in the spring and larval feeding stimulates gall formation. There is likely more than one generation per season.

Damage/Symptoms: The 1/3 inch diameter gall is woody, tan and round with a rough surface. They are found on the twigs in clusters of three or more. Twig galls may cause injury to trees, but healthy trees are rarely damaged by their presence.

Comments: Oak trees have a number of gall-forming insects associated with them and they are generally not harmful to the health of the trees. The different gall wasps produce their own distinctive galls.

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Oak lace bug

(Corythucha arcuata) family Tingidae

Host(s): Bur oak

Description/Biology: Overwintering adults lay eggs in the spring. There are five nymphal stages. The nymphs are blackish with white markings and have spines on the abdomen. They mature to the adult form by midsummer. There are two generations per year, with the second generation completing development by fall. The adults are inch long. The wings of these true bugs have a lacelike appearance. The insect's wings are partially transparent except for dark markings at the base of the wings.

Damage/Symptoms: The nymphs feed in groups on the undersides of leaves. They deposit specks of tarry excrement. Leaves become mottled with loss of chlorophyll at feeding sites. Injured leaves are leathery, often dropping prematurely when trees are water stressed.

Comments: Damage is rarely harmful to the tree. The greatest concern is with ornamental plantings where foliage becomes discolored. Summer sprays of soap or oil controls nymphs and acephate, malathion, or permethrin kill adults and nymphs. None of these treatments kill eggs.

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Oystershell scale

(Lepidosaphes ulmi) family Diaspididae

Host(s): Wide variety of hardwoods

Description/Biology: Mature females lay eggs in the fall and the eggs overwinter beneath the protective coverings. The pearly white, oval eggs hatch in mid to late June. The crawlers move around until they locate a favorable feeding site on twigs and branches. Then, they insert their mouthparts and begin feeding. As they grow, they lose their legs and increase the size of the protective covering. The covering of a mature scale is brown to gray and resembles a tiny oyster shell, 1/8 inch long. The female scale dies after laying eggs.

Damage/Symptoms: The oystershell scale can be found on many different hosts. It can be very damaging to lilac, ash, and dogwood. When present, the scales can be so abundant that the protective shells form a crust on branches of the host plant. Heavily infested branches lose vigor and dieback can occur.

Comments: Treatments with summer sprays of oil or soap should be applied by the first week of July or when crawlers are observed emerging from under the shells. Acephate, chlorpyrifos, or malathion will kill crawlers; however, these chemicals will also kill natural enemies of the scale insects and could ultimately make the infestation worse. Since shells do not fall off after death, good assessment of treatment performance requires removal of shells. A shell is easily dislodged with a thumbnail.

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Pear slug sawfly

(Caliroa cerasi) family Tenthredinidae

Host(s): Cotoneaster, fruit trees, hawthorn, mountain-ash

Description/Biology: These insects overwinter in the ground as fully grown larvae. Larvae look like slugs and are dark olive green to black and covered with slime, changing to translucent yellowish green as they age. In spring, larvae pupate and emerge as adults in June. Adults are shiny black with dark wings and are about 3/16 inch long. Adults deposit eggs singly on the lower leaf surface. Larvae hatch from the eggs in about two weeks and feed on the upper leaf surface for about four weeks. Mature larvae drop to the ground to pupate. A second generation emerges by August. There may be one or two generations per year, depending on the weather.

Damage/Symptoms: Defoliation occurs due to leaf skeletonization and premature leaf drop. There is usually little detrimental effect on the hosts, but the skeletonized leaves and the slug-like larvae are unsightly.

Comments: The exposed larvae are easy to control during feeding. A strong jet of water can wash them from the foliage. Sprinkling wood ash on larvae will provide excellent control. Summer oils, insecticidal soap, and conventional insecticides labeled for sawflies also work well.

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Pine moth

(Dioryctria sp.) family Pyralidae

Host(s): Pines, spruce

Description/Biology: Little is known about pine moth life history in North Dakota. These moths overwinter in the larval stage in silken cases. Adults become active and emerge in May. Adults have narrow forewings and range from gray to reddish brown in color. The hind wings are unmarked with a narrow dark border. A wing span of 1 to 1 1/4 inches is typical for this genus. Larvae bore into bark, stems, shoots or rust galls during the summer. Larvae are usually pinkish-green and up to 3/4 inch long. Pupation occurs during mid summer and adults emerge about three weeks later, usually mid July to August. The larvae from these adults overwinter.

Damage/Symptoms: Pitch masses are characteristic at the entrance to the tunnel. They often occur on the stem at a branch whorl or on shoots near the terminal leader. Symptoms may also appear as a discolored or broken leader (sometimes a lateral) directly above the pitch mass. This damage may be confused with wind or snow damage. Repeated stem attacks may cause branches to break at the points of injury.

Comments: Remove and destroy (by chipping or burning) infested trees by early July before adult moths emerge. Control in Nebraska is obtained by spraying lindane during the second week of August. For greater control, a second spray may be applied in mid April. If acephate or dimethoate is chosen, two or three applications at 10- to 14-day intervals are required. Control with acephate or dimethoate is reported to be less consistent than with lindane. Permethrin may also be used.

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Pine needle scale

(Chionaspis pinifoliae) family Diaspididae

Host(s): Conifers. White spruce is the preferred host, but other hosts are Colorado spruce, various pines and Douglas-fir.

Description/Biology: Pine needle scales overwinter beneath the female scale covering as reddish eggs. Each female lays up to 100 eggs, which usually hatch in May or June. The tiny red crawlers or nymphs (1/80 inch) emerge and are dispersed by the wind to a new uninfested host or crawl to a new location on the same host. Young crawlers settle on the foliage, lose their appendages by molting, and begin feeding. Nymphs become sexually mature in late July and August and the adult scales emerge. Female adults are wingless, while male adults have wings and are smaller. After mating, the female lays eggs until late October. She shrinks in size as she lays eggs.

Damage/Symptoms: Scales suck juices from the needles. Moderate populations can cause the foliage to become yellow and then turn brown. Heavy infestation can cause branches and even whole trees to die. Symptoms include sickly looking trees with sparse, off-colored foliage and waxy white coverings over the scale insects. The scale cover looks like drops of white paint on needles.

Comments: Inspect ornamental trees for crawlers early in spring. Most populations can be managed by keeping hosts healthy along with timely applications of insecticidal oil or soap. Conventional insecticides such as acephate and malathion can be used; however, eliminating the scales' natural enemies with conventional insecticides can make the situation worse.

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Poplar borer

(Saperda calcarata) family Cerambycidae

Host(s): Aspen, cottonwood, poplar, willow

Description/Biology: Adults, known as longhorned beetles due to their long antennae, are elongate in shape and grayish in color. Adults emerge from branches in late May to July and feed on the leaves of host trees. Females lay eggs in small holes gnawed through the bark creating a U-shaped egg niche. White, legless larvae hatch in about two weeks and feed in the cambium before boring into the wood. A swollen, spindle-shaped twig gall results from the feeding wound. The larvae are often referred to as roundheaded borers. The life cycle usually requires one to two years to complete, but three years may be required depending on when the eggs were laid. Usually one or two adults complete development in each gall.

Damage/Symptoms: Larval feeding causes spindle-shaped twig galls to develop. When galls are numerous, the twigs easily break at the point of injury and normal tree growth characteristics are modified. Damage provides a point of entry for disease organisms, particularly the Hypoxylon canker fungus.

Comments: This insect attacks living trees but is more aggressive in weakened trees. See "Maintaining Healthy Trees and Shrubs." Remove low value brood trees (where insects mate). Treat trunks and lower limbs of high value trees in late July with lindane as adults begin to emerge. Repeat at two-week intervals through August.

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Poplar bud gall mite

(Cosetacus para populi) family Eriophyidae

Host(s): Cottonwood, poplar

Description/Biology: The mite is reddish and spindle-shaped. Mites overwinter in the galls. They become active in the spring and exit the old galls as buds are expanding, crawling over the surface of twigs and buds. There may be as many as eight generations in a season.

Damage/Symptoms: The gall is an irregular, lumpy, solid mass of plant tissue. It develops on one side of the twig and the gall eventually encircles the base of the bud or shoot. Young galls are greenish; older galls are red to brown and cork-like. Old galls persist for several seasons.

Comments: Although trees are seldom killed, lower branches often become crooked or stunted and may be killed. Continuous attack may weaken a tree, increasing its susceptibility to drought, frost, or other injuries. Heavy infestations are very unsightly. If chemical control is necessary, carbaryl can be sprayed as buds and leaves are expanding in the spring. See "Mites (gall, rust, bud, and blister)."

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Poplar petiole gall aphid

(Pemphigus populitransversus) family Aphididae

Host(s): Cottonwood and other Populus spp.

Description/Biology: The aphids overwinter as eggs laid on Populus spp. twigs. They hatch as the tree foliage develops. The newly hatched nymph feeds on a leaf petiole, stimulating growth of a gall. The small, dark colored aphids are found inside the round, hollow galls. These aphids secrete a white, waxy material which coats their body. After two weeks, the females bear live young that mature into winged females. These females leave the gall and find plants in the mustard family. A generation is produced on the alternate host. In the fall, the winged aphids return to Populus spp. and a male and female generation is produced. One egg is then produced by each female.

Damage/Symptoms: Round hollow galls form on the leaf petioles. Several species of Pemphigus aphids occur in the region. Infested leaves may drop prematurely in late summer. They are not a serious problem on Populus spp. and control is not necessary for these species. The aphids may be a serious pest of the alternate hosts, which include crops such as sugarbeets, lettuce, and mustard.

Comments: See "Aphids (general)."

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Prairie tent caterpillar

(Malacosoma californicum lutescens) family Lasiocampidae

Host(s): Hardwoods, chokecherry is the preferred host

Description/Biology: Adult moths are similar to M. americanum, the eastern tent caterpillar, and only an expert can properly identify them. Egg laying habits are the only indicator to differentiate the species in the field -- M. americanum have rounded egg masses which encircle twigs while egg masses of M. californicum lutescens do not encircle twigs and are deposited near the bases of hosts in the ground. There is one generation annually and it overwinters as fully developed embryos in eggs. Larvae hatch in early spring, usually coinciding with flushing of their host's foliage. The fully mature larvae (2 inches long) have black backs with a white mid-dorsal line and light blue sides. Larvae live in colonies in large silk tents in forks of trees. After feeding, larvae spin silken cocoons in folded leaves, bark or litter, and adult moths emerge in mid-summer. Adult moths are yellowish-brown, medium-sized (1 to1 1/2 inch wingspan) and stout bodied, with a hairy body, legs, and eyes. Two oblique whitish bands run across the forewings.

Damage/Symptoms: This is the most common species of tent caterpillars. Defoliation is caused by the larvae. The protective webs are conspicuous and unsightly.

Comments: Larvae feed outside of the web nest, which makes control with insecticides easy. Bt works well to control young larvae, while pyrethrins or synthetic insecticides are needed for older caterpillars.

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Red-headed ash borer

(Neoclytus acuminatus) family Cerambycidae

Host(s): Ash, elm, hackberry, linden, oak

Description/Biology: There is usually one generation per year. The adult overwinters in trunks and begins to emerge in April. Adults are about 1/4 to 2/3 inch long and reddish-brown in color with three yellow transverse bands on the elytra. Females lay eggs on weakened or newly planted ash trees. The larvae bore into the inner bark and summer wood, disrupting the flow of sap.

Damage/Symptoms: Young trees infested with the red-headed ash borer are susceptible to breakage during high winds. Larvae bore into sapwood of live trees and cause serious damage to ash logs left in woods or logs stored with their bark attached.

Comments: Healthy trees are rarely attacked. See "Maintaining Healthy Trees and Shrubs."

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Scurfy scale

(Chionaspis furfura) family Coccidae

Host(s): Ash, aspen, cotoneaster, elm, linden, other hardwoods

Description/Biology: The dirty white female scales are pear-shaped and 1/8 inch long. The scurfy scale overwinters as purplish eggs beneath the female shell. The purple crawlers hatch in late spring. The crawlers move away from the mother's shell and begin feeding on the bark. There is probably only one generation per year.

Damage/Symptoms: When infestations are large, the dense numbers of scale give the bark a rough, ugly appearance. Large infestations reduce the vigor of trees. Infested branches and limbs may die.

Comments: Prune and destroy infested branches when practical. Treatments with summer sprays of oil or soap should be directed at controlling the crawlers when they are observed emerging from under the shells. Acephate or malathion will kill crawlers; however, these chemicals will also kill natural enemies of the scale insects and could ultimately make the infestation worse.

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Spider mites

family Tetranychidae

Host(s): Wide variety of hardwoods

Description/Biology: Mites are very tiny and very diverse, so positive identification is only possible by an expert. Spider mite adults have eight legs and tiny globular bodies that are translucent or colored. The life cycle of different species of spider mites is similar. Most mites pass through an egg stage, a six-legged nymph stage, and then an eight-legged adult stage. A complete generation can be completed in two weeks at moderate temperatures. Mites usually overwinter as eggs or adult females on bark or leaf litter. Mite populations increase under hot and dry weather conditions and decrease under high humidity and wet weather conditions.

Damage/Symptoms: Mites puncture the plant cells with their mouthparts and suck the fluids. Injured foliage is stippled, yellowed, and may eventually turn brown and dry. A fine webbing on foliage indicates the presence of spider mites. A prolonged heavy infestation can cause slow plant growth, leaf drop and death of young plants.

Comments: Mite infestations can be confirmed by holding a white piece of paper under leaves and sharply tapping the foliage to dislodge the mites. Mites will be moving dots on the paper, or stain the paper red when crushed. Mites often prefer the lower leaf surface, so be sure to inspect the undersides of leaves. Summer sprays of oil or soap may be used. Some diazinon, dicofol, and spinosad products are labeled for twospotted spider mites; however, these chemicals will also kill natural enemies of the mites and could ultimately make the infestation worse.

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Spruce needleminer

(Endothenia albolineana) family Tortricidae

Host(s): Spruce

Description/Biology: There is one generation per year. The insect overwinters in the larval stage. In late May to late June, adults emerge from the puparium. Adults are small, brownish gray moths (1/2 inch wingspan) with three irregular white bands on their forewings. Adults lay eggs on needles. Larvae bore into the needles in mid-June or later. There is usually only one larva per mine. Larvae are greenish in color with dark brown heads, and about 1/3 inch long. When fully mature, larvae will spin together groups of needles to form silken nests for overwintering.

Damage/Symptoms: Needles are killed by larval mining. Infested trees acquire a brownish cast. Severe infestations can result in up to 85 percent mined needles.

Comments: This insect usually causes only minor injury in North Dakota. Nests can be dislodged with a strong jet of water or by hand in the spring before buds swell. Carbaryl is labeled for spruce needleminer; however, spray timing in North Dakota is not well understood. Sprays should be targeted at larvae as they emerge from eggs and begin feeding.

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Spruce spider mite

(Oligonychus ununguis) family Tetranychidae

Host(s): Arborvitae, Douglas-fir, juniper, spruce, occasionally pine

Description/Biology: Adults range in color from green, to pink, to brown, are smaller than the size of a fine pepper flake, and feed mostly on older needles. These mites overwinter in the egg stage. Larvae hatch from the eggs in late April or May and feed on the needles. The larvae are pink and turn green after feeding on the foliage. Larvae have three pairs of legs and are oval. After three days, larvae molt to the nymphal stage. The nymphs have four pairs of legs and are light to dark green in color. Nymphs transform into adults after six days of feeding. Larvae and adults can be dispersed by the wind. Females live for about a month and lay 40 to 50 eggs. The complete life cycle of egg to adult only takes two to three weeks, depending on the temperature. A total of six or more generations may occur in a summer. Spruce spider mites are "cool season" mites. If temperatures consistently remain over 90°F, these mites will lay eggs and become dormant. Overwintering eggs are laid from early September until frost.

Damage/Symptoms: The spruce spider mite produces a webbing around the needle base; however, this webbing may be difficult to see. Symptoms of feeding are a speckling or bleaching of affected foliage. Damage is often noticed on hot, dry summer days when injury from spring feeding becomes evident under the drying conditions. As a result of a heavy mite infestation, the needles may turn brown and later fall off. Severe infestations may kill branches or trees, especially during periods of drought.

Comments: Population build-ups are most common in the spring and fall. Syringing and chemical controls can be used in controlling spruce spider mites. Spraying foliage with a forceful jet of water (syringing) can be an effective method for controlling mite populations in home landscapes while maintaining natural predators. Insecticidal soaps can be used to manage spruce spider mites in warm weather, while horticultural oils (1-2% rate) may be used during the summer and dormant oils (3-4% rate) can be used to kill mite eggs and adults during the spring and fall. Horticultural oils can injure conifers if applied when temperatures are not appropriate. Read labels carefully. Dicofol, or spinosad may be sprayed when adults are active, with a follow-up spray seven to10 days after the first spray to control later hatching nymphs. Do not use carbaryl or lindane for chemical control unless a specific mite-controlling chemical (acaricide) is added to the spray tank.

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Uglynest caterpillar

(Archips cerasivorana) family Tortricidae

Host(s): Chokecherry and other hardwoods

Description/Biology: There is one generation per year. The uglynest caterpillar overwinters in the egg stage. Eggs hatch in the spring. Caterpillars feed for three to four weeks. The caterpillars have yellowish bodies with dark brown or black heads, thoracic shields, and anal shields. There is a brown spot at the base of the body hairs. Mature caterpillars are 1 inch long and are a darker, yellowish green. Moths are active from late June to early September. The adult moths are 1 inch long with dull reddish-orange colored heads and forewings. The hindwings are bright orange. The eggs are laid in masses on the bark of host plants.

Damage/Symptoms: Chokecherry is the most common tree infested by the uglynest caterpillar. The caterpillars are gregarious, living in a silk-covered nest spun to enclose the ends of branches. The nests become littered with frass and are unsightly on ornamental plantings.

Comments: The silk nest provides protection to the caterpillars. Caterpillars may be controlled by pruning out unsightly webs. If insecticides are used, treat early before nests become well established.

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Variable oakleaf caterpillar

(Lochmaeus manteo) family Notodontidae

Host(s): Bur oak, other hardwoods

Description/Biology: The caterpillars overwinter in earthen cells, pupating in the spring. Adult moths emerge in early June, laying single eggs on leaves. The caterpillars feed for five to six weeks, then drop to the ground. The full grown larvae reach a length of about 1 1/2 inches. The caterpillars vary in color but at maturity they are yellowish green with a reddish brown band bordered by yellow stripes running down the back. The head has black and white curved bands on each side.

Damage/Symptoms: Caterpillars defoliate trees. Outbreaks can be locally severe. When outbreaks occur for several years, trees may die. Outbreak populations usually collapse after two or three years.

Comments: Foliage may be sprayed with acephate or carbaryl when caterpillars are small. These insecticides will kill predators and parasites which feed on variable oakleaf caterpillar eggs and larvae.

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Yellowheaded spruce sawfly

(Pikonema alaskensis) family Tenthredinidae

Host(s): Spruce, primarily a pest of shelterbelt and ornamental plantings

Description/Biology: Adult sawflies are not flies but stingless wasps. The insect is called a sawfly because the female's ovipositor has serrated teeth resembling a wood saw. Adults are reddish-brown in color and 1/3 inch long. There is only one generation per year. Sawflies overwinter as cocoons. In late May to mid June, adults emerge, mate and females begin to lay eggs. A single egg is deposited at the base of a needle. Eggs hatch in five to10 days. Larvae are 1/8 inch when they first hatch. Mature larvae are 3/4 inch long, and dark glossy green with a light lateral stripe and reddish brown head. Larvae feed for 30 to 40 days consuming the new foliage first and then the older needles. When mature, larvae drop to the ground and spin cocoons for overwintering.

Damage/Symptoms: Defoliation is caused by larval feeding. Heavily infested trees appear ragged, especially near the top, and can be completely stripped of foliage. Severe infestations over one to several years can kill trees directly or make trees susceptible to attack by other insects or adverse weather conditions.

Comments: Open grown trees that are five to nine years old (3 to 18 feet tall) are more vulnerable to yellowheaded spruce sawfly damage than are older trees or trees in dense stands. Although rodents will feed on the prepupae and birds on sawfly larvae and adults, these predators, in addition to various parasites, are not always effective in keeping yellowheaded spruce sawfly populations at acceptable levels. If infestations are light, adequate control may be achieved by simply removing young larvae by hand. When an isolated ornamental tree is infested, spraying young larvae off of the tree with a strong jet of water will often be effective in reducing insect numbers. Yellowheaded spruce sawflies tend to attack the same trees repeatedly; therefore, chemical control often becomes necessary as sawfly populations increase. Acephate and carbaryl are labeled for use against sawflies. Since most yellowheaded spruce sawflies are believed to overwinter very near the soil surface, removing the duff beneath infested trees may reduce the impact of this insect.

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Insect and Disease Management Guide for Woody Plants in North Dakota -- f1192, Revised 9/2005