Ash (Fraxinus)

Leaf Feeders

Azalea caterpillar
Chris Evans, University of Illinois,
Azalea caterpillars have one generation each year during August and September. Small larvae skeletonize leaves, large larvae consume entire leaves. In sufficient numbers they can defoliate plantings in a short time. These hairy caterpillars have 7 light stripes along the body; its head and legs are red. Full-grown caterpillars are about 2 inches long. Azaleas are the preferred host but the caterpillars also feed on blueberry foliage.

Fall cankerworm larvae
A. Steven Munson, USDA Forest Service,
Fall cankerworm is a looper caterpillar that can vary from light green with yellow stripes to green with a dark stripe down the back. Overwintering masses of about 100 eggs hatch in later April or early May; small caterpillars chew small holes in young leaves at branch tips. Larger loopers leave only the midrib and major veins. Fall cankerworms are about an inch long when full grown. Mature larvae descend from trees on silk threads to pupate in the soil. They emerge as adults during periods of freezing temperatures to mate and lay eggs on host plants. There is one generation each year.


Sap Feeders

Azalea lace bug adult
Pest and Diseases Image Library,
Azalea lace bugs are 1/8 to 3/16 inches long sap-feeding insects with clear, ornate, lacy wings; The immature stages (nymphs)are spiny and wingless. Adults and nymphs live on the lower surface of leaves. As they feed, they leave tiny yellow to white spots on leaves and dark, varnish-like waste spots on the under sides.

These lace bugs spend the winter as eggs inserted into leaves. The eggs hatch in early spring and the nymphs begin to feed on plant sap. Development from egg to adult takes about 5 weeks. There are several generations each season. Usually, there are only a few insects in the first generation so feeding symptoms are not noticed. Numbers and damage to plants increase to a peak in late summer. When abundant, feeding can make plants unsightly and may cause premature leaf drop.

Azalea lace bug damage

Azalea mealybug
United States National Collection of Scale Insects Photographs,
USDA Agricultural Research Service,
Azalea mealybugs produce cottony white sacs on twigs and in crotches of limbs. They produce large volumes of liquid waste that drops on lower limbs and branches. Black sooty mold will grow on these deposits.

Southern red mite
Tracy Wootten, University of Delaware,
Southern red mites are tiny (1/50 inch) arthropods with a dark red or brown color. They live on the underside of leaves and use needle-like mouthparts to remove the contents of individual cells. This produces tiny white to yellow spots on leaves, sometimes called flecking or bronzing. Infestations are usually most serious during cool periods of spring and fall.

Greedy scale
United States National Collection of Scale Insects Photographs , USDA Agricultural Research Service,
Greedy scale are small armored scales that create a conical shaped cover. As they grow and shed their old exoskeleton, it is incorporated into the wax that makes up the shield. Eventually this results in a characteristic off-center nipple or dot on the outer coating. There are often concurrent overlapping generations on plants

oytershell scale
Whitney Cranshaw, Colorado State University,
Oystershell scales are about 1/10 inch long and resemble crusty accumulations of oyster shells on the bark. Their drab, bark-like appearance makes them easy to overlook, even on close inspection. Heavy infestations can kill twigs or branches. This scale overwinters in the egg stage under the waxy covering of the female. The eggs hatch and the crawlers are active from late May to early June.

John A. Weidhass, Virginia Polytechnic Institute and State University,
Aphids are soft-bodied insects that use their piercing sucking mouthparts to feed on plant sap. They usually occur in colonies on the undersides of tender terminal growth in the spring. Heavily-infested leaves can wilt or turn yellow and senesce prematurely because of excessive sap removal. While the plant may look bad, aphid feeding generally will not seriously harm healthy, established trees. Some plants are very sensitive to feeding by certain aphid species. Saliva injected into plants by these aphids may cause leaves to pucker or to become severely distorted, even if only a few aphids are present. Also, aphid feeding on flower buds and fruit can cause malformed flowers or fruit.

Aphids produce large amounts of a sugary liquid waste called "honeydew". The honeydew that drops from these insects can spot the windows and finish of cars parked under infested trees. A fungus called sooty mold can grow on honeydew deposits that accumulate on leaves and branches, turning them black. The appearance of sooty mold on plants may be the first time that an aphid infestation is noticed. The drops can attract other insects such as ants, flies, and wasps that will feed on the sticky deposits. For more information, see Entfact 103.



Emerald ash borer adult
Leah Bauer, USDA Forest Service Northern Research Station,
Emerald ash borer is an invasive species that feeds on all ash species and some closely related plants. The adult is a small metallic green beetle and the larva is a flat headed borer. Larvae feed in the cambium of ash plants and are 100% lethal for untreated ash trees. Common symptoms including branch suckering, die back, increased woodpecker feeding, and "D" shaped exit holes in the bark. There is one generation per year, with adults active in the early season and larvae overwintering in their last instar. For more information, see Emerald Ash Borer (EAB) on the University of Kentucky Entomology webpage.

Loepard moth larva and adult
larva: Petr Kapitola, Central Institute for Supervising and Testing in Agriculture, ; adult: James Solomon, USDA Forest Service,
Both the caterpillar and adult of the Wood leopard moth are very distinctive. The caterpillar is the damaging stage, feeding under the bark of host trees. It is a white-orange color with numerous spots on its body. The adult is white with six black dots on the thorax and black markings on the remainder of the body. Adults may be active June-September and larvae feed inside of plants for 2-3 years.

Lilac borer larva and adult
larva: David Cappaert,;
adult (inset): James Solomon, USDA Forest Service,
Lilac borers are the caterpillar stage of a wasp-like moth that lays its eggs by wounds or roughened areas on the bark in August and September. The larvae tunnel under the bark and spend the winter there. They resume development in the spring. The larvae tunnel into the bark but maintain an opening where they expel their sawdust-like waste. The wound can be an entryway for a wood-destroying fungus. There is one generation per year.

Flatheaded appletree borer
Jim Kalisch, University of Nebraska-Lincoln Dept of Entomology
The Flatheaded apple tree borer is particularly a problem for small, newly planted trees. Larvae are active all summer and feed in the cambium. The feeding damage progresses from the bottom, up the tree, girdling it. Trunks are often deformed and sucker growth may also be seen. As adults they are copper-colored jewel beetles that emerge in May.

Redheaded(top) and Banded ash borers
Redheaded ash borer: Howard Ensign Evans, Colorado State University,;
Banded ash borer: David Cappaert,
These two round-headed borers, the Redheaded ash borer (top) and the Banded ash borer, are not serious pests of ash. They take advantage of dead and dying plants to lay their eggs. Specimens are often found when people bring ash firewood in for winter fireplace use. The adults are one half inch long. Redheaded ash borers have reddish orange coloration and horizontal yellow stripes on the back while Banded ash borers are black-brown with two cream ovals and two stripes on the back.


Root Feeders

Black vine weevil grub and adult
grub: Peggy Greb, USDA Agricultural Research Service, ;
adult: Cheryl Moorehead,
Black vine weevil grubs are white legless larvae with yellow brown or red heads that live in the soil and feed on plant roots. Moderate root feeding may cause plants to show signs of drought stress. Girdling can occur and nutrient transmission is disrupted, occasionally leading to death of the plant. The adults (0.5 inch long) are dark snout beetles that may chew crescent-shaped holes in leaves while feeding at night. Normally there is one generation per year with the larva overwintering. Pupation and adult emergence occurs in the spring. Sometimes adults may overwinter which can result in damage occurring from larvae earlier in the season.



Ash flower gall mites damage
Dawn Dailey O'Brien, Cornell University,
Ash flower gall mites are small, banana shaped mites that infest the male flowers of ash. As the mites feed, the flower buds will develop galls that start green but eventually turn brown. They resemble numerous pom-poms in the plant. This is strange to see but causes no damage to the plant and is more of a curiosity.


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