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Diagnosing Apple Tree Leaves with Holes or Webbing

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Caterpillars and worms are often the reason your apple tree leaves may have holes and webbing start appearing. Learn the most common species to expect in our area and how to manage them.

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Eastern Tent Caterpillar

Malacosoma americanum

Symptoms

Eastern tent caterpillars feed on the leaves of apple, crabapple, chokecherry and cherry trees.
Caterpillars hatch at the time leaves are breaking bud in the spring and will continue feeding for six to eight weeks.
The larvae then spin cocoons and the adult moths appear in late June to early July.
Feeding damage is conspicuous because caterpillars will consume entire leaves.
At night and during cool, rainy weather, caterpillars will congregate in a webbed tent spun at branch junctions in trees.
These hairy caterpillars are blue and black and have a creamy-white stripe down the middle of their backs. The stripe is bordered by orange stripes on either side.

Eastern Tent Caterpillars have prominent white and orange stripes

Caterpillars have prominent white and orange stripes. (David Cappaert, Bugwood.org)

Silken tents from eastern tent caterpillars appear in the crotches of tree branches.

Silken tents appear in the crotches of tree branches. (Steven Katovich, U.S. Department of Agriculture Forest Service, Bugwood.org)

Management and other important facts

Mature trees can handle tent caterpillar defoliation better than younger trees.
A simple organic control method is to use a stick to remove the webbing and caterpillars when they congregate in the silken tents during cool weather. Dispose of this mass to prevent further feeding and caterpillar maturation.
If chemical control is to be used, pesticide applications should take place when larvae are outside the tent and feeding on leaves.
If the tree is in flower, apply Bacillus thuringiensis (Bt) to the foliage near the tent. Bt is a biorational pesticide that will poison the caterpillars feeding on the treated leaves without hurting the bees or other pollinators.
Other biorational pesticides include spinosad and insecticidal soap.
If larvae are larger, conventional pesticides that include carbaryl or malathion may be more effective. Do not apply carbaryl within 30 days of petal fall to avoid apple drop.

Author: Esther McGinnis

Forest Tent Caterpillar

Malacosoma disstria

Symptoms

Forest tent caterpillar feed on the leaves of apple, crabapple and other fruit trees.
Caterpillars hatch in early to mid-May and will continue feeding for five to six weeks.
The larvae then spin cocoons and the adult moths appear in mid-July.
Feeding damage is conspicuous because caterpillars will consume entire leaves.
Despite their name, caterpillars do not spin silken tents.
These caterpillars are blue and black and have white keyhole spots down their backs.

Forest tent Caterpillars have prominent white keyhole markings.

Caterpillars have prominent white keyhole markings. (James B. Hanson, U.S. Department of Agriculture Forest Service, Bugwood.org)

Management and other important facts

Mature trees can handle tent caterpillar defoliation better than younger trees.
If the tree is in flower, apply Bacillus thuringiensis (Bt) to the foliage. Bt is a biorational pesticide that will poison the caterpillars feeding on the treated leaves without hurting the bees or other pollinators.
Other biorational pesticides include spinosad and insecticidal soap.
If larvae are larger, conventional pesticides that include carbaryl or malathion may be more effective. Do not apply carbaryl within 30 days of petal fall to avoid fruit abortion.

Author: Esther McGinnis

Fall Webworm

Hyphantria cunea

Symptoms

Fall webworm caterpillars are active from late July into September.
The hairy caterpillars are yellow to green and have two rows of black spots on their backs.
Fall webworm skeletonize leaves that are enclosed within a webbed shelter.
Their webs differ from those of tent caterpillars in that the webbing covers branch ends rather than tree crotches.

Fall webworm caterpillars with distinctive black spots. (Milan Zubrik, Forest Research Institute-Slovakia, Bugwood.org)

Fall webworms in their tent in tree branches

Webbing covers branch ends. (Lacy L. Hyche, Auburn University, Bugwood.org)

Management and other important facts

Mature trees can handle fall webworm infestations and control measures usually are not required; this is more of an aesthetic issue.
Fall webworm infestations in younger trees should be removed to prevent severe defoliation.
Webbing and caterpillars can be removed with a stick and dropped into a pail of soapy water.
Chemical control usually is not effective because the webbing protects the caterpillars.

Author: Esther McGinnis

Diagnosing Apple Tree Leaves with Holes or Webbing

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