5 Defoliating Insects to Look Out For This Summer

Defoliating Insects

Defoliating insects cause damage to trees and shrubs by eating their leaves or needles. By doing this, you remove the tree’s ability to use photosynthesis in order to produce the next year’s growth.  This damage also increases the tree/shrubs susceptibility to be attacked by other insects and diseases.

It’s important to keep any eye out for defoliating insects this summer. Knowing the early signs and getting immediate treatment can stop them in their tracks before they kill your trees and shrubs.

Bagworms on Evergreens 31. Bagworms

Native to the eastern US, bagworms are defoliating caterpillars that create unsightly cone shaped bags. When populations get high, excessive feeding can strip away large quantities of leaves.

Susceptible Trees:  arborvitae, fir, hemlock, juniper, pine and spruce, bald cypress, black locust, honey locust, sweetgum and sycamore, boxelder, cotoneaster, maple, elm, buckeye, willow, crabapple, linden, poplar, and many more.

Time of Year: Late Summer

Signs & Symptoms:

  • Yellow spots on leaves/needles
  • 1-1/2” – 2” cone shaped bags hanging from tree branches (seen in late summer).
  • Heavy defoliation

2. Eastern Tent Caterpillar

Eastern Tent Caterpillar - Defoliating InsectThese hairy insects, with areas of blue, white, black, and orange, are social species that form communal nests in the branches of trees and shrubs. These communal nests look a lot like spider webs and the caterpillars in them can easily defoliate your trees and bushes.

Susceptible Trees: Maples, willows, poplars, cherry, and crabapple.

Time of Year:  Spring to Midsummer

Signs & Symptoms:

  • Rapid Defoliation
  • Easily spread to other shrubs & trees
  • Silky nests in the crotches of branches (Sometimes referred to as webs or tents)
  • Dark colored larvae visible on the tree and in the nests

3. Japanese Beetle

Japanese Beetle - Defoliating Insect 2First brought to the United States in 1916 in a shipment of iris bulbs, this invasive insect can defoliate an entire tree in a matter of days.

Susceptible Trees: Linden, crape myrtle, flowering crabapple, Norway maple, Japanese maple, flowering cherry, elm, sycamore, black walnut, horse chestnut, plums, roses, and many more.

Time of Year:  June & July

Signs & Symptoms:

  • Large amounts of brown, chewed, skeletonized leaves.
  • Leaves falling off trees
  • Trees that look scorched by fire from a distance.
  • Beetles with a dark metallic green head and metallic dark tan wings on plants & trees.Japanese Beetle - Defoliating Insect

4. Gypsy Moth

Introduced in Boston in the 1860’s this exotic pest has become a big problem throughout the Eastern United States. Gypsy moth larvae defoliate trees leaving them vulnerable to secondary invaders. The first defoliation may only cause dieback and other infestations/infections but repeated infestations can kill the tree directly.

Susceptible Trees: Oak, aspen, willow, linden, hawthorn, apple, and alder. Less susceptible trees that are commonly still infested include elms, maples, hickory, beech, hemlock, pine, spruce, cedar, and sassafras.

Time of Year:  Spring through summer

Signs & Symptoms:

  • Holes in leaves
  • Thinning of tree canopy
  • Sprouting of old buds on the trunk and larger branches

5. Cankerworms

Cankerworm - Defoliating InsectCankerworms don’t occur in the summer but you should be on the lookout for them in the spring & fall. Mature, healthy trees may be able to withstand a few years of infestation; however, if you have young, weak, transplanted, or new trees, one infestation of cankerworms can severely damage your tree.

Susceptible Trees: Cankerworms have a wide host range, but prefer elm, apple, dogwood, cherry, a variety of oaks including Willow oak, linden, ash, hickory, hackberry, maple, and beech.

Time of Year:  Spring & Fall

Signs & Symptoms:

  • Small holes on leaves
  • Complete defoliation that leaves the leaf veins intact.
  • Limb dieback
  • Loss of Vigor

Defoliating Insect Treatment:

If you see signs of defoliating insects this summer make sure to book a consultation with our arborist online or call 703.573.3029. Treatment may consist of a soil drench, trunk injection, foliar spray, or even beneficial control. Our arborists will be able to provide an effective treatment specific to the type of defoliator, tree species, and the level of infestation.

If you’ve seen signs of defoliating insects in previous summers your trees and shrubs are more likely to be re-infested this summer. It’s best to catch the infestation before it begins through preventative treatments. As our arborists say, an ounce of prevention is worth a pound of cure.

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Samantha Huff

Samantha Huff is the marketing coordinator at RTEC Treecare. She enjoys learning about the technical aspects of trees and the insects and diseases that prey on them. She hopes that these articles can help homeowners gain control of their tree and shrub maintenance by being aware of the signs and symptoms of unhealthy trees.

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