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This month’s Tree Tip was written and researched by our Director of Plant Health Care, Britt Hubbard, ISA Certified Arborist #SO-5792A. He may be contacted directly via email with any questions concerning this article or any tree related issues.

Over the past few weeks our office has had several calls about caterpillars chewing up local oak trees.  Many of our clients have had small trees defoliated almost overnight and large trees have been defoliated within a few weeks. These caterpillars have damaged the trees, and made a mess of patios, driveways, and swimming pools.  The culprit is the Yellowneck Caterpillar.  

Hosts and History

The Yellowneck caterpillar occurs throughout much of the US, but is more common east of the Rocky Mountains. So far we have only seen oaks being attacked, but the caterpillars are know to attack hickories, Pecans, Maple, and Elms. The insect will spend the winter and spring as a pupa in the soil. Adult moths begin to emerge in July.  Moths are tan to reddish brown, with four narrow dark lines across each front wing. 

Female moths lay egg clusters of 50-300 on the lower surface of leaves.  Small larvae usually begin to appear in late July or early August. The larvae feed together in colonies during summer and fall.

Newly hatched larvae have black heads. The young caterpillars are mostly red with patches of yellow on the back and alternating yellow or white lines along the sides. These early stage larvae rip off the lower surface of the leaf.  Skeletonized leaves turn brown, so small clumps of dead leaves canopy are early signs of caterpillar feeding.  

As they mature, entire leaves are consumed, leaving only a nub of the petiole. By the time tree damage is noticed, the larger caterpillars will now have a black head with a bright orange to yellow collar or neck – this gives the insect its common name.  Yellow-necked caterpillars have a black body with 8 thin yellow to white stripes.  They are also identified by their sparse, long white or gray hairs.

When they reach full size of almost 2 inches, they drop to the ground to pupate in the soil.  In other areas several generations per year may occur, but in Florida there is only one generation per year.

Importance

Colonies of caterpillars of different ages may be found through August into mid-October. They travel and eat in groups of thirty to a hundred for protection. On large trees with ample foliage, only a few branches may be stripped by the time larvae reach full size. However, small trees with fewer leaves can be completely consumed by a single colony. 

Several consecutive years of severe defoliation will stress trees. The health of a tree may deteriorate if other stress factors also occur, like drought, hurricanes, construction damage, and the like. Landscape trees are more often bothered by these insects than hardwoods found in a forest setting.

Besides the loss of tree foliage, homeowners report that falling frass (dark pellets of caterpillar excrement) is a problem on sidewalks and patios. Typically, feeding colonies defoliate one branch then move to another. 

Management

Predators, parasites, disease, and unfavorable weather usually keep caterpillar populations low. Outbreaks like we are having this year are rare, and the factors that cause occasional outbreaks are not known. Foliar spray or trunk injection insecticides are required for caterpillar control and to reduce defoliation for high-value lawn and common area trees. Trees should also be deep root fertilized to promote tree vigor and health to aid in the recovery from defoliation.

Healthy trees usually survive and recover; however, defoliation can cause dieback of branches and twigs, loss of growth, or even tree mortality, if defoliation continues through several consecutive years.

Early detection of the small caterpillars is a key management step that reduces the need for pesticides. Bacterial and chemical insecticides are most effective if applied when the larvae are small. 

If you have any questions or need any assistance with your trees, pests, or just questions, contact the experts at Woodland Tree Service.  Email us or call (901) 309-6779.

Terran Arwood
President

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