Cankerworm

I received a call recently about using banding to prevent outbreaks of cankerworm.

A female fall cankerworm. Note that she is wingless and has to crawl up the trunk to lay her eggs. Photo credit: James B. Hanson, USDA Forest Service, Bugwood.org.

Egg mass of fall cankerworm. All of these eggs have hatched. Photo credit: Pennsylvania Department of Conservation and Natural Resources, Forestry Archives, Bugwood.org.

Larvae of fall cankerworm. Photo credit: E. Bradford Walker, Vermont Department of Forests, Parks and Recreation.

 

There are two species of cankerworm; the fall cankerworm (Alsophila pometaria) and the spring cankerworm (Paleacrita vernata). Both of these moths are in the geometer or inch-worm family, Geometridae. Both are very polyphagous, that is, they have wide host ranges, including oak, elm, apple, and beech, among many others. Both species are native to North America. In both species the female is completely wingless and must climb up the tree to lay their eggs. The fall cankerworm does so in November and December and the spring cankerworm does so in spring. The eggs of both species hatch at budbreak and begin to feed on the tender young foliage, leaving just the veins of the leaves.

Defoliation caused by cankerworm. Photo credit: USDA-Forest Service, Ogden ARchives, Bigwood.org.

 

Because the females have to crawl up the trunk to lay their eggs applying a band of sticky substance, such as Tanglefoot™, can completely control infestations on that tree. Banding, as this practice is called, is used by many homeowners and by some cities to keep populations at low levels.

Bands applied to trees to keep female cankerworms from climbing up the trunk to lay their eggs. Photo credit: Keith Douce, University of Georgia, Bugwood.org.

 

Charlotte/Mecklenburg County in North Carolina has had increasing populations of cankerworms, despite aerial pesticide applications. Because the defoliation occurs almost every year many urban trees are weakened and made susceptible to other pests and diseases. These dying urban trees often drop limbs and can cause property damage or injury in urban environments. The caterpillars can become so numerous that they cause allergic reactions in some people. As such, Charlotte has implemented a banding program. The city identifies especially susceptible trees, particularly older, weaker willow oaks, and applies bands to these trees in November and December to keep the female cankerworms from crawling up the tree.

Trees are more resilient than we often give them credit for. Most trees can withstand complete defoliation if they are healthy and if the defoliation is not repeated soon. In these cases preventative action does not need to be taken.

Trees that have been exposed to drought or other stress will likely decline after a defoliation episode and so these need to be protected. If you noticed a large outbreak last spring now (November and December) is the time to act. You can band the tree by wrapping a cotton cloth around the trunk of the tree. This cotton cloth should be at least three feet above the ground and below any limbs. The cloth can be attached with electrical tape. Place a strip of roofer’s felt over cloth, attached with a staple gun on larger trees or electrical tape on smaller trees. Using a rubber glove or a spatula apply a thick layer of Tanglefoot™ to the roofer’s felt. Apply it as if you were icing a cake.

Take care of your trees and they will take care of you!

Bark splitting

Many trees have noticeable splits in the bark of their trunks or limbs. There are a number of potential causes.

The outer layer of bark is a dead protective layer. As the trunk grows outward adding a new bark layer the old layer may split or slough off. This is especially noticeable in some trees, like river birches, white oaks and shagbark hickories.

The trunk of a shagbark hickory, Carya ovata.

Tree species with thin bark, including, ornamental cherries, maples, and fruit trees, can be damaged by sunscald or frost cracks. Damage by both sunscald and frost cracks will always be on the side of the tree receiving the most sun… the south or southwest. The temperature of bark receiving sun can change drastically in a short period of time. This causes tissue to shrink and expand and could rupture the bark. Frost cracks are likely to form in previous injuries.

Normal bark splits in a red maple, Acer rubrum.

Usually these splits are harmless and the tree heals itself. However, it can allow decaying fungi or wood-boring insects to enter, especially if it hasn’t healed in the spring and summer when these organisms are active.

Sunscald on the trunk of a peach tree, Prunus persica.

Some activities make trees more prone to bark splitting. Over-pruning limbs can suddenly expose more bark to the sun without giving the tree time to adapt. It is better to gradually prune any unwanted limbs, if you have to prune at all. Fertilizing, particularly with nitrogen, at the end of the growing season (late summer, early fall) can induce growth, making the tree more susceptible to bark splitting and frost damage. Trees that do not get adequate water during the growing season may be more prone to bark splitting damage.

Frost crack in the trunk of a black cherry, Prunus serotina.

A frost crack that has developed in a red maple, Acer rubrum. Although ugly, the tree is still able to efficiently translocate sugars and nutrients. However, this opening has allowed fungal rots to decay the heartwood and carpenter ants are nesting in the rotting wood.

Fruit growers prevent bark splitting by painting the trunks of their fruit trees with a white reflective paint. This will buffer the trunk bark from excessive temperatures during the day.