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Dealing With Spring Pests in Fruit Trees

With spring’s arrival, fruit trees are blooming across home landscapes, as their owners hope for a tasty harvest. However, pests that afflict them can throw a wrench into those plans.

How should pests that attack fruit trees be handled? Iowa State University Extension and Outreach horticulturists can help decipher these issues. To have additional questions answered, contact the ISU Hortline at 515-294-3108 or hortline@iastate.edu.

The leaves on my peach tree are puckered and reddish in color. What is the problem?

The symptoms are those of peach leaf curl. The disease is caused by the fungus Taphrina deformans. Infections occur as the peach tree buds begin to swell in spring.

A single fungicide application will control peach leaf curl. Fungicides, such as chlorothalonil, should be applied in fall after leaf drop or in late March before the buds begin to swell. To achieve control, all branches and twigs must be thoroughly sprayed.

A small greenish worm is eating the foliage on my cherry tree. What should I do?

The greenish worm is probably the pear slug. The pear slug is not an actual slug. It’s the larval stage of an insect (sawfly). The pear slug feeds on pear, cherry, plum and several other woody plants.

The slug-like larvae are yellow but usually appear olive green or black because of a covering of secreted slime. The mature “slug” is about 1/4 to 3/8 inch long. Larvae feed on the leaves for about four weeks. When full grown the larvae drop to the ground, burrow into the soil and pupate. Adult sawflies emerge in May and June (first generation) and late July and August (second generation). After mating, female sawflies insert eggs into the leaf surfaces of suitable plant hosts. The eggs hatch in one to two weeks.

The larvae feed on the upper surface of leaves, eating the tissue between the leaf veins, but leaving the veins themselves. (This feeding pattern is known as skeletonization.) Leaves that are heavily fed upon by the larvae turn brown, as only the veins and a thin layer of tissue remains on the leaves. Heavily damaged leaves may drop from the tree. Fortunately, pear slugs seldom cause serious damage to healthy, well-established trees. Pear slugs are easily controlled with insecticidal soap, neem oil, bifenthrin, carbaryl, malathion, permethrin, spinosad or other general landscape insecticide sprays.

There are caterpillars and tent-like structures in the crotches of my apple tree. How do I get rid of them?
The caterpillars are likely eastern tent caterpillars. Eastern tent caterpillars emerge in late April and early May from eggs that were laid on small twigs last summer by female moths. The caterpillars feed on the buds and foliage of apple, crabapple, wild plum, cherry and similar trees. On cloudy, rainy days and at night, the caterpillars remain in the protective confines of their tent. On warm sunny days, they go out and feed on the tree’s buds and foliage. Tents are initially small, but are gradually enlarged as the caterpillars feed and grow in size. The caterpillars are full grown about six weeks after hatching.

While eastern tent caterpillars may defoliate branches or portions of a tree, they do not seriously harm most healthy, well-established trees. The defoliated branches will leaf out again in a few weeks. Trees may be seriously weakened if heavily defoliated in several consecutive years.

Damage to trees can be minimized by removing and destroying the tents and caterpillars as soon as they are noticed. Tent removal should be done in early morning, late evening, or on cool rainy days when the caterpillars are gathered in their tents. The tents and caterpillars can be removed with a broomstick, forked branch or by hand.

Do not attempt to burn the tents and caterpillars. This is a dangerous procedure that may injure the tree.

It is seldom necessary to control eastern tent caterpillars with insecticides. If insecticides are used, they should be applied when the caterpillars are small. Insecticides are less effective on mature caterpillars. Spray the tree’s foliage within two feet of the tents. (Tents are water repellent so spraying them with water based insecticides are not very effective.) Effective insecticides include Bacillus thuringiensis (Dipel, Thuricide, etc.) and carbaryl (Sevin).

Source: Richard Jauron and Greg Wallace, Iowa State University 

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