Caseload at the UW Insect Diagnostic Lab (IDL) has trended upwards over the last month and is expected to reach “summer” levels in the near future. A summary of fruit crop insects reported to the lab in May as well as important insect trends can be found below:

Spongy moth (formerly known as “gypsy moth”): Dry spring conditions in 2021 and 2022 have set the stage for very high spongy moth populations this year.  Egg hatch began several weeks ago and caterpillars are currently active throughout most of the state.  Spongy moth caterpillars feed on a wide range of trees, including fruit trees.  With the current outbreak, significant damage is expected in wooded areas in some parts of the state.  Growers should keep an eye out for spongy moth caterpillars and manage them as needed.  Over the next few weeks, caterpillars will become larger and more damaging.  Rainy conditions can encourage the beneficial fungus Entomophaga maimaiga to knock down spongy moth populations, but much of the state has been dry recently.

Aphids: One of the commonest insect pests reported to the UW Insect Diagnostic Lab this spring has been aphids.  Recent cases have involved fruit trees such as apple, cherry, and pear.  Early in the year, aphids tend to get a “head start” but over time natural enemies (predators and parasites) tend to “catch up” and help keep their numbers in check.  Before spraying, closely check for “mummies” (aphids parasitized by tiny stingless wasps) and predators such as lady beetles and lacewings.  I’ve had several reports of natural enemies starting to attack aphid populations.

Eastern tent caterpillars:  I’ve had many reports of eastern tent caterpillars in fruit trees this spring.  Reports have been scattered around the state.  Usually the silken tents stand out, making this pest easy to spot.

Variegated Cutworms: These caterpillars can be an occasional pests of fruit crops, such as strawberries.  I’ve recently had several reports of small (~3/4 inch long) variegated cutworm caterpillars from southeastern and south-central Wisconsin. 

Fruitworms: I’ve had a number of recent cases of fruitworms from southern Wisconsin.  Two species have been reported to the IDL: the humped green fruit worm (Amphipyra pyramidoides) and the speckled green fruitworm (Orthosia hibisci).  Both species can feed on fruit trees and other hardwood trees in the landscape.

Strawberry budworm: While often associated with strawberries, this insect can occasionally feed on other plants from the rose family, including tree fruits.  I recently had a case of minor damage caused by the adult beetles to an apple tree in central Wisconsin.

Spider mites: I have not run into any issues yet this year, but if dry conditions continue, we could see spider mite pressure similar to last year.  Growers should keep an eye out for speckling damage on leaves and tiny mites on the undersides of leaves.  Spider mites thrive under hot/dry conditions and outbreaks can be induced by certain insecticides (e.g., carbaryl).

Reminder about diagnostic support from the IDL: Growers and consultants in need of insect diagnostic services are always welcome to submit a sample to the UW Insect Diagnostic Lab.  Lab services are provided free of charge.  You can find additional information about the IDL here: insectlab.russell.wisc.edu

This article was posted in Insects and tagged aphids, eastern tent caterpillar, fruitworms, Insect Diagnostic Lab, insects, PJ Liesch, spider mites, spongy moth, strawberry budworm, variegated cutworms.