Caseload at the UW Insect Diagnostic Lab (IDL) is very high and is expected to remain high throughout the growing season.  A summary of recent cases at the IDL involving fruit crop insects can be found below:

Aphids: Aphids have been a common pest on fruit tree leaf samples at the UW Insect Diagnostic Lab recently.  Most of these reports have been from southern and eastern Wisconsin.  Apple and stone fruit (cherries and plums) have accounted for most cases.  

Spongy moth:  Similar to the last issue of Wisconsin Fruit News, the spongy moth has been one of the commonest fruit tree insects reported to the UW Insect Diagnostic Lab recently.  Damage has been noted on a wide range of fruit and landscape trees with most reports of damage coming from south-central, southeast, and central Wisconsin.  I’ve also had a few noteworthy reports of spongy moth caterpillars in cranberry.  This species is generally considered a minor/occasional pest of cranberries and young caterpillars may have ballooned in from nearby wooded areas.

In southern parts of the state, caterpillars are beginning to reach the fourth larval instar and are taking on the characteristic appearance with pairs of raised blue and red bumps along the back.  Spongy moth caterpillars do most of their feeding in the final two larval instars (i.e., 5^th and 6^th instars), so damage is expected to increase dramatically in the coming weeks.  In northern Wisconsin, caterpillars are still small and will lag behind southern areas by 1-2+ weeks depending on location.  With the recent weather patterns, it’s possible that the beneficial fungus Entomophaga maimaiga could kick in this year to infect and kill caterpillars. 

Eastern tent caterpillar: Larger eastern tent caterpillars are being reported in southern Wisconsin.  Luckily, their tents are usually conspicuous and easy to scout for.

Currant spanworm: These white and yellow inchworm caterpillars with black spots have a flamboyant appearance, and can cause notable damage to currants if abundant enough.  I had a recent report from southern Wisconsin at the IDL.

Slugs: While usually not a concern for tree fruit, slugs can be problematic for low-growing fruit crops like strawberries.  Just in the last week, I’ve seen cases of slug damage on strawberries and other plants (soybeans, landscape ornamentals, garden vegetables) in southern and central Wisconsin.  Damp, rainy conditions can favor slugs, so growers should have these are their radar with our weather patterns this spring.

Periodical cicadas: The first reports of periodical cicadas were from Lake Geneva on Friday, May 17^th, with 50+ reports coming in over the last two weeks.  Thus far in 2024, periodical cicadas have been reported to the IDL from Crawford, Dane, Grant, Iowa, Racine, Rock, Walworth, and Waukesha Counties.  The two biggest hotspots would be the Lake Geneva area and Janesville (esp. NW of town).  Periodical cicadas can have a very spotty distribution, but if they occur in orchards, damage to trees can occur when the females go to lay eggs and cut slits in twigs.  In locations where periodical cicadas are active, they’ll likely be present into late June or early July.   

Visit the Wisconsin Periodical Cicada Website (cicadas.wisc.edu) for additional details and consider sharing your sightings and photos of periodical cicadas on that website.

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, currant spanworm, eastern tent caterpillar, Insect Diagnostic Lab, insects, periodical cicadas, PJ Liesch, slugs, spongy moth.