Insect update for the week of June 12, 2011

A crop insect update on armyworms, cereal leaf beetles, soybean aphids, bean leaf beetles, alfalfa weevils and potato leafhoppers.

Armyworm in corn and wheat

Reports of armyworm in corn are generally coming in from the southern tier of counties, while other areas report finding nothing. Tank-mixing with fungicide applications on wheat is a cost effective way to treat for armyworm, but don't add an insecticide unless the field is infested. Spraying for black cutworm in corn will also control armyworm.

Cereal leaf beetle in oats

An interesting insect – since they cover themselves with their own excrement – but not an economic problem unless defoliation is heavy.

Soybean aphid

My crew found a whopping two plants with aphids in Montcalm County. Numbers are very low and the only way we will get infested is from aphids moving on wind currents from the states to our west, like Minnesota and Wisconsin, if populations increase there.

Bean leaf beetle in soybean

With the relative lack of early-planted beans this year, fields that did make it out of the ground are attracting bean leaf beetles. These beetles overwintered and were just waiting for something to eat. The bean leaf beetle threshold in seedlings is 50 percent defoliation, i.e. 50 percent of all leaf tissue gone. The chewing looks ugly, but unless stand is threatened or defoliation is over 50 percent, plants will rapidly grow and make up for the few holes in the leaves. However, Ron Hammond from Ohio State University points out that fields with a large number of overwintered beetles should be checked later in the season (July/early August) for first generation bean leaf beetle. These beetles are more concerning because they can chew into pods.

Alfalfa weevils

There are reports of high weevil populations in some fields, but before you spray, check for pupation. Weevils are done feeding and pupating in the fields I visited (see photos). There isn't another weevil generation, so the feeding is done for the season. Treating pupating weevil will simply kill the numerous parasitoids that usually keep weevil in check.

Alfalfa weevil pupae
Alfalfa weevil pupae. Weevil larvae spin a white, net-like cocoon among the leaves.

Potato leafhoppers

Adult potato leafhoppers have been in Michigan for a few weeks. Like cutworm and armyworm, they moved north with weather fronts in May. Numbers are currently low.

Dr. DiFonzo's work is funded in part by MSU's AgBioResearch.

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