Corn leaf aphid (CLA), is typically an occasional presence in cornfields within the Midwest – they can be found in most fields closer to harvest time, when corn is starting to senesce and they don’t/can’t have much impact. They are typically not a pest of concern during the summer months.
This year is different! In Indiana and throughout the Midwest, this aphid has made its presence known this year. We don’t know all the reasons why this year’s populations have been so much worse, but it is very likely progression of remnants of Hurricane Beryl from south to north (July 8 and 9) distributed winged aphids throughout our region; this is a common route of aphid transport.
Since last week’s Pest&Crop article, winged aphids have been found on multiple plants/crops, including many that CLA are unable to feed on. This morning while running the dog in the yard, John Obermeyer pulled out some nutsedge at his suburban estate and noticed winged CLA on them! They are grass feeders only. Sedges and broadleaf plants, e.g., soybean, will not sustain them. But they will land on some of these hosts and “probe” them just to see if there is any nutrition, or at least a drink, to be gained.
As quickly as this CLA event has unfolded, it seems to be coming to abrupt end. Joel Wahlman, SEPAC farm manager, in southeastern Indiana alerted us that the plots he was assessing for treatment on the 29th contained dead aphids. The next day, at the Purdue research farm (ACRE) northwest of town, over a hundred miles from SEPAC, it became obvious that CLA are dying from a fungal disease, known as an epizootic (see accompanying pictures). This is the typical end to many aphid infestations (including soybean aphid), and a “plague” of sorts that accompanies dense populations, coupled with high humidity. You will likely find the same thing in your corn!
Controls at this point will not correct damage already done by these suckers, as scattered plants in some fields sustained damage, refer to last week’s pictures. It is unlikely that controls will be needed in any cornfields in the state, as the epizootic spreads quickly through the population. Many winged aphid are likely infected and a carrier of the disease. It is unknown what impact foliar fungicide applications may have. In theory, the fungicides could lower the incidence of aphid disease. Your shared observations would be appreciated.
As asked many times in the past week, the treat thresholds for CLA are as follows:
Pre-tassel: 15 aphids/plant whorl 3 weeks before tasseling and plants under moisture stress. Post-tassel: 50% of tassels covered prior to 50% pollination and plants under moisture stress. There are no guidelines after pollination, for obvious reasons. By this time, the story is written and aphids won’t be a factor. As soon as the CLA were being exposed with the tassels, predators and disease were quickly decimating them. Natural enemies at their best. Happy scouting!
Close-up of diseased corn leaf aphid, winged and “babies” (live birth), on corn leaf.
Multiple Asian lady beetle larvae devouring remaining corn leaf aphid on this sweet corn tassel.
Diseased corn leaf aphid, winged and nymphs, revealed on whorl leaves.
Winged aphid attempting to disperse to a new field/county/state. She climbed over multiple dead bodies, got to the leaf tip, spread her wings, then proceeded to fall to the ground.
Close-up of live corn leaf aphid, winged and “baby” nymphs, found within tightly rolled whorl leaves. If you look closely, some nymphs are beginning to discolor, indicating this isolated colony is becoming diseased.
