Earlier this week, I had the opportunity to visit a field with probably the worst grape colaspis injury I have seen. Note the phosphorus deficiency symptoms on the lower leaves of many plants and the aggregated nature of the injured plants. Usually, we see this in fairly isolated areas of a field—often at the high points—and several nearby fields had this more limited injury. But in this particular case, much of the field was affected. When you see this kind of injury above ground, dig up the plant and look for larvae, which resemble tiny white grubs. Some plants in this field had as many as eight or nine larvae on them, and we found at least one pupa. These should cycle out into adulthood soon.

I’ve received several reports of injury from grape colaspis; in some cases it’s pretty extensive. Scout lighter textured soils and high points in rotated corn (or soybean following soybean), especially in areas that have had trouble in the past. The adults lay eggs in legumes; the partially grown larvae overwinter, then feed on roots of corn, soybean, or most other plants the following year. They resemble tiny white grubs.

Corn rootworm egg hatch is underway in central Illinois, and will reach its peak in historical problem regions in northern Illinois over the next couple of weeks. I have not received dramatic reports of seedling insect injury so far this year – once corn is past roughly V5 and soybean gets a few true leaves on it, plants will mostly outgrow this sort of injury. Both crops are pretty resilient to early insect feeding as long as stand is not reduced.

We will participate in a regional monitoring program for corn rootworm adults again this year, beginning in early-mid July. If you are interested in participating, email me at nseiter@illinois.edu and we will send you traps and a protocol.

Black cutworm will likely become large enough to cut plants in most of Illinois over the next week or so; this is a good time to scout, with a special focus on fields where winter annual weed control was poor and/or weedy vegetation was dying while crops were emerging. While black cutworm (along with variegated cutworm and some other species) are more of a problem where broadleaf vegetation was present early, look out for armyworm in wheat and in corn where grassy weeds/cover crops were present early – again, the situation that most commonly leads to injury is when the crop emerges while grassy vegetation is dying/drying down. (Fields bordering wheat can be affected as well). We have nice, warm temperatures and (mostly) good soil moisture (perhaps a little too “good” in some areas), which will help seedling plants outrun early season insect injury. I have continued to receive only a handful of reports of injury – nothing out of the ordinary so far. (Note my own observations so far have been pretty limited to areas where we’re planting trials near Champaign and Monmouth – we’ll start to cover more of the state as our soybean insect sampling takes off in the next few weeks).

This is a good time to scout for seedling pests, particularly in fields that have been slow to emerge/develop – as we get into warmer weather over the next couple of weeks, plants can outgrow a lot of seedling insect problems. So far, I’ve only received a smattering of reports.

It’s a good time to scout for fall armyworms in grass hay, pasture, alfalfa, etc; a quick survey of my colleagues in the states to our south indicated it is a big year for this insect (though they were unanimous that it was not as bad as in 2021, the last time we saw widespread damage in Illinois).

I have had many reports of corn leaf aphids over the last couple of weeks, including several in pre-tassel corn. Corn leaf aphids are usually found inside of the upper whorl (unlike other species which are primarily found on the undersides of leaves), and are darker in color than other species we see in corn. This year, the wide variety of planting dates has resulted in corn that is all over the place in terms of stage – these aphids are particularly a problem if they are present in large numbers during pollination. (Fortunately, where we have adequate moisture and cool temperatures during pollination, this effect will be minimized). Consider an insecticide if 50% of plants have aphid colonies (~50-100 aphids) prior to or during R1. Once pollination has passed, it takes much greater numbers to cause yield loss.

I have received a few reports of cutworm injury, one from black cutworm and one from variegated cutworm. This injury should wind down once corn reaches V5 or so, but continue to monitor later planted corn (especially in fields where winter annual vegetation was present close to planting time).

Our recent heavy rains occurred at the same time as 50% egg hatch for western corn rootworm in east central Illinois – it will be interesting to see if that impacts the rootworm population this year. (Generally, saturated soils during egg hatch cause a lot of mortality). It was a quiet week for non-cicada-related insect questions. Continue scouting for black cutworm and other seedling pests up to about V5.

Black cutworm larvae should be approaching cutting size in most of Illinois – it’s a good time to scout fields where winter annuals were a problem at or around planting. We are right at 50% egg hatch for corn rootworms in central Illinois, so larval feeding will be occurring over the next several weeks.