It has been unusually quiet so far this year for insect reports. Late last week, I received a report of spider mite activity in soybean in south-central Illinois near Macedonia. Most of the state received a healthy (or even unhealthy) dose of rain at least once or twice in the last week – that will do more to eliminate spider mites as a threat than even the best miticides available. Cooler temperatures will also help. If you are in an area that remains hot and dry and have spider mites, evaluate the potential for continued growth in the population based on the weather forecast and the extent of current injury to make a control decision.

I’ve also received a report that grape colaspis are active again in at least a limited area near Mt. Auburn where they have been a problem in the past. Affected plants will exhibit nutrient deficiency symptoms, especially purpling of the lower leaves and often concentrated on higher/better drained portions of the fields. Digging up the plants will reveal the larvae, which resemble tiny white grubs. By this point, affected plants will be noticeably stunted relative to surrounding, healthy plants, and the larvae may be close to finishing their development and emerging as adults. There is no effective rescue treatment for this pest in corn.

We will again be distributing yellow sticky traps to anyone who wishes to participate in our regional corn rootworm monitoring network. If that applies to you, send me an email (nseiter@illinois.edu) with “rootworm monitoring” in the subject heading.

We had a few corn leaf aphid reports, but nothing approaching what we saw last year; those should be winding down as most of the crop progresses well into the reproductive stages. I’ve received several identification requests for the redheaded flea beetle, so I thought I would share a photo. These have been easy to find this year in both corn and soybeans; every few years, we see abnormally high numbers. As you can see from the picture, they resemble the corn flea beetle (the vector of Stewart’s wilt), but they are much larger—maybe 3/16″ to 1/4″ long—and have a reddish-brown head, as the name suggests. While they will feed on corn and soybean foliage and can be found quite easily in corn silks, I’ve never seen them approach economically damaging levels.

I have received a few reports of corn leaf aphid. This insect should be scouted prior to tasseling, during late vegetative stages; if you have colonies of aphids formed on around 50% of plants at this time, you should consider an insecticide. Beneficial insects and fungal pathogens usually do a number on this pest, and it takes extremely large populations to impact yield.

Now is the time to begin monitoring corn rootworm beetles — both to evaluate the performance of traits/insecticides used this year and to gauge the need for control next year. We will again be distributing yellow sticky traps to anyone interested in participating in our regional corn rootworm adult monitoring network in 2025 (for more information about the network and to see reports from previous years, visit www.rootwormipm.org).

If you are interested in participating and would like me to send you traps and/or the sampling protocol, please send me an email (nseiter@illinois.edu) with the following information:

• Your name and shipping address
• The number of corn and soybean fields you plan to monitor

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).