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.

Alfalfa weevil reports have started to wind down a bit as the insects cycle out – they’re still out there in some areas, so stay vigilant. Black cutworm larvae will soon be large enough to cut plants and reduce stands; projected cutting dates based on moth trap densities and degree day accumulations are available here: https://corn.ipmpipe.org/insects/black-cutworm/ (map at bottom of page). Pay special attention to fields where winter annual weed control was delayed and broadleaf weeds are present in the field and/or dying while the crop is emerging. (A clean corn field is not a very attractive oviposition site for the moths and usually will not experience much cutting). Even in areas with high moth numbers, injury is sporadic, so don’t assume you’ll need to control just because you have some weeds.

Reports of alfalfa weevil have been coming in pretty consistently for the last several weeks; we’ve now received reports as far north as Rockford. If you haven’t already, it’s a good idea to scout your alfalfa – look for defoliation (alfalfa weevil is the most likely culprit at this early stage) and confirm the continued presence of the small, green larvae before taking action. If you have a serious infestation and are in position to do so, consider cutting early to reduce the potential for further damage. Insecticide options are somewhat limited, and failures with lambda-cyhalothrin have been reported this spring.

I’ve received several reports of corn rootworms breaking through pyramided Bt traits over the last couple of weeks. Most of these are in the usual areas north of I-80, but I was able to collect a population from Sangamon County last week and had reports from Putnam and Bureau. Continuous corn is virtually always the culprit in these cases. We are always looking for both western and northern corn rootworm populations to bioassay; if you have large numbers of adults and wouldn’t mind us coming out to collect them, please don’t hesitate to contact me.

I remain concerned about spider mites in areas which are under drought stress; I received a report this morning about mite problems in White County. Hopefully the rains this past week have slowed them down, but stay vigilant in areas under drought stress. Corn rootworm adult emergence should be well under way throughout the state. As most of the rootworm adults will still be in the field they emerged from, this is a good time to inspect fields to get a feel for the extent of your rootworm problem and how your traits/insecticides are performing. If you have high adult emergence, consider digging some roots to assess the extent of larval damage.

Speaking of damage, we learned how corn rootworm emergence tents hold up to an 85-mph derecho; not well, as it turns out. However, it was probably worth the damage to get some healing rains.

On a trip to Monmouth this past week I saw the beginning of some likely spider mite infestations; if the drought continues, these become increasingly likely in soybean. This is a great reason to hold off on broad spectrum insecticide applications, which don’t touch the mites but eliminate their natural enemies. (Also, a good reason not to mow your grassways if you don’t have to).

I’ve started to receive a few reports of damage from early season caterpillar pests, including true armyworm, black cutworm, and variegated cutworm. Concentrate your scouting efforts on fields that border wheat, other small grains, or had a grass cover crop for armyworm, and fields that had sub-optimal winter annual weed control or a legume cover crop for the cutworm species. If you find larvae, note the sizes – larger (> 1 inch) larvae do the most damage, but are also the closest to pupating and “cycling out” of the damaging stage. Populations of larvae with mixed sizes or that include predominantly smaller larvae will be with us for longer.