As July ends warmer temperatures and humidity returned to NE Illinois. While some appreciate seeing a sunrise mist with morning coffee, I think of extended leaf wetness on crops and that it often favors fungal leaf diseases. Despite these occurrences, I continue to see very limited leaf disease symptoms in corn or soy. From a maturity standpoint in fields visited, corn is transitioning from R3 (milk) to R4 (dough) stage. The starch within the kernel is converting from a liquid to a pasty consistency. R4 is often the shortest reproductive stage dependent on environmental conditions. Soy has reached R4 or the full pod stage. At this stage a ¾ inch (2 cm) pod can be found on one of the 4 uppermost nodes on the main stem. R4 through R6 (full seed) is a critical time for the soybean plants exposed to environmental stresses. Issues at this time can cause more significant yield decreases than other growth stages.
Recently Dr. Doris Lagos (USDA-ARS) at the University of Illinois reported finding corn aphids in the suction trap network https://suctiontrapnetwork.org/data/ and in fields. Several have corroborated finding corn aphids and suggested treating specifically for the pest. In my scouting visits I am finding corn aphid populations where I often find them, on plants at or near field edges, and at very low densities (random mostly singular plants).

We have gotten quite a bit of rain in the last week in LaSalle County, with most areas seeing between 2-3 inches. Some areas in Bureau County received up to 4 inches of precipitation in the past week. With this, many fields have fairly saturated soils, but I have not noticed any ponding. Overall crops are looking very good and progressing well. I have not seen excessive disease or pest pressure in most fields. Corn is at R3 (milk), and soy is at R5 (beginning seed). Weeds are getting very large in some fields though (see image of waterhemp).

In general, all the crops are looking good with very few issues other than weather related problems. Last week’s surge in aphid populations is now a thing of the past with rainstorms, disease and predators sending the populations into a nosedive.

It’s been another wet week in Champaign County. While starting my survey in the southern half of the county on Wednesday (7/31) this week, yet another front was moving through the area with more rain in the forecast for the coming days. Although we have seen frequent storms, the Illinois Soil and Water Survey weather station in Champaign received only approximately 1 inch of rain in total in the past 7 days, with perhaps a bit more in the southwest portion of the county. In that part of the county, there were a few fields with flooded out areas, but crop loss from outright flooding or diseases associated with waterlogged soils appears to still be relatively minimal, with most corn and soybean fields in the area still looking very healthy. Soils were obviously wet as I walked through fields, but still firm and not waterlogged in most areas. Corn fields surveyed ranged from R1 to R3, and full-season soybean fields surveyed ranged from R2 to R4. The one field of double-crop soybeans I found was just starting to flower.

The good news is that it rained, but the bad news is it has not stopped for a few days now. The mid May planted corn is at brown silk and hopefully successfully pollinated. April planted soybeans are tall and a bit tangled after recent storms. No major issues found. Bacterial blight seems to reappeared after cool and wet weather.

This week, I went east and surveyed the southern half of Vermilion County. Overall, the corn and soybean crop looked healthy, and soil conditions were near ideal to only mildly wet in most areas. However, there were some low-lying soybean fields showing pockets of stressed plants showing symptoms of root rot and a few instances where the plants have died. This has been a common observation of my past few reports in surrounding counties with differing levels of severity. In southern Vermilion County currently, crop loss appears to be lower than it is a bit further west and southwest. Most soybean fields I stopped at were at late R2 to early R3. Japanese beetles are easy to find in most fields, but defoliation levels were still well below threshold in fields I stopped at. Most corn was R1-R2, and as noted in Nick Seiter’s post, a few of the fields surveyed had corn leaf aphid colonies present.

Scout continuously in corn and soybean field. Corn is the hot topic for the week. Corn Aphids have continued to move in the area and are taking their toll on certain hybrids. Soybeans have been fairly clean overall from insects or disease pressure

Another week of varied precipitation in northeast Illinois, but mostly favorable growing conditions. Corn has reached R3 (milk stage). At this stage the moisture of the kernel is about 80%. Leaf disease incidence continues to be low in corn and soy fields visited. Most soy is R3 to R4, beginning to full pod. In addition to the crops entering their reproductive stages, so too are some weeds, including waterhemp. This weed is dioecious, both male and female plants having flowering structures. Once mature, the plants can be easily sexed by the presence or lack of shiny black seeds.
This week I attended the Monmouth Research Center Agronomy Day and was able to gain insight explaining why many were seeing waterhemp uncontrolled by post herbicide applications. The surviving plants appeared weeks after the post herbicide application as bushier, more robust plants. University of Illinois ‘s Caleb Wepprecht discussed “HPPD Resistant Waterhemp- A Growing Concern” and shared his take on weed control challenges from this year. A few factors in waterhemp escapes were inadequate spray volume on larger plants, leading to inadequate coverage of the growing points, even with systemic herbicides, as well as low use rates/dosage of herbicide in the weed itself, along with the concept of metabolic herbicide resistance, leading to the waterhemp’s survival and altered plant structure. As farmers see waterhemp escapes in fields, Caleb encouraged attendees to take whatever steps possible to prevent the prolific seed-producing weed from maturing and causing future concerns

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.

Corn and soybeans across the area continue to look healthy, and growing progress remains steady. Many corn fields have been successfully pollinated. Spray planes have also been active the last couple of weeks, with producers putting on fungicides. Soybeans have nearly all flowered, with most also starting to grow pods. Some rain would be welcome, but there does not appear to be a lack of moisture in the soil.