Illinois Crop Update – August 8, 2025

Steve Brand – Commercial Agriculture Specialist

DeKalb County

Soil Conditions: Near Normal

Conditions over the past 2 weeks have reverted back to being dry with temperatures in the upper 80’s to low 90’s. The corn and soybeans have been progressing very quickly with the increased Growth Degree Units and just enough moisture. As we look at the drought map most of Northern IL remains in the D0 drought with a small area south of Chicago in a D1. Future forecast is more of the same, lower humidity and moderately high temperatures, so I expect growing conditions to be ideal as we move through ear and pod fill in both crops respectively. On the season we are approaching 1900 growth degree units

Corn is moving quickly through reproductive stages and is mostly at R3 or milk stage, with a few fields slightly behind at late stage R2. Within the fields, disease is starting to creep in but it is nothing I would be overly concerned about. Tar spot is replicating in the lower leaves thanks to some lower temperatures and heavy dews, but the fungicides are keeping the upper canopy clean and ideal for earfill. I have not seen much northern corn leaf blight, gray leaf spot is in the lower canopy but again, this isn’t anything to worry about. I’ve seen a few corn leaf beetles but again far below any threshold of economic loss. Overall, corn is looking great as we enter a bit of a lull in the growing season.

Soybeans have made a large jump in size thanks to the weather and ideal growing conditions. Fields with taller varieties are chest high on myself (6’3″ for reference) and are lush. Pods are beginning to fill out and are mostly R4 entering R5 as the beans begin to fill out. Over all this is one of the cleanest years disease-wise I have seen in soybeans. Ideal temperature and the general lack of moisture has produced very little disease. Other than the occasional wet spot from heavy rains in July, soybeans are looking great across the board.

Russ Higgins – Commercial Agriculture Educator

Grundy County

Soil Conditions: Mildly Dry (soil is drier than normal, plant growth may have slowed)

A week without precipitation and Northeast Illinois returns to abnormally dry on the US drought monitor. Disease pressure in corn is starting to build as much of the crop has reached R4 (dough stage). A Corn Fungicide ROI Calculator tool (accessible on the Crop Protection Network website), designed for both gray leaf spot and tar spot when corn is in the V10 to R3 growth stages requires an expected yield and marketing price input plus a low or high disease estimate. Tabulating those inputs, the tool will provide a breakeven probability on most commonly used fungicides. Iowa State suggests that regardless of the fungal diseases present, a fungicide application after R3 is not likely to provide a return on investment. This week I traveled to campus for the Youth Crop Scouting Competition, a windshield survey of the 90 mile trip of backroads from Champaign north to Grundy County suggests once again overall some remarkable corn and soy crops in this region of the state.

Doug Gucker – Local Food Systems and Small Farms Educator

Dewitt, Macon, and Piatt County

Soil Conditions: Mildly Dry (soil is drier than normal, plant growth may have slowed

Soil moisture conditions across the 3 counties vary from Normal to Moderate Drought. Soybeans planted in April are in the R5 stage, Full Pod. The April-planted corn is in the R4 stage, Dough, with ear tip kernels starting to dent. Recently, over the past 2 weeks, heavy rains have fallen in some areas, and Red Crown Rot is beginning to appear where those high rainfalls occurred. If you suspect you have Red Crown Rot, send a plant sample to the U. of I. Plant Clinic for positive identification. Remember, interveinal chlorosis of soybean leaves can be caused by Brown Stem Rot, Sudden Death Syndrome, or Red Crown Rot.

Nick Seiter – Extension Field Crops Entomologist

Champaign County

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 gets well into the reproductive stages. I have received a number of identification requests for the redheaded flea beetle, so thought I would share a photo. These have been easy to find this year in both corn and soybean; 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.

Talon Becker – Commercial Agriculture Specialist

Edgar County

Soil Conditions: Mildly Dry (soil is drier than normal, plant growth may have slowed)

Both corn and soybeans are progressing well so far in Edgar County. Soils in most fields surveyed were getting to be on the dry side, with cracks starting to form and minimal moisture in the top 3-4 inches. At the time of my survey in the afternoon of 8/5, small pop-up showers were in the area, but they provided minimal relief. Of the corn fields surveyed, most are in the late R4 “dough” to early R5 “dent” stage with a couple fields still in the late R3 “milk” to early R4 “dough” stages. Relatively minor tip dieback, presumably due to recent moisture stress, was prevalent in many but not all fields surveyed. Foliar and stalk diseases are starting to show up, but pressure still appears minimal at this time.

Soybean fields surveyed were primarily in the R4 “full pod” to R5 “beginning seed” stages, with some stragglers still in the R3 “beginning pod” stage. Again, no major signs of disease showing up yet in the soybean fields surveyed. Japanese beetle feeding was easy to find, although it was still below recommended thresholds for control (https://farmdoc.illinois.edu/field-crop-production/insects/japanese-beetle-management-guidelines.html).