Additional rainfall this week has brought weeds through the soy canopy in some fields, especially in areas where the population was thinned by earlier flooding or saturation. The soy fields I have scouted continue to be mostly disease free. That statement does not hold up for the corn crop. I have been scouting a 108-day hybrid that was planted on April 24th, this corn has reached R5 or the dent stage. At this stage within the kernel, starch begins to harden at the top and works its way down to the kernel tip attached to the cob. There is variation between maturities and hybrids, but corn plants are generally in R5 for 30 days before reaching R6 or physiological maturity. At the beginning of R5 the kernel dry matte content is estimated at 45% of the potential final accumulation. Unlike the soy crop, and not surprising with August environmental conditions, foliar diseases have increased markedly in the recent week in corn fields. Southern Rust, Tar Spot and Gray Leaf Spot is all currently present in fields scouted that did not receive fungicide treatment. Another interesting anomaly noted on hybrids with shortened husk, is frequent damage to the exposed ear tip, presumably by birds or insects.

The majority of the corn and soybean fields are in good to excellent shape. The exceptions are those fields that have suffered some type of weather issue – flooding, storm, or wind damage.
Soybean fields are mostly at the R5 stage, with some at the R6 (full seed) stage. I am noticing Japanese beetle feeding, but at levels below treatment thresholds. Also beginning to see bean leaf beetles showing up in the fields.
Corn fields are mostly in the R4 or R5 stage, dough to dent, but do see the occasional corn field in the R1, Silk stage. Corn leaves are showing minor leaf diseases currently, mostly a little gray leaf spot.

As of Wednesday (8/12) afternoon, the crop in southern McLean County was still standing and, for the most part, looking healthy following the storm system that moved through a couple hours prior to my survey. As I write this the following day, another strong storm system is moving through the region bringing more heavy rain and high winds, so I am uncertain if that has changed the crop conditions in that part of the county.

Soybeans in southern McLean County are primarily in the beginning seed (R5) growth stage, ranging from full pod (R4) to early full seed (R6), and are still relatively free of disease or insect issues. Corn is reaching late dough (R4) and early dent growth stages (R5). Remobilization of nutrients from lower leaves is starting to pick up pace in some corn fields that are a bit closer to maturity or in areas of fields affected by early-season wet conditions. Diseases, such as gray leaf spot and Physoderma brown spot, were present in a few of the fields visited, but still no sign of tar spot or southern rust in the fields surveyed. Both have been identified in neighboring counties, Livingston for tar spot and Champaign for southern rust. So, it is possible that those diseases are in the McLean County, but still at low levels. Counties where tar spot and southern rust have been identified can be seen on Crop Lookout from the Crop Protection Network. Links to that resource as well as more information about managing these diseases can be found in the following articles from Extension Field Crop Pathologist, Dr. Boris Camiletti.

Tar spot – https://farmdocdaily.illinois.edu/2025/07/tar-spot-on-the-move-tracking-and-managing-an-established-corn-threat-in-illinois.html

Southern rust – https://farmdocdaily.illinois.edu/2025/07/tar-spot-on-the-move-tracking-and-managing-an-established-corn-threat-in-illinois.html

To report either of these diseases in your area, email photos directly to Dr. Camiletti at bxc@illinois.edu and/or submit samples to the Plant Clinic (https://extension.illinois.edu/plant-clinic).

Continued timely rains in south-central Illinois are supporting excellent crop condition. Along with high heat and humidity and extended periods of leaf wetness, disease is taking hold. We are now seeing southern rust at 5 to 10% incidence up to the ear leaf and high severity on infected plants. This is triggering secondary fungicide applications in late corn.

Second set of pictures appears to be phytotoxic injury associated with a recent drone application. Field pattern suggests drone coverage may not have been good.

As we progress through the second half of the growing season for corn and soy, conditions have been mostly favorable for grain fill in the Northeast region. Most soy is at or near R5 also known as the beginning seed or beginning bean stage. As rapid seed fill begins later in this stage, the soy plant starts to remobilize nutrients from leaves and stems to meet the demand of pod fill. In fields visited, disease and insect pressure in the soy crop has remained very low. I have not come across red crown rot in soy fields visited, but reports have this emerging disease spreading in Illinois. It was announced this week that Illinois farmers can receive free red crown rot (RCR) testing thanks to the United Soybean Board and the Illinois Soybean Checkoff in partnership with the University of Illinois. If you suspect that you have RCR in your fields and would like confirmation, please consider sending diseased samples to the University of Illinois Plant Clinic in Urbana. While scouting R3 or milk stage corn, I noted white frass on a developing ear, almost always an indication of feeding by the corn earworm. The corn earworm is also known as the cotton bollworm and is a pest of several crops in addition to corn and cotton. The adult female corn earworm moth prefers to lay eggs on fresh silk. The hatched larvae follow the silk to the tip of the ear where they feed and produce excrement or “frass”. Larva inside the ear do not have effective insecticide control. While this pest is a challenging insect to control in sweet corn operations, it usually is a minor concern in yellow dent corn. As we diligently continue our foliar corn disease scouting, a slight uptick in gray leaf spot was noted, but fields I have visited are remarkably disease free at this stage compared to recent years.

Corn and soybean crops are generally looking good, with the only exceptions being areas of fields that experienced flooding or waterlogged soils earlier in the season. Leaf disease pressure is low in fields except those fields where plants experienced stress from waterlogged soils.
Last week’s timely rains had a noticeable impact on fields with low soil moisture and plant vigor. Soybeans are midway through the R5, Beginning Pod stage, and corn is in the R4, Dough stage, with kernels beginning to dent.