Both corn and soybean fields are maturing well and looking promising… or they suffered from recent heavy rains/winds and are visibly struggling. While flooded fields have mostly drained over the past week, you can still see the evidence of high waters in bean fields where plants were drowning and are now painted in a layer of soil, or in corn fields showing N deficiencies and early dry down. Some areas that needed the precipitation have soaked it up and appear dry again. The precipitation received this month, coupled with the more mild temperatures, will really help the soybeans as they finish off grain fill. As the saying goes: Beans are made in August.

One insect I’ve seen a lot of lately is thistle caterpillar. Thistle caterpillar, the larval stage of the painted lady butterfly, will build a very distinctive web in soybean leaves and cause defoliation. Threshold levels for control have not been met in fields I’ve scouted, but one double crop field I visited had notable pressure. Per Iowa State University Extension, these caterpillars are a migratory pest, coming north from the southern United States and Mexico, and likely do not overwinter in our climatic region.

Generally, the corn and soybean fields look very good. The exceptions are fields that have been damaged by severe weather, or flooding.
Over the past week, symptoms of Corn Crown Rot have become visible in areas of some fields. What I am seeing is these affected areas are patches of dead, lodging corn plants. Dr. Boris Camiletti, Extension Plant Pathologist, said the photo above appeared to be Corn Crown Rot. A sample is being sent to the U of I Plant Clinic for a diagnosis. Corn crown rot disease infects corn plants in the early portion of the growing season, and the disease is more prevalent in wet, compacted soils.

The heavy storms and even a derecho have passed and we have been left with some gorgeous weather to end the week before some more rain chances next week. Not too many updates agronomically from my last update. Corn has moved into R5 dent across northern Illinois, with many fields at the early stages of senescence. I did find a good amount of tip back in corn in the fields I visited, and I attribute that to the heat dome we experienced coinciding with the end of pollination. The extreme heat and low winds we saw will kill pollen, and lead to lower movement of the pollen that did survive. There will be yield reductions in the fields I saw today, but the severity of the tip back you may see in your fields will align with planting date, and where your fields pollination lined up with the severe heat events we have seen this summer.

Soybeans are looking healthy with little disease. I did not see pockets of SDS as I was expecting, but that may still develop in the coming weeks. Soybeans are moving through pod fill in R5, and were very tall and robust in the fields I saw today.

Overall I’ve found very little disease in the Dekalb sector, with little to no tar spot, and very little disease in soybeans. Cooler temperatures next week may change that, but I feel like I’ve been saying that for weeks now. Tip back and lack of kernel fill is the major concern seen today.

The region has received 9+ inches of rain over the past two weeks, leaving soils saturated, fields muddy, and drainage systems running at full capacity, with limited field activity. Soybeans are mostly at the growth R5 stage and benefiting from the August rainfall, while corn is moving from dough to dent stages as growers are beginning yield checks to see what harvest could look like. Weed pressure remains present, but disease levels are surprisingly low, with only some gray leaf spot and northern corn leaf blight being observed. Northern corn rootworm beetles have become more noticeable over the past few weeks.

Wet conditions have returned to much of central IL. Following a bit of a dry spell in late July and early August, the Illinois Soil and Water Survey’s weather station in Champaign has registered more than 8 inches of rain over the past 9 days. The recent storms also brought high winds and a tornado in the southwestern portion of Champaign County, near Giblin, leaving pockets of crop damage (mostly corn) in that area. Standing water is also back in low areas of some fields. Many of these areas were already absent of crop due to the same issues earlier in the growing season, but standing water could also be seen in some areas where the crop had survived that early-season stress.

Wind damage appeared to decrease as I continued toward Sadorus and Tolono during my survey of southern Champaign County, although the flooding in low-lying areas persisted. Corn conditions were a bit variable. Many fields still look healthy and green, but some corn fields are starting to “fire”, or lose color in their lower canopy, indicating remobilization of nutrients from those tissues to the developing ear. Most fields range from the late dough (R4) to dent (R5) growth stages; I didn’t find any fields at black layer, or full maturity (R6), quite yet. Some fields are starting to show more symptoms of foliar disease, primarily gray leaf spot, but also some northern corn leaf blight. But with those fields generally at early dent (R5) or later, the level of disease observed is unlikely to have a large impact on yield.

Soybean conditions are also starting to look more variable in the area. Again, many fields are looking healthy with a dense, green canopy and full pods, at or nearing the full seed (R6) growth stage. But some fields are starting to show areas with yellowing leaves, indicating some kind of disease issue. In a couple of those fields, I collected plants and split stems to identify pith symptoms characteristic of brown stem rot. This may also be the issue in other fields I observed with similar foliar symptoms, but there are a number of diseases that often present similar foliar symptoms that may be difficult to differentiate and properly diagnose in the field. Resources are available from the Crop Protection Network to help with identifying these diseases (https://cropprotectionnetwork.org/publications/scouting-for-soybean-stem-diseases), and samples can always be submitted to The Plant Clinic (https://extension.illinois.edu/plant-clinic) to get a lab diagnosis. Having an accurate diagnosis is essential for selecting resistant varieties and developing a successful integrated pest management plan for future growing seasons.

The area has started to show signs of water stress up until today, when we are receiving some rain that was not in the forecast. We have received minimal amounts, but we are not complaining. Due to heat and water stress as well as possible nitrogen deficiency, the early April planted corn at late dent stage has started to senesce. Corn has not reached black layer yet, but will very, soon if the heat remains in the forecast. The early April planted soybeans look good at the R5 to R6 growth stages, but we are hoping for more rain for grain fill. There were no evident pests. Foliar disease has held off due to weather and earlier fungicide applications. Gray leaf spot appears to be increasing in areas of the field that may have missed fungicide. Soybean vein necrosis viral symptoms have become visible in soybeans. Lastly, be on the lookout for stalk rot and standability in corn to know which fields may take priority at harvest.

A very active weather pattern across northeast Illinois that spawned tornados, a derecho, and significant rainfall and flooding across the region. In corn fields, foliar leaf diseases are now more easily detected, including Southern rust. A Southern rust report was received by Dr. Boris Cameletti, University of Illinois Plant pathologist on July 23rd in Williamson County in southern Illinois. While the presence of the disease in not good news for northeast Illinois cornfields, the fact that it has appeared later in the season when compared to recent years is good news. With much of the corn crop now at R4 or dough stage, the benefit of a fungicide application, unless exhibiting severe pressure, is low. By comparison, in Grundy County Southern rust made it appearance by mid-July in 2024 and 2025. R4 is one of the shortest reproductive stages in corn plant development before reaching R5 or Dent stage. In fields where scouting has included the pulling of ears, we are finding along with neighboring states, incomplete or scattered kernel set on some ears. Suggested causes include temperature and moisture extremes during pollination, lack of wind during pollen shed, and hybrid characteristics. We are encouraging growers to check variations or responses between hybrids. Yesterday Dr. Conner Sible and Steve Brand from the University of Illinois visited with local producers as guests of the Kendall-Grundy Farm Bureau and local Illinois Extension offices in Kendall County and shared their growing season observations along with nutrient use and crop genetic (root structure) interactions.

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).