Entering September an intense shift in weather as a “heat dome” became established in Northeast Illinois. While fields near the Wisconsin state line received precipitation, most areas did not. The ninety degrees plus days provided ample Growing Degree Days (GDDs) for crops finishing grain fill. On lighter soils the temperatures are causing a water deficit reflected by the wilting/yellowing plants. As mentioned in previous reports, there is very good corn, and not as good, depending on where you collect samples. This week I collected from fields that should be very high yielding.

Few things are left to surprise me in this growing season, but a sunflower field in Kendall County did just that! Not sure when the field was planted or harvest plans for the crop, but an interesting rotation option. Several winter wheat fields that had been harvested earlier in the season are now supporting a robust weed population. Farmers should consider mowing, tillage or a chemical option to prevent these weeds from adding to the weed seed bank. For those considering a third or fourth cutting of alfalfa, an often asked question is when? Adequate time is needed for regrowth of alfalfa to replenish root carbohydrates to increase overwintering ability of the perennial crop. Our general answer has been four to six weeks before a killing frost for the hay crop. Newer recommendations encourage farmers to look at GDD’s, with a minimum of 500 GDD’s between last cutting and a killing frost.

Black layer is near for some corn fields in the Northeast region. Utilizing the U2U Decision Support Tool – Corn GDD suggests a 108-day Hybrid planted April 25th in Grundy County will reach black layer between September 1st and the 6th. In corn fields scouted, especially those that did not receive a fungicide application, foliar leaf diseases continue to hasten leaf area necrosis and yellowing of plants. This is going to be a challenging year for accurate corn yield prediction from the perspective of in-field variation. Growers are encouraged to sample multiple locations within the field, accounting for pollination differences in ears to more accurately assess predicted yield. Some soy fields are starting to show very limited disease symptoms including Sudden Death Syndrome. This fungal pathogen can survive the winter in both corn and soy residue. Infection takes place early in the growing season, enhanced by cool and wet soil conditions. The visible symptoms we see are the result of a toxin produced by the disease that is translocated to upper canopy leaves. There are several other diseases including Red Crown Rot and Brown Stem Rot that exhibit similar leaf symptoms.

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.

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.

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.

This past week saw hail, substantial rain, and missed opportunities for needed precipitation in varying fields across the northeast region of Illinois. Corn has reached R3 or the milk stage in the field I have been scouting this summer. At this stage the kernel no longer adds new cells to the kernel endosperm but fills the existing cells with liquid starch. If punctured the liquid or “milk” will spray or shoot out of the kernel. Foliar disease pressure in this field continues to be low, I have noted very sporadic purplish lesions in leaf midribs and on corn stalks. This is symptomatic of the fungal disease Physoderma brown spot. Especially on lighter soils or areas where significant nitrogen loss occurred, likely due in part to extreme rainfall, considerable remobilization of carbohydrates is taking place as corn plants cannibalize lower leaves to meet their nutritional needs of ear development. Soy has reached R4 or full pod stage, the beginning of a critical stress response period for the soy plant. New flower growth slows and plants lose their ability to remake new flowers and pods. Similar to the corn crop, disease and insect pressure currently are low in the 2026 soy fields I have visited.

A favorable week for crop growth in the northeast region of Illinois. Corn is pollinating, despite predicted 90 degrees plus highs this week, most fields have adequate moisture and should not suffer despite elevated temperatures at this critical stage for the corn crop. I enjoy my early morning coffee looking across several corn and soy fields. This past week I noted most mornings start with a mist or fog. The mist does not come directly from the corn and soy crops, even though both put water vapor in the air through the process of transpiration. The morning mist is the result of the cooling of the moist air. As the air cools overnight, it reaches its “dew point” and can no longer hold water as a gas, causing water vapor in the air to turn into liquid droplets. Of significance to those scouting for crop diseases, the morning mist extends periods of leaf wetness, a favorable requirement to several fungal leaf diseases. This week, with the appearance of brace roots in the corn crop, the question of underground root expansion was raised. There are many limiting factors to root growth, too much or limited moisture, soil compaction or other natural barriers. However, the general suggestion is that root expansion in the corn crop continues through pollination. At this point the crop redirects energy toward grain fill. By this time with favorable soil structure, it is not uncommon for corn roots to extend to six feet in depth. Our soy plants tend to generate roots further into the vegetative stages, to R5 and R6, beginning and full seed.
The corn crop is R1 with kernel fertilization underway. Soy is between R2, full flower and R3, or beginning pod. Despite favorable conditions for leaf diseases, I have yet to see an outbreak of tar spot on corn or soy leaf disease in fields I have scouted. Growers are encouraged to remain diligent with both field visits and local reports.

This week farmland in the northeast region received additional precipitation and winds over the July 4th weekend. Rainfall totals reported ranged from 1+ inches to isolated fields that received 9+ inches. When sharing an update, the challenge is whether to report on the part of the field that has been unaffected (or even enhanced) by the rainfall, or the parts of the field that have been killed or damaged by ponding or saturated soils. Depending upon where you look, there are outstanding portions of fields, but if you evaluate the field as a whole and note the unevenness and drowned out areas the field overall rating diminishes. Soybean are at R2 or full flower, at this stage the plants begin a period of rapid dry matter and nutrient accumulation. This week shorter season or earlier planted corn hybrids have reached R1 or pollination and scouting for foliar leaf diseases has intensified. This job will soon be less pleasant when pollen shed increases. In fields scouted, I have yet to find symptoms of Tar Spot. I have noted black specks on corn leaves, but the Tar Spot stromata (lesions) cannot be brushed off. What I have found are either wind deposited dirt or possibly insect frass or excrement. If you can wipe off the black spot on a leaf it is not Tar Spot. Follow our weekly reports for updates on Gray Leaf Spot, Tar Spot, Southern Rust and other diseases found in both corn and soy across the state.

In a recent report, I stated that warmer weather would benefit the 2026 crop, perhaps in the future I should qualify my term of “warmer weather”. A week of 90 degree plus days in Northeastern Illinois has allowed farmers and agribusiness the opportunity to play catch-up applying post herbicides. Last week, you could not travel a rural road without meeting a sprayer. Most fields have weed populations that have easily exceeded weed size management recommendations and most have drowned out areas that will likely germinate later season weeds. Fields this year are unlikely to have “perfect” weed control. Growers are encouraged to evaluate post herbicide applications and start scouting for leaf diseases in corn. Tar spot symptoms have been reported in the state, and one tool that can be utilized to see if a crop disease has been reported in your area is visiting the Crop Lookout Website. Crop Lookout is a real-time, interactive map that highlights emerging field crop issues across the United States and Canada. Updated throughout the growing season by university Extension specialists and research partners, the tool visualizes reports of diseases, pests, and other agronomic challenges as they develop. Northern Corn Leaf Blight or Goss’s wilt have been found in Grundy County as the crop is near the Tassel stage.

Another week with precipitation, in many areas ground sprayers have been unable to operate since June 7th. Many fields that are inherently poorly drained are ponded and both corn and soy are suffering. Farmers are facing the challenge of post applications of herbicide for corn and soy, and in some cases nitrogen for the corn crop. Warmer and dryer weather is desperately needed for the crops in the area. Most soy in the area not stressed by saturated soil has reached R2 (full flower), corn has reached V11. Waterhemp has reached 18 to 24 inches in untreated fields. Area alfalfa fields are flowering and Japanese Beetle have emerged in Northeast Illinois.