Soybeans in many fields are reaching the R6, or full seed, stage, and late-season insect and disease pests are beginning to appear. A few fields are nearing R7, or beginning maturity.

Precipitation this past week brought substantial rainfall totals to some fields in Northeast Illinois. Isolated corn fields are showing significant disease pressure but are also nearing maturity. In the R5 stage, the corn kernel contains both “soft” and “hard” starch. The transition, or hardening, of the soft starch into hard starch begins at the top of the kernel and progresses to the tip. This progress is visible as the kernel’s “milk line.” Corn is typically about 55 percent moisture at the beginning of R5 and 30 to 35 percent at its conclusion. Corn plants generally complete the R5 stage in about 30 days, during which they accumulate dry matter content.

The soybean crop is nearing the R6 stage. At R6, or full seed, plants have a green seed that fills the pod at one of the top four nodes on the main stem. Once soybeans reach R6, new leaf growth ceases, and lower leaves begin to yellow and drop. We are encouraging growers, especially those with a history of the disease, to monitor their fields for white mold.

For those attending the Farm Progress Show next week, visit Illinois Extension at the University of Illinois College of ACES tent on West Progress Avenue.

It has finally stopped raining. Even though we were supposed to have a cool down, it has continued to be very hot and humid. The fungicide on corn appears to be holding fungal diseases below the ear. I did see some Southern rust on the end rows of corn, but not bad as you go into the field. There are obvious disease differences on different hybrids. Corn is almost at full dent. Soybean disease symptoms of SDS are starting to show. Red crown rot has not been a major issue in Montgomery Co., but this year, this disease has unfortunately made its debut and is here to stay. Soybeans are at R4 growth stage.

Southern Illinois experienced planting delays this spring due to excessive rainfall, which pushed field activities into late May and early June. Despite these challenges, soybeans are currently at the R2 (full bloom) growth stage, and the corn that was planted has also reached reproductive stages. One field I scouted showed significant defoliation caused by insect pressure from bean leaf beetle, Dectes stem borer, and striped blister beetle, all of which can continue to impact soybean growth and development if not properly managed. At the R2 stage, the defoliation threshold for bean leaf beetle is 15–20%, and for blister beetle, it is 15%. At these levels, an insecticide application is warranted to prevent economic yield loss.

Despite the seasonally warm temperatures during the last week, many crops across Logan County benefited from a rain shower early in the week. Most of the county saw 1 to 2 inches of rain, which will undoubtedly help crop growth. Many corn fields are moving into the R5 “dent” stage, with not many lagging behind the leaders. Much the same can be said for soybeans, with most fields in the R5 seed stage.

Soil moisture conditions across the three counties vary from wet to moderate drought. Rainfall has been quite variable across this area.

Soybeans planted in April are in the R5 (full pod) stage. The April-planted corn is in the R4 or R5 stage. Crops look good even in the dry areas at this time.

Weed control has been very good. I have noticed that conventionally farmed soybean fields with weed issues typically only have a problem with one weed group—either the Amaranthus family or velvetleaf (Abutilon theophrasti). Grassy weeds have not been an issue across the area in conventionally farmed fields.

This week, Dr. Giovani Preza Fontes, assistant professor and agronomy extension specialist at the University of Illinois, visited the Grundy-Kendall County area and met with area producers, where he shared expectations for both state and local yields. Farmers were provided with recent weather data and were encouraged to take kernel and population counts to determine yield estimates in their own fields.

The pattern of variable rainfall and pop-up isolated thunderstorms discussed was demonstrated that day, with rainfall ranging from 0 to 2-plus inches within a 40-mile radius. Most corn is at the R5 stage, and the likelihood of a return on investment from a fungicide treatment (or additional treatment) at this stage is unlikely. That said, scouting corn that did not receive a fungicide treatment in some fields is like taking an introductory course in plant pathology. Symptoms of tar spot, northern corn leaf blight, gray leaf spot, and southern rust can all be found.

Recent environmental conditions have been especially favorable for the development and spread of southern rust. All leaf diseases are reducing photosynthetic leaf tissue that would aid in grain fill.

This week’s survey in the southern half of Iroquois County showed good crop conditions overall, but with some variability across the surveyed region. At the time of this survey (8/12), overnight rains in much of the area had replenished topsoil moisture in most fields surveyed. However, soil cracking and tip dieback in corn were found in several fields.

Corn fields surveyed tended to be in the R4 “dough” to early R5 “dent” stages. About a third of the fields showed an inch or more of tip dieback, presumably due to moisture stress, given the soil conditions in the field and the lack of evidence of N stress in the plant canopies. Signs of foliar disease were minimal in corn.

Soybean fields surveyed tended to be in the R4 “full pod” to R5 “beginning seed” stages. Plant health looked good overall, but some fields showed areas of stunted growth and a lighter canopy color. At this stage in the disease progression, observed symptoms did not provide a clear diagnosis. If you are seeing this in your field, submitting samples to the Plant Clinic (https://extension.illinois.edu/plant-clinic) can help with early diagnosis.

The beans are TALL as they enter the mid-R stages of growth. All fields I scouted this week were between R3 and R5 (beginning pod to beginning seed), depending on planting date. Corn is currently around the R3 to R4 (milk to dough) stage.

Stephanie and I saw some red crown rot in soybean fields around the Shelby/Macon County area, specifically in fields where she found it two years ago. The disease shows very visible symptoms, including yellowing and browning between the leaf veins (interveinal necrosis) as well as reddish discoloration at the base of the plant near the root. When you look at the root of a soybean plant infected with red crown rot, you’ll often notice white fungal growth (mycelia). Warm soil temperatures (77–86°F) are ideal for this fungus to thrive, so the recent warm days have likely contributed to its presence.

Soil moisture conditions across the three counties vary from normal to moderate drought.
Soybeans planted in April are in the R5 stage (Full Pod), and the April-planted corn is in the R4 stage (Dough), with ear tip kernels starting to dent.

Over the past two weeks, heavy rains have fallen in some areas, and Red Crown Rot is beginning to appear where those high rainfalls occurred. If you suspect Red Crown Rot, send a plant sample to the University of Illinois 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.