Regional Crop Update August 10 - August 25, 2026

Regional Update: 

As the growing season starts to wind down, sudden death syndrome, western bean cutworm, Goss’s wilt, southern rust, tar spot, weed escapes, and the start of corn silage harvest are some of the topics or issues ISU Extension and Outreach field agronomists are seeing or hearing about in fields across the state. Read on for more specifics. 

Leah Ten Napel (Region 1)

Cherokee, Ida, Lyon, Monona, O'Brien, Osceola, Plymouth, Sioux, Woodbury counties

“At this point in the growing season, we are moving on from additional in-field decisions to preparing for harvest. Corn is R4-R6 stages, with many fields fully dented. Many soybeans are at the R6, full seed, stage. Corn silage chopping has begun in the region. Disease pressure has been fairly low across fields I have scouted, but it is still worth scouting your own fields for foliar diseases, stalk issues and ear rots. Fields that experienced hail, wind or other stress should receive extra attention, as those areas may be more susceptible to stalk deterioration and may need to be prioritized as we move into harvest. In soybean fields, keep an eye on the upper canopy and look for plants that are dying prematurely or showing unusual symptoms. Red crown rot is something to be aware of, as it has recently been confirmed in an eastern Iowa county. Western bean cutworms are being found in fields in northwest Iowa. Injury is similar to that caused by corn earworm: caterpillars consume kernels and leave frass behind. Although insecticides are not effective once caterpillars are inside the ear, it is still worthwhile to scout ears for injury to determine whether molds have developed on the ear that may decrease grain quality or be harmful to livestock. Late-season weeds are also becoming easier to spot. While there may not be many opportunities left for control this year, now is a good time to identify problem areas and make notes for fall management and next year's weed control program. Overall, weed control in northwest Iowa this growing season was much more successful than last year.” 

Angie Rieck-Hinz (Region 3)

Cerro Gordo, Franklin, Hamilton, Hardin, Humboldt, Webster, Worth, Wright counties 

“Corn is changing quickly with some hybrids starting to show leaf senescence, ear drop, and husks turning yellow/brown. Nearly all corn field I have been in are R5.5 to R5.75. Southern rust has shown up more frequently in the past 7-10 days. This should not be surprising as our cooler temperatures (low 80s) and humid mornings (greater than 6 hours of leaf wetness) are prime conditions for southern rust. It is still at extremely low levels, and it is too late in the growing season to consider any fungicide application.  I have also noticed a major uptick in the incidence and severity of Goss’s wilt in corn fields. In some fields, the leaf senescence at the top of the plant is due to large lesions of Goss’s wilt. Remember, this disease is a bacterial infection and is not treated with a fungicide. Soybeans are R6, but you can begin to note a color change in the soybeans as we speed to maturity. Sudden death syndrome (SDS) is become more noticeable across NC Iowa and I have received reports of white mold.”

Josh Michel (Region 5)

Allamakee, Buchanan, Clayton, Delaware, Dubuque, Fayette, Jones, Linn, Winneshiek counties

“A stretch of dry weather last week allowed farmers to start harvesting their fourth crop of alfalfa. Some scattered light rain showers did come through the area delivering up to 0.50 inches in isolated areas, but most of the region only received 0.10 to 0.25 inches of precipitation. Corn is generally at R4-R5, while soybeans are at R4-R6. I would expect corn silage harvest to begin shortly as some fields may approach quarter to half milkline. Reminder to continue scouting fields that received wind and hail damage for stalk, corn ear and bean pod issues. Here’s a great article to reference Ear Rots and Mycotoxins. Pastures continue to look good with the rainfall we received earlier in the month. Recent field calls have centered around storm-related crop damage, silage management and late-season insect scouting.

Meaghan Anderson (Region 7)

Boone, Dallas, Jasper, Madison, Marshall, Polk, Story, Tama, Warren counties 

“Central Iowa has received another few rainfalls in the last couple weeks to help finish the crop out. The cooler temperatures have likely been good for grain fill. Most corn is in the R5 (dent) stage. Many fields are beginning to show signs of preparing for harvest, with leaves and husks turning, and some ears even turning down already in fields. In my recent scouting, I’ve noticed crown rot at low levels in many fields but very low overall foliar disease pressure, even in some central Iowa fields that were not sprayed with fungicide. R5 is a great time to walk corn fields for yield estimates, check for early signs of crown and stalk rots that might make harvest a challenge, and evaluate the presence and severity of foliar disease symptoms. While itchy, it can be a very eye-opening experience. Soybeans are in the R5-R6 stage and sudden death syndrome (SDS)-like symptoms and weeds have both made themselves well known in many fields in the last week. Scout fields with those SDS-like foliar symptoms to make sure it is what you think it is as red crown rot continues to knock at our door here in Iowa. Most phone calls in the last week were about foliar disease, yield estimates, weed management, and fall fertilizer plans.”

Rebecca Vittetoe (Region 8)

Iowa, Jefferson, Keokuk, Poweshiek, Washington, Johnson counties

“Since August 10 rainfall totals have ranged from 2 to more than 5 inches in the counties I cover. The heaviest amounts were in Jefferson County. Corn is in the R5 or dent stage. While doing corn disease assessments in addition to seeing a little bit of everything with foliar diseases, I’ve observed crown rot (random plants that are already dad with the ears hanging down). This week I have seen a little more tar spot and southern rust. While I have come across small pockets that have higher disease pressure, the average disease severity on the ear leaf in the fields I’ve assessed is less than 3%. Soybean fields are mostly R5.5 to R6, and over the last week I’ve really started to noticed pockets of what appears to be sudden death syndrome (SDS) showing up. However, the foliar symptoms of SDS are similar to red crown rot. Double check those pockets in fields to make sure they aren’t actually red crown rot. Plants with red crown rot will have a red discoloration on the lower portion of the soybean stem. The Iowa Soybean Association is offering to provide free testing of plants suspected with red crown rot. Questions this last week have been on western bean cutworm, testing the germination on cover crop seed, last season diseases, and late season weed management.” 

Virgil Schmitt (Region 9)

Cedar, Clinton, Des Moines, Henry, Jackson, Lee, Louisa, Muscatine, Scott counties

“During the last two weeks, areas south of Highway 22 received 4 to over 10 inches of rain while the counties north of Highway 22 received from 2 to 4 inches of rain. Most corn fields are about R5.25 to R5.5 and generally look good. Little disease or insect pressure is present. Most soybeans are at R5.5 and also look good. Again, little disease or insect pressure is present. Forages also are doing well. Many fields of third cutting hay have been mowed. Calls during the last weeks were mostly corn diseases, late season weed management, corn tip back, soil sampling, and soil fertility. Also, a sample was sent in from a soybean field in Des Moines County and was confirmed for red crown rot. This is the first confirmation of red crown rot in Iowa.”