Regional Crop Update: July 27 - August 4, 2026

July really pushed corn and soybean development along. Corn fields across the state are mostly in the late R3 to R5 growth stages, and soybeans are mostly in the R4 to R5 growth stages as well. Even though it may feel like we are heading into the downhill stretch for these crops, continue to scout fields. Below, ISU Extension and Outreach field agronomists share what they have been finding and hearing about in fields around the state this past week.

Angie Rieck-Hinz (Region 3)

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

“The weather in July really pushed crop development. You can see from the table below (Iowa Mesonet: April 10 - July 31) the above average growing degree day accumulation and the shortage of rainfall in some places. Corn ranges from very late R3 (milk) to R5 (dent). Insect pressure has been extremely low in the fields I have been in and even my rootworm beetle counts seem lower than normal. Nearly every disease is present somewhere out there, but still at low incidence and low severity.  Soybeans are mostly at R4, with a few fields R5. Last week I found a few soybean aphids but at very low numbers and very sporadic in one field.  I also found soybean gall midge (SGM) in a field that was confirmed in 2024 in Wright County. I have been scouting that field every two weeks since mid-June and finally found SGM. There were no plant symptoms visible while walking, but if I had not accidentally kicked some plants and broke the stems at the soil line, I am not sure I would have found them. Just to be clear, I have not found SGM in any field that has not already been confirmed. The researchers on campus have added Franklin, Lucas, and Worth counties to the list of counties confirmed for soybean gall midge, so keep an eye out. Disease pressure continues to be low in soybean fields that I have been in.”

Josh Michel (Region 5)

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

“Farmers were able to take advantage of a mostly dry week, before heavy rainfall came through the region over the weekend. While most of the region received anywhere from 1.5 to 3 inches of rainfall, some isolated areas in Dubuque, Jones and Linn counties received up to 4.5 inches of precipitation. In general, most of the corn is around R1 to R3, while soybeans are around R2 to R4. Disease management continues to be a concern while crops are going through early reproductive stages. That said, disease pressure remains moderately low across most of the region. Third crop of alfalfa is getting finished up in a few places and regrowth looks good at this time. The majority of recent field calls have centered around scouting for insect pests and crop diseases.”

Meaghan Anderson (Region 7)

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

“Central Iowa received a shot of needed rainfall last week to keep the crops fed in reproductive stages, and we’ll be looking forward to another round of rain this week. Corn is mostly in the R3 to R4 growth stage. By R4, kernel number is set and we’re worried about filling the kernels on the corn ear. Disease and insect pressure remain relatively low in most fields I walk in. I can find a little of numerous diseases but not a lot of anything. I’ve seen more ‘oddities’ in corn than I can remember in the past couple years, including grape colaspis beetle adults in silks and apparent abiotic speckling on leaves in the upper canopy of corn plants that can look suspiciously like disease. Soybeans are in the R4 to perhaps early R5 growth stage. Like in corn, I can find a little of a number of things but nothing standing out as a serious concern across the fields I’ve walked in recent days. Soybeans appear very tall this year and are already beginning to lay down in some fields. These tangled fields are very difficult to walk and may make for an interesting harvest this year. Most phone calls in the last week have been questions about disease vs. not disease in corn, fungicides, weed identification, and spider mites.”

Rebecca Vittetoe (Region 8)

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

“After another warm week, some welcomed rainfall fell across the region late last week, with totals ranging from about 0.1 to 1.5 inches. The warmer temperatures have pushed crops along, and corn is mostly R3 - R4, while soybeans are mostly at R4, although some earlier planted fields have likely reached R5. While I found a little more gray leaf spot in corn last week (still in the lower canopy) and observed some leaves with southern rust, overall disease pressure remains low. The same is true in soybeans with low disease pressure. Insect pressure also has been low. In fact, I received several calls last week asking about the lower corn rootworm beetle pressure this year. I have had a few reports of corn aphids. Last week, I received a handful of calls and questions about corn pollination concerns. In the fields I walked, about 1% of the plants were affected. Many ears with the pollination concerns appeared to have two pollination windows as most kernel were at R3 but there were some kernels that were still at R2. These pollination concerns likely trace back to the hotter daytime temperatures and warmer nighttime temperatures experienced during pollination. Thankfully, it appears to be a small percentage of the plants affected, and on many ears the kernels around will fill in. However, this is a good reminder to keep scouting fields. Other questions focused on fungicide applications, weed identification, and aphids in corn.”

Virgil Schmitt (Region 9)

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

“During the last week, the counties I cover have generally received from 0.2 inch of rain near the Missouri border to over 3 inches of rain in many locations north of Highway 92. Most corn fields are just reaching or in R4 and generally look good. Little disease is present. Most soybeans are at R4 and also look good. Again, little disease is present. Forages also are doing well. Calls last week were mostly corn and soybean diseases and fungicide application decisions and late season weed management.”

Logan McCrea (Region 11)

Appanoose, Davis, Lucas, Mahaska, Marion, Monroe, Van Buren, Wapello, Wayne counties

“Last week brought anywhere from 0.25 inch to 1.5 inches across the area, which was welcome for most producers. Some more rainfall this coming week will be welcome as well as we move closer to the finish line for both corn and soybeans. Corn ranges from R3 to R4 and is breezing through its reproductive stages. Some foliar diseases are beginning to become easier to find, but overall pressure still is low. Varying levels of ear tip back have been noted from producers across the area. Soybeans are mainly R3 to R4 and as we creep into the month of August, many weed escapes are beginning to poke through the upper canopies in fields and becoming noticeable while driving by. Pastures have been struggling recently and welcomed the precipitation received last week, but they really could use some more paired with cooler temperatures to catch up a bit. Hay cutting continues to occur with many well into third cutting. Calls over the past week have centered around disease identification and fungicide decisions.”