More rainfall in areas, southern rust, SDS, white mold, western bean cutworm, and fall armyworms were some of the concerns or issues observed in fields across the state this last week. ISU Extension and Outreach field agronomists share more specifics about what is happening or being seeing in their respective regions across the state below.
Terry Basol (Region 4):
Benton, Black Hawk, Bremer, Butler, Chickasaw, Floyd, Grundy, Howard, Mitchell counties
"Both corn and soybeans continue to look very good for my region. Most of the corn is in the R4 (dough) stage, with the early planted acres at the beginning of R5 (dent) stage. Soybeans range from R4 to early R5. Southern rust is the most common foliar disease being found in cornfields, but other diseases include northern corn leaf blight and tar spot. For soybeans, we have started to see sudden death syndrome (SDS). In addition to SDS, continue to scout for white mold, frogeye leaf spot, and other foliar diseases that impact soybeans. As far as insects, scout for defoliators such as Japanese beetle, and bean leaf beetle. Soybean aphids have been slow to develop so far, but we've had favorable conditions for populations to start building. Continue to scout for soybean aphid until the soybeans have reached the R6 (full seed) stage. Precipitation totals so far in August at the Northeast Iowa Research and Demonstration Farm near Nashua (NERF), is 2.96 inches and for the 2025 growing season (April 1 – August 17), we are at 28.28 inches. To put that into perspective, the historical 30-year average for the farm for the growing season is 30.42 inches. Last month (July) we ended up with a total of 11.01 inches of rain, which is 6.6 inches above the farm’s 30-year average July rainfall totals."
Josh Michel (Region 5):
Allamakee, Buchanan, Clayton, Delaware, Dubuque, Fayette, Jones, Linn, Winneshiek counties
“A few dry days allowed farmers to get back into the fields last week before severe thunderstorms came through over the weekend. Rainfall totals generally ranged from 1 to 2 inches. However, some isolated areas received up to 4 inches or more. In general, most corn fields are at R4 (dough stage) to early R5 (dent stage), while most soybeans are currently at R4 (full pod development) to R5 (beginning seed fill). Southern rust pressure continues to slowly increase, while tar spot has remained relatively low. While soybean-related disease concerns remain low, reports of SDS and white mold continue to show up in isolated areas. Corn silage harvest has started in some areas. Oat harvest is wrapping up, with nearly 90% of fields harvested. The third crop of alfalfa is nearing completion as well. Pastures continue to look good with ample rainfall over the past couple of weeks. The majority of field calls this past week centered around crop disease management and late season weed management.”
Meaghan Anderson (Region 7):
Boone, Dallas, Jasper, Madison, Marshall, Polk, Story, Tama, Warren counties
“Most of central Iowa made it through this last week with less than an inch of rainfall. Almost all of my counties are now over 20 inches of estimated rainfall since April 21 and parts of Story County sit over 30 inches of rainfall during the same timeframe. Corn is now mostly in the R5 growth stage, which means at least half of the final dry matter has been accumulated in most corn fields and kernels will quickly fill the rest in the last 30 days of growth. Soybeans are in the R5 to R6 growth stage. While phone calls have mostly slowed down, the one consistent thread in the last week continues to be questions about SDS in soybean and southern rust in corn. This was a banner year for disease. Now is a great time to get out and evaluate corn fields for yield estimates and to check on those corn leaves and see how bad the disease actually got. The Severity Estimate Tool from Crop Protection Network is a handy guide to help give you an idea of how bad disease pressure is on the ear leaf.”
Rebecca Vittetoe (Region 8):
Iowa, Jefferson, Keokuk, Poweshiek, Washington, Johnson counties
“Rainfall totals in my area over the last week ranged from couple of tenths to parts of Iowa County getting over 3 inches of rain. Most corn fields have now reached R5, and soybeans are mostly R5 to R6. Southern rust continues to be the hot topic in corn, but last week I also got a several calls on western bean cutworm feeding on corn ears. This is not typically a pest we see in this part of the state. I've also noticed it is easier to find corn aphids in the lower part of the canopy (below the ear leaf) in some fields. In soybeans, SDS and white mold were the big issues I saw or received questions on, which at this point in the season it’s past doing anything for them. However, it is good to note what you are seeing in your fields. I also have received several reports of fall armyworms in alfalfa fields that were being harvested for third cutting. Most of the armyworms were closer to 1.5 inches in size, which is when they will pupate. Continue to keep an eye on hayfields and pastures for this pest. We could see another generation of fall armyworms in 3-4 weeks. Besides the armyworms, forages and pastures look great for this time of year.”
Virgil Schmitt (Region 9):
Cedar, Clinton, Des Moines, Henry, Jackson, Lee, Louisa, Muscatine, Scott counties
"In general. the counties I cover received 0.5 to 1.5 inches of rain last week. Most corn is R5 with about ¼ milk line and generally looks good. Southern corn rust is showing up in many fields. Other corn diseases continue to easily be found. Soybeans are mostly R5 and generally look good. More spots of soybean sudden death syndrome are appearing. Generally, they are scattered plants in the field or patches in low spots or compacted areas, such as field entrances, fall 2024 grain loading sites, etc. Forages continue to look good. Calls last week mostly centered around fungicides and weed management. Western bean cutworm was reported in northwest Cedar County”
Aaron Saeugling (Region 10):
Adair, Adams, Cass, Clarke, Decatur, East Pottawattamie, Fremont, Mills, Montgomery, Page, Ringgold, Taylor, Union, West Pottawattamie counties
“As we make the final stretch for the 2025 crop, Mother Nature is making the final stretch difficult to say the least. Corn is now in the R4 (dough) to R5 (dent) stage of development. We can follow the starch line or commonly referred to as the milk line as the crop races towards R6 (physiological maturity). Dent stage of corn can take upwards of 30 days to complete and is a critical phase in kernel dry matter accumulation and weight. This year has brought unwelcome challenges, with southern rust, and corn insect pressure being the most common while moisture is adequate to excessive. Time will soon tell how this crop finishes, especially with the excessive moisture. Soybeans look good and are in the R4 to R5 growth stage. Rapid seed filling has begun and will utilize excess moisture to fill pods with seed development. When soybeans reach this stage of development, good nodulation is critical for nitrogen use in soybeans because root growth has slowed. Remobilization of nutrients is a key factor in development of seed fill. Late season challenges include weed escapes and rapid development of sudden death syndrome in fields. Hay and pastures are in an outstanding position for late season growth and a second cutting on grass hay. Quality will be an issue depending on the conditions after cutting and prior to baling. Remember to stack hay away from other bales and structures if baled a “little” wet. The hard part now is having patience in the last 45 days to finish the crop with few agronomic management decisions left to make, Mother Nature and Father Time are going to finish the season for us.”
Logan McCrea (Region 11):
Appanoose, Davis, Lucas, Mahaska, Marion, Monroe, Van Buren, Wapello, Wayne counties
“The last week has been a bit of a fresh air for SC Iowa, as after the precipitation that came through on August 11 and 12, it has been relatively dry compared to the past two months. This gave a great window for forage producers to get some hay put up. Notably, I have been hearing about quite a bit of fall armyworm activity across the area from those that were out in their hay fields as well as some retailers hearing from their growers. Other field agronomists across the southern portion of Iowa have been hearing reports as well, so get out and scout in your forages. The early morning or late afternoon works best for assessing the presence and determining if action needs to be taken. Much of the corn is in the R4 to R5 range, with plenty of disease pressure to go around. I have noticed some chopping equipment stirring, as that season will be upon us very soon. Soybeans are in the R4 to R6 range, with pod counts on plants appearing to be very high. SDS continues to pop up in fields with the ideal conditions that we had earlier on this spring/summer. Calls in the last week have centered around fall armyworms and corn/soybean diseases.”
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- Field Agronomist in EC/SE Iowa