Corn rootworm, armyworms, wrapped tassels, and foliar diseases/fungicide application decisions were some of the concerns seen or heard from extension field agronomists in the last week. Read on for more specifics about what is happening in crop fields around the state.
Josh Michel (Region 5):
Allamakee, Buchanan, Clayton, Delaware, Dubuque, Fayette, Jones, Linn, Winneshiek counties
“Rainfall continued across most of the region last week with amounts ranging from 0.75 - 1 inch along the MN border, up to 2.5 inches of precipitation in areas along Highway 20 and south towards Cedar Rapids. In between rain showers, some producers were able to start harvesting oats and continue trying to finish up the second crop of alfalfa. I’d estimate that 80% of the oats have turned and harvest is expected to continue as the weather allows. In general, most corn fields are at VT (tassel) to R2 (blister stage), while most soybeans are currently at R2 (full flower) to R3 (beginning pod development). Low severity levels of gray leaf spot and northern corn leaf blight are starting to show up in several corn fields. I haven’t seen or heard any reports of tar spot at this time. I have heard several reports of armyworm feeding. Producers are reminded to continue scouting for them even if they apply an insecticide. Despite warm temperatures, many pastures continue to look good with the recent rainfall over the past couple weeks. The majority of field calls this past week centered around insect and disease management, and assessing various herbicide drift and crop injury reports.”
Rebecca Vittetoe (Region 8):
Iowa, Jefferson, Keokuk, Poweshiek, Washington, Johnson counties
“This past week brought more rain to add to our July 2025 totals. Most areas in the counties I cover received between 1 to 4 inches, though some localized spots saw over 6 inches. As a result, flooding did occur in these areas. Corn is currently ranges from VT/R1 to R2, while soybeans range from R2 to R4. One of the most common questions this week has been about tassel wrapping, along with concerns about foliar diseases in both corn and soybeans and corn rootworm pressure. If you’ve observed tassel wrapping in your fields, follow up and check pollination. In the ears I’ve examined from affected fields, pollination has been variable—some ears are fully pollinated, others show uneven timing with pollination, but the kernels pollinated, and some ears I’ve seen misses with pollination. Regarding foliar diseases, southern rust and gray leaf spot are the most common diseases I’ve observed in corn fields. The recent warm and humid conditions have been favorable for their disease development. I’ve also seen some northern corn leaf blight, tar spot (mainly in susceptible hybrids), and bacterial leaf streak. In soybeans, bacterial diseases are most prevalent, though I’ve also heard reports of sudden death syndrome showing up already. Continue to scout fields for disease pressure, especially southern rust and gray leaf spot. If you decide to spray, keep in mind that not all fungicides are effective against southern rust. Corn rootworm has been the main insect pest I had questions on this last week, including more reports of them causing issues in first-year corn. Now is also a good time to start checking soybean fields (look closer along field edges that butt up to where soybeans would have been last year) for soybean gall midge. Let me know if suspect you may have soybean gall midge. Forages and pastures are looking good, especially for this time of year. The biggest challenge continues to be finding a good window to cut and bale hay due to the wet conditions.”
Virgil Schmitt (Region 9):
Cedar, Clinton, Des Moines, Henry, Jackson, Lee, Louisa, Muscatine, Scott counties
“Most of the area I cover received from 0.5 inch to 2.5 inches of rain last week. Most corn is R1 to R2 and generally looks good. Low levels of many corn diseases can easily be found, but I have not yet seen a field requiring a fungicide application. Soybeans are mostly R3to R4 and generally look good. Minor insect (Japanese beetles and grasshoppers) feeding continues. There is little disease pressure. Forages are doing well but harvest of some fields has been slowed by rain. Calls last week mostly centered around herbicide drift and fungicides.”
Aaron Saeugling (Region 10):
Adair, Adams, Cass, Clarke, Decatur, East Pottawattamie, Fremont, Mills, Montgomery, Page, Ringgold, Taylor, Union, West Pottawattamie counties
“July 2025 will be one to remember as the year with ample July rainfall. So far this month, Atlantic, IA has received 5.94 inches of rainfall. This may feel excessive but do keep in mind that corn will use approximately 0.32 inch of water per day during the tassel through early dent stage. So, with that math the corn over the past 23 days has used 7.36 inches of water. With the recent rains, some minor ponding or flooding have occurred on lowland soils. Corn looks good for July with Japanese beetles and disease present. At this point very few corn rootworm beetles have been seen, possibly due to higher mortality due to saturated conditions. While I’ve seen little to no tar spot, southern rust is a disease I have been seen and is one to be watching and scouting your fields for. Soybeans are making use of the warm temperatures and sunshine to continue leaf development and pod initiation. Soybean will begin peak potassium uptake and use 3.5 to 5.2 pounds of plant available K2O per acre per day. If you start to see potassium deficiency showing up, think about if you have cut potassium applications in the past few years? Additionally, the above normal precipitation may provide more favorable conditions for disease development in soybeans. Continue to scout fields for diseases as well as for Japanese beetle damage. Forages and pastures are in good shape for July. The major issue with forage is the window to cut and bale due to wet weather, high humidity, and saturated soils. Additionally, the wetter conditions are making mowing for pasture weed control more challenge. Common pasture weeds this time of year include: Buffalobur, Hemp, Chicory, Prickly lettuce, and Wild Carrot. Mowing can be beneficial when done prior to seed production. If you do mow weeds in pastures, be careful of mowing Canada thistle this time of year due to the likelihood of spreading seed. A fall herbicide application is likely a better option now.”
Logan McCrea (Region 11):
Appanoose, Davis, Lucas, Mahaska, Marion, Monroe, Van Buren, Wapello, Wayne counties
“Over the past week, much of the region received anywhere from 1 inch to 4 inches of precipitation, with some isolated amounts coming in higher through parts of Lucas and Wayne counties. Much of the corn crop ranges from VT through R2/R3, with early reports of pollination looking good. Many soybeans are in the R2 to R3 range, and some ground rig applications of fungicide have started over the past week or so. Soybean disease pressure appears low, while corn diseases like southern rust and gray leaf spot are leading the charge. Forage wise, the wet summer has made cutting windows abrupt and much of the cuttings are overlapping now and beginning to get hard to keep track of. Pastures are hitting their summer slump but have held up reasonably well with the precipitation. Calls recently have mostly been around weed escapes, improving future hay production, and disease/fungicide questions.”
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- Field Agronomist in EC/SE Iowa