The hot and dry conditions this past week resulted in crops showing more signs of stress, especially in the drier parts of the state. Drought stress, spider mites, corn rootworms, and questions regarding fungicide applications were the big questions or issues observed by ISU Extension field agronomists this past week. Read on for more specifics on what's happening in different regions across the state.
Gentry Sorenson (Region 2): “There was no significant rainfall to report across the area this week. Rainfall would be welcomed with the forecasted high temperatures that are scheduled for this week. Stress has been observed from the dry conditions and high heat in the afternoon in the area. Corn growth stage is R1 to R2 and the soybean growth stage was R3 during field visits. Oats were harvested in the eastern counties that I cover last week, and hay was also cut last week. Spider mites were reported in a couple of soybean fields in Kossuth County. You can read about scouting and managing for spider mites here. When scouting soybean fields for insects it would be a good idea to scout for spider mites as well as soybean aphids. Field call questions were about corn rootworms, fungicide applications, insecticide applications for corn rootworm, and off-target injury to soybeans.”
North Central Iowa
Angie Rieck-Hinz (Region 3): “Corn is R2 to R3, and drought stress through parts of Hamilton and Hardin County is highly evident. Soybeans are R3 to R4. I have seen spider mites in fields in Hamilton and northern Story County. Spider mite damage is found in the lower canopy and looks like stippled or mottled leaves. They are found on the underside of the leaf and are very difficult to see without a hand lens. Place a white sheet of paper in between the rows and shake the beans over the paper. They will look like small specks of dirt moving on the paper. This 2018 ICM article provides a good reference for scouting and control. Disease pressure continues to be extremely low to non-existent and fungicide applications are nearing completions. The majority of the oats are harvested. Drought conditions are considered to be the biggest crop concern we have right now with the area from Ames to Webster City to Eldora looking the worst. Webster City and Eldora areas continue to be some of the driest areas with 45% and 46% of normal rainfall amounts from April 1 to July 27, 2021. Crop conditions north of Highway 3 look considerably better.”
Josh Michel (Region 5): “Most of NE Iowa has remained dry throughout the past week and over the weekend. Corn is generally around R1 to R2, and soybeans are generally around R2 to R3. Lack of rainfall and increased temperatures have slowed down alfalfa and pasture growth, resulting in several reports of increased potato leaf hopper activity. Oat harvest continues to take place with reports of average to slightly above average harvests and test weights. Recent field calls continue to center around herbicide drift complaints and damage to soybean fields. Other field calls have included questions regarding corn rootworms, potato leafhoppers, and fungicide applications.”
Meaghan Anderson (Region7): “The heat and lack of rain is beginning to cause some stress on central Iowa crops, but overall, the crops look remarkably good considering the conditions we’ve had this growing season. We continue to rack up the precipitation departure and the forecast looks daunting for rain chances to help alleviate any stress. Corn is mostly in the R1 to R2 growth stage and soybeans are mostly R2 to R3. Most phone calls recently regarding corn have been focused on fungicide applications and corn rootworm issues. Now is a good time to be checking roots for feeding and looking for adult beetles in fields. Most phone calls regarding soybean have been on fungicide applications and plant growth regulator symptoms. With the heat and drought conditions, spider mites are a significant concern in soybean (and possibly corn). I’d also encourage farmers in central Iowa to keep an eye out for symptoms of soybean gall midge along their field edges.”
East Central, Southeast, and South Central Iowa
Rebecca Vittetoe (Region 8): “This past week brought drier and warmer conditions. Corn is mostly in the R1 to R2 growth stage, and soybeans are R2 to R3. The pest of the week has been corn rootworm, either due to corn lodging as a result of root feeding and pruning from rootworm larave or concerns about the number of adults noted in field canopies. If you haven’t taken some time to check for rootworm feeding below ground, I encourage you to do so. Check out this video to learn more about souting and managing corn rootworm. Disease pressure is still low in both corn and soybeans. I’m just seeing a little gray leaf spot and have seen the tiniest amount of tar spot at the SE Research and Demonstration Farm near Crawfordsville this past week. In soybeans, I’ve seen just a little bacterial pustule, Septoria brown spot, and starting to see some sudden death syndrome (SDS) appearing in fields. With the warmer and drier conditions, don’t forget to keep an eye out for potato leaf hoppers in alfalfa fields and also spider mites in corn and soybean fields.”
Virgil Schmitt (Region 9): “Rainfall during the last week in the counties I cover was generally nonexistent, and temperatures were 2 to 3 degrees above normal. Corn is generally VT/R1 to R2 and soybeans are generally at R3. There are few insect or disease problems currently. Most oats fields are turning or have turned color. I have not seen any harvested yet, but harvest should start soon. Calls and farm visits last week mostly involved fungicide applications, soybean viral diseases, soybean cyst nematode, corn rootworms, and pasture weed management.”
Clarabell Knapp (Region 11): “This week temperatures were warmer, and rainfall only occurred in pop-up shower systems that scattered the region. Cornfields are in the R2 to R3 stage, and soybean fields are around R3 to R4. Disease pressure has been low but in a few later planted fields that had issues with wet feet, some physoderma brown spot is being seen. Second cutting for hay and alfalfa fields is still going strong. Potato leaf hopper burn is being seen fairly frequently in alfalfa fields. Oat harvested started this past week and yields have been above average.”
Check out the map below to find your local ISU Extension field agronomist and find their contact information here!