Regional Update: July 17-25, 2023   

July 25, 2023 10:50 PM
Blog Post

Limited rainfall, the hot weather this week, corn rootworm, weed escapes, insect defoliators, and questions on foliar fungicides have been the more common issues or questions Iowa State University Extension and Outreach Field Agronomists have seen or heard about over the last week. Read on for more specifics about what’s happening around the state.

Northwest Iowa

Leah Ten Napel (Region 1): “Corn stages are ranging from VT to R1. Soybeans are staging R1 to R3. There is very little disease and insect pressure in both corn and soybeans. Weeds are starting to break through the canopies, but crops are looking healthy overall. The moisture and cooler temperatures the last couple of weeks was very helpful for pollination, but things may change this coming week with warm temperatures and dry weather.”

Gentry Sorenson (Region 2) “The region did not receive any measurable rainfall last week. Per the U.S. Drought Monitor, my area ranges from D0 to D2 severe drought. D2 drought is affecting parts of Buena Vista and western Pocahontas County. Corn ranges from the R1 to R2 stage. Corn disease pressure is low in the fields that I have scouted. The soybean growth stage ranges from R2 to R3. Main questions regarding soybeans are about weed escapes. I have observed oat harvest in some areas of the region. Field calls or phone questions have been about herbicide carryover from counties that were dry last year and waterhemp weed escapes in corn and soybeans.”

North Central Iowa

Angie Rieck-Hinz (Region 3): “This past week brought very little, if any, rain to NC Iowa. Lawns are starting to turn brown and pasture growth and quality is quickly fading. Oat harvest has started. Corn is R1 to R3. Corn that has already pollinated looks good and is pollinated to the tip. Corn that will pollinate this week may experience more challenges due to the hot weather and dry conditions. Hot, dry weather can impact silk elongation and reduce pollen shed and viability. Disease pressure continues to be low in cornfields. I have found gray leaf spot, northern corn leaf blight and tar spot, but I have really had to hunt find any signs of corn leaf diseases. Corn aphids are starting to show up. Soybeans are R3 to R4. I have had two reports of white mold in soybeans, but I have not found it myself. I have seen Septoria brown spot (very commonly found in Iowa) and Sudden Death Syndrome (SDS) is just starting to show up.  I have yet to find any soybean aphids, but there have been a few scattered reports of low numbers of aphids.“

Tar spot (small black dot at the end of my thumb)  on corn in central Iowa. Found very low in the canopy and at very low severity. Photo credit: Angie Rieck-HInz, ISU. 

Northeast Iowa

Terry Basol (Region 4): “Crops are looking better than they should considering the rainfall we’ve received for the growing season so far. Corn is at the R1to R2 stage. Upper canopy leaves continue to be pretty clean of foliar diseases (including tar spot) but continue to scout and monitor. Tar spot has been confirmed in Bremer County in at least one field. To monitor confirmed tar spot for each county in Iowa, as well as other foliar diseases, check out the Corn IPM Pipe map here. The moisture that we received a couple of weeks ago has really helped, but we are starting to see some leaf rolling for corn that’s planted in fields with lighter soils due to dry conditions. Soybeans have also started to flip their leaves to help mitigate water loss in warm dry conditions. Soybeans are flowering and range from R2 to R3 stage for the area. Foliar diseases are also scarce in soybeans. Continue to scout for insect activity, particularly grasshoppers and twospotted spider mites. Favorable conditions for increased populations of twospotted spider mites are whenever temperatures are greater than 85°F, humidity is less than 90 percent, and moisture levels are low, which is like what’s forecasted for us here this next week. The last measurable rainfall for the area was received a couple of weeks ago, which averaged 1.74 inches according to the Iowa Mesonet, with accumulations over 3.0 inches in isolated areas. According to the Iowa Mesonet, the Northeast Iowa Research and Demonstration Farm near Nashua has only received 0.9 inch of rain so far for the month of July.”

Josh Michel (Region 5): “Scattered rain showers delivered anywhere from 0.10 to 0.50 inch of rain throughout NE Iowa last week and over the weekend. These timely rains were greatly welcomed as temperatures are forecasted to increase this week. Despite very low disease pressure, fungicide applications continue as most corn fields are VT to R2. Corn rootworm management continues to be a topic of discussion as adults are being observed. Japanese beetles can also be found along most field edges. Soybeans are generally around R1 to R3. Japanese beetles and grasshoppers continue to be the main leaf defoliators. Oats continue to be harvested for grain as all but a few of the fields have turned. Forage regrowth continues to be slow and potato leafhoppers can be found in most alfalfa fields. Field calls last week centered around fungicide applications and timing, soybean herbicide injuries, crop damage assessments, insect identification and forage management."

East Central, Southeast, and South-Central Iowa

Rebecca Vittetoe (Region 8): “Rainfall was basically non-existent across EC Iowa last week, but the slightly cooler temperatures last week were much welcomed. Corn ranges from R1 to R3. In the corn fields I’ve looked at that have pollinated, it looks like they pollinated well. Corn rootworm continues to be one of the bigger issues noted in corn fields, especially in first year corn along the Hwy 30 corridor. While I’ve had plenty of questions about foliar diseases in corn, I must look pretty hard to find any. In the fields I’ve been in across EC Iowa, I have been able to find gray leaf spot, tar spot, northern corn leaf blight, and common rust, but all at very low levels. Soybeans mainly range from R2 to R3. Like in corn, I’ve seen very little to no disease pressure in soybeans. The main insect pests I’ve seen so far are defoliators including grasshoppers and Japanese beetles. I've also had more questions on weed escapes in soybeans. Do keep an eye out for spider mites in fields this week. I did see some spider mite activity in a soybean field in northern Linn County early this week.”

Stippling on a soybean leaf due to spider mite activity found in a field in northern Linn County on July 24, 2023. Photo credit: Rebecca Vittetoe, ISU. 

Check out the map below to find your local ISU Extension field agronomist and find their contact information here


Rebecca Vittetoe Field Agronomist in EC Iowa

Rebecca Vittetoe is an extension field agronomist in east central Iowa. Educational programs are available for farmers, agribusiness, pesticide applicators, and certified crop advisors.

Areas of expertise include agronomy, field crop production and management of corn, soybeans, and...