Regional Update: July 31 – August 8, 2023

August 8, 2023 4:31 PM
Blog Post

While some much welcomed rain fell across most of the state over the last week, parts of NE Iowa missed out on the rain and other parts saw 6+ inches of rainfall. From the field, aphids (in corn and soybeans), spider mites, soybean gall midge, concerns about tar spot, and downy mildew in soybeans were some of the issues or topics of questions Iowa State University and Outreach Field Agronomists received last week. Read on for more specifics about what’s happening in fields around the state.

Northwest Iowa

Leah Ten Napel (Region 1): “Significant rainfall was received across NW Iowa this past weekend. Rainfall totals ranging from 2 to 10 inches! This rainfall came at a critical time as crops had just dealt with a stressful period of hot, dry weather the week prior. Some wind came with that system, but little crop damage has been reported. Soybeans are staging around R4 to R5, and corn is staging R3 to R4. Disease and insect pressure remain low in this part of the state. When scouting some producers are seeing adult rootworm beetles in corn and gull midge in soybean fields. The question I get asked most is about tar spot. At this time it has not been reported in our area. Check out this website for more on tar spot IDs across the state.”

Gentry Sorenson (Region 2) “The region received rainfall through the weekend which was welcomed. Rainfall ranged from 1 to 3 inches per observations submitted to the CoCoRaHS website. Before the rain, areas that were short on rainfall in corn and soybean fields were showing drought stress. Corn is around the R3 growth stage. Corn disease pressure remains low in the fields that I have scouted.  The soybean growth stage ranges from R3 to R4. I have heard scattered reports of soybeans aphid present and of a few fields that have been treated. I have also received phone calls with questions on two-spotted spider mites.”

Northeast Iowa

Terry Basol (Region 4): “Crops are hanging in there. Corn is at the R3 to early R4 stage, depending on planting date. Upper canopy leaves still remain pretty clean of foliar diseases (including tar spot), but it’s always important to continue scouting and monitoring. According to the Corn IPM Pipe Website, both Floyd and Bremer counties have at least one field that’s been confirmed with tar spot. The last week has been fairly dry, with the crops showing signs of moisture stress, as corn leaves are rolling and soybeans are flipping their leaves to mitigate water loss, particularly in parts of the fields with lighter soil textures. We’ve been getting reports of  aphid colonization and activity in the northern counties of Iowa, especially for the NC and NE part of the state. Soybeans are flowering and range from R3 to early R4 stage for the area. Again, the same for soybeans in regard to foliar diseases, whereas leaves in the upper canopy are looking pretty clean with a low incidence of pathogens. Continue to scout for insect activity, as we’ve heard reports of two-spotted spider mite activity in the area due to favorable conditions for development. For the NE Iowa Research and Demonstration Farm at Nashua, the last couple of weeks have been dry. According to the Iowa Mesonet, the farm has received a total of 0.56” of rain from July 23 through August 7. The largest portion of that was received this past Sunday, August 6 with 0.29 inch. For the area, amounts ranged from 0.25 to around 0.5 inch for most of the area on Sunday, with isolated areas receiving more." 


To help give a perspective of where we are in the state regarding this season’s rainfall for the growing season, this map shows the precipitation departure from normal (1951 – 2022 climatology) in inches for the time period of April 1 – August 8, 2023. Source: Iowa Mesonet.

Josh Michel (Region 5): “Most of NE Iowa remained dry over the past week, except for a couple isolated showers that went through over the weekend delivering up to 0.25 inch in a few areas. I continue to find very low disease pressure as fungicide applications are finishing up in both corn and soybeans. Corn and soybeans are both generally around R3 to R4. Japanese beetles and grasshoppers continue to be the main defoliators in soybeans, while corn rootworm adults can be found in some corn fields. Oat harvest is finishing up across the region with many reports of average to slightly above average bushels per acre. The third crop of alfalfa has been ongoing with reports of potato leafhoppers being found in many areas. Field calls last week centered around fungicide applications and timing, insect thresholds, and small grains and forage management.”


In general, tar spot remains at low levels in NE Iowa. If you can find it, it's not uncommon to just see one lesion on a leaf that is lower in canopy (below the ear leaf). Photo credit: Josh Michel, ISU. 

Southwest Iowa

Aaron Saeugling (Region 10): “Needed rainfall fell in areas that have been dry all season to help elevate recent moisture stress. Corn is mainly in the R3 to R4 stage. Pollination looks to be good despite dry conditions. Farmers have reported tip back. The picture below was taken from a dry part of Pottawattamie County and these ears are from 11 consecutive plants in a row, no cherry picking. You be the judge on final yield. Isolated reports of tar spot continue to come in with most reporting low incidence of the disease. Soybeans range from R3 to R5 stage depending on planting date and maturity. It appears the fuller season maturity soybeans may benefit more from the recent rains. Soybean disease in general appears light but reports of white mold, sudden death syndrome (SDS), and brown spot have been received. This week’s soybean photo was also taken from dry portions of Pottawattamie County. After walking both fields, I will make the general comment I am pleased with the corn outlook and disappointed in the pod count on the soybeans. I do know the soybeans are an early group 2 soybean and may have been too far along to benefit in pod count from last week’s rain.”


Eleven consecutive corn ears collected from a field in a drier part in Pottawattamie County. Photo credit: Aaron Saeugling, ISU. 


Soybean pod count collected from a soybean field from the drier portion of Pottawattamie County. Photo credit: Aaron Saeugling, ISU. 

East Central, Southeast, and South-Central Iowa

Rebecca Vittetoe (Region 8): “Over the last week, particularly over the weekend, we received some much-welcomed rain in EC Iowa. Rainfall totals for the week ranged from about a 0.25 inch to over 4 inches. Some isolated areas had closer to 6 to 7 inches Sunday into Monday. Corn is mostly in the R3 to R4 stages and soybeans are mostly R4. While it looks like corn fields pollinated fine overall, I have noticed some tipping back due to the drier conditions in areas as well as some pod abortion in soybeans. Gray leaf spot and tar spot can be found in corn fields across EC Iowa, but in most you must look for them. There have also been some reports of northern corn leaf blight and Goss’s wilt. Overall, disease pressure remains at pretty low levels. Corn rootworms continue to be the main insect pest of concern in corn. In soybeans, downy mildew is more prevalent in fields. As a reminder, fungicides aren’t effective on this disease. Other diseases I’ve either observed or confirmed in soybean fields include some SDS, mainly in Mahaska and Marion counties, and white mold. Last week we did add four new counties in Iowa that have soybean gall midge, including one in EC Iowa – Marion County. Other questions coming in have been on plans for late summer seeding of forages as well as for seeding cover crops this fall.”


Soybean gall midge was confirmed in Marion County as well as three other counties in Iowa this last week. Photo credit: Rebecca Vittetoe, ISU. 


Downy mildew on a soybean leaf. If you look on the underside of the leaf, you will likely see fuzzy growth. Photo credit: Rebecca Vittetoe, ISU. 

Virgil Schmitt (Region 9): “Rainfall in the last week in the counties I cover ranged from over five inches in parts of Des Moines and Lee counties to less than 0.5 inch in Clinton and Jackson Counties. Most corn is R3 to R4 and generally looks good to excellent. Most soybeans are R4 and generally look good to excellent. Phone calls, emails, and field visits last week mostly involved two-spotter spider mites in soybean, grasshoppers, and the need, or lack thereof, for fungicide applications.”


Source: mrcc.purdue.edu/CLIMATE/Maps/stnMap_btd2.jsp. 

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

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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...