Blog

Finding the first Japanese beetle each June is a point of pride for some, including folks in my lab. They found adults in corn this week. Hurrah!? Checking the accumulating degree days for 2025 confirms they should be emerging all throughout Iowa. They need about 1,030 growing degree days (base 50°F) to complete development and will continue emergence until around 2,150 degree days.  

Weeds have been a continual challenge in recent years, but this year has to have been one of the most challenging in recent memory. We've heard of numerous issues: dry soil conditions, herbicide drift and intense winds, preemergence herbicide injury, sprayer clean-out problems, waterhemp control issues with preemergence and postemergence herbicides. How do we better manage some of these challenges that don't seem to be going away?

Tar spot was observed in Poweshiek county on 13 June 2025.  This is no surprise! In previous years, tar spot was observed on 30 June 2022, 23 June 2023, and 7 June 2024 in Central Iowa.

The triangle rules!

Fairly widespread precipitation fell across Iowa at the beginning of June. Approximately 80% of the state received at least 0.5 inches of rain on June 3^rd. Localized areas received greater amounts of rain where thunderstorms popped up.

With many corn fields across the state reaching that V5 to V9 growth stage, they are getting a dark deep color and rows in some fields are getting close to canopying. Soybeans in general seem a little slower this year and could really use some sunshine and heat. Herbicide injury, weeds not dying, IDC in soybeans, and Rapid Growth Syndrome in corn were some of the issues or concerns heard or seen by ISU Extension field agronomists this last week.

The Crop Protection Network (CPN) has launched an exciting new free resource, the Crop Risk Tool, designed to give farmers the power to better understand the best time to manage foliar diseases in corn and soybeans. This tool is the culmination of many years of pathologists walking fields collecting disease data to provide field-specific risk values to guide timely and informed fungicide decisions. 

Stalk borer can be a reoccurring pest along the edge rows of corn adjacent to perennial grass borders, waterways, or terraces. The caterpillars move from grasses to corn when the stalk gets too small. Like all insects, they develop based on accumulating temperatures and right now, you could expect to see caterpillars moving throughout the southern half of Iowa. 

Maintaining healthy pastures is critical for supporting livestock productivity and forage quality. But weeds can threaten those goals by outcompeting desirable species, reducing grazing efficiency, and in some cases, posing toxicity risks to animals.

It was a warm, dry, and windy week across the state last week. Planting is winding down across the state, and the early planted corn fields are reaching the V4-V5 stages and soybeans earlier planted soybeans are around V1. Weeds coming through PRE herbicides, soil crusting, replant decisions, sand-blasting/leaf-tattering, and herbicide/seed treatment injury were some of the common issues or concerns heard by the ISU Extension field agronomists.

Soybean sudden death syndrome and Phytophthora root and stem rot reduced soybean yield by 57 million bushels in 2024. This cost soybean farmers $576 million, or $6.40 per acre of soybeans planted. 

Extension workers from universities across the U.S. engage in research and outreach to help farmers and industry manage these crop diseases. One way soybean stem disease information is made available is through the Crop Protection Network (CPN).

The week of May 11 – May 17, 2025 was another relatively quieter week for both black cutworm and true armyworm moth across the state.

A total of 33 black cutworm (BCW) moths were reported last week, with no significant flights being reported. As a reminder, now is the time to be scouting for black cutworm based on our predicted cutting dates from significant flights from earlier this spring combined with growing degree days. 

During the past two weeks, temperatures across the state have been warmer than normal, as much as 0-8 degrees above average. Northwest Iowa has had the largest departure from normal during this time period. Spotty precipitation has fallen across the state in the past 14 days, with southeast Iowa receiving the largest amounts at around 1 inch. Despite that, the entire state is below average for precipitation during the last 14 days.