Blog

I recently attended the Iowa State University Weed Science Field Day at the Curtiss Farm outside of Ames. During this field day, I noticed an area of shorter, yellow corn as compared to the surrounding corn (Figures 1 and 2). My initial thoughts were 1) this area was a wet area and probably had experienced significant denitrification, or 2) perhaps they missed applying nitrogen in this research block. 

Tassels shedding pollen while still wrapped in the flag leaf is an uncommon occurrence in Iowa and across the Corn Belt. I think I've only seen it once before in my 20+ year career as an agronomist. However, based on conversations with colleagues, it appears to be widespread throughout the region. It does not seem to be brand-specific, but it does appear to be hybrid-specific.

Over the past few days, I have received several reports of southern rust from southwest and southeast Iowa.  In addition, I and others have observed southern rust in central Iowa (Fig. 1). Incidence (number of plants affected) and severity (area of leaf diseased) is very low (Fig.2). 

Fig. 1.  Map showing counties where southern rust has been observed in Iowa (July 16, 2025). This map available at CPN is updated daily as reports are received. 

With older tools like Tarspotter and Sporecaster no longer supported, the Crop Protection Network (CPN) has introduced the Crop Disease Forecasting Tool, a new free web-based tool to assess risk for diseases in corn and soybeans. This tool builds on years of university-led field data collection and modeling to provide field-specific risk forecasts for foliar diseases.

July typically brings a lull in soybean diseases. By this time, plants have grown out of early-season issues, and late-season diseases usually haven’t arrived yet. But every season brings its own challenges. With the frequent rains this year, some of the typical “August diseases” are starting to show up earlier than expected.

Are you seeing Japanese beetles in field crops? Watch this 4-minute video to learn more about how to estimate Japanese beetle defoliation and use economic thresholds in soybean: 

 CPN: Soybean insect defoliation training tool link

Agronomists have discovered several new populations of Palmer amaranth across Iowa in the past couple years. These finds have again reminded us the importance of paying attention to those weeds and making sure you know for a fact that the waterhemp is just waterhemp. 

Asian copperleaf (Acalypha australis) remains a new species of concern in Iowa. Currently, we’re aware of infestations in eight Iowa counties: Calhoun, Humboldt, Wright, Boone, Franklin, Hardin, Grundy, and Black Hawk (Figure 1). This species is often first detected at harvest, where farmers discover a carpet of green plants under corn and soybean canopies. Now is a great time to look for this species and other new weeds (like Palmer amaranth) when scouting fields.

Like Alison remarked last year, this is another big season for bacterial leaf streak (BLS). I’ve seen low levels in numerous fields, but one field yesterday stopped me in my tracks, an obvious susceptible hybrid. A casual observer may mistake BLS for gray leaf spot (GLS). While GLS can be effectively managed with fungicide, BLS cannot. Take care to distinguish between the two when scouting fields before fungicide applications in the coming weeks.

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?