Insights from CFE Agronomy Technologist Specialist Jeff Blauwet.
By now, hydraulics have been checked, filters and oil changed and seed is stacked on pallets in the shed, all ready for the 2026 spring planting season. Now comes the waiting: for soil temperatures to warm, fields to dry and for spring rains to show up in the forecast.
Technology today has taken preparing for spring planting beyond the grease gun and field prep. With a smartphone and an app, farmers can check two-week weather forecasts in seconds, taking much of the guesswork out of when that first seed can go in the soil.
Forecasting crop disease, however, isn’t nearly as simple. According to Jeff Blauwet, CFE Agronomy Technology Specialist, while tools and computer models continue to improve, disease forecasting still relies heavily on biology. What matters most is knowing which diseases can survive here, whether they’re already present and if the weather is lining up to let them get going. From there, growers can better gauge what risks are realistic and where management decisions might pay off.
Forecasting Biology
Crop disease forecasting starts with biology. Agronomists rely on what’s known as the disease triangle, which outlines the three conditions that must align for a disease to develop:
- A host crop
- Disease inoculum (spores or pathogens)
- The right weather conditions
If any one of those pieces is missing, disease doesn’t develop. Some diseases overwinter (survive cold winter temps) in crop residue and are already in the field when the season starts. Others, like southern rust, typically cannot survive cold winters and have to be carried north on air currents from the southern U.S. or Mexico.
Weather then becomes the wild card to forecasting. Temperature, humidity and leaf wetness all determine whether a disease stays quiet or explodes. Cooler, damp conditions favor some diseases. Warmer, wetter canopies favor others.
Hybrid selection adds another layer. Different hybrids have different disease tolerances, which can help growers prioritize where fungicide dollars will provide the most return.
Lessons From The Past Few Seasons
The last two years may have reshaped how many growers think about disease risk, especially when it comes to southern rust. Historically, southern rust has been rare in northwest Iowa. That’s why its return in 2025, and at even higher severity, caught many by surprise.
“Southern rust has always been a low-probability disease for us because it doesn’t overwinter here. We’d only seen it once in about 30 years before 2024. But having it show up two years in a row, and worse the second year, really caught everyone’s attention,” states Jeff. “At the same time, tar spot is now here, and it can overwinter, which changes the long-term risk if the weather lines up.”
While southern rust drew attention recently, tar spot has quietly re-entered the picture. First detected locally in 2024, infections remained light and did not impact yield. However, because tar spot can overwinter in crop residue, its presence carries longer-term implications. After two consecutive seasons, inoculum is now assumed to be present across much of the CFE area, increasing future risk if late-summer conditions turn cool and wet.
Your CFE agronomist can help you understand the disease risk factors in your fields and make fungicide decisions accordingly.
What’s Brewing for 2026?
Looking ahead to the 2026 growing season, the odds of another severe southern rust outbreak remain low. A cold January pushed freezing temperatures far south, making it harder for southern rust inoculum to survive and reach Iowa. While back-to-back years are possible, history suggests the risk is minimal.
Tar spot, however, is a different story. Because it can overwinter in residue, cold temperatures do not reduce its presence. If late summer turns cooler and damp, tar spot has the potential to escalate quickly. Other familiar diseases like Goss’s wilt, gray leaf spot and northern corn leaf blight, which also overwinter, remain weather-dependent and will continue to surface when conditions are right.
One thing that hasn’t changed in forecasting crop health is unpredictability. July moisture, dense canopies, hail damage and wind events can all create ideal entry points for disease. Think of a leaf like your skin. If you have an open wound, that wound is more apt to get infected if not protected. The same with a leaf, hail and wind damage can make a plant more susceptible to disease.
Managing Risk
Disease forecasting will always involve some level of probability, but there are ways growers can manage risk without treating every acre the same.
Focus on diseases that can overwinter. Southern rust grabbed headlines the last two seasons, but from a planning standpoint, the bigger concern are diseases that are already here if weather conditions turn favorable. Think Goss’s wilt, gray leaf spot, northern corn leaf blight and now tar spot.
Understand your seed’s limitations. Once disease risk becomes clearer, hybrid ratings become a management tool. If conditions begin to favor disease development, fields planted to hybrids with weaker tolerance are more likely to move to the top of the list for closer monitoring and, if needed, fungicide applications.
Think preventatively, but selectively. Most fungicides work best as prevention. Once disease is visible, yield loss may already be occurring. At the same time, spraying every acre by default may not be realistic or economical. The goal is to identify which fields are more likely to respond and focus inputs where they have the best chance to pay.
Watch weather trends, not just symptoms. Extended leaf wetness, cooler temperatures and dense canopies are often better indicators of disease risk than what’s immediately visible in the field. Short-term forecasts help identify when conditions are lining up before symptoms fully show.
Factor in real-world application timing. Unfortunately, in-season decisions don’t happen on a schedule. Weather delays and application backlogs all affect timing. Waiting until disease is confirmed in a field can mean missing the window entirely, which is why proactive planning often outperforms purely reactive approaches.
Eliminating The Crystal Ball
No one can predict the season with complete certainty. But as Jeff notes, today’s technology is doing a better job of forecasting disease risk. Tools like those from the Crop Protection Network help growers assess the probability of disease developing in their fields and track how diseases are moving across the region. This information supports better planning before problems show up.
Disease forecasting is not about knowing exactly what will happen. It is about understanding what could happen and being prepared when conditions line up. After the past two seasons, growers have a clear reminder that rare does not mean impossible, and that preparation still pays.
As Jeff puts it, “It’s all probability. But the better you understand the biology and the environment, the better decisions you can make when it counts.”
If you would like more information about preventing disease in your fields this growing season, contact your CFE agronomy team to discuss what makes sense for your acres. <<
