“What diseases should I be looking for this season? How can I prevent or treat them?”
These are questions we commonly hear from customers this time of year. As we progress through the hot summer months, the threat of disease looms in fields.
Kurt Maertens, technical agronomist at BASF, joined Dr. Jake Vossenkemper to discuss what to expect for fungal diseases this season and best management practices for fungicide application in our latest L.E.A.D. Academy Webinar.
If you have high-performing fields, you may wonder whether a fungicide application is necessary. In a 2020 study on soybeans, we found that high-yielding fields actually see an even bigger impact from fungicide and insecticide applications.
In the study, we tested a set of “normal management” plots and a set of “high yield management” plots. The study was conducted over three sites and replicated a minimum of six times per site.
In the end, we saw a yield increase of 5.5 bushels per acre in the normal management and 8.1 bushels per acre in the high yield management category, all from an R3 fungicide and insecticide application.
Identifying Fungal Diseases in Corn
Common diseases we are seeing in corn in Eastern Iowa and Western Illinois include Gray Leaf Spot, Northern Corn Leaf Blight and, on the top of many farmers’ minds, Tar Spot. Generally, moisture and temperature determine which of these diseases we see in fields, and to what extent.
Gray Leaf Spot
Gray Leaf Spot is distinguished by long, rectangular lesions that may resemble a cigar. Some hybrids handle Gray Leaf Spot a little bit differently and may have smaller lesions. If left untreated, Gray Leaf Spot will continue to grow and take over the leaf area throughout the season, affecting yields.
Tar Spot
Tar Spot has become fairly familiar to farmers in the Eastern portion of the Corn Belt, but others in the West may experience the disease for the first time this season. As its name implies, Tar Spot lesions look like small raised flecks of tar on the leaf surface—almost like a paintbrush was flung towards the plants—and cannot be rubbed off with a fingernail.
This disease can be very hard to see at first because those first few tar spot lesions are often very small and infrequent. But, as the disease progresses, the spores multiply and the quantity of lesions on your leaves are very noticeable. By the end of the season, you may have leaves completely covered in them. And, based on what we’ve seen in fields, this progression can be very rapid.
Overwintering is another important consideration for Gray Leaf Spot and Tar Spot. The spores from disease last year overwinter in the crop residue, just waiting for the right weather conditions to multiply and infect fields this season.
Rust
Rust is another disease to keep in mind. Tar Spot is easily confused with rust, especially early on. However, Tar Spot lesions are much deeper brown—almost black—compared to the orange or red appearance of rust.
There are two primary species of rust we see in our customers’ fields: Southern Rust and Common Rust.
Common Rust is more frequently seen in our service area than southern rust, but Southern Rust has a more serious impact. Common Rust typically shows up as a raised lesion with a dark red color, and there may be three or four lesions in any given area.
Southern Rust lesions are more light red to orange in color and have a lot of powder. If you knock a leaf and orange powder comes off, it’s most likely Southern Rust. We see some instances of Southern Rust almost every year, but the big concern is when it arrives. If you suspect you have Southern Rust in your fields, contact us right away for help controlling this very aggressive species.
Identifying Fungal Diseases in Soybeans
Septoria Brown Spot
The most common soybean disease we see around Eastern Iowa and Northwest Illinois is Septoria Brown Spot. This disease usually starts at the lower canopy and works its way up, slowly impacting yield potential and resulting in significant losses at harvest. It’s important to protect all of the leaves on soybean plants, because they all help build sugar, produce pods and increase yields. Learn more in one of our weekly short videos on the soybean fungicides.
Frogeye Leaf Spot
In other areas, Frog Eye Leaf Spot is of greater concern. We are seeing some resistance to certain fungicides in that disease. If Frog Eye Leaf Spot infects a field, it produces a larger lesion that can have detrimental effects on soybeans.
Frog Eye Leaf Spot in soybeans is similar to Southern Rust in corn. It’s not a common occurrence every year, but when it does appear, it can drastically lower yields.
Much like the corn diseases, Frog Eye Leaf Spot and Septoria Brown Spot overwinter in last year’s crop residue, waiting for the right weather conditions to appear.