This year we have seen slow early growth, reduced tillage, persistent rain and heavy storms. We have also seen an increase in corn-on-corn acres and other agronomic challenges. All these problems can add up to more inoculum in the field and poor overall health leaving plants more susceptible to infection. The early season diseases we think about with corn are typically Anthracnose and seedling diseases (V2-V8); however, Gray Leaf Spot, Northern Corn Leaf Blight, Goss’s Wilt, Southern Rust and Tar Spot can all show early foliar symptoms (V8-R4). Its important to note that bacterial diseases like Goss’s can’t be controlled with a fungicide.

There is very little economic support for early season fungicide application. Depending on the individual fungicide, you may see protection against disease for anywhere from 7 to 21 days. Be sure to check the label for specifics on how long they retain efficacy on the crop. If your focus is on Anthracnose, you may stave off the leaf blight phase of the disease, but this doesn’t mean that the stalk rot phase of the disease won’t infect the plant late season.

It’s also important to remember that coverage is critical with fungicides. This not only means good coverage during your spray operation with correction nozzles, pressure and volume, but it also means that if you spray early in the season, your corn will grow a new leaf approximately every 3-5 days with average GDUs. That new tissue is not protected because fungicides are not very mobile in the plant.

When to Spray? 

The best bang for your buck is still going to be around VT to R2 time period because you will be able to suppress diseases that may be present on the leaves and protect them for a few weeks of any diseases trying to get into the plant. Corn is also done putting on new leaves at this point. Typically a 5-8 bu/A yield increase will pay for the investment depending on grain price and application costs. If you are facing heavy disease pressure, be sure to select the right fungicide for the diseases you have. Fungicides with dual modes of action in the Group 3 (Triazoles) and 11 (QoI) will provide suppression and some lasting protection. Look for the active ingredients that end in “ole” (Triozoles) and “in” (QoI).

If you’re facing the fungicide decision to protect valuable yield in a tough year scout your fields for disease. If you don’t see any issues now, then skip an early application and focus on tassel. Take a look at the susceptibility of that hybrid to the disease you are seeing and then evaluate the weather outlook and if you’re in a corn-on-corn or reduced tillage situation. Lastly, monitor fields closely that had Tar Spot last season

It has been an interesting year with all the weather components we have had to face. If you have any questions, don’t hesitate to call in to the Latham Office.