Kentucky Corn: Keep Watch for Gray Leaf Spot
This is just a reminder of the factors that favor a positive yield response from a strobilurin fungicide in corn. Figure 1 lays this out graphically.
Disease pressure is, of course, the primary factor determining the probability of a benefit from a foliar fungicide in corn. With all the rain this season, gray leaf spot (Figure 2) may be widely active. Producers may wish to scout fields for evidence of disease activity.
Scouting guidelines for gray leaf spot originated from Iowa State University, and many universities have adopted these with little to no modification. They are:
1. Consider a fungicide application if:
a. The hybrid is rated as susceptible or moderately susceptible, AND,
b. 50 percent of the plants in a field have disease lesions present on the third leaf below the ear leaf or higher prior to tasseling.
2. Consider a fungicide application if:
a. The hybrid is rated as moderately resistant, AND,
b. 50 percent of the plants in a field have disease lesions present on the third leaf below the ear leaf or higher prior to tasseling, AND,
c. Additional factors or conditions that favor disease development are present (See Figure 1)
These are approximate guidelines, and the disease can be unpredictable. Nevertheless, these guidelines can be helpful tools in making rational spray decisions.
The cotton crop bug zoo is open for business and there’s more than plenty for everyone. Stink bugs and lygus are jumping from corn to cotton, while fleahoppers are entering