By Del G. Voight, M.S., Senior Extension Educator - Agronomy

Figure 1 Penn State SEAREC- 2014 Corn Response to Fungicide Applications- D.G. Voight and A. Collins.

During times of continued wet, humid weather, many growers ask about foliar applications of a fungicide on tasseling corn. Research performed in 2014 at the Southeast Agricultural Research and Extension Center (figure 1) tested 4 different fungicides on corn, with products applied at the V5 and R2 (blister) stages.

In 6 out of the 10 treatments, there was a significant response to the application of a fungicide exceeding 11 bu./acre. However, the decision is not as much which product to use, but whether the hybrid will respond to an application. And in the case of this study, the hybrid used was susceptible to leaf diseases.

When considering products and their effects on specific diseases, Purdue Extension’s Fungicide Efficacy for Control of Corn Diseases is an excellent starting point.

When asking whether a fungicide application is necessary, consider the following criteria:

1. Disease history: Low-lying fields with a history of disease are more likely to respond to a fungicide.
2. High-yield history: High-yield fields are more likely to show an economic response.
3. Hybrid resistance: The lower the genetic resistance to gray leaf spot, northern corn leaf blight and anthracnose, the more potential for an economic response.
4. Crop rotation: Corn following corn tends to harbor more disease inoculum.
5. IPM: Corn diseases are just starting to appear, especially in no-till corn-on-corn fields. Fields that already show 5-10% visible disease may have a higher risk of further development.
6. Fertility: Low potassium (K) levels and compacted soils could exacerbate disease effects on lodging and yield. If the field has poor fertility, the likelyhood of increased disease invasion is higher.

If one or more of these criteria apply to your situation, then a fungicide application may provide an economic return and it may be time to discuss options with your agronomist or seed supplier. Both growers and agronomists should consider conditions field by field and take action from there.

Most labels dictate that applications be made between the VT and R1 stages. In addition, the labels I reviewed also require that adjuvants are not to be used after corn has reached the V8 stage. Some recent research has shown that beer can ears can result from the application of adjuvants near VT.

In addition, growers may be tempted to add additional products to the tank while going over the field. Most labels allow for the inclusion of insecticides, but the labels also caution that growers only apply approved tankmixes and observe the most restrictive labeling.

Finally, on some products, there is a 30-day harvest restriction for forage and grain, so bear in mind that an early forage harvest might need to be delayed should an application be made.