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Serving: Central

Southern rust hit in 2004: Should you spray corn with fungicide?

During 2004, Arkansas corn farmers expected a bumper corn crop, given good planting weather in March which resulted in excellent stands, ample summer rains, and mild temperatures during June and July. The crop looked great with high yield potential in June.

Then, for the first time in many years, southern corn rust appeared and caused problems across the southern two-thirds of Arkansas. Once infected with southern rust, leaves died prematurely and stalk-rotting fungi from the soil infected stalks, resulting in lots of lodged corn.

The bottom line was that instead of bumper yields, many farmers ended up with corn that lodged, which was very frustrating to harvest and resulted in lower than expected yields.

Southern rust was not the only foliar disease causing problems in 2004. Gray leaf spot and northern corn leaf blight damaged some fields, especially where corn was planted following corn. Crop rotation is very important to reduce the incidence of these two diseases.

“I started getting calls the third week of July”, said Rick Cartwright, University of Arkansas Extension plant pathologist. “And by that time, based on the literature and past experience, the crop was made. So I advised against applying fungicides. After looking at certain fields, it appears a fungicide application may have been a benefit.

“On the other hand, 2004 conditions may have been somewhat unique, so I doubt that growers would be justified in blanket spraying of fungicides every year. Clearly, we need to determine when and if fungicides are justified on field corn under various conditions.”

To address the question, the Arkansas Corn and Grain Sorghum Promotion Board recently funded a research project led by me, David TeBeest, and Cartwright to evaluate the use of foliar fungicides in corn. This research will be conducted at various locations across Arkansas to assess potential benefits from foliar fungicide use, including yields, test weight changes, and reductions in lodging under various disease situations.

Fungicide treatments will be applied in two cropping systems — corn following soybeans and corn following corn. Depending on the study, fungicide timing will include pre-tassel, tassel, silking-to-brown-silk, and grain-fill applications.

Observations on the first appearance of disease and severity of the disease in fields, and disease development over time at different locations will be made. An economic analysis of the results will be conducted.

In a separate study, TeBeest and graduate student, Jerry Moore, will assess the effect of a standard preventative foliar fungicide treatment on disease development on a wide number of corn hybrids. Their work will provide important data on the impact of fungicide use on disease development and corn yield response across a wide collection of corn hybrids that are currently being grown by Arkansas producers.

Over time, this work should provide corn growers with the decision-making tools needed to use foliar fungicides profitably and without risking loss of yield potential to foliar diseases.

Jason Kelley is the Arkansas Extension agronomist for wheat and feed grains.

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