Corn and grain sorghum producers in Louisiana encounter similar challenges when trying to manage foliar diseases that threaten crop yields and quality.

AgCenter plant pathologist Trey Price is conducting a series of ongoing research projects to develop management strategies, including fungicide efficacy studies.

“We are looking at which fungicides work best on different foliar diseases and what application timings are most beneficial at various stages of plant growth or if a fungicide application is needed at all,” Price said.

Years of data collected on similar trials indicate that no benefit exists for applying a fungicide on sorghum in the absence of disease, he said, adding that growers frequently used this strategy in the past when commodity prices were higher as a type of insurance against disease infestation.

“We can manage many foliar diseases proactively to save input costs,” he said.

In corn, northern corn leaf blight and southern rust traditionally cause the most concern among growers, while other less common pathogens, such as anthracnose, southern corn leaf blight and gray leaf spot, can be occasionally problematic.

Each year, official experimental and commercial hybrid corn trials are rated for naturally occurring diseases at multiple research stations across the state.

“Ratings from the official hybrid trials are notoriously inconsistent because the location is rotated each year, resulting in low disease pressure,” Price said.

At the Macon Ridge Research Station, Price has initiated an exact duplicate of the official corn hybrid trial in a nearby field where he has grown corn for many years in a no-till cropping system. The duplicate trial is an important part of the study as it provides more favorable conditions for disease development.

“By planting corn exclusively on these plots and keeping debris levels high, the pathogens living on that debris will overwinter, improving our chances for seeing heavier disease pressure in that canopy,” he said.

“We then can provide growers with a better set of disease ratings,” he said.

Other corn research projects include potential threshold development for foliar diseases and novel disease discovery.

Curvularia leaf spot was recently discovered in Louisiana and will be monitored to determine if significant losses occur and if hybrids exhibit resistance.

“If previously unreported diseases start to emerge, we want to identify them and develop the integrated disease management strategies needed to help producers manage them,” he said.

The same research concepts used in corn will be applied to study foliar diseases in grain sorghum.

“Grain sorghum seems to be more susceptible to foliar problems, especially in a wet year,” Price said, adding that even in dry conditions, a long dew period overnight can drive foliar diseases in sorghum.

Anthracnose is the most common and destructive foliar disease in grain sorghum in Louisiana, but target leaf spot, gray leaf spot and zonate leaf spot can also be challenging.

A significant amount of the research concerning foliar diseases is aimed at developing improved recommendations to aid growers with their seasonal integrated disease management decisions.

There is limited information pertaining to hybrid susceptibility for these foliar diseases, so screening for resistance presents an excellent opportunity to provide producers with economical management options, Price said.

“Resistant hybrids cost the same as susceptible ones, and the most important decision in disease management is hybrid selection,” he said

Head blights in sorghum also cause significant concern for growers, Price said, particularly in the central part of the state when rain frequently interferes with harvest season.

Fungicides are not effective on head blights; therefore, identifying hybrids that are resistant to head blights is important, he said.

Grain sorghum hybrid trials will be conducted at three AgCenter research stations — Macon Ridge in Winnsboro, Northeast in St. Joseph and Dean Lee in Alexandria.

“The greatest contribution from this research is identifying hybrid susceptibility to foliar diseases and head blights so we make accurate recommendations to growers,” Price said.

Karol Osborne

AgCenter plant pathologist Trey Price scouts for foliar diseases in official hybrid corn trials conducted at the Northeast Research Station in St. Joseph.