Plant pathologists are advising Louisiana and Arkansas producers to scout for  Southern rust after heavy infestations were reported in early- to mid-July.

According to Trey Price, LSU AgCenter plant pathologist at the Macon Ridge Research Station, a moderate to heavy infestation of Southern rust was found in a fungicide trial at the LSU AgCenter Dean Lee Research and Extension Center in Alexandria and in commercial fields in southwest and south central Louisiana. Lighter disease levels have been observed in northern Louisiana.

Corn planted in mid- to late-April is more susceptible to the disease,” Price said. “If corn is in the milk to dough stage right now, you should be scouting for it.”

Strobilurin and triazole fungicides may help reduce the effects of disease if an infected crop has yet to reach the dent stage, Price said. After the dent stage, fungicides likely will not provide an economic benefit.

Fungicide applications, if warranted in late-planted corn, will slow disease development and preserve yield, Price said.

The disease infects leaves and interferes with photosynthesis, resulting in reduced yield from decreased kernel development. The disease usually starts on lower leaves and spreads upward.

“Warm, humid conditions with consistent rainfall are ideal for Southern rust,” Price said.

According to University of Arkansas Extension plant pathologist Travis Faske, Southern rust was detected on July 7 near McGehee, Eudora and Rector.

Rector said in a University of Arkansas blog, “The current weather forecast of scattered showers this week in much of the state will provide good conditions for rust development. Given the favorable conditions and how far the spores can spread on prevailing winds, southern rust will likely be found this week in other fields.”

Faske recommends that growers scout fields to determine if a treatment is warranted.

Price said variety trials at the Dean Lee Center may help reveal which hybrids have resistance.

The start of Louisiana’s corn harvest is three to six weeks away