- Associated Press - Friday, March 7, 2014

WINNSBORO, La. (AP) - LSU AgCenter scientists are warning Louisiana farmers about a new pest infiltrating sorghum crops, and urging them to be on the lookout.

Entomologist David Kerns, in a news release Thursday, says sugarcane aphids were seen infesting sorghum in Louisiana, Mississippi, Texas and Oklahoma last year. Kerns said it’s now been found in johnsongrass, sweet sorghum and sorghum-Sudan.

“Aphids also were found in one state in Mexico, and Arkansas may be infested,” Kerns said.

He said the pest was detected in 38 counties and parishes in the four states.

The sugarcane aphid has been found in sugarcane in Louisiana since 1999. It’ a significant pest of sorghum in China, Taiwan, Japan, India, South Africa, South America, Botswana and Zimbabwe.

There was one unconfirmed report of an infestation in Louisiana sorghum in 2008. Infestations also were found in sorghum beginning in mid-July. Kerns said it is not known why the pest shifted from sugarcane to sorghum.

“It is interesting that in places where there were heavy infestations of sugarcane aphids in sorghum in 2013, the aphid was not found in nearby fields of sugarcane, energycane or Sudan grass,” Kerns said.

Injuries to sorghum by aphids include drying of plant tissue, which causes the plant tissue to become red, or purple, and die. In addition, dry conditions make the aphid problem worse. Aphids also interfere with crop harvest.

“The number of aphids needed to cause yield loss depends on plant growth stage, plant moisture stress, and duration of the infestation,” Kerns said. Direct yield loss is unlikely once sorghum is at the milk stage, but late infestation affects harvest efficiency, he said.

Grain sorghum is planted in south Louisiana between April 1 and May 1 and in north Louisiana between April 7 and May 15. Crops planted later normally will suffer from more severe insect and disease pressures, Kerns said.

“Grain sorghum is typically harvested in August in Louisiana,” he said.” By far the most severe issues that the aphid caused in 2013 were those associated with harvest efficiency.”

Large aphid infestations at harvest can result in accumulations of honey dew, sooty mold, and the aphids themselves on the leaves, which can clog combines. Farmers reported as much as 50 percent grain loss from clogged combines in 2013. Dry weather can accelerate these accumulations.

A late-season infestation of sugarcane aphids can result in a delayed harvest of up to 14 days, seven days is the average, as well as additional application expenses and possible moisture issues at the elevator, he said.

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