As grain sorghum harvest picks up in South Texas and the Coastal Bend, Texas AgriLife researchers, pest management specialists and county agents are reporting increased sugarcane aphid (SCA) activity in the Lower Rio Grande Valley.
"I have received several calls that sugarcane aphid populations are growing again in grain sorghum fields that have not been harvested," reported Dr. Raul Villanueva, assistant professor and Extension entomologist, Texas AgriLife Extension -Texas A&M University South District 12. "They can be found in all green areas of leaves and are moving into the panicles but not causing damages yet."
Villanueva and Integrated Pest Management specialist Danielle Sekula-Ortiz began inspecting fields across the Valley early this week and report heavy populations of aphids even in fields being harvested.
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"We noticed the sugarcane aphids are feeding on any green parts of the plants they can find and we saw many aphids on combines, but there has not been enough honeydew to cause problems to the combines yet," she said.
Last year Upper Coastal Bend and Louisiana producers experienced gumming problems in their combines associated with harvesting plants with heavy deposits of honeydew caused by heavy sugarcane aphid populations.
But Villanueva says because of last year's late season problems with the aphid, researchers have been warning producers all across the Southeast and Southwest to scout regularly for signs of SCA infestations.
It was long into the growing season when Deep South Texas growers began spotting signs of aphids moving into sorghum fields. Almost overnight, the problem intensified significantly with population levels jumping from a few hundred to thousands of aphids per leaf.
Sekula-Ortiz says that’s when staff at the Texas A&M Extension and Research Center in Weslaco staged a producer meeting to alert farmers of the developing and critical explosion of the pest.
"We had pest specialists from across the border in Mexico attend the meeting, which attracted about 200 producers and pest specialists," she said. "It was a consensus opinion that a concentrated spraying effort be launched on both sides of the border in an effort to reduce populations all at the same time."
The strategy worked well over the following weeks. By the second and third weeks of June, the area-wide infestation had been reduced to low numbers with some fields reporting 90 percent to 100 percent kill.
The treatment of choice was Dow AgroScience's Transform, a chemical that received Section 18 approval for use in Texas grain sorghum in late April of this year. One of the advantages of Transform is the residual characteristic. Travis Hirst, with Dow AgroScience's Southwest District, says effective residual can last up to 21 days.
Section 18 guidelines allow Texas growers to spray twice with Transform this year with no more than three total ounces of Transform.
Mike Bowers, Texas AgriLife entomologists at the Texas A&M Research Center near Corpus Christi, says another effective chemical to fight sugarcane aphids in grain sorghum is an older and reliable chemical, Dimetholate.
"We're looking at a much shorter residual period, maybe seven days plus, but it performs exceptionally well against this aphid," Bowers told Coastal Bend producers during a June meeting held to discuss the spread of SCA into the Coastal Bend. But producers must be aware of pre-harvest interval limitations associated with Dimetholate.
While grain sorghum has only recently reached full maturity in the lower Coastal Bend, a few producers have chosen to apply harvest aids to fields to help dry down sorghum. A few of those fields now have been harvested with great success.
While aphid infestation levels in the Coastal Bend mirrored those experienced in the Valley in a few fields, treatment options were initiated slightly sooner, and many growers opted to treat initially with Dimetholate and followed that with Transform only after SCA populations began growing again.
Texas A&M researchers in the Valley are not recommending spraying again "this late in the game," but say they are recommending that producers speed up harvest activities and get the grain out of the field as soon as possible.
A few sorghum producers in the Valley have expressed interest in planting a second crop, and the sooner harvest is complete, the sooner SCA populations will fall, allowing sufficient time to get the new crop into the ground.
While South Texas has been the focus of SCA problems so far this year, the sugarcane aphid is making problems for growers not only in north Texas now, but also, like last year, in southern and central Louisiana. David Kerns, associate professor of entomology at the LSU AgCenter at the Macon Ridge Research Station, is recommending growers consider spraying a high rate of sodium chlorate plus 1 percent crop oil to dry down the upper sorghum plant to prepare for harvest if harvest is too near to allow for most commercial harvest aids.
"Last year when we were having such a terrible problem with honeydew at harvest time, there wasn't enough time to use Roundup or other harvest aids, so we discovered that by using sodium nitrate and crop oil, we could dry the sorghum plant about half way down and could still roll combines within three to seven days." Kerns said.
Producers who didn't use a burn-down lost as much as 6 percent of their grain last year because of gumming problems in the combine.
Kerns says heavy infestations of SCA are in Louisiana fields again this year but growers have had good success with Transform. He warns that most sub-tropical sorghum fields are far too close to harvest to use Dimetholate as a 30-day pre-harvest interval is required after use. He didn't rule out use for early stage development.