Sugarcane aphid numbers are increasing rapidly in the Texas Lower Rio Grande Valley and appear to be moving into corn as well, according to several Texas AgriLife Research and Extension reports.
Charles Allen, Texas AgriLife Extension Statewide IPM coordinator, San Angelo, in an email this week to Southwest Farm Press said a combination of factors including recent rainfall that may have forestalled some aphid population decline, aphids infesting grain sorghum heads and aphids moving into and reproducing in corn fields “affects control options.”
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Allen also noted that although sorghum growers in the High Plains may be concerned, so far no one has seen the pest west of Interstate 35. “Currently its known distribution on sorghum is the Lower Rio Grande Valley, the Coastal Bend, the Texas Blacklands to the Red River and into southern Oklahoma, through Louisiana to eastern Mississippi.”
Also, a recent report from Texas AgriLife media specialist Rod Santa Ana, Weslaco, warns that South Texas grain sorghum producers should be on the lookout for the new insect pest, which, if left unchecked can “wipe out their entire crop.”
Santa Ana referred to recent reports from Raul Villanueva, an AgriLife Extension entomologist, and Danielle Sekula-Ortiz, an AgriLife Extension integrated pest management agent, which indicate “explosive populations of sugarcane aphids at levels never seen here before.”
Field Day Scheduled
Because of those heavy infestations Texas AgriLife will host a “Sugarcane Aphid Informative Meeting and Field Day” from 9-10 a.m. May 20 at the Texas A&M AgriLife Research and Extension Center at Weslaco, located at 1015 E. U.S. Highway 83. (For more information, contact Villanueva or Sekula-Ortiz at 956-968-5581.)
“We saw damaging populations of the sugarcane aphid in grain sorghum late in the season last year, but we didn’t see any major problems in the head, where the grain is produced,” Villanueva said. “We were hoping it was a one-time event or only a late-season event, or that it wouldn’t affect the head.
“But it’s now obvious that is not the case. We started seeing very high populations three weeks ago, about the time plants were putting out their grain heads.” Without treatment, the insects migrate from lower leaves to the head, the “cash crop” area of the plant, Sekula-Ortiz said.
“Why populations increase so dramatically at this stage is not known,” she said. “It could be environmental, in that they prefer higher temperatures, or that the aphids prefer mature plants, or that the seed treatment, which is designed to protect the plant from aphids in the plants’ early stages, simply wears off. Or it could be a combination of those factors.”
Regardless, if growers don’t treat before they migrate to the head, serious crop losses can occur.
She strongly advises scouting. “If you have a sorghum field completely headed out, and you have not sprayed for sugarcane aphids, or were not aware of this pest, check or have your consultant check your field,” she advised in her weekly newsletter, Pest Cast. “You probably have heavy sugarcane aphid infestations and will need to spray. The sugarcane aphids are being observed on grain sorghum that is just about to head to sorghum that is already heading.”
Sekula-Ortiz says growers or consultants should check field edges and on the bottom stalks for signs of infestation. “You may notice honeydew or sooty mold on your stalks starting at the lower leaves; this is an indication of high sugarcane aphid populations. You will also notice a slight glistening on the leaves; this is honeydew, deposited by sugarcane aphids feeding, that then falls onto the lower leaf. Inspect underneath the leaf above. Sugarcane aphids populate in much greater numbers than the yellow sugarcane aphid and are a lighter yellow in color.”
The yellow sugarcane aphid affects the lower leaves of plants, Villanueva said. Because it is present only during a plant’s early stages, its populations are kept in check by seed treatment and do not pose a problem.
Sekula-Ortiz said aerial and ground applications are providing adequate control. “In two different locations when the spray was conducted by ground using drops on a boom it provided great control. Air and ground sprays should use the highest rates of water to provide good coverage.”
Currently, no treatment threshold exists for sugarcane aphids since it is a new pest in sorghum in Texas and the nation. “We are recommending that you do not let infestation levels exceed 30 percent to 50 percent since they are hard to control,” Sekula-Ortiz said.
She recommends using drops on spray booms and hollow cone nozzles to apply the chemical under the bottom leaves where aphids feed. “A surfactant helps ensure thorough coverage. A high rate of water, 15 to 20 gallons per acre, is recommended for good coverage. The main thing is to keep infestations of the sugarcane aphid from infesting the sorghum head.”
“The aphids consume the plants’ chlorophyll and interfere with the plants’ photosynthesis,” Villanueva said. “So it’s very important that growers spray a recently approved insecticide before the aphids move up into the head, or panicle.”
Once aphids migrate to the head of the sorghum plant, yields are reduced because grains don’t mature; they fail to grow to normal size or numbers, Villanueva said.
EPA has authorized a Section 18 to Texas Department of Agriculture for the use of Transform WG (sulfoxaflor) on sorghum to control sugarcane aphid (Melanaphis sacchari) as of April 24, 2014. “Hopefully, that will help avoid serious crop losses in the current crop of about 250,000 acres, planted in mid-February to be harvested in late June or early July.”
Because of its subtropical climate, Lower Rio Grande Valley growers typically plant a second, much smaller crop of about 50,000 acres in August, which they typically harvest in December.
“The sugarcane aphid…is a serious threat,” Villanueva said. “As are most aphid species, it is parthenogenetic, meaning populations are all female and don’t require a male to reproduce. When populations become overcrowded, some develop wings and fly off to other fields or plants to colonize there. As soon as they land they don’t lay eggs, they simply give birth to new female aphids. That’s one reason why populations can quickly spread and reach critical levels.”
Aside from the Rio Grande Valley, the sugarcane aphid has also been reported this year in Mexico, Corpus Christi and Beaumont. Both Villanueva and Sekula-Ortiz believe populations will continue moving north as they did last year when they migrated as far as Oklahoma.