Sugarcane aphids take an unexpected nosedive in South Texas, Mexico

WESLACO  —  In an unexpected turn of events, insect populations of the sugarcane aphid on grain sorghum fields in South Texas are extremely low, possibly due to a combination of both weather and science, according to experts at the Texas A&M AgriLife Research and Extension Center at Weslaco.

Dr. Raul Villanueva, a Texas A&M AgriLife Extension Service entomologist, said he and other experts were expecting damaging, high numbers of the insect in this year’s crop.

“By the end of April, we noticed that we just weren’t seeing the population outbreaks that we were expecting,” he said. “Very few fields have populations of the sugarcane aphid and those that do are easily controlled with insecticides.”

Sugarcane aphids feed on plant leaves, leaving a sticky waste called honeydew to clog up harvesting equipment, Villanueva said. Once in the grain head, they can keep the grain from maturing, reducing both quality and quantity. They also force growers to spend money on insecticides to control them.

Sugarcane aphids were first reported in the U.S. in Florida in 1977 in sugarcane. In Texas, they were first found feeding on sorghum near Beaumont in 2013. By October of that year, the new sorghum-feeding biotype had spread to the Rio Grande Valley. They then made a northward trek through Texas and beyond.

“By October 2014, the aphid had reached about a dozen states in the south and several states in Mexico,” Villanueva said. “It spread much farther and faster than anyone had predicted and quickly became the No. 1 pest in grain sorghum.”

But this year, the insect appear to be all but gone from South Texas, including the Coastal Bend area, which also suffered high populations last year, according to Robert Bowling, an AgriLife Extension entomologist at the Texas A&M AgriLife Research and Extension Center in Corpus Christi.

“To date, the sugarcane aphid has been hard to find in most sorghum fields along the Coastal Bend region of Texas,” Bowling said. “Slow sugarcane aphid population growth here may be associated with heavy rain events and early season natural enemy activity such as ladybugs and parasitic wasps.”

Bowling said some areas of the Coastal Bend were starting to see increased aphid populations this week, including Atascosa and Jackson counties, where insecticide treatments will likely start next week to control the “moderate to heavy sugarcane aphid populations in scattered sorghum fields,” he said.

Mexico is also seeing reduced populations, Villanueva said.

“There could be one or several factors playing in our favor,” he said. “One is the weather. Rain, overcast skies and high humidity help keep populations down. Also, growers are planting sorghum varieties that have a tolerance for sugarcane aphids. We now have two approved insecticides that are highly effective, and we are seeing abundant numbers of natural enemies. One or a combination of all these factors is likely reducing sugarcane aphid populations.”

Natural enemies include a fungus that grows on the aphid like an infection and eventually kills it, Villanueva said. Other abundant predators and parasites include numerous species of ladybugs, syrphid – or pollinator – flies, wasps and chrysophids, or lacewings.

“Mexico, which has a more advanced growing season than South Texas, is also seeing fewer sugarcane aphids,” he said. “Like many of us in the U.S., Mexican growers are more concerned now about too much rainfall this year.”

Lower Rio Grande Valley growers usually plant some 400,000 acres of grain sorghum, most of which is usually exported to Mexico as cattle feed, although most of last year’s crop was exported to China.

“This sudden drop in populations has been a pleasant surprise for everybody,” Villanueva said. “We were expecting a very bad year for sugarcane aphids. But, the season is just beginning and we’ve had staggered and late planting dates due to rain delays. So, growers and consultants still need to keep an eye out for sugarcane aphids and midge, especially late in the season.”

To help stakeholders monitor populations of sugarcane aphids, AgriLife Extension has printed laminated information cards, “Scouting Sugarcane Aphids,” that help determine thresholds for effective insecticide treatments. Villanueva will soon be translating the information to Spanish to help Mexican growers, which should help prevent insect migrations to Texas, he said.

After the initial sugarcane aphid outbreak, AgriLife Extension and Texas A&M AgriLife Research confronted the situation on many levels, including conducting research into the insect’s biology, holding field days to keep growers informed, testing insecticides for efficacy and coordinating area-wide synchronized spray treatments.

AgriLife personnel also collaborated with Dr. Scott Armstrong, a U.S. Department of Agriculture scientist, to identify grain sorghum varieties with tolerance to the invasive pest.