Populations of the sugarcane aphid in Texas, a recent bane of sorghum growers, have been well below the threshold level for treatment, but the recent warm and dry weather suits the aphids just fine.
That was the word from Texas AgriLife Extension Agronomist Ronnie Schnell at last month’s Stiles Farm Field Day near Thrall. He delivered good news and bad news to the sorghum growers in the crowd.
“Sorghum looks real good here this year. We have a good crop coming,” Schnell said, but added, “We also have sugarcane aphids coming.”
The wet, cloudy and cool weather over much of the state this spring kept populations in check early, but the weather now favors the aphid, he said. They hit their reproductive peak when it gets hot, which is especially bad news because a sugarcane aphid embryo already has an embryo inside it, giving newborn aphids the chance to reproduce without waiting for nature to take another course.
“They’re born pregnant, and with this heat, they’ll reproduce very quickly. If you find winged aphids up high, they will move down the plant to get out of the heat. Check five or six spots around the field,” Schnell advised.
Sugarcane aphids are tiny and pale yellow with dark cornicles and antennal tips. They feed on the underside of sorghum leaves, which become shiny with honeydew. Winged aphids appear when numbers reach a certain level, allowing them to fly away from the crowded conditions, thereby expanding their range. They don’t inject toxins into the plant but they cause its leaves to turn purple and then yellow before they die.
Most of the damage the sugarcane aphid does is indirect, a result of the large quantities of honeydew they secrete in large quantities to keep predators at bay. The gooey honeydew, sometimes accompanied by a black, sooty mold fungus, inundates the plant leaves and jams up combines at harvest, slowing the harvest and often fouling the equipment in the process.
The aphid, first discovered in this country in Florida in 1997, has been in Louisiana since the 1990s, but it caught Texas agriculture by surprise by just showing up here three years ago, with no advance warning of its arrival. It packed another surprise — the sugarcane aphid switched from feeding on its namesake plant to munching on grain and forage sorghum.
Some farmers lost 25 to 50 percent of their yields in 2013 and others suffered a total loss, either through the loss of the plant or because of damage to combines caused by honeydew. Last year it expanded its range to several other states, but infestations in Texas weren’t as heavy as many had feared.
Schnell said the mild winter helped aphids overwinter here, mostly hiding out in Johnson grass. He said farmers, Extension agents and researchers found them as far north as Lubbock. He emphasized that the aphids will show up this year and urged producers to continue scouting for them.
Extension sets the control threshold for SCA at about 100-250 aphids per plant but also suggests taking action when the plants have 50-125 aphids to account for preparation time.
Transform WG from Dow AgriScience and Sivanto 200Sl from Bayer CropScience are the most common and effective chemical treatments for the aphid. The Environmental Protection Agency (EPA) banned Transform after a Ninth Circuit Court of Appeals questioned its safety for pollinators, but earlier this year the EPA approved a request by the Texas Department of Agriculture for a Section 18 emergency exemption use of the product on up to 3 million sorghum acres in the state.
The new emergency use label for Transform in Texas addresses pollinator concerns by banning applications from three days before bloom all the way to seed set.
Schnell emphasized that the aphids won’t affect the yield this year but could still cause damage at harvest time.
“The yield is pretty much set with this crop,” Schnell said. “We’re not going to lose yield to the sugarcane aphid, but we do have to worry about a clean harvest so we don’t have issues with our combines.”