Kendal Wright made a good grain sorghum crop last year, one of the best ever. The 2014 crop, he says, “could be better. It looks excellent.”

So he doesn’t intend to let a heavy infestation of sugarcane aphids jeopardize his chances. “Aphid populations are getting pretty bad,” he says. “So far, we’ve only had to spray 800 of the 2,500 acres of milo we plant.” He farms with his father, Kenneth, in Hunt County, Texas, about 100 miles east and a bit north of Dallas.

“We’re keeping a close eye on aphid numbers,” Kendal says. “They can go from just a few to a whole lot in a few days. So far, we haven’t had a lot of damage, but we’ve seen a lot of honeydew.”

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They had that last year, too, a sticky, shiny secretion aphids leave on plant leaves. Kendal says it was so bad last year he thought he had a fluid leak from his combine. “It can be a nightmare if you don’t take care of the aphids.”

The potential for damage is greater this year, says Jim Swart, Texas AgriLife Extension integrated pest management specialist.

“They came in late last year,” Swart says. “They didn’t cause a lot of yield loss but they did create some harvest problems with the honeydew. They started about three weeks earlier this year, and we’ve seen a lot of honeydew. We’ve been watching closely since they identified infestations in South Texas and moved north.”

Economic thresholds

He says Extension specialists have worked out some basic treatment thresholds for application of Transform WG insecticide, a product made available this year with a Section 18 special exemption from EPA. The product has performed well with “not a lot of damage to beneficial insects. As infestations get heavy, we will need the beneficial insects to help control the sugarcane aphid.”

Swart checked several fields earlier this week, one that had not been treated and several that had been sprayed. The untreated field was heavily infested, yellow aphids crawling over the underside of most leaves and the top of the leaves slick with honeydew.

He found very few live aphids in treated fields, and suggested kill rate was close to 99 percent. Instead of the yellow, active aphids, leaves had “white specks, the cast off skins of dead aphids on the grain sorghum leaves.”

Swart says farmers should consider spraying Transform if they find 30 percent to 40 percent infested plants.”

“Transform is working,” Kendal says. “A field we sprayed last week has no aphids left.”

“The aphids just showed up here in northeast Texas the last week to 10 days,” says Allen Knutson, AgriLife Extension entomologist in Dallas. “Now is the time to be scouting fields for the aphid.”

New sorghum pest

The sugarcane aphid is a new challenge for grain sorghum producers. “It became a pest of sorghum for the first time in Texas in 2013,” Knutson said. The same year outbreaks occurred in South and East Texas, Louisiana, Oklahoma and Missouri.

Knutson agrees with Swart that the pest poses a much greater threat this year than it did last summer when it showed up in Northeast Texas grain sorghum fields too late to cause much damage.

Sugarcane aphids are a light green and somewhat yellowish in color, Knutson says. “It’s very tiny; a colony the size of nickel will typically be comprised of 30 or 40 individual aphids. It’s unlike any of the other aphids we have in sorghum.”

Damage results from aphids feeding on plant sap. The fed-upon leaves discolor, turning yellow, red, and brown. Extensive leaf injury can greatly reduce grain yield. The honeydew poses a risk to harvest machinery.

As Kendal Wright notes, the population can explode quickly. “Infestations can increase very rapidly, so fields should be inspected every three to four days to determine if an insecticide treatment is needed,” Knutson says.

Swart says about one-third of the grain sorghum in Northeast Texas has reached the application threshold and has been treated. Beneficial insects also are helping to keep the pest below treatment levels in some fields. Kendal says one field he was getting ready to spray last week has seen aphid number drop below the threshold level. He believes beneficial insects have helped knock the population back.

“I hope we don’t have to treat all our sorghum acreage,” Swart says.

Harold “Thump” Witcher, an agronomist for CPS in Paris, Texas, says sugarcane aphid infestations have been heavy in his areas but some farmers have been reluctant to spray. And some of those have seen populations decline after a few days. Beneficial insect predation is the most likely reason for the reduced numbers.

Witcher says the heaviest infestations he’s seen are at the turn rows. “After we get into the field we see some honeydew and expect to see aphids on the underside of the leaf above the honeydew. But we often don’t find many.”

He agrees that uncontrolled aphids can create a harvest headache. “It makes harvest difficult.” He says the sticky secretion can gum up combines and coat seed to the point that it causes problems in the elevator. Spraying with Roundup a week before harvest, he adds, dries out the plant and lessens the honeydew issue.

Keep Scouting

Swart cautions growers who are seeing honeydew and aphid numbers beginning to build to watch closely to prevent a population explosion with potential yield loss and harvest issues. Some reports from the Lower Rio Grande Valley and the Coastal Bend area indicate untreated sorghum fields can lose as much as 50 percent of yield potential.

With a good crop in the balance, needing maybe just one more rain to finish it out, Kendal Wright is not taking a chance on aphids. He’s hoping he doesn’t have to spray all his fields, but he’s watching closely to be prepared to treat if he needs to.

So far, North Texas is the northernmost boundary of heavy sugarcane infestations, but a few have been identified in a USDA-ARS test plot on a research station near Lane, Okla.

“An ARS researcher found a few,” says Lindsay Kennedy, external affairs director for the National Sorghum Producers in Lubbock, Texas. “We’ve seen them move from South Texas into central Texas and now into the Northeast part of the state.”

Kennedy says farmers in South Texas have been successful treating the pest with Transform. “We keep telling folks that Transform works.” Farmers in south Texas are seeing some aphid populations building back in late harvested sorghum, but treatment may not be necessary in those late maturing fields, she says.

Kennedy says grain sorghum producers should continue to scout fields until near harvest time as populations of the new pest can explode quickly. “And it takes more than a windshield observation,” she says. “Farmers need to get into the field and turn up some sorghum leaves.”

Pest management experts are still trying to get a good read on economic thresholds on a pest that is a new threat to grain sorghum. The 30 percent to 40 percent infestation rate remains the standard. And Transform has been effective in controlling the aphid without damaging populations of beneficial insects.

Kennedy says, long-term, growers may see aphid-resistant hybrids available. “ARS is screening for resistance, and they have identified some promising lines.”