Expect Sugarcane Aphids to Move North into Sorghum States
Not since greenbugs swarmed onto grain sorghum 80 years ago has there been an aphid wreaking as much havoc on grain sorghum acres as the sugarcane aphid. Until this year, much of the impact of these sucking pests occurred in the Gulf Coast of Texas and Louisiana. However, sugarcane aphids are following the wind stream north into key sorghum-producing states such as Oklahoma, Kansas, and Nebraska.
Sugarcane aphids – so named because they were first discovered in sugarcane plants – can damage grain sorghum in numerous ways. They can chew on young sorghum plants and thin out the stand until the plants reach reproductive stage. At that time, the aphids will chew on panicles, resulting decreased grain weight and resulting in yield loss. Finally, the aphids secrete “honeydew,” which covers the mature plants and makes harvest a sticky mess.
Mike Brewer, field crops entomologist with Texas A&M AgriLife in Corpus Christi, says damage from sugarcane aphids to sorghum topped $50 million last year; as the aphid spreads, damage could be much higher this year. Already, massive populations of the pest have been found in sorghum-producing regions of southern Texas and Louisiana.
“I think it is a good expectation that severity would increase. The worst-case scenario is that up to 50% of fields could be infected. Assume 50% yield loss, based on what we know from earlier aphid infestations, and we could have a $400 million economic loss statewide,” Brewer said at a meeting in Corpus Christi in January.
Sugarcane aphids overwinter in Texas, and reproduce in the spring. They are able to breed from two to seven days after birth, laying as many as 20 nymphs per cycle.
They simply overwhelm host plants, Brewer says. “Within six weeks of the first winged aphid landing on the plant, you will see sooty mold and honeydew. The plant begins giving out,” he explains. “On the positive end, it takes a lot of aphids before the plant succumbs to aphids sucking fluid out of the plant.”
In an interview with Kansas State University’s Radio Network, J.P. Michaud, Extension entomologist at K-State, says sugarcane aphids are expected to be in Kansas and Nebraska this season. “We can be fairly sure we will have some migrants arrive here at some time, but we don’t know how well they will survive,” he says.
Michaud urges producers to pay attention to sorghum fields throughout the growing season. The sugarcane aphids are tiny, greenbug-size whitish-buff pests. “They are noticeable because they have very short, black tailpipes on a very pale nymph,” he explains. “They colonize first on the underside of the lower leaves, and move up the plant as those leaves die. It is a very similar feeding pattern to greenbugs.”
There are no insecticides labeled for sugarcane aphid in grain sorghum, although there are emergency exemptions in Louisiana and Texas for Transform insecticide. In pre-boot sorghum, the treatment threshold is 150 to 200 aphids per plant. The threshold lessens as plants are smaller; Michaud says new plants can only handle 10 to 25 aphids per plant.
Michaud says that beneficial insects such as lady beetles could help suppress sugarcane aphids, but it may take a few years for that to happen. “It may be advisable to leave small areas of a field unsprayed in order to let first responders evolve into natural control,” he points out.