New threshold and monitoring recommendations save sorghum growers at least $25 million

In July 2013 the sugarcane aphid, or Melanaphis sacchari (Zehntner) was reported on sorghum in Texas. By the end of November the pest had spread through Texas and into Oklahoma, Louisiana and Mississippi. In addition to decreasing sorghum yields, the aphid produces a sticky resin called honeydew that causes the grains to stick to the plant, clogs up harvesting equipment, and attracts other insects and fungi. The pest has infested between 25 and 50 percent of fields in south Texas. Losses in South Texas range from $5.6 million to $62.5 million per year.

Sugarcane aphid, natural enemies, credit T. Ahrens, Del Mar CollegeSugarcane aphid overwinters in remnant sorghum in harvested fields and johnsongrass. With no threshold or monitoring protocols, growers have been forced to use pesticides preventatively, before knowing whether aphid populations are reaching a problematic level. More recently scientists have discovered natural enemies and parasitoids.

By conducting intensive sampling of sugarcane aphid populations through the southern Texas and Louisiana region, Brewer and his team were able to establish monitoring recommendations and action thresholds that would allow growers to manage the aphid while maintaining predator populations. An experiment that compared the effectiveness of insecticide sprays on susceptible and resistant sorghum crops helped develop a threshold of 50 to 125 aphids per leaf, pre-head emergence. When growers sprayed when aphid counts were at threshold, they were able to reduce aphid populations to manageable levels, while only slightly reducing predator populations.

Monitoring efforts as a result of the new protocols showed that aphids had spread further north than expected, into the Great Plains to southern Kansas. Research and outreach activities from the project resulted in the effective control of the sugarcane aphid over about 400,000 acres of sorghum, at a benefit of $25 to $50 million for 2014. Savings were at least doubled, based on prevented losses.

Photo: Sugarcane aphid, natural enemies (syrphid fly and lady beetle adults), and sooty mold on sorghum leaf. Credit: T. Ahrens, Del Mar College