As sorghum planting has concluded across the Coastal Bend Region and good stand establishment has been observed, growers should be watchful for the sugarcane aphid to move into fields. The aphid may be a new variant of sugarcane aphid, Melanaphis sacchari, which has a high preference for sorghum.
An outbreak of this invasive aphid was discovered damaging grain sorghum in Texas, including Nueces County, and neighboring states in 2013. Infestations detected were very heavy, often with hundreds of sugarcane aphid per leaf. Leaves became sticky and shiny from honeydew and coated with sooty mold fungus, which hampered harvesting operations. The 2013 outbreak appeared late in the season; however, it caused severe damage in infected fields.
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Texas A&M AgriLife Extension Service and AgriLife Research personnel have been monitoring aphid populations on Johnson grass, as well as production fields of sorghum throughout the region. One or two winged aphids have been observed in a handful of locations across the Coastal Bend Region on remnant sorghum and Johnson grass, which means we could see winged aphid flights in a few weeks. While they are poor fliers, winged aphids have the ability to get up into the air enough to be carried by the wind to infest new areas.
So far, we have not observed sugarcane aphids in any of the recently emerged sorghum fields in Nueces County. Most, if not all, sorghum fields were planted with insecticide treated seed that should control the aphid the first 3 to 4 weeks after planting. At this time in Nueces County, most grain sorghum is 2 to 4 inches tall.
This aphid does not currently appear to vector any type of plant disease and plants do not show “warning signs” such as yellowing of lower leaves as they typically do for other aphid species. However, as the aphid load builds up on individual plants they eventually succumb and quickly defoliate. This highlights the need for continued scouting of fields during the growing season and much sooner than when we start scouting for head worm.
The Texas Department of Agriculture is working through the process to obtain a Section 18 label from the Environmental Protection Agency to permit applications of Transform WG to control this pest. They anticipate having a decision soon.
An economic threshold for this pest needs to be determined. Entomologist say growers will not need to treat at the first sign of this pest because it does not appear to vector any plant disease. Sorghum should tolerate a fairly heavy population before treatment is necessary. However, when populations of sugarcane aphids are increasing rapidly, insecticides may be needed to prevent yield losses and honeydew buildup before harvest. More detailed information about the sugarcane aphid can be found in a newly released extension publication ENTO-035 “Sugarcane Aphid: A New Pest of Sorghum.”