The sugarcane aphid, Melanaphis sacchari, is a new and potentially serious pest of grain sorghum in Texas. It was first identified in North Texas in 2013 when it infested thousands of acres of grain sorghum. It’s back earlier this year.
The sugarcane aphid first came to my attention when growers began calling me about harvesting difficulties associated with the heavy coating of honeydew on the plants. The honeydew, a sticky sugary substance secreted by the aphids, was gumming up the augers in the combines and grain wagons. Upon further inspection of these plants, I found huge populations of this aphid, coating the underside of the leaves and the stalks. I believe the aphid arrived late enough in the growing season that it did not significantly reduce yields last year.
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It came in earlier this year and poses a significant threat to grain sorghum in North Texas. I could find some aphids in almost every field I inspected on July 1, with damaging numbers in a few fields. Research is currently underway to determine a damage threshold for applying an insecticide, but definitive results are not yet available. We are using an action threshold of 30 percent to 40 percent infested plants to trigger an insecticide application.
I would define an “infested” plant as one with at least one aphid colony (one or more adults with multiple nymphs) on at least one leaf. Leaves from the mid an upper canopy should be inspected (10 upper leaves and 10 mid leaves per location) from 5 to 10 locations across the field. Avoid sampling field edges as aphid populations are often higher on borders than in the middle of the field. Where aphids are found, check fields every 3 to 4 days to determine if the population is increasing. Sticky honeydew on the leaves is a good indicator of their presence.
The sugarcane aphid has explosive reproductive capability, unlike any other aphid pest we have observed in grain sorghum. Beneficial insects can help reduce lower populations of this pest, but they cannot keep them in check when the populations explode. We think the sticky leaf surfaces may help protect the aphids from predators and parasites.
When a damage threshold is reached, we suggest the use of a new insecticide, Transform, to reduce sugarcane aphid numbers. Transform was recently approved under a Section 18 emergency exemption for Texas and has provided the most consistent control and longest residual of anything that tested. It also appears to be easier on beneficial insects, which may be needed later in the season to keep sugarcane aphid populations from resurging. Transform use rate for sugarcane aphid is 0.75 to 1.5 ounces per acre. Be sure to use an adequate amount of water to penetrate the foliage and get coverage on the lower leaves. Read the label thoroughly before mixing and applying.