By Pat Miller,
Sugarcane aphids appeared in sorghum fields as far north as Boone County in the last week.
They worked their way north to central Missouri, according to retired University of Missouri Extension entomologist Ben Puttler. The aphids are low in number in central Missouri and not expected to cause economic damage.
However, MU Extension agronomy specialist Pat Miller, Vernon County, reported large numbers of the tiny aphids in the southwest region of the state three weeks ago.
Puttler says the tiny bugs are difficult to see. They are light yellow and have dark feet. Their dark parts at the rear look like tailpipes.
The bugs damage sorghums, including most sorghum-Sudan crosses. They also damage Johnson grass and dallisgrass.
Feeding damage causes discoloration of both sides of leaves. Sugarcane aphids suck plant juices and excrete a sugary, sticky liquid waste called honeydew.
The honeydew clogs harvest equipment, Miller says. Sticky material from plant juices gums up equipment.
Infestation of young plants can result in plant death. Late infestations can prevent grain from forming.
Threshold levels vary. “One conservative threshold is 25 percent infested leaves with 50 or more aphids per leaf at whorl from preboot stage through dough stage,” says Miller. “In other areas, the threshold at preboot and boot stages is 20 percent infested plants with large aphid colonies—100-plus—and localized areas of heavy honeydew present.
“From bloom through dough stage, the threshold is 30 percent infested plants. Either of these sets of thresholds should prevent serious yield losses and I would suggest using whichever threshold is easiest for you to use. Once threshold is reached, do not delay application because infestations can very quickly go from the threshold level to 100 percent infested plants and hundreds of aphids per leaf.”
Sugarcane aphids multiply quickly if pesticides are not applied. Their numbers can double every five to seven days under the right conditions.
Sugarcane aphids are difficult to control, Miller says. Farmers may need to spray as many as four times to control aphids. Pyrethroid insecticides are not effective and may flare infestations, Miller says. Most pesticides do not kill sugarcane aphids, she says.
Yields may be reduced as much as 50 percent, according to a 2013 study by Texas A&M Extension.