Winged Corn Leaf Aphid Landing In Pastures, Corn, And Tobacco In Kentucky And Neighbor States
DR. RAUL T. VILLANUEA
LEXINGTON, KENTUCKY
Population outbreaks of the corn leaf aphid, Rhopalosiphum maidis (Hemiptera: Aphididae) have occurred some years, but they have hardly caused significant damage to corn, sorghum, or pastures. This aphid species is a native insect of North America and present across the entire United States, Canada, and Mexico. This aphid feeds on corn, sorghum, small grains, and several grasses. In small grains, high populations can occur in fall or early spring; it is a vector of the barley yellow dwarf virus.
Corn leaf aphid coloration varies from bluish grey to green and can occur in very dense clusters in the whorl (Figure 1). Aphids in these clusters are composed of wingless specimens, but under heavy aggregation, winged individuals develop to move and colonize new fields.
Current Situation
On July 19, 2024, Dr. Lagos-Kutz (USDA-ARS, IL) noticed the presence of this aphid in suction traps and in fields in Illinois. I noticed the presence of winged corn leaf aphids landing on grasses and corn on July 24. Recent communications with extension specialist from Ohio, Illinois, Michigan, Wisconsin, and Ontario, Canada indicated that the presence of corn leaf aphids occurred in those states and this outbreak seems a widespread event.
Surprisingly, Dr. Bailey (Tobacco specialist at UK-REC, Princeton) noticed that this species was landing on tobacco leaves the next day, July 25 (Figure 2). Similar observation were made by tobacco farmers in western Kentucky as reported by Dr. Bailey. Their presence on tobacco may be due to the large tobacco leaves, dark-green coloration of leaves, or other unknown reasons. Tobacco farmers seeing corn leaf aphids on tobacco, may be worried and may want to treat their fields; however, this aphid will not thrive on tobacco or feed on these plants as tobacco is not a host. However, there is a potential that winged aphids, also called foundress, that landed in corn, sorghum, or grasses may lay nymphs and outbreaks may occur in nearby corn, soybeans, or pastures.
Scouting during the weekend and Monday (July 29), showed that aphid numbers were reduced in corn (2 to 3 winged aphids were observed). Most aphids may have been washed away, and few dead winged aphids remained on leaves after rains on Friday and Saturday.
Management
Corn leaf aphid rarely causes economic losses, as they are controlled by several natural enemies (lady beetles, syrphid fly larvae, parasitoids, entomopathogens, lacewing adults and larvae) or environmental conditions, such as heavy rains. However, county Extension agents, scouting personnel, farmers, and consultants need to be aware of the presence of this aphid and check for its abundance. If insecticides are necessary, consult with the county Extension agent.
Observations from July 26 to July 29 showed high mortalities of aphids in corn and sorghum in Princeton, but this can be a localized event; and population outbreaks may occur somewhere else. Several factors may have contributed to this mortality including lady bugs and Orius spp., observed in fields, rains that occurred on 04/26/24, and an unknown entomopathogen that may cause this mortality (Figure 3). ∆
DR. RAUL T. VILLANUEA: University of Kentucky