Photo Library: Insects
The sunflower moth, Homoeosoma electellum (Hulst)
Sex-pheromone traps can be used to monitor populations. In Kansas, early plantings usually have higher infestations than later plantings. However, in other locations, planting dates have to be adjusted for conditions such as moth flight, available moisture, and length of the growing season. The microbial insecticide, Bacillus thuringiensis (Berliner), can be used to suppress sunflower moth infestations and may be as effective as synthetic insecticides. Despite the research on cultural and biological controls and plant resistance, the control method of necessity is usually an insecticide.
The adult is a shiny gray to grayish tan moth about 0.38 inch long, with a wingspan of about 0.75 inch. When at rest, the wings are held tightly to the body, giving the moth a somewhat cigar-shaped appearance. The larva has alternate dark and light-colored longitudinal stripes on a light brown body and about 0.75 inch long at maturity.
Life Cycle: The moths are highly attracted to sunflower that is beginning to bloom. Individual female moths will deposit up to 30 eggs per day on the surface of open sunflower heads. The eggs hatch within 48 to 72 hours and the newly emerged larvae feed on pollen and florets. The larvae begin tunneling into seeds upon reaching the third instar (larval growth stage). This tunneling continues throughout the remainder of larval development. Larval development from hatching to full maturity takes about 15 to 19 days.
Damage: The young larvae of the sunflower moth feed primarily on florets and pollen. Older larvae tunnel through immature seeds and other parts of the head. A single larva may feed on three to 12 seeds and forms tunnels in both the seeds and head tissue. Larvae spin silken threads, which bind with dying florets and frass to give the head a trashy appearance. Severe larval infestations can cause 30 percent to 60 percent loss, and in some cases, the entire head can be destroyed. Sunflower infested with sunflower moth has an increased incidence or risk of Rhizopus head rot.
Scouting Method: Sampling sites should be at least 75 to 100 feet (23 to 31 m) from field margins. The X pattern should be used in monitoring a field, counting moths on 20 heads per sampling site for a total of 100 heads. Scouting is most accurate in the early morning or late evening, when moths are active.
Economic Threshold: The economic threshold for sunflower moth is one to two adults per five plants at the onset of bloom or within seven days of the adult moth’s first appearance.
READ ABOUT A SIMILAR PROBLEMATIC MOTH: BANDED SUNFLOWER MOTH