One of the insects that needs to be scouted for after the inflorescences begin to open (R4) through head maturity is the sunflower moth. Sunflower heads are most susceptible to damage caused by sunflower moth caterpillars from the onset of anthesis (R5.1) to when the petals begin drying (R6). Adult sunflower moths are attracted to sunflowers during the early stages of blooming and will deposit eggs near the base of florets. Each female sunflower moth has the potential to lay as many as 400 eggs. In other states where this insect is a pest, populations of the caterpillars can range from 15-200 per head. In South Dakota, we generally will observe 1-5 sunflower moth caterpillars per head. However, the potential for larger populations to occur is possible, which is why scouting for the sunflower moth is important for South Dakota sunflower producers.
The adult sunflower moths are relatively small, measuring approximately 3/8” in length with a wingspan of approximately ¾”. The moths are tan or light gray in color, and have their wings tucked tightly to their bodies when at rest (Figure 1). The caterpillars of the sunflower moth have very distinctive coloration. They have a bright orange head with a black body and white stripes that run the length of their bodies (Figure 2). The caterpillars range in size but reach approximately ¾” during their final developmental stage.
Figure 2. Sunflower moth caterpillar. Credit: A. Varenhorst
Sunflower moths do not overwinter in South Dakota, and migrate each year from southern states. They arrive in South Dakota when sunflower begin flowering. The moths can be observed on sunflower heads during early flowering stages. During the first two instars, sunflower moth caterpillars will feed on pollen, but transition to feeding on the seed during their later developmental stages. The caterpillars will feed directly on the seed, and will also tunnel into the sunflower head tissue. This tunneling can lead to secondary infections of Rhizopus head rot, which are the main source of yield loss associated with this pest. A single caterpillar may feed on 3-12 seeds within a head. Additionally, sunflower moth caterpillars spin silken threads that will bind dying florets and other materials to the head, which give the head a trashy appearance (Figure 3).
Figure 3. Silken webbing that is spun by the sunflower moth caterpillar. Notice the accumulated debris in the webbing. Credit: A. Varenhorst
Scouting for the sunflower moth should begin at the R4 growth stage. The best way to scout for sunflower moths is to use a flashlight and examine fields 1 hour after sunset, which is when moth activity peaks. Count the number of moths on the heads of 20 sunflowers from five random locations throughout the field. The threshold for sunflower moth is 1-2 moths per five sunflower heads.
When applying insecticides for management of insect pests on sunflower heads be sure to orient the application so that maximum coverage reaches the head. Remember to be aware of pollinators that are also present around the heads. Apply insecticides when pollinators are less active or not present on the heads. If hives are placed near the field, notify the associated beekeeper to prevent hive losses. Apiary locations can be found through the SDDA Sensitive Sites Registry.