By Adam Varenhorst
Gray sunflower seed weevils have been spotted in sunflower fields this week. Although they are a non-economic pest there are times when they can have population outbreaks and reduce sunflower yields. However, I don’t expect that 2021 will be one of those years.
Identification and Biology
The gray sunflower seed weevil adult is covered in small gray hairs that cover most of its body (Figure 1). They are approximately 1/5 of an inch long and have gray legs. It also has a black snout that has small antennae that originate from it. The gray seed weevil emerges approximately 10 days before the red sunflower seed weevil.
The larvae are small and feed on the developing seeds. They are cream colored and take on a “C” shape when disturbed.
There is a single generation of gray sunflower seed weevils each year. They are typically active in sunflower fields from R1-R3 but can be observed in later reproductive stages as well. Their populations typically decline after flowering begins.
Gray sunflower seed weevil females lay eggs on the buds. After hatching, the larvae move to the base of the achene and begin feeding. The presence of the larva results in the achene becoming enlarged and it will protrude from the head.
Scouting for adult gray sunflower seed weevils should begin at R1. Gray sunflower seed weevil infestations are more concentrated in the rows of achenes in the middle of the head. Look for protruding achenes as indicators of the larva feeding on the seed. Source : sdstate.edu