Photo Library: Insects
Red Seed Weevil
The red sunflower seed weevil, Smicronyx fulvus (LeConte)
Newly emerged adults feed on the bracts, sunflower buds, and pollen. Peak emergence is usually in late July and early August. The female seed weevil must feed on pollen for fertile egg development. Field scouting for adults should begin when plants are showing yellow ray petals (R5.0) to 30% of the head shedding pollen (R5.3), and should continue until most of the plants have reached 70% pollen shed (R5.7). A plant that has reached R5.7 has few seeds still suitable for red seed weevil egg laying and should no longer be susceptible to further significant damage. The easiest method for scouting for adult seed weevils can be done with a can of insecticide/mosquito spray with DEET, such as Deep Woods Off. Spray the sunflower heads and wait 15 or more seconds for the adult weevil to move to the front of the head. Then, count the number of adult weevils on numerous sunflower heads at several locations and calculate the average number of adult weevils per head.
CONFECTION sunflowers: The economic threshold is only ONE WEEVIL PER HEAD.
Insecticide Spray Timing: Insecticide spraying is targeted at the adult weevil to prevent egg laying. The best time to treat is when more than half of the plants in a field are beginning to show yellow ray petals (R5.0) to 30% of the head shedding pollen (R5.3) and the rest of the plants in the field are still in the late bud stage. Although insecticides applied to sunflower at the bud stage will kill weevils, treatments at that stage are not economical or effective because (1) seeds have not developed to a stage suitable for oviposition, (2) eggs within the weevil are not mature, and (3) adult weevil emergence is still continuing. If spraying is done too early, weevils can re-infest a field requiring a second treatment. Banded sunflower moth and red sunflower seed weevil can both be ontrolled with a well-timed spray, usually near 10% of the head shedding pollen or R5.1. Fields should always be scouted for both insect pests.