Scout for Red Sunflower Seed Weevil (07/29/21)
Red sunflower seed weevils (RSSW) are emerging in most areas of the state and scouting should start as sunflower starts to flower. Please send me your reports including locality and numbers when you start finding RSSW.
Identification: RSSW are small (⅛ inch long) weevils with a snout and are reddish-orange.
Scouting: When sampling, use the X pattern and begin counting at least 75 to 100 feet into the field to avoid field margin effects. Rub your hand vigorously across the sunflower face. Count the number of RSSW adults on 5 plants at 5 sites for a total of 25 plants per field. Scout for adults in the early blooming sunflower fields when the yellow ray petals are just beginning to show. RSSW is attracted to early blooming sunflowers, as females must imbibe pollen before laying eggs.
An NDSU YouTube video is available on Scouting for Red Sunflower Seed Weevil in Sunflowers.
Scouting should continue until the economic threshold (Tables 1 & 2) is reached or when most plants have reached 70% pollen shed. At 70% pollen shed, plants are no longer susceptible for egg laying or significant damage. On older flowering plants (after R5.7), larvae of RSSW (and banded sunflower moth larvae) will be feeding inside the seeds and are protected from the insecticide. By then, much of the feeding damage has already occurred.
The threshold for RSSW in oilseed sunflower can be calculated using the following formula:
The ideal plant stage for treatment is when most individual plants are at 40% pollen shed. However, we recommend that treatment be considered when three out of 10 plants are just beginning to shed pollen.