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Red Sunflower Seed Weevil Threshold for 2015 (07/30/15)

Red sunflower seed weevil (RSSW) adults are emerging now and will fly to the nearest flowering sunflowers.

Red Sunflower Seed Weevil Threshold for 2015

Red sunflower seed weevil (RSSW) adults ent.knodel.4.red sunflower seed weevilare emerging now and will fly to the nearest flowering sunflowers. The USDA NASS reports that 25% of the sunflowers were blooming in North Dakota (USDA NASS News Release – July 27, 2015). I have received one field report of adult weevils near Dickinson in SW, ND. Please send me your reports of locality and numbers if you find them. Weevils are small (2.5 to 3.1 mm long) and reddish-orange.

Scout for adult seed weevils in the early blooming sunflower fields when the yellow ray petals are just beginning to show. A NDSU YouTube video is available on Scouting for Red Sunflower Seed Weevil in Sunflowers. Counts should continue until the economic threshold level has been reached or most plants have reached 70% pollen shed. At 70% pollen shed, plants are no longer susceptible for egg laying or significant damage. When sampling, use the X pattern and begin counting at least 70 to 100 feet into the field to avoid field margin effects. Count the number of weevils on five plants at each site for a total of 25 plants. Assuming the field is at threshold, we recommend that treatment be considered when three out of 10 plants are just beginning to shed pollen.

For RSSW, insecticide treatment is directed at the adult stage. The 2015 economic threshold for RSSW is calculated at 4-5 weevils per head for oilseed sunflowers and only 1 weevil per head for confection sunflowers. Please see Tables 1 and 2 (next page) for details on RSSW thresholds based on market price and plant populations at $8 or $10 insecticide cost per acre.

ent.knodel.5.tables economic threshold sunflowers

Janet J. Knodel

Extension Entomologist

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