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Continue to Scout for Red Sunflower Seed Weevils (08/13/20)

Be vigilant scouting for red sunflower seed weevils (RSSW) until sunflowers are passed R5.7 crop stage where they are no longer attractive to the female weevils for egg laying.

Be vigilant scouting for red sunflower seed weevils (RSSW) until sunflowers are passed R5.7 crop stage where they are no longer attractive to the female weevils for egg laying. NDSU IPM scouts and agronomists are observing more RSSWs in the southeast, south central, southwest and north central areas of North Dakota. Some insecticide applications have been applied to early blooming sunflower fields where RSSW populations were above the E.T., an average of 4-6 weevils per head for oilseed sunflowers and 1 weevil per head for confection sunflowers. See the past issue #13 of NDSU Extension Crop & Pest Report for scouting and E.T. for RSSW.

Red sunflower seed weevil has a single generation per year. The adult weevil begins to emerge from the soil in July and continues until August. Peak emergence occurs in late July to mid-August. Newly emerged adults feed on the bracts of sunflower buds. When the sunflower head begins to bloom, the adults feed on the pollen, and as the seeds begin to fill, females lay eggs within the seed. Because of this internal oviposition as the seed development progresses healing the scars, seeds look absolutely healthy and normal in external appearance. Most of the egg deposition involves a single egg per seed, although research has revealed that 8 to 12 percent of seeds may have multiple eggs per seed. The small, white, oval-shaped eggs hatch in approximately one week. Larvae consume the seed, causing the economic yield loss. The majority of the larvae drop to the ground after a hard freeze in the fall. They overwinter in the soil at a depth of about 6 inches. Larvae pupate the following year in mid to late June and the pupal period lasts about one week.

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Janet J. Knodel

Extension Entomologist

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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