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Red Seed Weevil Management
Red seed weevils, at population levels of 1-2 per plant, should be controlled in confection sunflowers. There has been some concern about the correct stage of sunflower plant development at which insecticides should be applied. Unlike crops that develop uniformly, sunflower plant heads develop at varying rates. This differential development makes management of the red sunflower seed weevil difficult.
Determine sunflower plant growth stage before pesticide application. The red sunflower seed weevil does not begin to oviposit (lay eggs) on a sunflower head before that head reaches 40 percent bloom, i.e., the outer 40 percent of the florets have opened. Until the head is at this stage, the seeds have not developed sufficiently to be suitable for eggs of the seed weevil. Treat when three out of every 10 plants are at the 40 percent bloom stage. The width of the ring of open florets that is equal to 40 percent varies with head size, but it is about 25 percent of the radius of the head. Experience has shown us that insecticides are efficient enough to control seed weevils when applied from first bloom to 40 percent bloom. In practice, this means that growers should begin scouting for seed weevils as soon as 3 out of 10 plants begin blooming. If they decide to treat, insecticides should be applied before three out of 10 plants reach 40 percent bloom. Remember: 40 percent bloom does not mean that 40 percent of the plants in the field are blooming. Recheck fields in 2-3 days to determine control levels.
For more information consult the Insect Control Guide at http://www.ext.nodak.edu/extpubs/plantsci/pests/e1143w1.htm
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