NDSU Extension - Mercer County

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Adult Red Seed Weevil

adult red seed weevil, sunflower weevil

Submitted by Craig Askim, Extension Agent/Agriculture and Natural Resources

Sunflowers are starting to bloom across the county. Therefore, this is the prime time for the red/gray sunflower seed weevil to start hatching. The sunflower crop looks good so producers are encouraged to scout their fields for these insects so yield potential is not lost.  

This is the most common damaging insect group on flowering sunflower. The red seed weevil is the more common of the two weevils. Both are easy to scout, identify and control. The red weevil adults are 0.1 to 0.12 inch long and the gray weevils are slightly larger. Both weevils have pronounced ‘snouts' that make them recognizable. 
 
Life Cycle: Weevils usually emerge in late July early August in North Dakota.  Once the plant is flowering and making pollen, the weevils feed on the pollen for several days before laying eggs in the developing seeds. The eggs hatch and the larvae consume part of the developing kernel. The larvae then burrow out of the seed, drop to the ground, and prepare for overwintering. 
 
Damage: The red seed weevil female lays eggs in as many as 27 seeds. The hatched larvae consume a portion of the kernel before dropping out of the seed. The gray seed weevil female lays fewer eggs but lays them earlier in the R-3 or 4 stage. The gray seed weevil larvae generally consume the majority of the kernel before dropping out. The infested gray weevil seeds are generally blown out of the combine. However, that is not the case of for the red weevil. Damaged confection seeds are discounted and most contracts have a minimum percent of infestation allowable. This is not the case for oil-type sunflower; however, it is likely that the farmer is losing test weight and yield. 

Scouting Method: Like most insects, field borders generally will have higher weevil numbers stages and continue to R-5.7. At the bud stage, the weevils tend to feed and hide among the bracts. An easy way to get them to emerge is spray a mosquito repellent containing Deet on the face of the heads. The same can be used when the buds have opened. NDSU has created a video in which Dr. Jan Knodel, NDSU Entomologist, walks you through the process of scouting for the weevil and determining potential crop loss. Watch it here:https://www.youtube.com/watch?v=-Cmychnf4yM... 

Management: There are many effective insecticides labeled for the adult weevils. Since the red seed weevil adults need to consume pollen before laying eggs, spraying at early pollen shed when about 30% of the plants are at R-5.1 is recommended. It is recommended that confections be sprayed even earlier and two sprays may be warranted depending on populations. The timing of control of the red seed weevil is well suited for controlling both the banded and the sunflower moth. For the gray weevil, spraying at early bud stage R-2 is recommended. However, gray weevil populations have historically been low and no control has been required. Waiting too long to scout and take control measures are historically the most common mistake with the red seed weevil. 

Source: Janet Knodel – NDSU Extension Entomologists 

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