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Thursday, April 28, 2011

Vegetable weevil in tobacco

Warm weather always brings new and unusual insect questions, and this week was full of interesting phone calls. On Tuesday, one of those calls was about about a tobacco field in the North Carolina sandhills with damage to recent transplants. The insects described were beetles with light chevron patterns on their backs, and they had nearly defoliated several plants in the first three rows. After receiving photos from David Dycus, NCDA & CS regional agronomist, it was clear that the insects responsible were vegetable weevil adults (Listroderes costirostris obliquus).

Vegetable weevils are a relatively common occurrence this time of year, and growers and homeowners should be on the look out for populations and damage.

Tobacco seedling with feeding injury from vegetable weevil (Listroderes costirostris obliquus). Photo: David Dycus.
Adult vegetable weevil. Photo: David Dycus.
Vegetable weevil is a non native pest in North America and was first detected in 1922. Originally from South America, adult vegetable weevil are active in fall, winter, and spring. Both adults and larvae feed on young plants, including turnip, carrot, collard, mustard, tomato, potato, tobacco, and a number of weeds. Adults disperse into crops fields in spring from their overwintering locations, and damage is often most severe along field borders. Because of this damage pattern, spot treatments may be sufficient to control populations.

The treatment threshold for recent transplants is 5-10%, and the field in the sandhills had sufficient damage to justify treatment. Several of the labeled insecticides in tobacco are registered for vegetable weevil. See the NC Ag Chem Manual for recommendations. One addition to the vegetable weevil recommendations not yet listed is lambda-cyaholthrin (Warrior or Karate in tobacco). This pyrethriod insecticide was the material I recommended for use in the case of the sandhills site. See a note on pesticide recommendations.

David and his fellow regional agronomist, Don Nicholson, also noted that several beetles appeared dead or dying near some of the plants. Don and David visited the field about 5 days after transplant, and the grower had used Platinum (thiamethoxam) in the transplant water. The Platinum applied at transplant may also have provided some protection against vegetable weevil, although transplant water application may take several days to move into plants. This may be why the beetles appear affected now but were able to significantly damage several rows of plants.

Damaged tobacco plant with dead or moribund vegetable weevil to the left. Photo: David Dycus.
More information
Vegetable weevil - University of Georgia Cooperative Extension

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