The carrot weevil is a major pest of carrot and celery in the northeastern U.S. and Canada. Processors tolerate no more than 5% injury to the roots from larval tunneling, so control measures must be efficient. Bacillus thuringiensis subsp. tenebrionis, a strain pathogenic to various beetles, and six unidentified strains isolated from Canadian soils were tested for their ability to kill adult carrot weevil.
The various Bt strains were incorporated into artificial diet fed to adult weevils. Three of the seven strains tested are pathogenic to adult carrot weevil; B. t. tenebrionis was the most toxic. Weevil feeding was significantly reduced by the third day.
Saade, F. E., G. B. Dunphy, and R. L. Bernier. 1996. Response of the carrot weevil, Listronotus oregonensis (Coleoptera: Curculionidae), to strains of Bacillus thuringiensis. Biol. Control 7: 293-298.
Suppression of Carrot Black Rot with Burkholderia cepacia
Black rot (caused by Alternaria radicina) is a seed-transmitted disease that produces a black ring of decay around the top of the carrot root, reducing quality. The effects of seed and root treatments with nine different isolates of microorganisms were evaluated in lab and greenhouse tests.
Carrot seeds treated with Burkholderia cepacia had significantly better germination and emergence and reduced disease severity than non-treated seeds or seed treated with other antagonists. B. cepacia was as good in promoting seed emergence and controlling disease as the fungicide iprodione.
Both B. cepacia and Bacillus amyloliquefaciens reduced black rot lesions on mature carrot roots inoculated with the pathogen and antagonist. B. cepacia also significantly reduced black rot on the foliage.
Selected antagonists, especially B. cepacia, can effectively control black rot and should be investigated for commercial use.
Chen, T. W. and W. S. Wu. 1999. Biological control of carrot black rot. J. Phytopathol. 147(2):99-104.
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