The crucifer flea beetle, Phyllotreta cruciferae (Goeze) (Coleoptera: Chrysomelidae), has recently emerged as a serious pest of canola (Brassica napus L.) in Montana. The adult beetles feed on canola leaves, causing many small holes that stunt growth and reduce yield. In 2013, damage to canola seedlings was high (approximately 80%) in many parts of Montana, evidence that when flea beetles emerge in large numbers, they can quickly destroy a young canola crop. In the current study, the effectiveness of several
biopesticides was evaluated and compared with two
insecticides (
deltamethrin and
bifenthrin) commonly used as foliar sprays as well as seed treatment with an
imidacloprid insecticide for the control of P. cruciferae under field conditions in 2013. The
biopesticides used included an entomopathogenic nematode (Steinernema carpocapsae), two entomopathogenic fungi (Beauveria bassiana and Metarhizium brunneum), neem, and
petroleum spray
oils. The control agents were delivered in combination or alone in a single or repeated applications at different times. The
plant-derived compound neem (
azadirachtin),
petroleum spray oil, and
fatty acids (M-Pede) only showed moderate effect, although they significantly reduced leaf
injuries caused by P. cruciferae and resulted in higher canola yield than the untreated control. Combined use of B. bassiana and M. brunneum in two repeated applications and
bifenthrin in five applications were most effective in reducing feeding
injuries and improving yield levels at both trial locations. This indicates that entomopathogenic fungi are effective against P. cruciferae, and may serve as alternatives to conventional
insecticides or seed treatments in managing this pest.