Author
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Wraight, Stephen |
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Ramos, Mark |
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Submitted to: Biological Control
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 9/24/2001 Publication Date: N/A Citation: N/A Interpretive Summary: The Colorado potato beetle is a key pest of potatoes in the US. Uncontrolled adult and larval populations are capable of completely defoliating potato crops and causing complete yield loss. Conventional management systems rely almost exclusively on applications of synthetic chemical insecticides; however, this insect exhibits an exceptional capacity to rapidly develop resistance to chemical insecticides , and alternative control agents are needed for integrated management programs. The common insect pathogenic fungus Beauveria bassiana is one of the most important natural enemies of the Colorado potato beetle. While high levels of natural infection are most commonly encountered in populations of pupae and overwintering adults in the soil, larval stages are also susceptible, and there exists a long history of efforts to develop B. bassiana as a biological control agent. Past results, however, have been highly variable eand efficacy of B. bassiana against larval infestations has been generally unsatisfactory. This study examined the effects of various spray application parameters, including application rate, spray interval, sprayer design, and fungal formulation on effectiveness of this pathogen. Spray applications made from below the crop canopy targeting the small larvae feeding on the leaf undersides significantly increased effectiveness, as did applying the fungus at 3-4 day intervals rather than 7-day intervals. These and other of the presented results will contribute to the continuing scientific and commercial development of this natural control agent. Technical Abstract: The Colorado potato beetle-control potential of Beauveria bassiana was evaluated over three field seasons (1997-1999). Applications were made in small field plots using a backpack sprayer fitted with hollow-cone nozzles mounted on swivels affixed to lateral drop tube; these nozzles were carried 15-20 cm above the ground and were directed upward at a 45 angle. The sprayer delivered 280 l/ha at 50 psi. Three doses (1.25, 2.5, and 5 x 101 conidia/ha) of an oil-based formulation of B. bassiana strain GHA and two spray intervals (3-4 versus 7 days) were tested. Three sprays of the intermediate and high doses applied at 3-4 day intervals produced equivalent control of ca 50-65%. The low dose and sprays at weekly intervals were less effective. A wettable powder formulation was also compared to the oil formulation. Three sprays at the intermediate rate were applied at 3-4 day intervals. Rainfall followed applications on numerous occasions, and the oil formulation was significantly more effective than the WP formulation under these conditions (ca 65 vs 20% control), suggesting greater rain fastness of the oil formulation. Tests with the oil formulation also compared applications from a sprayer configured as described above to those from a sprayer configured with nozzles directed to spray downward from approx 30 cm above the canopy. The sprayer with drop tubes deposited an average of 864 spores/mm2 onto the upper surfaces of the leaves and 406 spores/mm (32%) on the lower surfaces, while the alternative sprayer deposited 1,060 spores/mm2 onto the upper surfaces and only 50 spores/mm2 (5%) onto the leaf undersides. The applications from below canopy provided greater control of early-instar larvae. |
