Biorational/Biological Management Program for Potato Pests

Biorational/Biological Management Program for Potato Pests

Summary

Key findings
This project compares the effectiveness of different combinations of four biologically based pest management agents for control of aphids and Colorado potato beetle (CPB) in potatoes. First-year results indicate that some treatment combinations are more effective than others against CPB. Three combinations maintained densities of large larvae (the most damaging stage) below economic thresholds.

Laboratory assays currently underway will provide supporting data for determining the effects of timing, sequence, and mixtures of the biorational controls on CPB larval survival.

Objectives
1. Compare the effectiveness of combinations and rotations of two biorational insecticides Bacillus thuringiensis (Bt) and neem extract and releases of two natural enemies the fungal pathogen,
Beauveria bassiana (Bb) and the predator, Perillus bioculatus (Pb) against Colorado potato beetle and aphids in potatoes (years 1 and 2).
2. Compare the effectiveness of the most promising combinations and rotations from objective 1 across several soil amendment, potato variety, and possibly irrigation regimes in large plot field tests in reducing insect pest populations, protecting natural enemy populations, and maintaining the quality and quantity of potato tuber yields at harvest (year 2).

Approach and Methods
The conventional approach to potato pest management is heavily reliant on the use of chemical insecticides. Such reliance has lead to deleterious environmental impacts and the development of genetically based insecticide resistance among insect pest populations.

There are several biological or biorational agents which are registered for use in potatoes which could be used as safer alternatives to conventional chemical insecticides. Some of these materials may be more effective if used in combinations that take advantage of their biological effects on insects, such as feeding
interference, slowed development, or altered physiology. However, the compatibility of these agents with one another has not been previously examined.

This project compares the effectiveness of different combinations of four biologically based pest management agents for control of aphids and Colorado potato beetle (CPB) in potatoes. These four
agents, a botanical insecticide made from neem seed extracts, the bacterial insecticide Bacillus thuringiensis (Bt), the insect fungal pathogen Beauveria bassiana (Bb), and the stink bug predator Perillus bioculatus (Pb) were applied in all one-way and two-way combinations to determine which combinations were most effective for potato pest management.

The first-year results of this study indicate that some treatment combinations are more effective than others against CPB. Only three of the treatments (Bt alone, Bt + Bb, and Bt + Pb) maintained densities of large larvae (the most damaging stage) below economic thresholds. Bb + neem was the least effective treatment, followed by neem alone and Bb alone. Laboratory assays currently underway will provide supporting data for determining the effects of timing, sequence, and mixtures of Bt, Bb, and neem on CPB larval survival.

Of the biological agents compared, all four were compatible with one another in two-way mixtures with the single exception of Bb + neem which appears to be an antagonistic combination We found poorer CPB control and potato yields in this combination treatment.

The best CPB control was provided by Bt. There did not appear to be any improvement in yield with the addition of any of the other three agents (Bb, neem, or Pb) to Bt. There was no evidence of synergism among any of the other agents in the field tests, although neem+Bt did appear to have an additive effect on CPB control. Bb+neem appeared to be an antagonistic, or less than additive, combination. That is, CPB control and tuber yields were lower with this treatment than the sums of Bb alone and neem
alone.

At present, the high costs of neem and Bb are prohibitive for practical use for potato insect pest management, however, with increased demand and competition, and improved extraction
efficiency it is hopeful that the price will be more affordable in the near future.

Similarly, the predatory insects used in this study are not commercially available at present, however, it is hoped that these predators, presently reared only experimentally, will be available from commercial insectaries in the future.

Potential Contributions
We showed that half of the biological treatment combinations tested provided control of potato pests below economic thresholds with no use of conventional insecticides. Conventional growers in this region usually apply imidicloprid (Admire) at planting to all of their acreage, therefore there is no opportunity for using IPM practices. Some conventional growers substitute foliar applications of imidicloprid (Provado) or other chemical insecticides during the growing season, and can afford some pesticide savings by scouting and spraying only when densities exceed economic thresholds, but apply three sprays on average for control of CPb and one or more additional sprays for control of aphids. Thus we were able to save approximately 0.15 lbs or 0.25 lbs active ingredient of conventional insecticides compared with three foliar sprays or one in-furrow application of imidacloprid per acre, respectively.

Reported December 1997.

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