Utilization of a Neem Product in a Reduced Synthetic Chemical Insecticide Management Program for Colorado Potato Beetle

Utilization of a Neem Product in a Reduced Synthetic Chemical Insecticide Management Program for Colorado Potato Beetle

Summary

Key Findings
This project was conducted on commercial and organic farms to demonstrate the efficacy and cost of different strategies for utilizing a neem-based insecticide for reducing crop damage caused by Colorado potato beetle (CPB) on potato farms.

The results suggest that the amount of conventional insecticide used for CPB management can be reduced by applying neem-based insecticide to interfere with CPB egg-laying activity, followed by larvicidal applications of neem, Bt, or conventional insecticides.

On the commercial farm, CPB egg-laying was reduced by 70 percent with two applications of neem and was reduced by 53 percent with a single half-rate application of imidicloprid. We found no treatment-related effects on non-target arthropod pests (flea beetles, aphids) or beneficial arthropods (ladybugs, spiders).
At the organic farm, all three treatment regimes were effective in keeping CPB densities below recommended threshold levels, however neem mixed with Bacillus thuringiensis (Bt) was less effective than either material alone. Bt was more effective than neem or the neem-Bt mix in reducing the density of summer-generation CPB adults and resulted in 10 percent higher tuber yields. Neem reduced densities of the black and red stinkbug (an unusual pest of potatoes) but also appeared to have a deleterious impact on ladybugs (an important group of beneficial insect predators).

At present, the high cost of neem products is prohibitive, however, with increased demand and competition, and improved extraction efficiency it may be more affordable in the near future.

Objectives
1.Demonstrate the effectiveness of a neem product used to reduce crop damage by the Colorado potato beetle through interference with egg-laying.
2.Demonstrate the costs and effectiveness of a neem product used in combination or in rotation with conventional chemical or microbial insecticides in a reduced insecticide management program for Colorado potato beetle on commercial potato farms.

Background
This project was conducted to demonstrate the efficacy and cost of different strategies for utilizing a neem-based insecticide for reducing crop damage caused by Colorado potato beetle (CPB) on commercial potato farms. In addition we examined effects on non-target arthropods, including natural enemies and other potato pests.

Neem seed extracts are known to be highly effective against a number of insect pests, but the utility of these natural plant-derived products as an alternative to, or in combination with conventional synthetic insecticides, are not well recognized in the US.

We designed several treatment regimes to demonstrate the efficacy and cost effectiveness of a two-pronged strategy for utilizing a neem product in combination with other insecticides against the Colorado potato beetle in potatoes.

A commercially available neem formulation was applied to half of the fields early in the season in an effort to reduce colonization of potato fields by interfering with egg-laying. In mid-season, efficacy and effects on non-target arthropods were compared among several larvicidal treatments using neem applied in rotation or tank-mixed with other insecticides.

The project was conceived and designed in collaboration with Brian Campbell, a potato farmer located in Central Maine. Before planting we recruited another Central Maine farm, Hillacre Farms, owned and operated by Carl W. Smith and Carl E. Smith. Unfortunately, after considerable effort in planning the project with these farmers, establishing plots, and scouting fields, we found that densities of Colorado potato beetle were exceptionally and unexpectedly low throughout central Maine (lowest densities in 6-8 years). The fields were almost completely uninfested at both farms. Therefore we had to abandon these plots and relocate the project to northern Maine after the start of the growing season. Although this presented a challenge, we were able to conduct the demonstration at two Aroostook County farms.

Activities and Results
At a 300-acre conventional potato farm we compared costs, efficacy, and non-target impacts of neem product (Align 3EC, Biosys Corp.) applications timed to reduce CPB egg-laying, followed by applications of neem used in rotation or mixed with the conventional insecticide imidacloprid (Provado 1.6F, Bayer Corp.) for management of Colorado potato beetle.

At an organic farm, we compared three treatment regimes: neem alone; Bt, a microbial-based insecticide product applied alone; and neem and Bt mixed together.

At the conventional farm, we found the CPB egg-laying rate (numbers of eggs produced per adult beetle) was reduced by 70 percent with two applications of neem and was reduced by 53 percent with a single half-rate application of imidicloprid. In comparison, egg-laying rates doubled when no adult-targeted spray was applied. However, two applications of neem (one adult spray followed by one larvicidal application) was insufficient to keep CPB below recommended threshold densities. In contrast to earlier studies showing enhanced efficacy when neem was applied in rotation with some conventional insecticides, we were unable to demonstrate that neem increased effectiveness when applied either in rotation with, or mixed with, imidicloprid. We found no treatment-related effects on non-target arthropod pests (flea beetles, aphids) or beneficial arthropods (ladybugs, spiders).

At the organic farm, all three treatment regimes were effective in keeping CPB densities below recommended threshold levels, however neem mixed with Bt was less effective than either material alone. Compared with neem or the neem+Bt mix, Bt was more effective in reducing the density of summer-generation CPB adults and resulted in 10 percent higher tuber yields. Neem reduced densities of the black and red stinkbug (an unusual pest of potatoes) but also appeared to have a deleterious impact on ladybugs (an important group of beneficial insect predators).

The results of this study indicate that the amount of conventional insecticide used for CPB management can be reduced by applying neem-based insecticide to interfere with CPB egg-laying activity, followed by larvicidal applications of neem, Bt, or conventional insecticides. Further reductions in conventional insecticide use can be accomplished by replacing the conventional material with either neem or Bt to control the early larval stages of this pest. Although this strategy is more expensive, at current product costs, than conventional insecticides used alone, we demonstrated effective pest management at high pest densities with a 30 percent reduction in the amount of conventional insecticides used. We estimate that a three-fold reduction in conventional insecticide use could be achieved on conventional farms at lower CPB densities.
In earlier research we found that mixtures of neem with reduced rates of other conventional insecticides produced a synergistic effect, thus providing good control of CPB larvae with very small amounts of conventional insecticides. In this study, however, we found that adding neem to imidacloprid did not provide any added benefit. Imidacloprid was equally effective alone or in mixture with neem. Furthermore, we found that a mixture of neem plus Bt was less effective than Bt alone, indicating that neem and Bt are not compatible with one another in an insecticide mixture.

Laboratory assays thus far have confirmed our field observations. We found that although Bt mixed with neem produces a synergistic effect against newly hatched CPB, the effect is antagonistic against 2-day old larvae. Similarly, when neem was followed by Bt, the effect was additive, but when Bt was applied first, followed by neem, the combination was less effective than either material alone. Thus, the effect of the mixture or a sequential treatment of neem and Bt in the field, with larvae of various ages present at once, would be expected to be less effective than either material applied alone. Similar tests with neem and imidacloprid are almost complete. The results of these assays will be included as an addendum to this report when completed.

Recommendations
Because of prohibitively high prices for neem products and pending completion of laboratory studies, no recommendations are yet proposed.

Areas Needing Additional Study
Research into the efficacy of neem products for plant disease management is needed. Neem is known to have anti-fungal properties. Further research into the effects of neem on non-target arthropods is needed. Our study indicates that neem may have deleterious effects on some non-targets, including arthropod predators of plant pests. Most previous research in this area has been done in the laboratory. Field studies are needed to adequately assess the impact on non-target organisms. Research leading to formulation and commercialization of other plant-derived products for pest management is needed. Increased availability and enhanced technology leading to affordability of neem and other natural products is needed.

Reported November 1997.

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