[Note to online version: The report for this project includes tables and figures that could not be included here. The regional SARE office will mail a hard copy of the entire report at your request. Just contact Northeast SARE at (802)-656-0471 or email@example.com.]
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.
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: 1) neem alone, 2) Bacillus thuringiensis (Bt), a microbial-based insecticide product applied alone, and 3) 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% with two applications of neem and was reduced by 53% 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% 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% 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 effective 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.
This project was conducted to demonstrate the effectiveness of a neem-based insecticide for reducing crop damage caused by Colorado potato beetle on commercial potato farms. 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 U.S.. 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.
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.
Site Information. Both farms involved in this demonstration are located in Aroostook County, the major potato growing region of Maine. This area has cool climates and a short growing season. Kenney’s farm is a 300 acre conventional farm, owned and operated by Gary Kenney. Potatoes are grown for certified seed, table-stock, and processing, in a 1-3 year rotation with barley. Bondeson’s farm, owned and operated by Peter Bondeson, grows table stock potatoes under both conventional and organic potato production in a 2 or more year rotation with barley. Both farms have sandy loam soils.
Conventional Farm (Kenney’s): One end of a 40-acre field of table-stock potatoes cv ‘Katahdin’ was selected for the demonstration. Synthetic N-P-K fertilizer, (14-17-17) was applied at 900 lbs/A at planting. The field had been treated with imidacloprid (Provado, 2 oz./A), applied with a tractor-mounted band sprayer to kill Colorado potato beetle adults moving into the field in high numbers. We felt that the effects of this early treatment, being short-term and uniform across all of our demonstration treatments, did not significantly influence the outcome of our demonstration.
Five blocks, 1 to 2.5 acres each, were marked (see Fig. 1). One of each of five demonstration treatments were randomly assigned to each block. The treatment schedule is shown in Table 1. The first neem application (adult-spray) was applied about one week after eggs appeared in the field.
Densities of insects were estimated 1-2 times per week in each block by counting the numbers present on 50-100 plants. Treatments targeting CPB larvae (larvicidal treatments) were applied when densities of larvae exceeded a threshold of 4 small larvae or 1.5 large larvae per plant. A larvicidal treatment was applied on 08 July 1996 to all blocks except the ‘I’ block (in which densities of CPB larvae were well below the threshold). Densities of larvae were near or exceeded treatment thresholds in three of the five blocks the following week, however miscommunication resulted in imidicloprid being applied to all blocks on 15 July.
A detergent spreader (X-77, Loveland Industries) was added at 0.05% to all treatments. Treatments were applied using a 20-row SpraCoupe using 3 drop nozzles/row at a volume of 10-12 gallons/A and 30-40 psi pressure. A fungicide (Maneb), which was applied weekly for protection against late-blight, was added to each insecticide spray. Aphid infestation levels were very low, requiring no insecticide treatments.
Organic Farm (Bondeson’s): Three demonstration blocks were established in a 2.5-acre planting of cv ‘Corolla’ potatoes within a 5-acre field of potatoes (see Fig. 2). Soybean meal was applied at 140 lbs nitrogen/A as a fertilizer. Densities of insects were estimated 1-2 times per week in each block by counting the numbers present on 50 plants. Egg-laying activity had already declined by the time plots were established, therefore no adult treatments were applied. Larvicidal treatments were applied when Colorado potato beetle densities were near the threshold of 4 small larvae or 1.5 large larvae per plant on 21 July and again on 26 July (see Table 1).. A detergent spreader (X-77, Loveland Industries) was added at 0.05% to each treatment. Sprays were applied in a volume of 60 gals/A, with 180 psi pressure, using an 8-row tractor-drawn Friend sprayer fitted with 3 nozzles/row. The field was treated weekly with copper sulfate for late-blight protection. No treatments were needed for control of other insect pests.
At harvest, tuber yields were estimated for each treatment by weighing a sample of tubers dug from each block. A 3.3-m long swath was marked running across the rows from one side of the field to the other. Tubers dug from the four inner-most rows within the swath in each block were weighed, for a total sample of 13.3 m of row/block. In addition, the total number of barrels of tubers harvested from each block were recorded.
Laboratory Bioassays: Laboratory bioassays were conducted to compare the effects of reduced rates of neem used in various combinations with imidicloprid (Table 2) or Bt (Table 3), on survival of Colorado potato beetle larvae. In each experiment, potato leaflets were sprayed with one or two materials, each at a concentration estimated to kill about 30% of the larvae over the duration of the experiment. Newly hatched larvae were fed treated potato leaves for 48 hrs, then were transferred to freshly treated leaves for another 48 hrs, and finally, larvae were transferred daily to fresh untreated foliage for 5 more days. The number of larvae surviving at 9 days after the start of the experiment were tallied. Thus, the effects of single treatments (imidicloprid, neem, or Bt alone) were compared with mixtures of two compounds, or sequential treatments in which larvae were treated with one compound on Day 1 followed by a different compound on Day 3. Sequential or mixture treatments resulting in mortality which was greater than the additive mortality of the corresponding single treatments was considered to be evidence of synergism between the two compounds.
Effects on Egg-Laying (Kenney’s Farm): Among the neem treatment regimes, reductions in egg-laying rates (numbers of egg masses/adult) from prespray rates were proportional to the amount of neem applied (Fig. 2). The egg-laying rate in the NR treatment regime (2 neem applications), dropped from 4.1 egg masses/adult before the first treatment to 1.2 egg masses/adult after the second treatment–a 70% reduction. The NM treatment (1.5 neem applications) showed a 49% reduction from prespray egg-laying rates. In contrast, the egg-laying rate doubled in the M treatment (0.5 neem applications). The I treatment also reduced egg-laying by 53%, though estimates of adult densities (Fig. 3a) indicate that reduced egg-laying was due, in part, to toxicity ultimately resulting in mortality of adult beetles. Egg densities (egg masses per plant) did not differ among any of the treated or untreated blocks until after the first larvicidal spray, when the two blocks which did not receive the adult spray (M and R) showed significantly higher egg-mass densities compared with the adult-treated blocks (Fig. 3b).
These results are consistent with numerous reports of neem-caused interference with egg-laying activity, including our own tests conducted at a commercial farm in central Maine in 1995 in which we showed a 50% reduction in egg-laying rate and 51% reduction in egg-mass density in a 1-acre neem-treated field compared with an adjacent 1-acre field treated with a conventional insecticide (unpublished data).
Effects on adult and larval CPB densities: Kenney’s Farm: There were no significant differences among treatments in weekly densities of adults (Fig 3a), although seasonal density (which reflects density over the entire season) showed densities of colonizing adults (adults present in early summer) were significantly lower in the I, NM, and M blocks, compared with the R and NR blocks, indicating the effectiveness of imidicloprid, even at half rate, against CPB adults (Fig. 3d). Seasonal incidence of summer generation adults was very low in all treatments.
Weekly densities of larvae remained below treatment thresholds except for the two rotation treatments (NR and R) which did not provide adequate control of CPB larvae (Fig 3c). However, in the NR treatment larvae were primarily small larvae; the density of large larvae (the most damaging stage) remained below threshold (=1.5 large larvae/plant). Accumulation of larvae in early stages of development is often seen with applications of neem, due to its effect as an insect growth-regulator (Schmutterer 1995) which points to the drawbacks of relying on conventional treatment thresholds when using non-traditional pest management materials.
When treatments were adjusted for among-block differences in prespray densities of colonizing adults, the treatment regimes most effective in reducing seasonal densities of large larvae were NM (0.33 large larvae produced/colonizing adult/plant) and M (0.68 large larvae/colonizing adult/plant). These two regimes each used three times less conventional insecticide compared with the conventional treatment regime (I). Treatment NR was intermediate (1 large larva/adult/plant) and R and I were least effective (2.15 and 2.28 large larvae/adult/plant).
Bondeson’s Farm: Weekly densities of larvae were higher in the M treatment (neem + Bt) compared with the Bt and the N (neem alone) treatments, but CPB densities remained well below thresholds throughout the season in all blocks (Fig. 5a). There were no significant differences among treatments in seasonal densities of CPB except for summer generation adults which were less than half as numerous in the Bt block compared with the N and M blocks.
Effects of Treatments on Tuber Yields. Yield estimates at Bondeson’s farm indicated no significant differences among treatments (Fig. 5e), however, the actual yield from the Bt treatment block was 10% higher than the M treatment block and 3% higher than the N treatment block. Miscommunication prevented us from obtaining yield data from Kenney’s farm, but Gary Kenney’s observation was that there were no differences among treatments. Average yields at Kenney’s farm was 168 barrels/acre.
Effects on Non-targets. Beneficials. Densities of beneficial arthropods (ladybugs and spiders) were low across all treatments at Kenney’s farm and there was no evidence direct treatment-related effects (Fig. 4a). No ladybugs or spiders were found in either the M or the R blocks, however, there also were no aphids in these blocks suggesting that lack of prey may have been a factor in the low numbers of ladybugs in those blocks. At Bondeson’s, there was a significant neem-related reduction in ladybug densities, which were about four times less abundant in the N and M blocks compared with the Bt block (Fig. 5c).
Aphids. At Kenney’s, aphids were highest in the NM block and low in all other blocks (Fig. 4b). The location of the NM block at the southern end of the field may explain the high densities of aphids, which often colonize from the edge of a field. Since aphids did not arrive until four weeks after the last treatment, we did not expect to see any direct treatment-related effects on aphids. Aphid densities at Bondeson’s were almost zero in all blocks.
Flea beetles. Flea beetles were significantly lowest in the M block, intermediate in the NR and R blocks and highest in the NM and I blocks at Kenney’s (Fig. 4b). There are no logical treatment-related explanations for these differences. Flea beetle densities at Bondeson’s were almost zero in all blocks.
Black and Red Stinkbug (Cosmopepla bimaculata). This plant sap-feeding insect, which is not a common potato pest, was abundant before treatment in a number of fields at Bondeson’s, although the amount of feeding damage it inflicted on the potato plants is difficult to determine. Neem appeared to have a significant effect in reducing the density of this pest, as densities were lowest in the N, intermediate in the M and highest in the Bt blocks (though M and Bt were not significantly different) (Fig. 5d). The significant neem-related reductions in ladybugs and the stink-bug are consistent with reports of the somewhat broad-spectrum activity of this material against insects (Schmutterer 1995).
Laboratory Bioassays: The preliminary results of the laboratory bioassays are shown in Figs. 6 and 7. These early results show none of the neem plus imidacloprid treatment combinations resulted in mortality greater than the additive mortality from each single treatment (Fig. 6). Thus, there was no evidence of synergism between neem and imidacloprid when the two compounds were mixed or applied sequentially. This is consistent with our field results. It must be noted, however, that these bioassays are not yet completed. The final results will be added to this report by March 1998 as an addendum.
The results of the neem and Bt bioassays suggest there may be synergism between neem and Bt when the two compounds are mixed together and applied against newly hatched larvae. However, when applied against 48 hr-old larvae, the mixture was much less effective than the additive effectiveness of Bt alone and neem alone. In a natural population, where eggs do not hatch synchronously, we would expect the Bt + neem mixture to be ineffective. In fact, our field results showed that neem +Bt mixture was somewhat less effective than Bt alone. These laboratory results indicate that Bt is most effective against second stage larvae, while neem is more effective against newly-hatched first stage larvae. This is supported by the responses in the two sequential treatments. That is, the treatment sequence is much more effective against CPB larvae when neem is applied first, followed by Bt. The opposite sequence (Bt followed by neem) was about as effective as neem applied alone on Day 3. In the field, insects are of varying stages of development, therefore, synergistic effects are less likely to be seen in practical use. However, in earlier unpublished studies we have found that neem applied to reduce egg-laying, followed by Bt to kill larvae was a very effective strategy for protecting potatoes from CPB damage.
The results indicate that when neem is applied for control of CPB larvae, its efficacy is enhanced when neem is first applied to deter egg-laying. While earlier studies had indicated enhanced efficacy when neem was applied in rotation with conventional insecticides, in the study reported here, we did not find that neem applied in rotation or mixed with imidicloprid was more effective than imidicloprid applied alone. Based on these findings, it appears that CPB can be effectively managed by substituting neem for conventional insecticides, but not by mixing the two materials together. Neem applied to deter egg-laying followed by neem, Bt, or conventional insecticides when needed for control of CPB larvae provided acceptable levels of CPB control in these tests. When used as an alternative to Bt, neem provides acceptable control of CPB, but may be somewhat deleterious to some beneficial arthropods. Neem applied in mixture with Bt appeared to be less effective against CPB than either material applied alone. At present, the high cost of neem products is prohibitive, however, with increased demand and competition, and improved extraction efficiency it is hopeful that the price will be more affordable in the near future.
The results of this project have been shared informally with Cooperative Extension. The crops specialist will share these results with dozens of field representatives, farmers, and crop consultants, thereby disseminating the findings to all Aroostook County and central Maine potato growers. The findings have also been shared with the cooperating growers and will be shared with the Maine Organic Farmers and Growers Association. A written article summarizing the results of this project was published in Spring 1997 in ‘Spudlines’, a publication of the University of Maine Cooperative Extension. Preliminary findings were presented at a meeting of the Maine Potato Board Research Council in August 1996 and at the annual Entomological Society of America meeting in December 1996. A presentation to potato growers and industry field representatives, will be given in December 1997.
Murray, K., 1997. â€˜New Products for Colorado Potato Beetle Managementâ€™ article published in Spudlines (Univ. of Maine Coop. Extension Newsletter) vol. 35 (2).
We also anticipate submitting a manuscript summarizing these findings in a refereed publication such as Journal of Economic Entomology in 1998.
Impacts of Results/Outcomes
Potential Impacts. A 30% reduction in conventional insecticide usage on conventional farms such as we demonstrated, resulted in a savings of 0.025 lbs active ingredient (ai) of insecticides per acre. If adopted on the entire farm (ca. 150 A under potato production/year) this could result in a yearly reduction in conventional insecticides of 3.75 lbs. With the adoption of other practices to reduce colonizing densities of pest insects, conventional insecticides can be eliminated (as demonstrated on the organic farm), or reduced three-fold (as we estimate would have been possible with 25% lower pest densities at the conventional farm), thereby reducing the amounts of conventional insecticides used each year by 0.05 to 0.075 lbs ai per acre.
Potential Pesticide Reduction
Common Trade Names: Provado, Admire
Chemical Name: imidacloprid
Usage: general use (not restricted use)
Recommended Application Rate: 3.75 fl. oz. / A.
Reductions Achieved by this Project: 30% (0.025 lbs ai/acre).
Restrictions on Use: no more than 0.31 lbs ai/A/year may be applied.
Risk of insect resistance: high. Colorado potato beetle has a history of rapid development of resistance to all classes of insecticides used for its management. There is new evidence of a 4.5-fold decrease in susceptibility of this insect to imidicloprid after just two years of use (Grafius and Bishop 1996).
Alternatives: There are few conventional insecticides that this insect has not already become resistant to in most regions. Conventional insecticide alternative: Cryolite (an inorganic enzyme poison). Botanical and microbial insecticide alternatives: Bacillus thuringiensis (Bt), rotenone. Other cultural alternatives: flaming, barrier trenches, crop rotation.
See Table 1 for insecticide costs. No additional application costs were incurred at either farm because insecticide applications were combined with regularly scheduled fungicide applications. Some portion of the harvest has not yet been sold, however, estimated receipts based on current prices are presented here.
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, therefore it has potential use against plant pathogenic fungi. 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.
Schmutterer, H. 1995.The Neem Tree; Source of Unique Natural Products for Integrated Pest Management, Medicine, Industry and Other Purposes. [Ed.H. Schmutterer] VCH New York, 1995.
Grafius, E. and B.A. Bishop. 1996. Resistant Pest Management 8: 21-25.