Reduction of Imidacloprid resistance of Colorado potato beetles with an organic integrated pest management program

Reduction of Imidacloprid resistance of Colorado potato beetles with an organic integrated pest management program

Summary

Note to readers, attached is the complete annual report for FNE08-644

Goals

The main goal of this project was to analyze the correlation between farming practices and pest susceptibility to chemical control, with a specific focus on conventional versus organic farming. In addition to the main goal of the project we planned to observe the feasibility of transitioning from conventional to alternative farming practices by looking at both financial and logistical implications of such a change.

Farm Profile

Green Thumb Farms is a 2000 acre conventional farm in Southwestern Maine. We currently grow about 1044 acres of feed corn, 80 acres of heirloom dry beans, 620 acres of potatoes, 200 acres of turf. This year we also grew 2.5 acres of organic potatoes, 1.3 acres of organic Jacob’s Cattle dry beans, and approximately 3 acres of organic cover crops. These cover crops included an oat/sweet clover mix, a buckwheat/sweet clover mix, an oats/peas/vetch mix, and sorghum-Sudan grass. During this pilot year of the organic program we saw success and have decided that we will continue next year with increased acreage dedicated to organic production. A portion of conventional acreage will also be placed in transition and farmed with organic methods.

Participants

Dr. Andrei Alyokhin, Associate Professor of Applied Entomology at the School of Biology and Ecology at the University of Maine was the technical advisor for this project and completed the statistical analysis of all data related to this project. He also provided advice in the development process of this grant and provided input on field methods.

Earle Towle, the farm manager at Green Thumb Farms, acted as an advisor for this project. He provided information regarding best management practices for growing the crops listed.

Dr. Galen Dively an advisor, consultant, and Extension Specialist with Integrated Pest Management in the College of Agriculture and Natural Resources at the University of Maryland completed all bioassays for this project.

Project Activities

Three fields were chosen for the establishment of defoliation plots and for weekly scouting and observation. Of the fields selected, two were in the Webster piece, one was our newly established organic acreage and the other was several hundred feet away and managed conventionally. The third field, Long field, was about a mile away and was also managed conventionally. The organic field is the only organic acreage currently on the farm. The location for this field was selected based on certification opportunities. This particular section of the Webster piece had not been farmed or managed in any way for the past five years. As a result it could be certified immediately.

The Webster conventional field and Long field were planted with Norwis and Dark Red Norland potatoes respectively. These fields received in furrow fertilizer and the seed pieces were treated with fungicide as is general practice at Green Thumb Farm. The Webster organic piece received a treatment of manure the previous fall, in furrow soybean meal at planting, but the seed received no other treatment at planting.

From planting through harvest the fields were managed strictly by either conventional or organic practices.

As the plants began to emerge defoliation plots were set up within each of the three fields. Each field had 6 10’x 4 row plots. These plots were monitored on a weekly basis, or as often as possible, and evaluated visually using a 5-point scale with 0 being no defoliation and 5 representing complete defoliation. At the end of the season these plots were harvested separately and the yields were calculated. All plots were hand-dug and hand-picked into totes that were then weighed using a portable electronic scale.

In addition to observation of small plots, whole field evaluations were also made during weekly scouting of fields with sampling and counting of pests inhabiting 50 plants randomly selected from each field using methods prescribed by the cooperative extension for threshold scouting. Scouting was preformed as often as possible, but was not possible in every week due to heavy rains and frequent fungicide applications. Variations in potato variety emergence and die-back also prevented simultaneous scouting at the beginning and end of the growing season. No statistical comparison was made between field pests present or defoliation plots in weeks when scouting data was not available for all fields.

As a part of the necessary record keeping for organic certification, information was maintained regarding fertilizer, insecticide, and fungicide applications and rates. As a good farming practice and in compliance with the Maine Board of Pesticide Control this information was also maintained for all conventionally managed fields. All data was compiled using Microsoft Office Excel.

All data was then sent to Andrei Alyokhin for statistical analysis.

Results

Andrei Alyokhin preformed the statistical analysis of data gathered using two-way ANOVA, with field and week of scouting used as the main effects. No statistically significant difference was found between organic and conventional fields in regard to recorded populations of Colorado potato beetles at all life stages. Defoliation rates, when compared, were not statistically different between fields.

Pest control was a major concern for organic potato production in Fryeburg, but it quickly became apparent that there are a number of highly effective methods for this. We hand-picked beetles from plants during the early part of the season and then sprayed twice with a combination of a restricted organic spinosad and a restricted organic pyrethroid. This was highly effective in controlling our insect populations, and the insect of greatest concern, the Colorado potato beetle.

Conditions

This growing season was exceptionally challenging on all fronts. We had excessive rain and discovered late blight in all of our potato fields. A great deal of time in the later part of our growing season was dedicated to scouting the potato fields as a means of monitoring the effectiveness of late blight control and the further spread of the disease. As a result of frequent fungicide applications during this time it was impossible to complete scouting as prescribed by the cooperative extension. This was instead replaced with a less time consuming, more complete, and more typical spot-checking and thus data was not collected.

Unfortunately, there was one change in the program with regard to comparison of yield of the various crop management programs. No direct yield comparisons could be made due to differences in potato varieties grown in each of the test fields. For the purposes of attaining organic certification and to make our product interesting to local markets, we chose to focus on specialty varieties of potatoes for organic production. This also served to prevent any concern of commingling of organic and conventional products.

It should also be noted that the farm had exceptionally low populations of Colorado potato beetles during this past growing season. Our insect controls were highly effective this year and as a result our second or summer generation beetle collections for bioassays did not yield enough beetles for sufficient egg production. Although some beetles were collected and mailed our bioassays were not completed for the summer generation from any fields.

Economics

A direct comparison in cost/acre for organic versus conventional production was made for labor, seed, fertilizer, and chemical expenses. An organic acre cost about twice as much to grow as a conventional acre. A full third of the organic cost came from labor and about half of the labor cost attributed to organics resulted from the cleaning of equipment before it entered the field and the movement of equipment from more central outbuildings to the organic field about a mile away. The following three ways, listed by increasing feasibility, are methods by which this expense could be reduced. The farm could convert to entirely organic production practices, all equipment used in the organic acreage could be dedicated solely to organic production (some is), or the organic acreage could be increased.

In 2009 our organic acreage will be doubled which should reduce some of this labor cost. Increased acreage will also impact seed and nutrient purchasing with the reduced cost of bulk buying.

At this time it is not possible to determine from the data gathered the way in which alternative agricultural methods might impact the cost of conventional production with regard to imidacloprid use.

Assessment

In replication of this project it is crucial that all test fields contain the same variety of potato. Without this continuity no accurate yield comparisons can be made.

It may also be important to maintain an area of refuge in each field in order to maintain sufficient beetle populations for bioassay sampling.

Now that we know organic potatoes can be effectively grown in an area where Colorado potato beetles are numerous and difficult to control conventionally, it would be interesting to follow susceptibility trends for several years.

Adoption

During the 2009 growing season Green Thumb Farms will be doubling the acreage of its organic crops. This will be done to reduce the overall costs of the organic program. Many of the practices used on the organic acreage would have been more cost effective if we had been able to apply them over a larger region. Our primary expense was that of labor for cleaning equipment and time spent moving equipment for use in organic acreage. Therefore, greater acreage would decrease our per acre labor costs.

The mixture of spinosad with a pyrethroid was highly effective on the organic acreage and so this mixture will be used, with conventional insecticides, on test plots in our conventional acreage this year. It will be sprayed side-by-side with a treatment containing only spinosad.

Outreach

This portion of the grant was altered slightly. Due to late receipt of data, the intended outreach venues were missed. The outreach plan will be completed this following fall and early winter when these venues are scheduled to be held again.

Research was discussed informally at the Farmer-to-Farmer Conference in Bar Harbor, Maine hosted by MOFGA, at the Maine Potato Conference in Caribou, Maine, and with neighbors in the Fryeburg, Maine area.

Report Summary

The purpose of this project was to evaluate the impact of organic or otherwise alternative farming methods on Colorado potato beetles resistant to conventional agricultural chemicals, specifically imidacloprid. A number of methods including bioassay, field scouting, and defoliation plots were combined to determine the impact of organic farming on beetle populations. The overall productivity and feasibility of organic potato farming in an area where high beetle pressure exists was also analyzed using cost accounting as well as yield comparisons. Although all methods were attempted no proper comparison of beetle populations before and after exposure to organic practices could be made through bioassay due to abnormally limited beetle populations. This is the main method by which susceptibility and resistance is determined. Scouting data demonstrated no statistically significant difference in Colorado potato beetle populations in organic versus conventional fields. Repeating this project is necessary before any determination can be made as to the impact of farming practices on Colorado potato beetle chemical susceptibility. As a farm we have chosen to further adopt organic farming practices as a result of this project.

• FNE08-644 Annual

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