Northeast Region IPM Grants Projects Funded, FY 2001

Project Title:

Phytoseiids and Spinsad for Thrips IPM in Greenhouses: Efficacy and Compatibility

*Award shown is total amount to be used over the course of the project term.

Executive Summary

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Bedding plants (flowers and vegetable transplants for garden use) are a major crop nationally (Fig. 1, Appendix I) and in the NE U.S. alone, they generate a third of a billion dollars ($343,000,000) in annual sales. This is a "hidden" crop because it is composed of diverse plant material, but is unified by common production methods and timing and is a major contributor to the incomes of many small producers (458 in MA alone). In surveys, growers of bedding plants in MA have identified western flower thrips (WFT) (Frankliniella occidentalis) as their most important pest, as judged by pesticide application number (Smith 1998). This pest distorts flowers and infects plants with plant viruses (INSV, TSWV), ruining their aesthetic value and making them unsaleable. Growers in MA in a 1996 survey averaged 3.8 pesticide sprays to control WFT (in a crop that only lasts 10-12 weeks). In 1999, extension agent reports in MA suggested this approached 5-6 sprays per season. Crops infected with INSV may have to be destroyed, resulting in losses that have gone as high as $150,000 for single growers (Daughtrey unpub, Daughtrey et al. 1997). Currently one material, spinosad (Conserve®), is being relied on for thrips control by most producers, due to resistance to many older products. A clear need exists to develop an IPM program that incorporates natural enemies with selective pesticides, so that currently effective pesticides are not rendered ineffective by selection for resistance.
Work in MA in 2000 showed that the predatory mite Neoseiulus cucumeris can control WFT in spring bedding plants (Fig. 1, Appendix I). However, there is not enough information from realistic field trials to rely on this control method at this time. (Our 2000 test was done at only 3 growers). Here we propose further work in commercial greenhouses to gain more knowledge on the degree of thrips control that use of predatory mites can provide in bedding plant crops. We proposed to compare the efficacy of two mite species and to study the potential of each to be integrated with spinosad, the key insecticide in current use against western flower thrips in greenhouse crops.
We propose to test both N. cucumeris and a promising new phytoseiid from Australia that has recently been brought into commercial production by Novartis (a species not yet publicly identified and known as "Ozzie #1). We will also run laboratory tests to determine the degree of compatibility of spinosad with both N. cucumeris and Ozzie #1. Finally, we will compare the level of control provided by the better of these two mites when used alone versus its efficacy when combined with one mid-season application of spinosad (Conserve®). These trials will significantly advance the goal of integrating biological control into western flower thrips control programs in flower production.

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THE PROBLEM, BACKGROUND, AND JUSTIFICATION

THE PROBLEM
Bedding Plants Generate a Third of a Billion Dollars of Agricultural Sales Annually in the Northeast Region. Nationwide, bedding plants (e.g., marigolds, impatiens, petunias, begonias, etc., grown for landscapes and gardens) in 1998 produced sales of approximately 1.75 billion dollars, which was 51% of all greenhouse floriculture sales (Fig. 1, Appendix I, National Agricultural Statistical Service, 1999). In the northeast, bedding plants are also the dominant greenhouse crop, accounting in MA for 62% of all floricultural sales. In 1998 in MA, CT, NY, NJ, MD, PA, and VA combined, there were over a 1/3 billion dollars in bedding plant sales. Our region accounts for 20% of all bedding plant sales nationally.
Of these seven states, MA ranked number four in 1998, with $39,827,000 of bedding plant sales by growers with $100K or more in sales. When producers of all sizes are included, bedding plant sales in Massachusetts alone exceed $53 million.
In terms of larger economic effects, greenhouse businesses employ a sizable labor force, averaging 16 employees per business. Thus the 458 greenhouse operations in MA in 1999 (New England Agricultural Statistics Service, 2000) generated over 7000 jobs. At the regional level, this industry provides employment for tens of thousands. Finally, the industry is growing (Fig. 1, Appendix I). In MA, the industry has grown 61% since 1990.
This is an important industry whose pest control needs merit serious attention. Because climatic conditions and the level of greenhouse technology in MA are about average for the region, solutions that work in Massachusetts will work for the Northeast region as a whole. Greenhouse crops, pests and conditions are much more similar across the region than are outcrops and pests, which respond more to local variation in soils, temperatures and vegetation. Thus the work proposed here is directly relevant to the entire region.
THE PEST: WFT is the Key Pest of the Crop. Western flower thrips (WFT), Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is the most prevalent species of thrips attacking greenhouse crops (Robb 1989). Reasons for this high pest status include WFT's very large host range, rapid developmental cycle, high reproductive rate, and ability to spread plant diseases, especially INSV and TSWV (see Lewis 1973, Robb 1989, and Parker et al. 1995 for reviews). Frankliniella occidentalis feed on young seedlings and buds, which results in distorted growth. Even feeding on mature flowers may result in severe scaring. This damage to flowers and foliage significantly reduces the aesthetic quality of greenhouse flower crops, making the plants less valuable or even unmarketable (Parrella and Jones 1987). Also, WFT spreads impatiens necrotic spot tospovirus (INSV) and tomato spotted wilt tospovirus (TSWV), both devastating plant diseases (Milne and Francki 1984, German et al. 1992, Ullman et al. 1995). These diseases are present in most floriculture and nursery production areas of the United States, including the northeast (Law and Moyer 1989, 1990) and cause economically significant crop losses in the region (Daughtrey et al. 1997). Crops most commonly affected include chrysanthemums, cyclamen, exacum, impatiens, gloxinia, and reiger begonia (Parrella 1995). There have been complete losses of chrysanthemum crops in California (Parrella 1995) and gloxinia crops in North Carolina (Baker and Jones 1988). During the past several years, TSWV has caused severe damage to assorted crops (Daughtrey et al. 1997). Whole crops have at times had to be discarded, resulting in huge losses (e.g., in 1995 an east coast grower disposed of 30,000 potted exacum plants valued at $150,000 after thrips moved INSV into the crop from infected begonias; similarly, a west coast ranunculus grower lost a crop valued at $63,000 [Daughtrey et al. 1997]). Such losses are not a thing of the past: in spring 1999 a NY grower had to discard $150,000 worth of impatiens plugs (purchased from an out of state producer) because they were found to be INSV-infected on arrival. Control of these virus diseases in greenhouse crops is based on eliminating all infected plants and reducing numbers of WFT in the greenhouse as much as possible.
Chemical control has been the tactic of choice for WFT management by greenhouse growers, but failures of insecticides to control WFT have commonly occurred because of poor contact with thrips in flower buds and soil, and pesticide resistance. Robb (1989) and Robb et al. (1995) suggest F. occidentalis has developed resistance to chlorpyrifos, dimethoate, and cyfluthrin. Immaraju et al. (1992) have also demonstrated WFT resistance to four classes of insecticides, including two pyrethroids (permethrin and bifenthrin), an organophosphate (chlorpyrifos), a carbamate (methomyl), and a macrocyclic lactone (abamectin). Spinosad (Conserve®), a new macrocyclic lactone material, currently provides good control. However, single factor control programs, in which all control is provided by a chemical, select strongly for resistance and are not sustainable. To maintain the current utility of spinosad products, there is a need to develop an IPM program for bedding plants that integrates another form of control, such as predatory mites, with spinosad. To do this, we need further information on the efficacy of such mites in bedding plant crops and on the compatibility of spinosad and phytoseiids.

STAKEHOLDER ENDORSEMENT
In a 1998 survey, greenhouse producers in Massachusetts identified western flower thrips as the pest for which they most frequently applied pesticides to bedding plants (Smith 1998). The continued importance of this pest to MA flower growers was confirmed at the 1999 meeting of our MA Floriculture Team's Advisory Group (the Board of the MA Flower Growers Association, MFGA) at which western flower thrips was again identified as the most important insect problem of the industry. A letter attached here (Appendix II) from the MFGA attests to the facts that western flower thrips remains a key concern of growers and that development of an integrated IPM package combining predatory mites and compatible pesticides, such as proposed here, is a goal of this industry. Regionally and nationally, the floriculture industry has similar goals. For example in NY, the Cornell Greenhouse and Controlled Environment Agricultural Industry Advisory Board has also identified western flower thrips as the key pest of flower crops. Nationally, the industry group representing floriculture (the Society of American Florists) listed thrips as their top pest and integrated and biological control of thrips as their top pest research priority (see documents on this in Appendix IV). This was reconfirmed in SAF's February, 2000 priorities identification meeting in Chicago, at which thrips were unanimously viewed by all six participant breakout groups as a top priority for pest control research (see Appendix IV).

BACKGROUND:
Potential for Predatory Mites as Part of Thrips IPM in Bedding Plants
Past studies of the ability of predacious mites to suppress thrips in flower crops have produced mixed results in different parts of the United States. In California, releases of the predacious mites Neoseiulus cucumeris (Ouds.) or N. barkeri (Hughes) on chrysanthemum at 2.5 mites per leaf were unable to reduce western flower thrips densities below 2-7 per leaf (Hessein and Parrella 1990), an unacceptable level for mums. However, in Maryland, Gill (1994) found that releases of N. cucumeris in a slow release formulation reduced the number of pesticide applications needed for management of western flower thrips in bedding plants from 3.6 to only 0.4. In 2000 in Massachusetts and New York, a trial at three bedding plant growers found that N. cucumeris suppressed thrips to lower levels than did the use of insecticides (Van Driesche and Sanderson, unpublished). In the MA-NY trial, applications of 10,000 N. cucumeris per 1000 sq. ft. of greenhouse space, applied five times (in weeks 1, 2, 3, 5 and 7) in the 10 week bedding plant crop suppressed western flower thrips catches on sticky cards more than did the chemical controls applied by growers and provided acceptable control at all three sites (Fig. 2, Appendix I). At this rate of application, season long thrips control with this mite was achieved at a cost of only 2.9 cents per sq. ft. (=32 cents/m2) (given a price of $57.70 per 100,000 mites).
While several other phytoseiid mite species have been studied for thrips control in greenhouses, presently the only important species used commercially is N. cucumeris. Two other mites have received serious consideration, N. barkeri and Iphesius degenerans, but these are not presently serious contenders for practical use. N. barkeri is no longer commercially available, except on a very limited basis from one small firm in Europe. As a practical matter, growers in the U.S. are unable to obtain this mite. I. degenerans, while useful, has proven hard to rear and is dramatically more expensive than N. cucumeris. This limits use of I. degenerans to single inoculative releases in long term crops. It would not be practical in short term crops such as bedding plants.
A new mite species, however, is being brought into mass production and commercial distribution. In 2001, Novartis, a major supplier of natural enemies, will produce and sell a new predacious mite from Australia, called Ozzie 1 (whose species name is not yet revealed). This species is the result of a survey by Marilyn Steiner of Australian phytoseiids, undertaken with the express purpose of finding the most effective local species for western flower thrips control. Ozzie 1 is the best species that resulted from that effort. It is now going to be made available internationally. Nothing has yet been published on this species, but information presented by Steiner at international thrips and greenhouse IPM meetings (at which Roy Van Driesche attended) suggests that Ozzie 1 is a very promising species. For this reason we propose to compare it directly to N. cucumeris in bedding plants under northeast U.S. conditions. Assurances of adequate supplies of this mite and permits for legal importation to the U. S. have been provided by the Novartis representative (R. GreatRex) to Roy Van Driesche (see attached emails, Appendix III).
It is, however, possible that in some situations, such as crops with particularly high initial thrips densities, these mites may not provide sufficient control by themselves. Consequently, a compatible insecticide that could be used to supplement, but not replace, the biological control program would be useful. Western flower thrips is resistant to many older insecticides, but a member of new class of insecticides, spinosad (Conserve®), a macrocyclic lactone (Eger et al. 1998), is being used by greenhouse operators to suppress western flower thrips. Interestingly, this insecticide seems to have relatively little activity against mites, including phytoseiids (Cowles and Abbey 1999, Cowles et al. 2000). However a November 17, 2000 search of the literature (Agricola database) found no published articles on the impact of this material on phytoseiids. Also, on the same date, a search of Koppert's SideEffects List showed that spinosad was not included in that database. Thus a clear need exists to develop this information and see how compatible spinosad might be with the phytoseiid mites (either N. cucumeris or Ozzie 1) used for biological thrips control.

JUSTIFICATION
The justification for funding this proposal is as follows:
1. Greenhouse floriculture is an important, expanding segment of American agriculture, especially in the northeast.
2. Bedding plants are a major part of greenhouse floriculture, especially in the northeast.
3. Through advisory groups, such as the Massachusetts Flower Growers Association, and direct surveys, bedding plant growers have stated clearly that western flower thrips is their biggest insect pest.
4. Currently, control of western flower thrips is narrowly based, entirely chemical, and mostly reliant on a single effective pesticide (spinosad). This situation is not desirable and growers have stated that they would like to have either biological control options or IPM packages that combine biological and chemical control.
5. Within biological control options for western flower thrips, only predatory mites have performed well on flower crops.
6. Among predatory mites, the only commercially available viable option is use of N. cucumeris.
7. The only new mite being commercialized at the moment that has significant promise is Ozzie 1 from Australia.
8. MA greenhouses are fairly typical of the northeast in terms of crops, pests, level of technology used, and production conditions. Consequently, controls that work in MA will be useable in all of New England, NY, NJ, PA, DE, and VA without much need for modification or local research. In contrast, information from CA, TX and other out-of-region big greenhouse states is of relatively little use to us because of large differences in climate, pests, and greenhouse construction.
9. We have clear cut preliminary evidence from MA and NY in 2000 that the predatory mite N. cucumeris can control western flower thrips in spring bedding plant crops in the northeast (Fig. 2, Appendix I). Thus there is every reason to believe that the solutions proposed here for investigation have a high probability of being successful. We need the research, however, to gain a more robust knowledge of the system and to have more proof of efficacy, with which to promote grower adoption. We also need to develop information on compatibility of spinosad and these mites, as in some cases, such combinations would be needed.
10. Our proposal rests on all these preceding facts and proposes to conduct trials in a realistic setting (actual bedding plant crops of commercial producers) to test the relative value of N. cucumeris vs Ozzie 1 and, following laboratory tests to establish facts about compatibility of these species with spinosad, (2) to test the value of an integrated mite+spinosad package compared to mite releases alone.
11. This research will contribute to the following goals:
a. pesticide reduction (if mites replace insecticide control for thrips in whole or in part)
b. better thrips control leading to better crops and better profits
c. prevention or delay of development of pesticide resistance by western flower thrips to spinosad

Objectives

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Obj. 1. Comparison of WFT control by N. cucumeris and Ozzie #1 in bedding plant crops. The goal of this objective is to determine how well the major commercially available predatory mite (N. cucumeris) sold for thrips control works in bedding crops in commercial greenhouses under northeastern U.S. conditions and to compare its efficacy with what may well be the next important predator mite commercialized for thrips control (Ozzie 1, being brought into mass production in 2001 by Novartis). We believe, based on preliminary trials in MA and NY in 2000 that N. cucumeris will provide adequate control, but it may not do so in all cases. We don't know how well Ozzie 1 will work and we need to find out as this product will soon be marketed.

Obj. 2. Determination of compatibility of spinosad with N. cucumeris and Ozzie #1. Spinosad (Conserve®) is the major insecticide used for WFT control. Some evidence suggests that it may be compatible with phytoseiid mites, but there are no data on this. Growers who use predatory mites for biological thrips control may need to supplement these mites with chemical applications if control is insufficient or begins to fail before harvest. If there is a compatible chemical that could be used without persistent damage to the predatory mites, it would be beneficial. If spinosad, the compound most growers are now using for thrips control were compatible, it would be especially good as growers would be very comfortable with that as their back up product. We don't have this information and need to run some rather straight forward laboratory tests to get it.

Obj. 3. Assessment of integration of spinosad and phytoseiids in commercial greenhouses. Given the laboratory measurements of compatibility of these phytoseiids and spinosad, we next want to assess what happens to both thrips control and phytoseiid numbers when a spinosad application is added to a thrips biological control program in mid-crop. We will compare this to the use of mite releases alone to see if laboratory estimates of spinosad's compatibility are borne out in real crops. We will also include comparison to spinosad used alone to determine the contribution of the addition of mites to the IPM package.

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