Full article with graphics.

 

 

IPM Works in California Greenhouse Cut Roses

 

Christine Casey¹, Julie Newman², Karen Robb³, Steven Tjosvold⁴, Heidi Petersen⁵, and Michael Parrella⁶

 

¹Department of Entomology, University of California, Davis, CA 95616.  Current address: Assistant Professor, Department of Entomology, North Carolina State University, Raleigh, NC 27695

²University of California Cooperative Extension, Ventura, CA 93003

³University of California Cooperative Extension, San Diego, CA 92123

⁴University of California Cooperative Extension, Watsonville, CA 95076

⁵Syngenta Bioline, Oxnard, CA 93034

⁶Department of Entomology, University of California, Davis, CA 95616

 

Abstract

 

We developed and tested an integrated pest management program for the key pests of fresh cut roses that was based on fixed precision sampling plans, thresholds, biological control, reduced risk pesticides, and cultural control.  This program represents the largest effort to implement an IPM program in US floriculture.  Biological control of mites was successful at all locations and pesticide use was generally lower in the IPM greenhouses.  Future work will concentrate on reducing scouting time, use of more effective natural enemy release methods, and development of IPM techniques for secondary pests.

 

 Introduction

        Rose production is currently the largest component of the $500 million cut flower industry in California.  In 2001, California growers produced 66% of the US rose crop with a wholesale value of $45 million (USDA 2002).  The key pests of this system are the twospotted spider mite (Tetranychus urticae), the western flower thrips (Frankliniella occidentalis), and rose powdery mildew (Spaerotheca pannosa rosae).  The twospotted spider mite is a foliage feeder that extracts the cell contents from leaf parenchyma tissue, which causes foliar stippling and disrupts the plant’s photosynthetic and water balance mechanisms (Tomczyk and Kropczynska 1985).  The western flower thrips is both a foliage and flower feeder, although it feeds primarily on flowers in the cut rose system (Robb 1989).  Thrips enter the rose flower when the sepals of the developing flower bud split open and the flower color becomes visible.  Feeding by the thrips causes distortion and darkening of the flower petals.  Although the female thrips oviposits on the flower or the foliage directly below it, thrips egg hatch and larval development time is longer than the five to six days that pass between sepal split and flower harvest (Robb 1989).  Flower harvest removes these immature thrips from the greenhouse and thus there is little thrips reproduction in the rose greenhouse unless open flowers (those that are too mature for harvest) are left on the rose plant.  Teerling (2000) has measured significantly higher thrips populations in Canadian rose greenhouses when these flowers are not removed.

Fresh cut roses must be harvested twice daily, so re-entry intervals after pesticide application imposed by the federal Worker Protection Standard limits the number of pesticides that will fit this production system.  In addition, implementation of the Food Quality Protection Act will likely result in further loss of pesticides.  The frequency of pesticide sprays typical in a rose range has impeded the implementation of IPM procedures, particularly the use of biological controls.  Pesticides targeting hard-to-kill floriculture pests frequently kill natural enemies, which favors continued reliance on conventional pesticides while discouraging the adoption of biological control.  Heavy pesticide use against key pests in the greenhouse has resulted in the widespread development of pesticide resistance in western flower thrips (Immararaju et al. 1992; Jensen 2000), mites (Ramdev at al. 1988; Fergusson-Kolmes et al. 1991; Goka 1998), whiteflies (Prabhaker et al. 1985) and aphids (Kerns & Gaylor 1992).  The heavy use of pesticides in cut roses is a worker safety concern in foreign production (Tenenbaum 2002).  California rose growers reached a crisis point about four years as pesticide resistance, cost, and limited product availability threatened their ability to cost-effectively manage twospotted spider mites.  In response, they sought the help of University of California researchers, farm advisors, and the biological control industry.

At the same time, a new cut rose production system that favors the success of IPM was gaining widespread acceptance.  Roses were traditionally grown in soil with all shoots growing upward from the base.  Under the new bent shoot method, plants are grown in raised containers in a modified hydroponic system.  Most of the shoots are bent downward at the crown to intercept more light, creating a perennial lower canopy that exists for the five to eight years of crop production.  The upper canopy contains only stems that produce flowers, which take 45 to 52 days to develop.  The bent shoot method creates a spatial separation between the harvested flowers and perennial foliage that does not exist in standard roses (Fig. 1).  This facilitates biological control by permitting directed pesticide applications to the flowers, thereby conserving predatory mites in the lower canopy.  We have shown that this technique reduces spray volume by 35 percent with no effect on thrips control efficacy (Parrella et al.1999).  Pesticides for thrips and mildew control that are more compatible with mite predators have also recently become available.  These developments, coupled with the difficulty rose growers were facing controlling spider mites made us confident that we could develop a successful rose IPM program that would be adopted by growers.

This project was conducted with major funding support from the Pest Management Alliance program of the California Department of Pesticide Regulation.  The goal of the Alliance project is to foster a team approach to the development and implementation of IPM programs in a given commodity.  Our Alliance team included researchers, extension agents, growers, chemical and biological control industry representatives, and government agencies.  Our objective was to develop a cost effective IPM program for the key pests of cut roses that included sampling, thresholds, biological control, and reduced risk pesticides. 

 

Implementing the IPM program

Eight growers spanning the major rose producing areas of California (San Diego, Santa Barbara and Santa Cruz Counties) participated in the program.  Each grower contributed an IPM and a conventional practice house, each of which was between 5000 and 10, 000ft² in size.  All pest management decisions in the former were based on the IPM program we developed, while the grower did all pest management in the latter. Data were collected and compared on a weekly basis by trained scouts using a comprehensive sampling plan that provided information on the density of insects, mites, and diseases.  The project included growers with several different rose varieties and both bent cane and upright training techniques, but we tried to keep these two variables standardized within a location.  Implementation began in March 2000 and continued until January 2001.  Fixed precision sampling plans that were previously developed for twospotted spider mites (Casey 2002) and western flower thrips (Casey and Parrella 2000) were used in our scouting program.  This type of sampling plan is developed through intensive surveys of a crop to determine a pest’s spatial distribution in the crop.  The degree of acceptable error (the “precision” of the plan) is decided upon (or “fixed”) in advance and the number of samples needed to obtain that precision is calculated using a knowledge of the pest’s spatial distribution in the crop.  We used a precision of 0.25, which is acceptable for pest management sampling (Southwood 1978).  Generally, the more aggregated the spatial distribution, the more samples will be required to determine pest density with the desired precision.  Although they take effort to develop, these types of sampling plans are often more accurate and efficient than other sampling approaches; this represents the first use of such plans in a floriculture IPM program.  Sampling for all other pests was done as plants were inspected during twospotted spider mite sampling.    Data were collated and summarized by the scouts who then met with the growers to discuss control strategies.  Based on thresholds developed for each of the pests, no action was taken; cultural controls were used; biological control agents were released, or a pesticide application was made. 

Twospotted spider mites

The first leaf above the bend on 38 randomly selected plants was sampled per 10, 000ft² of greenhouse area to estimate mite density at the desired precision.  Plants were classified as infested if the scout found more than 5 mobile mites (eggs are not counted) on the sampled leaf or classified as not infested if there were 5 or fewer mobile mites.  These samples were also used to determine co-occurrence of twospotted spider mites with predator mites, Phytoseiulus persimilis, and they were inspected for secondary pests and for diseases.  In addition to the fixed samples described above, as the scouts walked down each row they took directed samples where damage symptoms of insects, mites or pathogens were present.  These plants were flagged for spot treatment.  In the IPM houses, mite treatments were initiated according to the percentage of infested plants as shown in Table 1. Chemical controls included Azatin (azadiractin), Floramite (bifenazate), or M-Pede (insecticidal soap), all of which are compatible with P. persimilis.  Releases of predatory mites were based on co-occurrence of twospotted spider mite and predator on the sampled leaf.  Co-occurrence is the percentage of plants with twospotted spider mites on which P. persimilis also occurs.  Co-occurrence has been discussed in the literature as a theoretical basis for natural enemy releases, but this idea has not been tested in practice (Nachman 1981, Ryoo 1996, Greco et al. 1999).  We choose to include this method in our program as our natural enemy supplier recommended it to growers. 

All predator releases were made to leaves just below those on which twospotted spider mites were present.  Predators were kept refrigerated and released as soon as possible after arrival at the greenhouse, as per the supplier’s instructions.

 

Western flower thrips

A fixed precision sampling plan for western flower thrips using yellow sticky traps was also developed (Casey et al. 2001).  The sampling plan for western flower thrips used yellow sticky traps and a general threshold of 25 to 50 thrips/trap/week.  Three 4in by 6in yellow sticky traps (   ) with both sides exposed were placed per 10, 000 ft².  The traps are placed at flower level and are evenly distributed in the house (at the ends and center of the middle row, for example).  The lower threshold of 25 thrips/trap/week is used in more susceptible varieties (generally white or yellow flowers) or in areas of heavy thrips pressure.  The higher threshold of 50 thrips/trap/week is used in less susceptible varieties (generally red flowers).  There is currently no cost effective biological control agent for western flower thrips in cut roses, so western flower thrips control included both cultural and chemical controls.  Cultural control was removal of open flowers, while chemical control was based on applications of Conserve (spinosad) or Azatin (azadiractin) directed to the flowers when the threshold was reached. This technique can significantly reduce spray volume with no reduction in efficacy (Parrella et al. 1999).  Lower volume, directed applications can reduce runoff into the lower canopy and help conserve Phytoseiulus persimilis that have been released there.

 

Secondary pests

            Plant inspections for whiteflies, aphids, mealybugs, Botrytis, downy mildew, and rust were done as part of the plant inspections for twospotted spider mites.  The same traps used to monitor for western flower thrips were also used to monitor whiteflies and winged aphids.  We emphasized the use of materials that were compatible with the Phytoseiulus persimilis predator for control of these pests.

 

Was the IPM program successful?

Twospotted Spider Mites

Predatory mites were successfully used in each of the IPM greenhouses and almost eliminated the need for miticide applications in those houses.  A comparison of twospotted spider mite levels under IPM and conventional control across all nurseries is given in Figure 3.  There were significantly more plants with no mites and significantly fewer plants with mites at the two levels measured under IPM.  Similar results were observed at the individual nurseries.  The cost of IPM during the first eight weeks was higher than the cost of conventional control (Table 2).  This is due primarily to the higher release rate that is needed during this period.  This was due in part to predator mortality due as growers learned proper release techniques and in part to the desire of some growers to begin biological control when twospotted spider mite densities were greater than the 25 percent infested threshold.  After several releases were been made and predators became established, the release rate dropped and costs of the two control programs was comparable.

 

Western Flower Thrips

The monitoring program and the use of reduced risk pesticides for control of western flower thrips worked very effectively in the IPM greenhouses.  This was a critical component of the entire program, since thrips are considered the key pest of roses (and for that matter, all cut and potted flowering crops).  The need to control thrips with pesticides often limits the use of biological control in floricultural crops. There were significantly fewer western flower thrips caught in the IPM houses than in the conventional houses across all nurseries.  The largest differences in thrips levels between the two treatments occurred during the summer months when western flower thrips pressure is generally highest (Figure 4).  There were also greater fluctuations in overall western flower thrips densities in the conventional houses as well as more variation between individual conventional houses.  We attribute both of these observations to the regular removal of open flowers in the lower canopy that occurred under IPM.  The majority of western flower thrips reproduction in the rose greenhouse occurs in open flowers (those that are too mature for commercial harvest); by removing these flowers the occurrence of extreme fluctuations in western flower thrips populations are reduced.

 

Secondary pests

Effective IPM implementation was hindered at two sites by the citrus mealybug, Planococcus citri.  This pest is generally not a problem for rose growers until IPM is implemented, when the cessation of broad spectrum pesticide applications can allow this pest to develop.  It is generally only a problem at sites where roses are or were grown adjacent to areas to crops such as Stephanotis, on which citrus mealybug is a key pest.  Unfortunately natural enemies of the mealybug are not currently available, and the most effective mealybug pesticides are detrimental to spider mite predators.  We are working with the natural enemy suppliers to try and change this situation.  In the interim, we will continue to evaluate reduced risk pesticides for efficacy against the citrus mealybug.

Overall, we are satisfied that the rose IPM program was successful.  A testament to the effectiveness of the mite biological control is emphasized by the fact that most of the growers wanted to abandon their conventional treatments in favor of using predatory mites.  We allowed this to occur after we felt enough data had been collected for a good comparison of the IPM to conventional treatments.  Future work needs to concentrate on reducing the sampling effort while still allowing the collection of sufficient information to allow good pest management decisions.  The development of effective IPM techniques for secondary pests is also needed.

This program represents the largest effort to demonstrate and implement an IPM strategy on floriculture crops in the United States.  Drawing on the partnerships that are central to the Alliance concept, we have shown that high quality roses can be produced with substantially fewer pesticides and with the incorporation of biological control into mainstream floriculture. Effective partnering with the biological control industry has also been a hallmark of this program. This has lead to the widespread use of predatory mites in commercial rose production in California, representing the largest use of biological control by the floriculture industry in the United States.

 

 

Acknowledgements

 

            We would like to acknowledge financial support from the American Floral Endowment, the California Association of Nurserymen, the California Cut Flower Commission, the California Department of Pesticide Regulation, the International Cut Flower Grower’s Association, the UC Davis Center for Pest Management Research and Extension, the UC Integrated Pest Management Program, and the USDA-ARS Nursery and Floriculture Research Initiative.

            We would also like to acknowledge the donation of Phytoseiulus persimilis by Syngenta Bioline and the cooperation of Aspen Nurseries, Dramm and Echter, Kitayama Brothers, Kocher Flowers, Myriad Flowers, Roseflor, Sunshine Flowers, and Westerlay Roses.  Finally, we would like to acknowledge the technical assistance of Sarah Cain, Steve Martin, Scott Parker, John Rodgers, and Deb Yamashita.

References

 

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