With the new bent-shoot method, plants are grown in raised containers in a modified hydroponics system. Most of the shoots are bent downward at the crown to intercept more light, creating a perennial lower canopy that exists for the 5 to 8 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. Pesticides to control western flower thrips and powdery mildew that are more compatible with mite predators have also recently become available. These developments, coupled with the difficulty that rose growers were facing in controlling spider mites, made us confident that we could develop a successful IPM program that rose growers would adopt. This project was initiated in 2000 with major funding from the Pest Management Alliance Program of the California Department of Pesticide Regulation and was later supplemented with additional funding. The goal of the Alliance project was to foster a team approach to the development and implementation of IPM programs in a given commodity and to document a reduction in traditional pesticide use. Our Alliance team included researchers, county-based advisors, growers, chemical and biological-control industry representatives,30 litre plant pots commodity associations and government officials. Our objective was to develop a cost-effective IPM program for the key pests of cut roses that included sampling, thresholds, biological control and directed sprays of reduced-risk pesticides.Each grower contributed an IPM and a conventional-practice greenhouse; all greenhouses were between 5,000 and 10,000 square feet in size.
All pest management decisions in the IPM greenhouses were based on the IPM program that we developed, while the grower made all pest management decisions in the conventional greenhouses. Data was collected and compared on a weekly basis by trained scouts using a comprehensive sampling plan that provided information about the density of insects, mites and diseases. The project included growers with several different rose varieties and both the bent-cane and hedgerow training techniques, but we kept these two variables standardized within a location. Implementation began in March 2000 and continued until January 2001. Fixed precision sampling plans that had been previously developed for two spotted spider mites and western flower thrips were used in our scouting program. This type of sampling plan was developed through intensive surveys of a crop to determine a pest’s spatial distribution. The degree of acceptable error was decided upon in advance, and the number of samples needed to obtain that precision was calculated using knowledge of the pest’s spatial distribution in the crop. We used a precision of 0.25, which is acceptable for pest management sampling . Generally, as spatial distribution becomes more aggregated , more samples are required to determine pest density with the desired precision. Although they take some effort to develop, these types of sampling plans are often more accurate and efficient than other sampling approaches. This study represents the first use of such plans in a floriculture IPM program. Sampling for all other pests was done during sampling and inspection for two spotted spider mites. Data was collated and summarized by the scouts and then discussed by members of the Alliance team. The scouts 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. Each greenhouse was a replicate, and ANOVA was used to determine whether there were differences between the conventional and IPM treatments.The first leaf above the bend on 38 randomly selected plants was sampled per 10,000 square feet of greenhouse area to estimate mite density at the desired precision.
Plants were classified as infested if the scout found more than five mobile mites on the sampled leaf, or not infested if there were five or fewer. These samples were also used to determine co-occurrence of two spotted spider mites with the predatory mite Phytoseiulus persimilis, and they were inspected for secondary pests and diseases. In addition to the fixed samples, the scouts took directed samples as they walked down each row and noticed damage by insects, mites or pathogens. These plants were flagged for potential spot treatments. In the IPM greenhouses, mite treatments were initiated according to the percentage of infested plants . Chemical controls included azadirachtin , bifenazate and insecticidal soap , all of which provide some level of compatibility with P. persimilis. Releases of predatory mites were based on the cooccurrence of two spotted spider mites and predators on the sampled leaf. Cooccurrence is the percentage of plants with two spotted spider mites on which P. persimilis also occurs. This idea has been discussed in the literature as a theoretical basis for natural enemy releases, but has never been tested in practice . We chose to include this method in our program because our natural enemy supplier recommended it to growers. Additional predatory mites were released when co-occurrence was less than 10%. All predator releases were made to leaves just below those on which two spotted spider mites were present. Predators were kept refrigerated and were released as soon as possible after arrival at the greenhouse, as per the supplier’s instructions.A fixed precision sampling plan for western flower thrips was also developed . This sampling plan used yellow sticky traps and a general threshold of 25 to 50 thrips per trap per week . Three 4-by-6-inch yellow sticky traps with both sides exposed were placed per 10,000 square feet . The traps were placed at flower level and were evenly distributed in the greenhouse . The lower threshold of 25 thrips per trap per week was used in more-susceptible varieties and in areas of heavy thrips pressure. The higher threshold of 50 thrips per trap per week was used in less-susceptible varieties . There is currently no cost-effective biological control agent for western flower thrips in cut roses, so control of this pest in the IPM greenhouses included both cultural and chemical methods.
Although the female thrips lays eggs in the flower or in foliage directly below the flower, the development time for eggs and larvae is longer than the 5 to 6 days between sepal split and flower harvest . Routine flower harvest removes immature thrips from the greenhouse and subsequently there is little thrips reproduction in the rose greenhouse unless open flowers are left on the rose plant. Teerling has measured significantly higher thrips populations in Canadian rose greenhouses when these flowers are not removed. Cultural control was the removal of open flowers, and chemical control was applications of spinosad or azadirachtin directed to the flowers when the thrips-per-trap-perweek threshold was reached. Research on the distribution of thrips in the rose range has revealed that most thrips are found near the developing flower . Based on these findings, we then conducted a trial to determine whether sprays directed toward the flowers would provide control equivalent to full-volume wet sprays. Such a study is critical to the implementation of IPM in the rose range, because a typical full-volume spray in roses may reach hundreds of gallons of water per acre. Such high volume thoroughly wets the foliage, but creates problems with runoff and affects biological control agents regardless of where they are on the plant. In separate rose greenhouses,25 liter pot plastic we initiated a replicated study where rose beds were divided into 20-foot sections and applications of registered pesticides were made using full-volume wet sprays at 275 gallons per acre versus the same material applied just to the upper canopy at 70 gallons per acre . Registered materials — acephate , methiocarb and spinosad — at label-recommended rates were used in the study. There were four replicated, 20-foot rows for each material per volume combination, and applications were made for 4 weeks. At the end of this time, 10 flowers were removed from each section and examined for the presence of thrips. Our effort to introduce IPM principles in the management of powdery mildew centered on an attempt to use a predictive model for powdery mildew of grapevines . The UC Davis powdery mildew risk-assessment model for grapevines is based on the effect of temperature on the reproductive rate of the pathogen following initial plant infection. As temperatures are recorded in vineyards, risk points are accumulated if temperatures are favorable or subtracted if temperatures are not favorable. When risk points reach a predetermined threshold, fungicide application is recommended. This model has been effective in determining if and when fungicide treatments need to be applied to grapevines, and has resulted in effective disease management with significantly reduced fungicide usage in California. In commercial rose greenhouses, growers spray regularly weekly during mildew season in Central California and all year long in Southern California. It is not unusual for half of all yearly pesticide sprays in a rose crop to be for mildew control, presenting a strong argument for matching applications to actual risks. Although the powdery mildew fungus attacking roses is a different species, its response to environmental conditions is similar to that of the species attacking grapevines. For this reason, we sought to determine whether the grapevine mildew model could be easily adapted to greenhouse grown roses. The greenhouses used in this effort were instrumented so that temperature, relative humidity and leaf wetness were measured at 30-minute intervals throughout the day and night. Temperature data was fed into the GMM to add or subtract risk points. In order to correlate actual disease development with the GMM risk points, a trained scout evaluated plants in the greenhouses weekly.
This was accomplished by walking through the greenhouses in a predetermined pattern, stopping at regular intervals and evaluating one plant at each stop-point to assess disease incidence and severity. Disease incidence was determined by the presence or absence of mildew lesions on the leaves of harvestable stems. Disease severity was determined by counting the actual number of lesions on leaves attached to the harvestable stems. This data was used to calculate an overall disease rating for the crop that could be compared to risk predictions based on the GMM. Along with the disease incidence and severity data, we recorded the timing of all chemical fungicide and insecticide applications made by the growers in the IPM houses so that we could evaluate these effects on disease ratings. As a resistance management practice, growers typically varied the fungicide materials used throughout the season. A few fungicides were common across all locations, but growers did differ in some of the materials applied. For example, if powdery mildew became severe in a greenhouse, growers at all locations would typically apply piperalin because of its eradicative properties. Other materials used at the various locations included myclobutanil , chlorothalonil , benzeneacetic acid , azoxystrobin , insecticidal soap and potassium bicarbonate .Plants in both the IPM and conventional greenhouses were inspected for whiteflies, aphids, mealybugs, Botrytis, downy mildew and rust as part of the inspections for twospotted spider mites. The same traps that were used to monitor western flower thrips were also used to monitor white flies and winged aphids. We emphasized the use of materials that were compatible with the P. persimilis predator for control of these pests when necessary.Two spotted spider mites. Predatory mites were successfully used in all of the IPM greenhouses and almost eliminated the need for miticide applications in those houses. A comparison of two spotted spider mite levels under IPM and conventional control across all nurseries revealed that there were significantly more plants with no mites and significantly fewer plants with mites at the two levels measured in the IPM greenhouses . Similar results were observed at the individual nurseries. The cost of IPM during the first 8 weeks was higher than the cost of conventional control . Higher release rates were needed during this startup period for several reasons, including increased predator mortality as growers learned proper release techniques and the desire of some growers to begin biological control when twospotted spider mite densities were greater than the 25% infested threshold. After several releases had been made and predators became established, the release rate dropped and costs for the two control programs were comparable. Western flower thrips.