Eggplants as habitat plants in Poinsettias

Eggplants as habitat plants in Poinsettias

Summary

The annual wholesale value of poinsettias in the U.S. is valued at over $181 million. In New England, poinsettias are a valuable source of farm revenue for growers at a time of year when sales from other ornamentals have declined and other crop production has not started. Greenhouse ornamentals, including poinsettias, represent an important option for diversification to supplement traditional crop production. Ornamentals are grown for their esthetics and growers’ tolerance for pests is low, and thus chemical pesticides are commonly used repeatedly. Growers recognize their reliance on chemical insecticides is neither sustainable nor desirable from an economic, human-health or environmental perspective. In recent years, pesticide resistance among whiteflies on poinsettias has been reported. Growers are eager to use biological control instead of chemical pesticides but they must be sure it works and is cost-effective. IPM approaches are being developed using plants that are highly attractive to the pest as either trap plants to draw the pest away from the crop or indicator plants for early detection. Natural enemies can be released onto these plants where they attack the pest, reproduce and then disperse throughout the crop, providing a continuous supply of biological control even if pest populations are low. This system is commonly called a “habitat plant”.

We propose to assess the use of eggplants as a habitat plant in a greenhouse in the pre-finishing phase of poinsettia production. This will provide an ongoing source of biological control to address whitefly problems early in production and reduce pest pressure in the later stages of plant finishing. This system will ultimately reduce the number of insecticide applications required to keep whitefly numbers below damaging levels. Results from this research could revolutionize IPM in poinsettia production nationally and internationally, allowing growers to produce young plant material that is pest-free, thereby reducing pesticide usage.

Objectives/Performance Targets

Determine the effectiveness of eggplant habitat plants as early detection tools and trap plants for whitefly in greenhouse-grown poinsettia cuttings.

Determine the reproductive ability of Eretmocerus eremicus on eggplant habitat plants naturally infested with whitefly and assess the sustainability of parasitoid releases throughout the production and finishing phases of poinsettia production.

Evaluate the efficacy of eggplant habitat plants as an IPM tool in poinsettia cuttings throughout production and finishing phases for managing whitefly and other arthropod pests.

Accomplishments/Milestones

Throughout the study, low levels of whiteflies (average: 0-7 adults/sticky trap, 0-0.5 adults per eggplant habitat plant) were present in the conventional control greenhouse and the biological control house where parasitoids were released. Whitefly adults were detected both on the sticky cards and habitat plants, but not on the poinsettia plants during routine crop scouting. This demonstrates the effectiveness of sticky cards and eggplant habitat plants as scouting tools for early detection of whiteflies. By inspecting the cards or habitat plants first, growers can save time on scouting, and are able to assess pest populations quickly to determine if intervention is required. Whitefly adults were not detected earlier on habitat plants than yellow sticky cards. However the sticky cards had one major disadvantage over habitat plants for scouting. When whiteflies are stuck to the card, it is extremely difficult to distinguish the two common species on poinsettias (greenhouse and silverleaf whitefly). In contrast, it is relatively easy to identify a live adult whitefly when resting on a plant leaf. Species identification is critical when deciding on a management action such as selecting the appropriate biological control agent to release or pesticide to use.

Throughout the pre-finishing phase, 1,000 Eretmocerus eremicus parasitoids were released weekly on each of four habitat plants. Parasitoids were found in low to moderate numbers on the habitat plants (average: 0-3.75 per plant) and yellow sticky cards (average: 0-46.25 per card). Because whitefly populations on the habitat plants were so low, parasitoids dispersed throughout the crop in search of the host, as evidenced by the higher numbers on the sticky cards. Adult parasitoids were never observed on the poinsettias during scouting. In addition, no whitefly nymphs were found on the poinsettias or on the habitat plants. This demonstrates that spot inspection of poinsettias is not a reliable means of scouting. Though whiteflies were found throughout the season in both greenhouses, based on sticky card and habitat plant inspections, they were not readily detected on the pre-finished crop. Because whitefly reproduction did not occur on the habitat plants, we could not evaluate the reproductive capacity of the parasitoids within this system. Interestingly, in previous years the grower has had whitefly problems during the pre-finishing phase of production. This demonstrates the variability in pest populations from year to year. Thus a grower must always be vigilant, anticipating potential pest problems.

When the poinsettias reached the finishing phase (based primarily on plant size), some were moved to a new greenhouse and others were left in the original greenhouse to maintain proper spacing. At this time, all parasitoid releases ceased, though the habitat plants remained in place. Parasitoids were found on the habitat plants and on sticky cards 2 weeks after the final release date. This suggests that conditions were suitable the parasitoids around the habitat plants, and that there was at least a 2-wk carry over effect. Considering this observation, when whitefly populations are low, growers could cut back on a weekly release schedule, and instead make releases every 2-3 weeks. We also found parasitoids on sticky cards 9 weeks after the last release. Whitefly adults were also detected. This shows that though releases had ceased parasitoids reproduced within nymphs on poinsettias despite extremely low levels of their host. This demonstrates that preventative controls of whiteflies early in the production phase of poinsettias can lead to effective control later in the finishing phase.

This study clearly showed that biological control can be an effective alternative to chemical controls when used early in the plant production cycle. For this trial, in the conventional control house, chemical insecticides were applied four times, targeting thrips and whiteflies. In contrast, no insecticides were applied against whiteflies to poinsettias in the biological control greenhouse. Further research is needed to define the most suitable release schedule to use, taking into consideration different pest population levels. The eggplant habitat system was an effective scouting tool. Its value in terms of attracting whitefly and serving as a means of enhancing parasitoid reproduction was not fully confirmed because whitefly populations were so low in the test greenhouse. Ideally, this study should be repeated in future years when whitefly populations may be higher.

Impacts and Contributions/Outcomes

Results from this trial will be presented at the 2009 annual Tri-State Greenhouse IPM workshops in Maine, New Hampshire and Vermont that targets primarily greenhouse growers, but also extension specialists and professional pest managers. At these workshops, participants get hands on experience identifying insect pests and diseases along with their associated biological controls. They also learn of new innovative research methods, like habitat plants, that are being conducted and introduced around the region. A handout will also be provided to growers detailing the results of this study along with the results of other IPM based trials we are conducting.

This project was a highly effective means of transferring IPM technology to the greenhouse owner/manager and his staff. They were actively involved in the project, assisting with data collection, decision making and other technical activities. Staff learned first hand how to correctly identify various greenhouse pests, scout for whiteflies and their natural enemies and the use of habitat plants. Involvement in the project also provided the growers with unique networking and professional development opportunities, such as attending the New England Greenhouse Conference held in Worcester, MA in October.

The value of these workshops and having a specialist provide hands-on research at the commercial site provides a unique experience for growers. It is the direct involvement that provides the most effective education by providing techniques modified for their own personal use. For example, some of these staff had been to workshops on pest id in the past. It wasn’t until they worked directly with a specialist on these trials and were faced with these pests and biological controls in the greenhouse that they really learned how to correctly id them. Furthermore, the effects of the use of fewer chemical insecticides impact the general community as a whole by providing more ecologically friendly plants improving overall human and environmental health.

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