Eggplants as habitat plants in Poinsettias

Project Overview

Project Type: Partnership
Funds awarded in 2008: $9,993.00
Projected End Date: 12/31/2009
Region: Northeast
State: Vermont
Project Leader:
Dr. Margaret Skinner
University of Vermont

Annual Reports


  • Additional Plants: ornamentals


  • Pest Management: biological control, cultural control, field monitoring/scouting, integrated pest management, trap crops
  • Production Systems: general crop production

    Proposal abstract:

    In the US, about 25,000 farming operations produce nursery and greenhouse crops with a total annual wholesale value of $14 billion. The income-generating potential of greenhouse ornamentals far exceeds that of most traditional corps in New England, especially when considered on a per acre basis. Based on the most recent USDA NASS survey, the annual wholesale value of ornamentals in 6 of the 13 New England states (CT, MA, MD, NJ, NY, PA), in 2004-05 exceeded $460 million, an increase of 17.5% since 2000. Over 12 million poinsettias with a wholesale value of $49.5 million were produced by 437 greenhouse growers with >$100,000 sales. Greenhouse ornamentals represent an important option for diversification to supplement traditional crop production. Poinsettias are a valuable source of farm revenue for New England growers at a time of the year when sales from other ornamentals (e.g., perennials, bedding plants, etc.) have declined, and production of other plants has not yet commenced. Because ornamentals are grown for their aesthetic value, grower tolerance for pests and damage is necessarily low, far less than for greenhouse grown vegetables. Therefore chemical pesticides are commonly used repeatedly, though growers in general recognize their heavy reliance on chemical insecticides is neither sustainable nor desirable from an economic, human-health or environmental perspective. In recent years several examples of pesticide resistance among key pest species have been reported. Specifically in poinsettias, a whitefly biotype (Q) has been found that is resistant to Marathon, the most commonly used insecticide for whitefly control. The Q biotype surfaced in Vermont a few years ago, resulting in a persistent problem that ultimately was only solved by hand-picking off infested leaves. Growers are eager to use biological control rather than chemical pesticides as part of IPM but they must be assured that these alternatives work and are cost-effective. The key to successful biological control is to minimize pest problems at the start of the season, i.e., “Start clean to stay clean.” Several aspects of poinsettia propagation make this goal difficult to achieve. To produce the millions of poinsettias sold annually, a few of the larger US growers propagate plants from cuttings under mist tables and sell them to growers regionally to finish off and sell retail in November and December. The one poinsettia propagator in Vermont, Chris Conant, Claussen’s Greenhouses and Florist, produces 40,000 poinsettias many that are sold to retail growers statewide. This crop generates a total $350,000 annually. Stock plants are started in April and grown to full size over the summer. Thousands of cuttings are taken from these stock plants from July-August and propagated under misters to produce young plants for finishing. Because the propagators are continually exposed to these cuttings for 8 hours a day for ~2 months, Conant decided 10 yr ago to use no chemical pesticides on his stock plants. As a result, cuttings and young plants are commonly lightly infested with whitefly. These low-level infestations serve as a pest source that can increase and spread throughout the crop over the summer and early fall because environmental conditions (day length and ambient temperature) are ideal for whitefly population growth. To maximize on the potential of biological control in poinsettias during the finishing phase, strategies are needed to minimize or eliminate pest infestations during propagation. However, if there are no pests, the beneficials have no host material on which to reproduce. Repeated releases of natural enemies are necessary in these situations which are expensive and time consuming. IPM approaches are needed that sustain reproduction of biological control agents when pest populations are low or absent so that they are endemic in the crop should a pest problem develop. To date reliable sustainable biological control strategies for whiteflies in poinsettias have not been fully developed or tested in the propagation phase. This leaves growers with few alternatives to pesticide-based control to produce pest-free plants in later stages of production.

    Project objectives from proposal:

    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 beneficials even when pest populations are very low. This system is commonly called a “habitat plant” because it serves multiple IPM roles, i.e., that of indicator and/or trap plant and natural enemy production system.

    We propose to assess the use of eggplants as a habitat plant in a greenhouse where poinsettia stock plants are grown. This will address whitefly problems early in production, thereby reducing pest pressure in the later stage of plant finishing stage. This SARE Partnership Project will expand on research we conducted in 2007 testing eggplants as habitat plants in the finishing phase of poinsettia production (Fig. 1). We demonstrated definitively that silverleaf whitefly was highly attracted to eggplant, confirming that it can be used as an effective trap plant. Eretmocerus eremicus was released on the eggplants and clear evidence of host feeding and parasitism was observed suggesting that the eggplant played a role in sustaining the parasite population over time. Parasitism rates of >45% were observed on the habitat plants, showing that they have great potential as a sustainable biological control system. However, in some of the test greenhouses whitefly populations were too high at the start of the season to achieve the level of pest control growers and the public demand. In these cases one or two pesticide applications were required. If whitefly infestations could be minimized or eliminated from the stock plants, the newly propagated plants will have fewer pest problems improving the chance for successful, less expensive biological control throughout the rest of the growing season.

    It has been estimated that when biological control is introduced into conventional pest management systems, pesticide use is reduced by 50-95% and “softer” classes of pesticides are selected that are compatible with natural enemies, and with less negative impacts on humans or the environment. We found this to be true in our 2007 habitat plant study in poinsettias which was conducted in two commercial Vermont greenhouses, where in past years pesticides were routinely applied. In one test greenhouse no pesticides were used for whitefly control, and the grower was very satisfied with the level of control achieved throughout the season. At the other test site, the grower reduced his insecticide use by 50% in greenhouses where habitat plants were used compared with four or more applications in the greenhouses where conventional pesticide-based control was practiced. We believe that the “habitat plant” system would have been even more effective if whitefly populations had been lower and parasitoid populations had been established earlier in the season. We propose to test this hypothesis by introducing biological control during propagation with eggplant habitat plants and parasitoids in greenhouses where the stock plants are grown.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.