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Using biological control methods in strawberries

Three strawberry IPM projects involved biological controls in 1996. One used Trichoderma harzianum, a naturally occurring fungus, to combat a fungal disease called Botrytis. The project went a second step and used a biological agent to deliver the Trichoderma to the plants: honey bees deposited spores of the beneficial fungus on strawberry blossoms during pollination.

Results from five growers' farms plus a research site in Geneva show that bee-delivered Trichoderma harzianum provides the same level of control of the disease as one commercial fungicide application. Furthermore, the berries in bee-visited plots were 30 percent larger on average than berries in plots not visited by the bees. Bioworks Inc., a company begun by scientists at the Geneva Experiment Station, hopes to have its strain of Trichoderma approved for commercial use this year.

Another IPM project focused on the root weevil. This pest has been particularly troublesome because growers have lacked an effective means of managing it. However, three formulations of nematodes (microscopic roundworms) that show promise for root weevil management are now available commercially.

In the IPM project, nematodes were applied to the soil in hopes they would find and feed on root weevils. Positive results were achieved in 1995, but tests were inconclusive in 1996, as the nematodes did not survive long in the soil. Some of the specimens may have died in transit from the manufacturer. Samples of future shipments of nematodes will be examined under a microscope upon arrival to make sure they are alive.

A third attempt to expand the array of biological control options for strawberries used Beauveria bassiana, a fungus that acts as a contact insecticide, to manage the tarnished plant bug, a major pest of strawberries in New York. Results from 1995 showed that the fungus reduced tarnished plant bug injury to a commercially acceptable level. In 1996, however, Beauveria appeared to have no effect on tarnished plant bug populations. This year's smaller plots with no buffer zones apparently allowed for migration of the bugs from one plot to another. This would account for the lack of difference between treated and untreated plots.

The outcome of this project underscores one of the factors that must be taken into account when working with biological controls. The fragility of living organisms such as the nematodes must be dealt with both by newly emerging biological control industries, as they develop their product lines, and by growers wishing to use such pest management methods. Biological controls can be more vulnerable than synthetic materials to changes in temperature, humidity, and precipitation. Despite these difficulties, biological controls are a necessary piece of an environmentally and economically sound agricultural system.