Using Honey Bees to Disseminate Trichoderma harzianum to Strawberries for Botrytis Control

Using Honey Bees to Disseminate Trichoderma harzianum to Strawberries for Botrytis Control

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METHODS

Six strawberry growers located in Oswego, Tompkins, Yates, Genesee, Wyoming and Wayne counties of New York cooperated on this project. At each site, a one to two acre field was selected. Flower data were collected from all fields, but fruit data came from only 5 grower fields because at one site, Sodus, fruit was picked before harvest evaluations could be conducted. A honey bee hive (nuke box) was placed on the edge of each test field on May 21, 22, 23 depending on location. An applicator device filled with T. harzianum powder containing at least 5 x 10 8 colony forming units per gram was placed in front of the hive exit and refilled when necessary (usually weekly). As the bees exited the hive to pollinate the strawberries, T. harzianum spores, were pick up by the bees and deposited on the flowers. Four treatments were assigned at each site and replicated six times. The four treatments were: 1) flowers visited by bees with T. harzianum spores; 2) two applications of a T harzianum spray applied at early (5/28-29), and mid - late bloom (6/2-5); 3) a grower standard (usually a spray of captan/benomyl, iprodione or vinclozolin); and 4) a bee excluded unsprayed check. Plot size was a 2 meter length of strawberry row. Bees were excluded in treatments 2 and 4 by using floating row covers. The rowcovers were placed over the strawberries before the hives entered the field and were removed immediately after the hives were removed (6/10, 6/12, 6/17). In treatment 2, the rowcovers were temporarily lifted during the application of the Trichoderma sprays and replaced immediately after the spray was applied. In treatment 3, growers were asked to put on at least one benomyl spray in the standard treatment to control Botrytis as well as to kill any T. harzianum that may have contaminated the flowers.

At all sites, flowers were sampled twice, once before treatments were in place (5/21, 5/22, 5/23) and again during the treatments (5/28, 5/29). Samples were taken from each replicate and placed on Trichoderma selective media to determine the percentage of flowers inoculated with T. harzianum. In addition, the number of colony forming units (cfu) per flower were estimated to make comparisons between bee disseminated treatments and sprayed treatments. Densities were classified as low, medium or high and assigned values of 1, 5, 20 for analysis.

All fruit from each plot was harvested when ripe, two picking per site were made (6/20, 6/24, 6/25, 6/30, 7/1, 7/2, 7/3, 7/7, 7/8). Berries were counted, weighed and the number of Botrytis damaged fruit was evaluated. To assess latent Botrytis infections, sub samples of approximately 25 asymptomatic berries per plot were incubated for 4 days at 22C, 95% RH, in a mist chamber, and the number of healthy and diseased berries were counted. An additional 5 berries per replicate were sampled and cut in quarters to determine the number of seeds per fruit. Data were analyzed statistically using standard analysis of variance models (SuperANOVA, Abacus Concepts). Log x+1 transformations were performed where appropriate.

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