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

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RESULTS AND DISCUSSION

Pretreatment sampling of the flowers showed that Trichoderma is naturally present on strawberries in commercial fields. At all of the growers sites some Trichoderma was present, especially at the Penn Yan and Castile sites (Table 1) which had 25-33% of the flowers testing positive for Trichoderma. Even though Trichoderma was detected in these fields, it probably was not a strain that controls Botrytis because the selective media used in this study is unable to distinguish between the different strains or species of Trichoderma. However, this natural occurrence of Trichoderma in fields should help reassure government regulators of Trichoderma presence and safety in the environment.

Table 1. Precent of flowers sampled on 5/21, 5/22, and 5/23 with *Trichoderma* present before treatments applied.
	% Trichoderma	Rating (1,5,20)
Grower	% flowers w/Trich.	est. of trich cfu density
Sodus	4 a	0.08 a
Lansing	8 ab	0.20 a
Bergen	8 ab	0.24 a
Penn Yan	25 bc	1.37 a
Castile	33 c	5.83 b
Means followed by the same letter are not significantly different (p<0.05, LSD). Data transformed Log x+1 prior to analysis.

The Trichoderma sprays were applied at a rate of 1.6 kg/ha (1.5 lbs/A) of formulated product per application. Since two sprays were applied, a total of about 3.2 kg/ha was used. The honey bees delivered an average of 7 g of Trichoderma per day for the 21 day period at the grower sites. In the plots that were sprayed with Trichoderma , over 90% of the flowers had detectable amounts of Trichoderma (Table 2). There was less Trichoderma detected in bee delivered treatments (75%). The check plots had close to 80% of the flowers with detectable levels of Trichoderma.. This contamination of the check could have been caused by spray drift, spores falling off of the bees while visiting other plots or background levels of non biocontrol Trichoderma. The fungicide spray that was applied by the growers to the grower's standard treatment did significantly reduced the level of Trichoderma detected in the flowers.

Table 2. Percent of flowers sampled on 6/2, 6/4, 6/5 from various treatments with Trichoderma.
Treatment	% flowers w/ Trich.	Treatment EST of Trich. cfu density
Grower standard	68 a	3.7 a
Check	79 b	4.9 ab
Bee delivered Trichoderma	75 b	5.5 b
Trichoderma spray (twice)	94 c .	9.6 c
Means followed by the same letter are not significantly different (p<0.05, LSD). Data transformed Log x+1 prior to analysis

Table 3 shows the percent of Botrytis damaged berries in the grower fields and after incubation in the mist chamber. Because of the dry weather prior to harvest,Botrytis infestation levels in field assessments were low and there was no significant difference between treatments. The mist chamber data shows that the bee delivered Trichoderma treatment was as successful as the grower standard in controlling Botrytis. Both of these treatments were better than the Trichoderma spray treatment which was better than the check. These results are consistant with results for our past studies and show that bee delivery of Trichoderma is an acceptable alternative to the use of fungicide in the control of Botrytis on New York strawberries.

Table 3. Percent of berries with *Botrytis* fruit rot between treatments in grower fields and from mist chamber.
Grower fields		Mist Chamber
Treatment	% Botrytis	Treatment	% Botrytis
Grower standard	3.3 a	Grower standard	12 a
Bee delivered Trichoderma	2.7 a	Bee delivered Trichoderma	12 a
Trichoderma spray (twice)	2.1 a	Trichoderma spray (twice)	20 b
Check	2.4 a	Check	28 c
Means followed by the same letter are not significantly different (p<0.05, LSD). Data transformed Log x+1 prior to analysis.

Table 4 includes the mean number of seeds per berry and the mean fruit weight for the different treatments. Strawberries in the bee delivered plots averaged 22% more seeds than non-visited sites and the berries weighed at least 26% more. The lower seed count and berry weight in the check and Trichoderma spray may have partially been due to rowcovers reducing wind speed and reducing pollination potential. However these pollination results are similar to numerous published results reported by other workers showing that the addition of bees increases strawberry fruit size.

Table 4. The mean of seeds per berry and mean fruit weight of treatments in grower fields.
Treatment	seeds/berry	wt/berry (g)
Check	248 a	9.2 a
Trichoderma sprays	277 b	9.6 ab
Bee visited + grower std spray	283 b	10.6 b
Bee + Trichoderma	318 c	12.4 c
Means followed by the same letter are not significantly different (p<0.05, LSD)

In conclusion, honey bee delivery of Trichoderma harzianum can be considered a useful technique for the biological control of Botrytis fruit rot. Bee delivered Trichoderma provides equivalent control as the present chemical fungicides available to growers and also maximizes strawberry yield through better pollination.

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

return to Using Honey Bees to Disseminate Trichoderma harzianum to Strawberries for Botrytis Control, CONTENTS

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