Evaluation of spray pruners for target delivery of fungicides to tomato leaf cut-wounds to control botrytis stem canker

Project Code : PRR06-590

Project Lead

Iris Bitterlich - National Greenhouse Vegetable Growers

Objective

To evaluate the efficacy of delivering registered fungicides with spray pruners directly onto leaf cut-wounds of greenhouse tomato during pruning to prevent the entry of botrytis stem canker (BSC) disease

Summary of Results

Botrytis stem canker (BSC) was identified as the #1 disease priority for greenhouse tomato at the Canadian Minor Use Pesticide Priority Setting Meeting in Ottawa (2005) as well as a national priority by the Pesticide Reduced Risk Steering Committee Meeting (2006).

BSC is caused by Botrytis cinerea and is the most prevalent disease on greenhouse tomato (Lycopersicon esculentum Mill.), affecting stems, twigs, leaves, blossoms and fruits at all developmental stages. The pathogen produces numerous spores on infected tissues that are rapidly dispersed by wind currents, irrigation, machinery, equipment and workers. Spores enter the plant primarily through wounds, natural openings, or even by direct penetration. BSC is often initiated at leaf cut-wounds, leading to lesions, cankers and girdling of stems, eventually causing wilting and death of tomato vines. Pruning wounds can remain wet for several hours post-cutting, providing an easy entry point for B. cinerea spores. Protectant fungicides used currently as a foliar spray do not typically prevent infection, since spray and pruning events do not coincide.

The objective of this study was to evaluate the efficacy of delivering three registered chemical fungicides, Decree (fenhexamid), Botran (dichloran) and Milstop (potassium bicarbonate), and one biological fungicide, Rootshield (Trichoderma harzianum), with spray pruners ( Felco Spray Pruner #19) directly onto leaf cut-wounds during pruning of tomato leaves to prevent the entry of pathogen through cut wounds.

In this study, the results showed that the fungicide Decree performed better than the other fungicide treatments on all three tomato varieties Trust, Tricia and Clarence when delivered with the use of spray pruners. Incidence and severity of BSC in the Decree treatments were comparable to that of the uninoculated healthy check and were significantly different from the inoculated disease check. None of the other fungicides applied with spray pruners reduced the incidence of BSC significantly compared to the inoculated disease check. Hence, delivering Decree with spray pruners directly onto leaf cut-wounds of greenhouse tomato during pruning can reduce both disease incidence and severity significantly.

Furthermore, the quantity and volume of a fungicide required for spray pruner application was 73-80% less than that of conventional foliar application. Therefore, the reduced amount of fungicide applied on a per hectare basis will reduce the overall production cost for greenhouse tomato producers. Worker-exposure to air-borne (aerosol) fungicide particles during spray pruning was also extremely low as determined by the volume (amount) of fungicide deposited on water sensitive strips during spray pruning. The residue level found on the leaf and fruit samples of all three tomato varieties treated with Decree and Botran was below the acceptable Maximum Residue Tolerance Limits.

Based on a survey conducted at the end of the experiment, greenhouse workers rated spray pruners as very high for efficiency, user-friendliness and overall performance. Although the larger size of the spray-pruners used in the experiment was a concern, such spray-pruners can be modified to suit grower convenience.

It would be beneficial to confirm the positive results obtained in the course of this short project with a study over one to two full greenhouse growing seasons.

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