Q. I have been hearing about a new fungicide to control late blight on tomatoes called Serenade. Can you tell me more about it?

A. Serenade is a biological fungicide that has a broad label to suppress and control many key diseases of fruits, vegetables and ornamental plants, including late blight on tomatoes. Biofungicides are made from beneficial bacteria and fungi. The active ingredient in Serenade is the QST 713 strain of Bacillus subtilis.

Serenade has multiple modes of action to protect plants. It inhibits pathogens from infecting leaves by preventing them from attaching to the foliage. If pathogens do manage to attach, Serenade out-competes them for space on the leaf and inhibits their ability to absorb nutrients. It also destroys their ability to reproduce.

Serenade, which can be used up to the day of harvest, is approved for organic production by the Organic Materials Review Institute. Like most fungicides, it? is most effective when used to prevent disease; it is not an effective "cure" once late blight starts. The label recommends application every seven days, and it can be applied more frequently when disease pressure is high or when environmental conditions favor rapid disease development.

Late blight has been detected again this year throughout Western Pennsylvania, including Allegheny County. Daytime temperatures between 70 and 80 degrees and nighttime temperatures of 50-60 degrees favor late blight, as does moisture on the foliage from rain, fog, dew or overhead watering.

If you are concerned about your tomato or potato crop, it is time to apply fungicides to protect them from late blight. In addition to Serenade, copper-based fungicides are available for organic gardeners. Conventional gardeners can use fungicides that contain chlorothalonil, which is in Daconil, to protect susceptible crops from late blight.

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