Maryland grower destroys tomato plants infected with late blight

Tomato plants in a St. Mary’s County, Md., greenhouse found to be infected with late blight caused by the fungus Phytophthora infestans have been destroyed. Some of the plants which had been planted in Charles County have also been destroyed.

Univ. of Md. extension plant pathologist Kate Everts reported that the grower who had the original outbreak did keep some high tunnel tomato production. Plants were found to have active sporulation on May 13 despite two fungicide applications.

Extension personnel have extensively monitored neighboring growing operations for additional infected sites and found none. The disease pathogen favors cool wet weather so the concern remains that it might spread to surrounding growing operations.

Commercial tomato growers in St. Mary’s and Charles counties and in nearby counties are being advised to apply a protectant fungicide such as chlorothalonil, Gavel or mancozeb. Growers should also scout aggressively looking for late blight symptoms. Growers should submit samples of suspect plants to a university or commercial diagnostic lab.

Univ. of Md. pathologists are conducting studies to try to determine where the disease originated and how it was introduced into the grower’s operation. The grower did not have any live plants that could have allowed the pathogen to overwinter. Officials are hoping that genotype information will provide some clues.