Late Blight Melt Down
Posted: August 27, 2014
To-date, late blight has been confirmed in 18 counties in PA including Cambria, Lancaster, Chester, Clinton, Lackawanna, Berks, Centre, Northumberland, Columbia, Snyder, Perry, Blair, Bedford, Montour, Lehigh, Lycoming, Indiana, and Schuylkill and is suspected in Franklin as well.
As expected, the cool wet weather last week was very favorable for the spread of late blight and it has moved from commercial fields into many home gardens. Home gardeners are being advised to harvest asymptomatic fruit and ripen them off the vine and remove and dispose of infected plants to reduce further spread of the disease. Growers who have been able to maintain a regular spray program that includes recommended late blight specific fungicides (in spite of the weather) have been able to keep it managed. The recommended organic products work best when applied regularly with good coverage before symptoms are observed and before disease pressure is too high. Rogueing and continued use of copper will help reduce the spread of secondary inoculum and help to protect new growth. Results from my product efficacy trials this year will be summarized and made available at the end of the season.
With much of the focus on late blight, don’t forget about early blight or Septoria leaf spot which are also showing up with the heavy dews and significant rainfalls. Early blight is characterized by small brown to black lesions that are surrounded by a yellow halo and typically found initially on the older leaves. As the disease progresses, the larger lesions will develop a concentric ring pattern. Within those lesions, spores are produced and frequently splash dispersed within the plant canopy and to adjacent plants. Septoria lesions are smaller and usually have a tan center and dark margin. Both of these diseases can also defoliate the plants from the bottom up. The fungicides used to manage these diseases are different from those for late blight. However, the tank mixed protectant fungicides including copper, chlorothalonil and mancozeb will provide some protection. See the 2014 Commercial Vegetable Production Recommendations for a list of recommended products and visit USAblight.org to the latest list of confirmed reports.