An Alberta Agriculture and Rural Development (ARD) specialist said that with careful monitoring, greenhouse and garden centre producers can play an important role in catching early infections of Late blight.
“Careful monitoring of incoming, growing and outgoing plant material is one of the best strategies for managing Late blight within a greenhouse,” said Rob Spencer, commercial horticulture specialist at ARD.
Spencer said that in the spring, growers should watch for older leaves that have dark, water-soaked lesions, sometimes with yellow edges, that move in from leaf tips/margins, becoming brown and brittle within a couple days. Late blight lesions are not contained by the leaf veins.
“In high moisture/humidity situations, a small amount of sporulation (observed as white, fluffy growth on the edges of lesions) may be visible on the underside of affected leaves. Late blight develops most quickly in wet/humid conditions and can spread very rapidly through tomato plantings or very young petunia seedlings. Plants may be rapidly defoliated and die,” he said.
As the season develops producers should watch plants for both foliar and fruit symptoms. Infected fruit may have irregular, sunken lesions. Tomato fruit rot can penetrate into skin of the fruits, causing rot and discolouration of the internal tissues. The rot often has a reddish-brown colour.
Spencer recommends disposing of diseased material by burying, burning or freezing.
“Dying plant material can still transfer spores to living plants, continuing the disease cycle. The Late blight pathogen thrives in warm, wet and/or high humidity conditions; therefore, careful ventilation can help to keep humidity at reasonable levels and can prevent condensation and prolonged periods of leaf wetness. Overhead watering will increase disease spread which should be addressed if there is a risk that disease is present,” he said.
Source : Agriculture and Rural Development