Pest Alert for western Washington – late blight

I know most of you are not residents of western Washington, but this information might be of interest to gardeners everywhere.

Pest: Late blight (Phytophthora infestans)

Hosts at risk: Tomato and potato

Conditions of risk: cool, moist environment

Found: Images typical of late blight infection on tomato have been submitted from two Puget Sound area (King/Snohomish county) farms.   Growing conditions were plants in field soil where the area was covered with a plastic hoop structure.

Potential impact: Significant crop losses may occur if not managed properly.

What action should be taken: Scout for evidence of the pathogen on the foliage, stems of tomato or potato, as well as the fruits of tomato. Look for black discoloration to the foliage and a halo of sporulation around the edge of the damage if conditions are moist. Keep the foliage as dry as possible. Maintain good air circulation around plants. A variety of preventative fungicides (both organic and conventional options) is available – click on the links above for tomato and potato.

Information is also available on the PNW Plant Disease Management Handbook website.

Published by

Linda Chalker-Scott

Dr. Linda Chalker-Scott has a Ph.D. in Horticulture from Oregon State University and is an ISA certified arborist and an ASCA consulting arborist. She is WSU’s Extension Urban Horticulturist and a Professor in the Department of Horticulture, and holds two affiliate associate professor positions at University of Washington. She conducts research in applied plant and soil sciences, publishing the results in scientific articles and university Extension fact sheets. Linda also is the award-winning author of five books: the horticultural myth-busting The Informed Gardener (2008) and The Informed Gardener Blooms Again (2010) from the University of Washington Press and Sustainable Landscapes and Gardens: Good Science – Practical Application (2009) from GFG Publishing, Inc., and How Plants Work: The Science Behind the Amazing Things Plants Do from Timber Press (2015). Her latest effort is an update of Art Kruckeberg’s Gardening with Native Plants of the Pacific Northwest from UW Press (2019). In 2018 Linda was featured in a video series – The Science of Gardening – produced by The Great Courses. She also is one of the Garden Professors – a group of academic colleagues who educate and entertain through their blog and Facebook pages. Linda’s contribution to gardeners was recognized in 2017 by the Association for Garden Communicators as the first recipient of their Cynthia Westcott Scientific Writing Award. "The Garden Professors" Facebook page - "The Garden Professors" Facebook group - Books:

2 thoughts on “Pest Alert for western Washington – late blight”

  1. Ooh, late blight. Late blight swept through veg. gardens here in MA a couple of years ago, and ruined whole tomato crops. In a wet summer season, it only takes a few short weeks, almost, to devastate a planting. Fortunately, the blight doesn’t survive our chilly winters (though I wonder about last winter, which was extremely warm), so the problem won’t necessarily recur in a second year. But while the fungus is active (we learned that it likely started here from tomatoes bought at big box stores), it can and will decimate a crop, and using the few good parts of any tomato for relishes, salsas, etc. — is usually the only way to salvage any part of the year’s production.

  2. Well, I guess one benefit of the hot and extremely dry summer we are having is a low probability of late blight. Actually, looks like a good year for tomatoes as long as I remember to water.

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