Report courtesy of Floral Notes NewsletterLate blight, caused by the fungus Phytophthora infestans, is a very destructive and very infectious disease that killed tomato and potato plants in gardens and on commercial farms throughout the eastern U.S. during 2009. As a result, many farmers across Massachusetts lost their tomato crops and incurred extra fungicide and labor expenses. While late blight is a problem on farms each year, the occurrence of late blight in 2009 was different compared to most seasons.
In 2009 it was the earliest the disease was reported over such a broad region of the country. More problematic for the Northeast, was that infected plants were distributed through large local retail stores throughout the region (Ohio to Maine). Never before has such an extensive distribution of infected plants occurred. This distribution, the exceptionally contagious nature of the disease and the cool, wet growing season all contributed to a disastrous year for farmers.
Garden retailers can help prevent the spread of late blight in gardens and on farms this growing season and provide customers with the facts about this disease.
Tomatoes. Late blight is not seedborne (however, it is tuber-borne in potato), so tomato plants started from seed locally (in the Northeast) would be free of the disease. Growing your own transplants from seed or purchasing from a reputable local grower will ensure a healthy start to the season for your customers and local farms. Disease-resistant or tolerant varieties of tomatoes exist, however seed is in limited supply this year. ‘Mountain Magic,’ ‘Plum Regal,’ and ‘Legend’ are three varieties with resistance or tolerance to late blight. Note that the variety ‘Legend’ has been grown primarily in the western U.S., where conditions are different than here.
In addition to late blight, each year tomatoes become infected with early blight and Septoria leaf spot, which look very similar. If possible, garden retailers can also offer tomato plant varieties that are resistant or tolerant of early blight; these include ‘Mountain Fresh,’ ‘Mountain Supreme,’ and ‘Plum Dandy’ and others.
Potatoes. Purchase certified, disease-free potato seed from a reputable source, and ask your supplier about their source of seed and if it was inspected in the field for late blight. Potato seed from the Northeast are less likely to carry the disease.
Know the FACTS about this important disease and share the information with fellow gardeners.
- Potatoes that freeze or fully decompose will not carry the pathogen over winter.
- Tomatoes will not carry late blight over the winter, because freezing kills the whole plant.
- Tomato seed, even from fruit that was infected with late blight, will not carry the pathogen, so no need to worry about the tomatoes left behind in the garden or compost pile.
- Certain perennial weeds can become infected with late blight, but none of their above-ground tissues live through the winter.
- Late blight will not survive on tomato stakes and cages.
The biggest threat for overwintered disease is on potatoes. In the spring, gardeners need to inspect last year’s potato plot and any compost or cull piles for volunteer potato plants that might come up. If potato plants are found, pull them out and put them in the trash or destroy them. If tubers were infected and survive, then the late blight could grow upward from the tuber, infecting the stem and producing spores when weather conditions are favorable. These spores could then disperse to other tomato and potato plants.
During the growing season, pay attention to pest alerts to learn about whether late blight has been observed in New England, and what actions should be taken. If you or a customer suspect a problem, or to confirm a diagnosis, contact the UMass Plant Diagnostic Laboratory.
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Author Tina Smith is the Outreach Educator, UMass Extension, Amherst
Report courtesy of Floral Notes Newsletter
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