Grow It Eat It: Maryland's Food Gardening Network

Late Blight of Tomato

Late Blight Tomato

Will Late Blight be a Problem in 2010??

We hope not, but nobody knows the answer to this question right now. The late blight outbreak of 2009 was devastating for many backyard and community gardeners in Maryland and other states who witnessed the rapid decline and death of infected tomato and potato plants. Many older, experienced gardeners had never before seen this disease.

A number of strains of Phytopthtora infestans were identified from different east coast states in
2009. The number of strains present is not as important as whether or not two mating types
occur. For sexual reproduction to occur, two mating types- A1 and A2- must be present. The
presence of the two mating types is necessary for the disease to overwinter in soil. This is the big
concern. There is no evidence that this has occurred in Maryland, although it is possible. The
reason for the severe outbreak in 2009 was the early introduction of inoculum on tomato transplants sold through retail stores, along with conducive weather (wet with cool nights and warm days).

Unfortunatly late blight was detected in a greenhouse in St. Mary's County on May 7, 2010. The grower has taken measures to eradicate the disease. We don't know at this time whether it will spread, or if the grower will be able to contain the outbreak. We also do not know if this outbreak is related to the 2009 outbreak. We are monitoring the situation.

What can I do now?

Educate yourself: check out our photos, video, and Q&A on this page.
Be observant and vigilant! Closely examine tomato transplants prior to planting. After planting, monitor your tomato and potato plants closely for symptoms of the disease.
Any pieces of potato from last year’s harvest should be dug up and removed now! That goes for any volunteer potato plants and seed pieces as well. Do not plant any store-bought potatoes or potatoes from gardens that were infected last year with late blight. Volunteer tomato plants do not need to be removed but should be monitored for late blight symptoms.
Contact the Home and Garden Information Center (HGIC) by phone (1.800.342.2507) or e-mail if you believe you have late blight. If possible, include a close-up photo of suspected late blight infections. We may ask you to send in a sample of your plant. Don’t send a sample unless you have talked to someone at HGIC.

Should I spray my tomato and potato plants with a fungicide?

HGIC does not recommend that gardeners spray fungicides at this time. We will recommend fungicide applications if we begin to receive reports confirming that the disease is active in home or community gardens.
Fungicides containing the active ingredient chlorothalonil are effective for controlling late blight. Fungicides containing mancozeb are also labeled in MD for use by gardeners to control this disease. Fixed copper is less effective but probably the best choice for organic gardeners. In all cases, you must apply the fungicide prior to infection for it to be effective.

Check this web site throughout the growing season for updates on this disease.

fruit & foliage symptoms