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Tomato and Potato Blight Disease

Posted on 12. Aug, 2009 by Tracey in Pests

With the warm and wet weather we have been having over the past few weeks, the conditions are ideal for the deadly disease called Blight to spread through Tomato and Potato crops.

A fungus called Phytophthora infestans creates spores which become air-borne via the wind and rain. These spores can land on tomato or potato plant leaves, stems and soil and cause an infection on the foliage. The spores can also be soil borne infecting previous years tubers which have been discarded or left in pots, if these are replanted with other tubers, potato plants can become severely infected with blight.

Symptoms

• Brown or black blotches on tips or middle of leaves which then spreads to the stem.
• Blotches or spots are often surrounded by a pale green or yellow border.
• The plant will become unable to stand up and will collapse.
• Sometimes it is possible to see white fungus on the underside of the leaves lining the veins.
• Leaves may eventually curl and wither as they become infected.
• Potato tubers with blight will be reddish brown due to the rotting, if you cut it open you will see rot right through the tuber and may have an unpleasant smell.
• Green tomatoes will have black blotches on the top by the stalk. When cut open it will reveal black or brown rotting.

Blight Photo Gallery

Treatment

• Earth up the potato stems to protect the tubers,
• A hot dry spell or cold weather will slow and stop the disease however if the conditions are favorable again the disease continues to spread,
• If foliage is infected, cut the stems from the tubers and destroy them, do not compost as it will infect the soil.
• Harvest tubers all together to prevent air-borne spores from settling in the soil around the area to infect the rest of your crop
• Check all tubers for signs of disease or rotting before storing. Once stored if any potato has blight it could infect all the other stored potatoes. Destroy any infected tubers.
• Blight spores can start infection through water droplets left on leaves from rain or watering. The blight spores can be carried by water down the stem to infect the tubers. Water at the base of the plant instead of on the leaves.
• Rotate your potato crops onto another area next year to prevent soil borne fungus re-infecting potatoes or tomatoes. This will not harm any other plant growing in the old potato soil.

Blight Resistant Potato Varieties
Many potato cultivars are still under trials but the varieties which have some resistance against blight are Cara, Orla, Valor, Remarka, Mira, Cosmos, Robinta and others.

Fight Against Blight 2009
Over the past 6 years, The Potato Council has collated blight incidents and reports them to the British potato industry. There are 300 blight scouts which report back when blight is discovered in various areas of the UK. Other Potato council’s worldwide are also reporting to local farmers and leisure growers about the spread of blight.

UK Blight Map

• Click here to see blight incidents in your area of the UK

USA Blight Incidents

• Click here for USA Blight Scouting in the Maine and Ohio Areas
• ABC News: Plant Diseases hits Eastern US Veggies Hard.
• Blight in Maryland with pictures.

Photos courtesy of Creative Commons Licence – Photographers credited:
Potato Blighted Stem, Leaves: Howard F. Schwartz, Colorado State University, United States,
Cut open Potato: Scott Bauer, USDA Agricultural Research Service, United States,
Cut open Tomato, Leaf and Plant: Division of Plant Industry Archive, Florida Department of Agriculture and Consumer Services, United States.