Diseases

Late Blight
The most destructive disease of potato is Late Blight, which can also infect tomato, egg plant, peppers and petunia.  Late blight is favored by cool, wet temperatures.  The late blight fungus survives and can be carried in infected potato tubers and can serve as the source of an epidemic.  Spores from the fungus may be wind borne and carried 50 miles or more.  Therefore, all infected cull potatoes and volunteer potatoes should be destroyed. Please call your County Extension office if you suspect you might have this disease.

Late blight lesions are light brown surrounded with a light halo.  Lesions can advance to decay entire stem.  Tubers can also be infected.

Other Pests

In addition to late blight, there are several other diseases, and also insects that can affect your potato crop.  Following are photos and descriptions of some important diseases and insects.  If you observe any of these problems, contact your county extension office.

Blackleg appears dark and inky.  May affect stems and rot tubers

Potato scab appears as raised or sunken lesions on potato skin

Potato mosaic is spread by aphids, infected tubers, and mechanically.  Leaves appear mottled and crinkled and may be dwarfed.  This disease is transmitted to the tuber and will cause disease in next years crop.

Insect Pests

Colorado Potato Beetle adults and larve chew potato leaves and can cause total defoliation

Potato Flea Beetle causes holes in leaves and larvae burrow into tubers

All Insect Photos - W. Cranshaw, CSU, Bugwood.org

Tri-fold with potato culture and disease information available by request
Questions?  MSU Potato Lab 406-994-3150
Website:  www.montanaspud.org

The following practices should be used to manage potato disease:

  1. Use Montana certified seed potatoes
  2. Do no plant table stock potatoes from the grocery store.
  3. Destroy diseased plants and tubers by freezing, heat treating, or disposal in a plastic bag.
  4. Do not compost potatoes, tomatoes, eggplants or peppers.
  5. Destroy volunteer potatoes.
  6. Inspect garden regularly for diseased or suspicious plants.  Contact the Extension Office immediately if you observe any sign of disease.
  7. Use certified seed each year.  Ask your garden store for “Montana Certified Seed”.

This brochure was printed through support from the Montana Specialty Crops Block Grant Program

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