The Online Gardener's Handbook 2010
Chapter 4: Vegetables
Potato

Table of Contents

  1. Introduction
  2. Anthracnose
  3. Colorado Potato Beetles and Blister Beetles
  4. Common Scab
  5. Early Blight
  6. Hollow Heart
  7. Late Blight
  8. Leafhoppers
  9. Learn More

Introduction

Always plant certified seed potatoes. Saving potatoes from previous crops can introduce viruses or other diseases into your garden, which remain in the soil and infect plants for years. Do not use table potatoes purchased from the supermarket. They are often treated to prevent sprouting and will not develop into good plants.

In this chapter, a description of various potato pests will be provided along with suggested management options. These management options will not include the use of pesticides. Some biopesticides and certain reduced risk pesticides are still available to the homeowner for controlling weeds and pests in lawns and gardens. For more information, refer to Chapter 2 of this handbook and the Ministry of the Environment's website. For suggestions on managing specific weeds and pests, consult local horticulturalists, Master Gardeners or your local garden supply centre.

Anthracnose

Anthracnose fungi persist in soil and crop residue and start below the soil surface on potato, causing brown dead areas along, and sometimes completely girdling, the stem. The tubers are infected causing black dots oin the outer skin of potato and inside hollow stems.

Management Options

Rotate crops. Clean up plant residue when digging potatoes to prevent overwintering of spores.

Colorado Potato Beetles and Blister Beetles

For information and management options, refer to the Colorado Potato Beetle section in Insects and Diseases Affecting Many Vegetables.

Common Scab

Common scab is a disease caused by soil-dwelling, bacteria-like organisms. Roughened, sunken or upraised discoloured patches occur on potato tubers. Deep pits on tubers are created when insects attack early infections. Neutral to alkaline soil pH, fresh manure and infected potato seed promote this disease.

Management Options

Check seed for symptoms of scab prior to planting - destroy any diseased seed. Keep soil pH at or below 5.2. Use well-rotted manure and certified seed potatoes. Avoid growing susceptible crops for at least three years in soil where scab has been a problem. Plant scab-resistant potato varieties such as Ontario, Superior, Onaway, Russet Burbank (Netted Gem), Norchip, and Sebago. Maintain high soil moisture for about four weeks after tuber setting begins.

Early Blight

Early blight is a fungal disease occurs annually in most of Ontario by midsummer. Large, brown target spots with concentric rings appear on older leaves and spread to younger ones. Lesions are frequently surrounded by a narrow yellowish border. Potato tubers or tomato fruit are rarely affected, but if the calyx of the tomato is infested, fruit will drop before ripening. If infected, tubers develop dark brown to black, slightly sunken external lesions. The fungus overwinters on diseased residue.

Management Options

Follow proper garden sanitation procedures. Avoid overhead watering and remove and destroy crop debris after harvest. Vigorous plants are less susceptible.

To control leafhoppers, Colorado potato beetles and blister beetles as well as early blight and late blight diseases without pesticides, plant early or medium-early varieties of potatoes. Presprout seed potatoes in trays under light during April and plant in early May. An acceptable crop can be harvested by mid-July, before extensive development of the blight.

Hollow Heart

Hollow heart is an abiotic disorder that can affect large potato tubers. When cut in half, the centre of the tuber shows an irregular hollow area. This cavity is usually outlined in brown, and if the cracks originating at the cavity extend to the surface, the tuber may rot. As a rule, there is no decay involved and the tubers may be used with a little extra trimming.

Management Options

Any condition such as over fertilizing that induces over-sized tubers can cause hollow heart. Closer spacing, less nitrogen and less water will aid in avoiding this disorder. Avoid over-watering when potatoes are sizing. Severity will vary from year to year depending on growing conditions. This condition is favoured by cool, wet soil conditions at flowering.

Late Blight

Late blight is a fungal disease that occurs under wet, cool weather conditions during late August and September. It is usually worse on low-lying, wet land and heavier clay or clay loam soil. Initially, small light to dark green water soaked spots develop on the leaves, and eventually become grey to tan, surrounded by a light green halo. Under humid conditions (e.g. early morning), a white, fuzzy fungal growth often develops on the underside of the leaf. Lesions on tubers are brown to purple and slightly sunken, with a reddish brown rot developing under the skin. Eventually, the entire tuber can rot from a combination of the blight and secondary bacterial infections. The disease originates from infected seed potatoes. Late blight has the potential to be an extremely destructive disease of potatoes in Ontario. This disease can also affect tomatoes, and late blight can be introduced to gardens on infected tomato transplants.

Management Options

Use only certified seed. Destroy volunteer potatoes and control host weeds growing nearby. Ensure plants can dry quickly - avoid overhead watering, water early in the day, do not crowd plants and plant in a sunny spots. Check plants regularly - at least twice a week. Destroy tubers showing dark spots when cutting seed potatoes. Do not compost. For tomatoes, remove and destroy lower infected leaves. Widely space, prune and stake tomato plants. Once the disease shows on leaves, it spreads rapidly. Harvest the potatoes immediately, if infected in late summer, by cutting stems at ground level and waiting two weeks before digging to allow vines to completely dry so fungus spores are not sprinkled on potatoes. If contact is made, potatoes will rot in storage. Vines can be placed on compost. During digging, discard and destroy tubers with brown spots under skin - do not store infected tubers.

Late blight can be introduced to gardens on infected tomato transplants and infected seed potatoes. Inspect all tomato transplants and seed potatoes for signs of disease before planting. Do not plant any diseased plant material. Destroy all transplants and seed potatoes showing symptoms.

To help control late blight, plant early or medium-early varieties of potatoes. Presprout seed potatoes in trays under light during April and plant in early May. An acceptable crop can be harvested by mid-July, before extensive development of the blight. This will work only if the seed potatoes are not themselves infected with the disease.

Leafhoppers

The leafhoppers affecting potato are pale green and about 3 mm long. For more information and additional management options, refer to Chapter 1 and Chapter 4.

Management Options

To help control leafhoppers, Colorado potato beetles and blister beetles as well as early blight and late blight diseases, plant early or medium-early varieties of potatoes. Presprout seed potatoes in trays under light during April and plant in early May. An acceptable crop can be harvested by mid-July, before insects have caused such extensive foliage damage that no further tuber growth is possible.

Learn More

 


For more information:
Toll Free: 1-877-424-1300
E-mail: ag.info.omafra@ontario.ca
Author: OMAFRA Staff
Creation Date: 21 July 2005
Last Reviewed: 25 June 2010