Q Potato scab prevention
Potato scab, caused by the bacteria Streptomyces scabies, infects tubers, roots, stems and rhizomes. Damage to the skin of young potatoes is the most serious economical consequence. Three types of symptoms occur: 1) russet scab with superficial, corky lesions; 2) raised scab with erupting lesions; and 3) deep-pitted scab with sunken dark brown lesions. Scab tends to be more severe in fields newly planted to potatoes and in fields with high undecomposed organic matter content. Scab is spread by infected tubers and contaminated soil and manure. http://www.cals.ncsu.edu/sustainable/peet/IPM/diseases/solanace.html
There are also several types of potato scab and there are apparently no chemical pesticide to deal with the problem.
The first line of defense is hygiene:
- Don’t plant any scabby seed potatoes. Use certified seed tubers free from common scab.
- Don’t compost scabby potatoes if you are using your compost in the vegetable garden.
- Rotate your potatoes i./e. don’t always plant them in the same spot.
Rotations out of potatoes for 3 or more years may be beneficial on some infested sites or rotation with green manure crops such as rye, millet, and oats; whereas, rotations with carrots, beets, spinach, turnip, and radish are not advisable. [http://www.ipm.ucdavis.edu/PMG/r607101011.html] Rotation with barley also increased scab http://www.springerlink.com/content/g071632887776617/
- Plant resistant varieties to the scab present in your patch.
i.e. The cultivars Atlantic, Norchip, Norland, Shurchip, Superior are considered resistant to common scab. http://www.cals.ncsu.edu/sustainable/peet/profiles/pppotato.html
Russet varieties show less tuber damage from powdery scab than smooth, red- and white-skinned varieties; russet-skinned varieties rarely show tuber symptoms although root galls are common. Susceptibility varies among red and white varieties. [http://www.ipm.ucdavis.edu/PMG/r607100911.html ]
Growing conditions: Maintaining high soil moisture (80–90% of available water storage) during tuber initiation and the 6 to 8 weeks that follow reduces the severity of scab and usually controls the disease adequately. [http://www.ipm.ucdavis.edu/PMG/r607101011.html]
Then keep your soil acid [with a pH of 5 or below] to prevent scab.
- Do not apply lime or wood ashes to your potato patch.
- Avoid soil application of animal wastes, which favors scab development. [http://www.ipm.ucdavis.edu/PMG/r607101011.html]
- You could try putting in wilted comfrey leaves, pine or spruce needles around when you plant your potatoes. [http://www.ghorganics.com/page8.html (May 23/08)]
http://www.ghorganics.com/page8.html (May 23/08) also mentions a pH of 7 or above (alkaline) to prevent scab. This is new information to me adna the only place where I saw that alkaline soils may prevent it.
It did not tke me long t find that information on the Internet when I searched 'potato scab natural solutions'. In the future, try going to one of the links on SNAP's site and search the linked sites, or type the words in google and it should bring you to good sites. Especially look for University sites or IPM ( Integrated Pest Management ) sites.
Paule Hjertaas,
President and spokesperson of the Saskatchewan Network for Alternatives to Pesticides Inc, (SNAP) (June 2008)