Garden Journal

Thursday, June 22, 2006

Potato Blight

Potato Blight:

The picture below shows the leaves of a potato plant in mid June. For the last two year my potatoes have become infected with Phytophthora infestans, a fungal disease that attack the leaves (usually first sign) stems and tubers of the potato. This the same organism that caused the Irish Potato famine in the 1840s depicted above. There have been an array of synthetic fungicides developed to control it but resistant strains or the organism are now infecting crops. The disease is very frustrating, but luckily I have found some good practices that allow us to still get a reasonable crop.

Start with seed potatoes that are certified disease free and that has some intrinsic resistance to the blight. I have found that Yukon Gold will last slightly longer without getting infected and produces some of the best tasting tubers.
When blight damage is spotted on leaves the leaves ought to be removed and buried in the compost pile. A plant that is wholly infected ought to be completely removed. I think next year I will try to plant pieces of seed potatoes instead of whole potatoes.
Also, dusting the seed potatoes with sulfur at planting and spreading some worm casings around the seed potato at planting is said to help.
The only organic methods of control I have been told of are 1: spraying with wettable sulfur and/or 2: spraying with a tea made from the juice from the vermicompost box. The microorganisms in the solution are supposed to suppress the fungi.


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