You might have heard of a new strain of late blight (Phytophthora infestans A2) that's causing problems for potato growers. It has been particularly devastating in the Northwest, where I garden, so I decided to plant seven popular varieties, including two new ones supposedly resistant to the disease, to determine their susceptibility.
I planted five 100-foot rows where no garden had existed for 10 years. I used only a little fish meal at planting, and I kept the patch weeded and watered.
The potatoes all grew well until the second week of September, when we had a week of cold, heavy rain, with daytime temperatures in the low 60° Fs and nights in the high 40° Fs. Blight hit with a vengeance in a matter of days, and all the plants had the characteristic water-soaked brown lesions on the leaves.
The weather went back to warm and dry for a while, and I started to dig the tubers. Before I had harvested half the patch, the tubers started to show little white spots -- the spore-forming bodies of the blight fungus. Any potato that showed those spots, or dark patches on the skin, was ruined. Affected tubers usually have a dark layer under all or part of the skin and sometimes streaks in the flesh. Even when the rest of the flesh seemed unaffected, they smelled and tasted foul.
Here's how the varieties I tested fared. 'Buffalo', 'Norland', and 'Yukon Gold' were very susceptible; 60 to 75 percent of the tubers were spoiled. 'Russian Banana' fingerling was almost a total loss, with more than 95 percent of the tubers ruined. 'Butte' was surprisingly resistant; the plants showed lesions, but 85 to 90 percent of the tubers were unaffected, though 'Butte' was the last variety harvested. So I learned that there is a difference between leaf and tuber susceptibility.
Two new resistant varieties also fared well. 'Mainestay', not yet commercially available, was 80 percent sound. Even better, 90 percent of 'Island Sunshine' tubers, a yellow-fleshed variety, were sound, and it's available to home gardeners.
From my test, 'Butte' and 'Island Sunshine' were the top choices.