I sent my first specimen of tomato/potato late blight off for analysis this week. I found symptoms on a purple potato that grows in the City College of SF garden. I sent it to a lab in Oregon, as I described in my March 2nd post, to become a part of the usablight.org project. They want to know which "clonal lines" of this disease organism are causing the disease in various parts of the country. For my part, I want to know which ones we have here in the Bay Area. Once we find that out, we will be better able to predict which tomato or potato varieties might resist the disease in our region.
This is the photo of the specimen I sent to the usablight.org lab. They want us to send leaves that are still partly green, like these, but clearly infected. The whitish stuff on the surfaces is, I hope, spores of late blght.
If you want to take part in this survey and find out more about your particular strain, or, more correctly, clonal line, of late blight, go to usablight.org and learn how to submit samples. The first step is to have them send you a copy of the permit that will let you ship your disease samples across state lines to be tested in a lab in Oregon. Do this soon, so you will have the permit in hand when late blight rears its ugly head in your garden.
If you have overwintering potatoes, you might see late blight soon. In last year's tomato trial, the disease showed up at the end of July. Gardens with cool, damp, foggy weather are more likely to be affected by this disease. Spores fly through the air from other infected plants, land on your plants, and begin to grow. Please see the March 11, 2012 post for more details.