I have been a lucky potato grower for many years because, although I live in a climate that is favorable to light blight, it has never been more than a minor problem toward the end of the growing season. That has now changed. Last year, I rogued out a small number of plants spread around the field that showed symptoms, after which no more appeared. This year, we have had a major outbreak in several areas. It remains to be seen how much it will spread this year and I will continue to remove plants that show symptoms, but it is now clear that it is established and will continue to spread. Because the ground does not freeze here, potato tubers are not killed over the winter. Even with very careful soil prep every year, I still miss quite a few tubers that come back to volunteer and some of those are likely to carry blight into the next growing season. That’s a bummer, but I have always known that this day would come and I’m glad that I made it this long.
So, practices now have to change in accordance with conditions. It won’t be possible for me to outdistance blight, so I will have to live with it. I could choose to grow with fungicides, but it isn’t my preference to fight nature with poisons. One way to look at this situation is as an opportunity: I now have a better testing ground for selecting resistance to late blight, a valuable trait in potatoes. But, that means that there is going to be blight in the soil and on the plants and there is no good way to ensure that any tubers that I sell would be free of blight, even if the plants themselves are tolerant or resistant.
This won’t affect true potato seed, other than making it more difficult to collect from susceptible varieties, so I expect that I will continue to breed potatoes and produce TPS. It also has no effect on the other plants that I work with, as none of them are affected by late blight.
I will offer tubers this year from beds that show no signs of infection, but that will be the last crop of potato tubers that I sell for the foreseeable future. I have closed preorders since I won’t know which lots are safe to sell until the end of the season. For preorders already placed, I will issue refunds for any varieties on which I observe late blight as the season goes on.
I will probably figure out a way to offer potato clones without selling field grown tubers, whether that means producing minitubers on potted plants or perhaps offering in-vitro plantlets, but it will take some time to work that out. Until then, I will only offer TPS. I may also experiment with moving to a system where I grow potatoes every other year. Because the blight organism is not able to persist without potato plants to infect, I might be able to bring it back to manageable levels by going a full year without growing potatoes. If that works, then I could potentially offer field grown tubers intermittently.