Tuesday, August 4, 2009

Potato Blight

Well, I unexpectedly and rather unhappily spent a good deal of time today dealing with potato blight. As it turns out, I have the dubious honor of being the first resident of my county to report a case of blight on potatoes. I knew I had to act quickly once I had identified it, but I had questions about how I might salvage some of the potatoes in the ground, if that were possible. Fortunately I did one smart thing; I called my county Agricultural Extension office. After briefly describing what I'd seen (darkish spots on the potato leaves, not starting at the leaf tip, and a faint white, fuzzy ring around the spot on the underside of the leaf), the Extension officer asked to come to our property to collect a sample for testing. I told him to come right over.

It was fortunate that I called him because he gave me good advice. We found the blight on only one of the four varieties of potato I planted this year, the La Ratte heirloom potato. Without his expert advice I would have pulled all these plants out of the ground, salvaged what potatoes I could find, and would have bagged the green parts of the plant for destruction. His advice was to cut the infected plants right down to ground level instead. He told me that the airborne fungal spores on the leaves will not travel down into the ground through the vascular system of the plant. (There are cases however of infected seed potatoes, in which the blight damages the plant from the ground upwards.) Had I dug for the potatoes in the process of getting the plants out, spores from the leaves would certainly have made contact with the potatoes. So right now, the tubers are probably not infected. But if the ground is disturbed, the spores may find their way onto the surface of the potatoes, which can then become badly infected during storage. Rain helps move spores from the leaves to the ground, and as the potatoes grow in the earth, they tend to crack the dirt apart, providing a perfect avenue of infection. He advised me to get rid of all traces of the above ground plants, let them bake in the sun in black plastic bags and wait a few days before digging up any spuds. I did that, then came inside to take a shower in order to get rid of any spores I had on me. The clothes I wore were washed and hung in the sun to dry. Then I sterilized the tool I used to cut the potato plants.

I plan to give it a few days before trying to harvest the potatoes. With some luck, I will have a limited crop of new potatoes from this variety. They won't store well and will need to be eaten up very soon. With a great deal of luck, I may have saved the other varieties of potatoes I'm growing from infection. But I'm not holding out too much hope there. I'd be fairly surprised if the other plants don't show blight soon, given our weather forecast of rain tomorrow.

I know I'm late with the Action Item for this month. I'll try to have it posted tomorrow. It's been a busy August thus far.


Anonymous said...

Bummer. Sorry about all the hassle you're experiencing, and the disappointment.
On the bright side, you're not in Ireland in the 19th century!
(Now you feel better!)

kathy said...

I am going to link this post on my site (www.justincasebook.net)tommorrow as many here have blight and this was the best advice I have come across. Have you considered drying the potatoes for storage? I have not done this yet but the directions seem pretty straight forward. I lost a lot of spuds toward the end of storage this year. I am thinking if I dry some I will keep those for April,May and June when the stored potatoes start to sprout.

Kate said...

Thanks, Jenny.

Kathy, thanks for the (forthcoming) link. I too am surprised that I haven't seen this advice mentioned elsewhere. Perhaps it's not a widely accepted salvage practice, though it seems sound to me. I should note that I did catch this at a fairly early stage - there was still very little damage to the plants when I cut them down. Just a few telltale damaged leaves. Perhaps this only works when the blight is caught early enough to prevent really bad damage. I simply don't know.

I dug a few potatoes yesterday and they look fine. We ate them for dinner last night. The extension agent thinks the potatoes will harden off at least partially in the ground, now that the plant tops are gone. He said if I give it two weeks from the time I cut them down the spuds should have some storage ability, though not as good as if the plant had died a natural death.

So far we've had no rain since I found the blight on that variety. My other varieties and the tomatoes are showing no blight right now. Possible rain on Sunday though, and the extension agent thought it was pretty inevitable that the other varieties would show it too. If it turns out I can use this triage technique to get *some* potatoes from each variety, well, I won't be thoroughly miserable. I just hope it helps someone else salvage some of their efforts too.