Monday, September 28, 2009

late blight again - the topic that just won't go away

As I clean up for next year, the Late Blight topic is coming up again. To bag and dispose or to compost?

There are two different camps out there:

Gardener's Corner (Interesting last comment here where they recommend leaving the tomato plants to overwinter in the field as is so they will self-sow.)

Maryland Cooperative Extension
Dave's Garden
Cornell University Extension

I hate the idea of bagging and disposing, but I am in this camp. It is impossible to predict what our winter weather will be and harder yet to predict the conditions in the compost pile. So best to do what we can to avoid worse blight worse next year.

It seems to me reasons to compost are:
- you garden in a heavily infected community garden where many gardens will not be cleared and hence there is little chance of reducing the number of spores AND you have a reason not to try improve the situation anyway
- you got minimal Late Blight very late (September) and live in a cold area and feel the risks are low compered with the effort to dispose
- you plan to just forgo tomatoes and potatoes for a few years anyway
- you plan to spray all sorts of chemicals next year
- you don't care about potential spread from your garden to a nearby Organic Farmer

Regarding the last point, I just read this story about Old Path Farm, Utica NY (and there are lots of stories like this around). Late blight is an extremely destructive disease.

I am looking forward to our Seed Swap Day this Saturday, when Gretta Anderson, a local farmer from Shared Harvest CSA, will come and speak. Her topic will be "Late Blight: Sharing the collective experience of local organic growers this summer".

And here is a question left today on an earlier post on this blog:
I thought that the problem with the blight this year was that it came so early. Don't NE gardens usually get blight every year, but much later in the season (like, now?) If that's true, then there is no reason to worry about the disposal of the blighted plants at this point. The whole reason for burying them earlier was so that the blight couldn't affect your neighbor's (or your other) plants at their peak moment of the season. I am not an expert, that's just what I thought was the case from everything I read. Is that right? September 28, 2009 2:29 PM

I answered: I don't know. I thought the reason for disposal reason was to reduce the spores around next year. I am going to start a new post on this topic. Thanks for the question. September 28, 2009 3:22 PM

Please leave your opinion. Hopefully this topic will be gone next year and we won't have to belabor it ad infinitum.


Jain said...

I'm not certain mine had Late Blight but the crop was definitely problematic compared to last year, and occurred during most of the ripening season. I bagged and destroyed all potentially-blighted plants. I think it's foolish and irresponsible to risk infecting my neighbors' gardens.

Daphne Gould said...

Oh there is so much controversy over how to deal with it all and I've read a lot of conflicting online publications from different universities. I think the major question is whether we actually have any oospores (sexually produced spores) or if it is just zoospores (asexually reproduced spores). Zoospores won't survive over the winter since they need a living host (except for potato tubers left in the ground). Oospores can. Most places say that we don't have oospores up here yet. If it is true then composting your tomato plants once they have been bagged and solarized (so they don't infect other plants before they are totally composted) should be fine. Personally I buried mine in the garden where they grew. I always do this with my tomatoes. I don't trust all the diseases we have up here to my compost bin. I'll rotate the plants elsewhere for the next couple of years, again as I always do.

There is the slight risk that oospores formed for the first time up here this year (probably not), but it is much more likely that potatoes that you have missed will be the downfall next year. If any were missed when you dug them up, that would be the source of infection next year. Right now I'm double digging the old potato bed and I'm finding a few small tubers that I missed. I'll be vigilant next year and if I see any volunteers I'll make sure to dig out the tubers. This could be real problematic in a community garden.

So I guess my answer is that I never compost tomato parts anyway. I think it is just asking for trouble with other diseases. The other ones can survive the winter just fine. But I don't waste that organic matter. I bury it deep where it grew.

Kelly said...

While visiting a farm in New Hampshire I learned the farmer was telling gardeners to get rid of their soil in addition to riddening the garden of diseased plants.

I think in theory the cold winter should destroy any spores left above ground on host plant material, but as you mentioned Kathy, why take any chances? I have found this a confusing topic as well, all sources seem to have an answer, but which one is best??

Dan said...

I am going to play it safe and dispose of all tomatoes, peppers, eggplants etc off site. I'm going to put it out for the yard waste pickup though so it will be composted by the city. At least then it is not a total waste.

MUDNYC said...

Thanks for opening up this topic again. I'm looking forward to seeing everyone's opinions.

We put most of our tomato vines out with the trash, but I think those could theoretically infect others if the spores don't die out over the winter.

Thanks for a great blog!

kathy said...

How deep Daphne? I think I'd rather dig than bag in plastic. I think I heard 3 feet?

Kelly, And how could anyone get rid of soil?

Dan, Where does your city compost go? In our town it goes to the community gardeners and we put it on our gardens. I think that's why the suggestion is to put it in the trash.

Daphne Gould said...

The depth I keep hearing is 2'. Mine is not that deep. I double dug this bed in the spring to a depth of 18'24" (there were some huge boulders down there). I dug down as far as I could and put the plants in (cut up into bits) then covered them up. The tomatoes have about 4" of debris so the ones closest to the surface ought to be about 14", but the reality is probably more like 12" since they are uneven. I think if you till your soil you need to bury them really deep, but I don't till and I'll leave all but the top 4" undisturbed. But the reality is that I was burying it to protect the gardens around me this year. I'll be extra vigilant about volunteer potatoes in the spring to protect my garden next year which is where I'm guessing the problem will be.

kathy said...

Thanks Daphne, I will do this too. I have a full plastic bag of tomato/potato debris "solarizing" in my plot now (actually just easier to let it sit there). Also several tomato plants I haven't taken down yet. I will dig them in deep.

I am wondering why you did this in the spring and not the fall?

Victoria B. said...

What time will Greta speak??

kathy said...

Probably around 2:30 or 3 pm.

pjkobulnicky said...

Kathy ... Bill McKay who runs Seeds from Italy and gardens in the CT River Valley had an iteresting take on blight in his recent newsletter:

I like it. I think the thing to do, composing or not, is to grow under plastic and with plastic on the ground for a year or two until the spores cycle through