How to Fight Late Blight on Tomatoes Organically

It's a major challenge, all right, but after losing all the tomatoes in New York, we're trying to see if at least one of the Maine tomato patches can fight off late blight (Phytopthera infestans), one of the most devastating vegetable diseases. It's the one that led to the Irish potato famine and it's just as deadly almost two centuries later.

P. infestans is always around, but it came early this year, and more ferociously than ever before. Farmers and home gardeners from Maine to South Carolina -- and quite a way west -- have already lost their crops to what has turned out to be the most widespread outbreak in U.S. history.

If you see any signs of late blight, experts advise destroying all infected plants at once, to stop the spread of spores. And if you live in an area where there are gardens or farms that have not yet been hit that is the advice to take; late blight is highly contagious. But if everyone else already has it and yours is the garden that's hanging in, you might as well join us in employing:

The Organic Gardener's Arsenal:

• Fungicide
• Fertilizer
• Being There
• Being Careful
• Being Realistic

And -- at least in our case -- Being a Procrastinator. If I'd done all the tomato grafting I'd planned to do, there wouldn't have been any leftovers in the greenhouse. Luckily, the tomato plants in the greenhouse (pictured) have so far escaped the blight.

* The Fungicide we're using is Serenade, available at well stocked garden centers or online at suppliers like Peaceful Valley Farm Supply. It's approved for organic gardening and is a fairly effective prophylactic as long as it's applied frequently. Late blight can't be cured, and if it's well established it can't be stopped. But if it hasn't yet taken hold it can be held at bay by Bacillus subtilis, the "good" bacteria that is Serenade's active ingredient.

Seven days is the recommended interval between sprays unless disease pressure is intense. We were only waiting 4 or 5 when the rain was incessant.

* The Fertilizer is mixed fish emulsion and liquid seaweed, alternating with half-strength commercial soluble 20 -20-20, to provide as much instant nourishment as the plants can use. (The 20-20-20 is not organic and can be replaced by more fish emulsion.)

In a good year tomato plants don't need much feeding, but this has not been a good year in the Northeast and mid-Atlantic. Our long stretch of cold wet weather -- also a record breaker -- kept them small and weak, with poorly developed root systems, ill-equipped to fight the blight organically. Being robust is a plant's best defense no matter what your gardening style, and it's especially important if you don't want to use strong toxins.

* Being There is essential. I'm sure one of the reasons we lost the New York tomatoes is that we weren't watching over them. Here in Maine I'm monitoring the plants several times a day, removing leaflets that show signs of blight before the lesions can spread (far) or produce (gazillions of) spores. In rainy weather, leaves that looked fine in the morning can show definite signs of distress by late afternoon.

Standard advice is to remove whole leaves, and it's true that even the smallest spot spells doom. But I've been removing just the parts that show spots -- so they can't make spores -- and leaving the rest of the leaf to feed the plant for another day or two, or however long it stays clean.

Stems are another story; once they get black spots , everything above the spots will almost surely perish. It's best to cut off the whole branch below the spot so the plant can spend its limited energy making new growth. Of course, after a few rounds of this you may not have much plant left (see Being Realistic, below).

Everything removed should be bagged at once, then deeply buried or sent to the landfill. Don't put it in the compost or on the ground in the deep woods.

* Being Careful can minimize the inevitable spread of spores. Try to avoid working in the tomato patch when the leaves are wet or when there is a breeze. If you have multiple tomato locations, start your patrols in the least infected.

And when the diseased material is deep in the plant behind other, apparently healthy growth, try to cut back by degrees from the outside in, to minimize disturbance.

* Being Realistic can be painful, but it's a big part of being a successful gardener, organic or conventional.

It is now mid-August. Before deciding to keep diddling in an attempt to have some tomatoes, look honestly at each plant's size, general health and leaf cover as well as the number of blossoms and baby fruits.

Is it realistic to expect mature tomatoes from this thing before frost and if so, how many? In a lot of cases it's going to make more sense to simply destroy the tomato and spend the saved gardening time caring for the crops that are doing well -- or would be if they got a bit more attention -- and planting fall salads, cooking greens and roots.

* Procrastination isn't really a virtue, even if it did give us some plants better protected from blight and thus the opportunity to test a (presumably) vulnerable heirloom alongside a (presumably) tougher hybrid. The leftovers were from a spring plan to graft 'Lilian's Yellow,' a very fussy heirloom, onto the rootstock of 'Big Beef,' a sturdy hybrid if ever there was one.

The successfully grated plants in New York died. The ones I was going to graft in Maine languished for months in not big enough pots until the blight drama started.

Now they are in bigger pots. If they keep on being healthy for another week or so I'll run strings to the greenhouse rafters and start having hopes.

Also from Leslie Land:
How to Extend the Rhubarb Season (Plus Rhubarb Peach Deep Dish Pie)
How to Make Your Tulips Rebloom
Tips for Success with Vegetable Seeds

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