Managing Late Blight Organically
Is probably impossible, but after losing all the tomatoes in New York, we’re trying to see if at least one of the Maine tomato patches ( 2 outdoors, one under plastic) can pull through and produce.
Organic management tools include:
Being fond of cherry tomatoes
And perhaps most importantly, Being a procrastinator – at least in our case… If I’d done all the tomato grafting I’d planned to do, there wouldn’t have been any leftovers in the greenhouse.
* The Fungicide is Serenade, approved for organic gardening and 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. Complete coverage is the goal but I’ve been paying special attention to stems since they take longer to replace.
* 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.
In a good year, tomato plants don’t need much feeding, but this has not been a good year. Cold and wet 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.
Stems are another story; once they get black spots all the leaves 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, sent to the landfill or burned as soon as possible. Don’t put it in the compost or on the ground in the deep woods.
Post Season Update: In the end it didn’t help – except in the greenhouse, where removing all infected material as soon as it appeared pretty much stopped the problem. But in the greenhouse there wasn’t much of a problem to start with. Henceforward I’ll be playing the percentages, trimming early if there’s not much damage, removing plants if early trimming doesn’t make a big, quick difference.
* 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.
* Being Fond of Cherry Tomatoes may or may not make any difference. The fact that our cherries are generally doing better than the main crop plants might be just an accident of placement – I plant the cherries nearest the main paths for easy browsing.
But as a subset cherry tomato plants do seem to be stronger than others. Might be because they have more leaves in proportion to fruit, might be because they’re closer to the original species. And of course might only be true in our gardens.
* Procrastination isn’t really a virtue, even if it did give us some plants better protected from blight.
The most interesting thing it’s given us is 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 reputedly 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 bits and pieces 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.