This is Part II of a three part series on the prevention and treatment of fungal diseases in the garden. Check out our first post on fungus prevention, too. In the third post in this series, we discuss organic fungal treatments!
Cover your tomatoes: Most people already know about the need to cover your tomatoes against late blight - by mid- August in the Vancouver area. The idea is to keep the plants from getting rained on, because wet foliage is a playground for the blight! Wheee!
The most common method of covering tomatoes is to construct a framework of 3/4" PVC pipe hoops over the tomato bed, and then stretch clear sheet plastic over the hoops. There are some great clips specially made to hold the plastic on the hoops. If you find it hard to force the clips onto the piping, try stretching them open first a bunch of times, to loosen them up a bit.
We don't run the plastic right to the ground - stopping it a good foot or two above the soil, so that the air continues to circulate fairly well. If you have the time, you can use the clips, or little spring clamps (ask at your local hardware store), to pin the plastic up higher on hot days and lower it against the dew or rain at other times. Also, take care that none of the tomato foliage is touching the plastic itself - cut back branches or leaves as needed, or top the plants if they're too tall for the structure.
Cut your watering schedule back to the bare minimum to keep the plants alive. When you do water, take care to water only the soil, not the plants themselves.
All of these measures have the added benefit that they will really push the plants to grow and ripen their fruit fast and hard, at a time when the season is winding down.
Watch and take action! Where you do start to get blight or mildew - it will happen - patrol daily and immediately remove any plant part that begins to show the mold (photo, below). In fact, most advice about blight, specifically, says that the moment a tomato plant begin to show signs of it, you should just tear out the plant entirely.
This is good advice, but hard to follow if you've just spent the entire season watching the plants grow and then have to pull them out before you've even tasted your first tomato! So, since we are weak-willed, and also practise rigorous crop rotation (below), we allow ourselves to slowly prune back diseased plants, rather than just eradicating them.
Put the removed plants or plant parts in the garbage, not in your compost, from which you'll just recycle the fungus into your garden again. And sterilize your hands and tools (below) before you reach to touch another plant or move to a different bed.
Rotate your crops: Fungus spores can certainly float in on the breeze, but they reside above all in the soil. So it is crucial to rotate your crops each year, over a 3 or 4 year cycle. This helps control not just fungi, but also any other diseases and insect pests.
In limited space, this can be a challenge, especially if there's only one sunny corner where your tomatoes or cucumbers will actually grow. But consider growing them the second year in containers, which will separate the new tomatoes' soil from that used the previous year. Set the containers up on plastic or stone blocks (not wood, which could still transmit the fungus), so that there is no contact between the previous year's soil and this year's. For the third year, replace the container soil with new soil, sterilizing the containers themselves (inside and out) before you replant.
Sterilize your tools: I always balked at this idea because as a gardener, you get pretty casual about dirt. But I've recently begun doing it, and it makes a real difference.
Clean your tools after every gardening session, washing dirt off all parts of them. Then give them a quick wipe-down with rubbing alcohol or a hydrogen peroxide (non-chlorine bleach) solution. Store the tools hanging up, not resting on the ground.
As you move from garden bed to garden bed, stop to wipe the tools down with a bleach or alcohol-soaked rag, or dip them in a bleach solution. And wash or wipe your hands with the same solution. I have to admit that keeping this up drives me crazy, but at least I'm not spreading diseases from bed to bed and crop to crop.
Be aware of stepping in one bed - not advisable anyway, because it compacts the soil - and then stepping in the next, without cleaning the soles of your shoes between beds.
Take care, as well, to sterilize things like tomato cages, garden stakes, or growing containers, if you plan to use them again in another bed, or in the next season.
It's the thought pattern that counts the most, here, rather than perfection in such practises. Probably the single most effective spreader of diseases in the garden is, unfortunately, the gardener him or herself. So over time, develop the habit of observing those moments where you've just pulled off the blight-touched leaf of one plant and then immediately reached to tie up part of a still-healthy plant: oops.
More on habits: If you're new to gardening, one of the least inspiring experiences is the sheer overload of gardening advice that you can be subject to. So if this seems like a lot of information at once, don't worry. Nobody gets things absolutely right in the garden - not ever. The main thing is to allow yourself time and thought to incorporate more and more good organic gardening habits over the years - and that is eminently do-able!
Next up: Organic fungal treatments!