It seems like the problems are coming fast out in the vegetable patch. One that I’ve battled every year has reared its ugly head: early blight on the tomatoes. This fungus gets its jollies by attacking plants as the temperatures soar, and now that we’ve gotten toasty warm outside my plants are showing their first signs of disease.
Early Blight is the common name of the fungus Alternaria solani. It overwinters on leaves or other plant parts left in the garden, then colonizes the plant by spores splashing up during irrigation or driving rain – something we’ve had a lot of this season.
Once symptoms show they appear as brown to black, target-like spots on older leaves lower on the plant. Effected leaves turn yellow, then drop from the plant. Once this begins it seems that the rest of the summer is a race against the disease. Fruit may or may not be effected, and you can still get plenty of love apples from the vine. But in severe outbreaks the fruit is ruined.
In the long term, good sanitation in the garden is the way to keep the disease pressure low: cleaning up all fallen leaves every fall and destroying them. Experts recommend rotating tomato plants out of the area for a couple of seasons, but in a backyard this isn’t exactly do-able. I have one vegetable garden and the plants will have to get tough or suffer.
Spacing plants far apart to get good air circulation is another way to keep disease low. I’m a big proponent of this and try to give my plants plenty of room when I pop them in the ground. But they have a nasty habit of growing, filling out and touching one another, then all hope for order in the garden is lost to chaos. Vines ramble where they want, grapes reach out to throttle their neighbors, the tomatoes stick shoots out at odd angles and the pumpkins produce leaves big enough to diaper a baby – there’s no such thing as good air space when August rolls around.
Fortunately this season I have a new weapon to try in the battle for tomato dominance: Potassium Bicarbonate, a.k.a. Green Cure. This organic fungicide was developed by Dr. Ken Horst of Cornell University to combat many fungal problems on roses, but it is also labelled for use on tomatoes and other crops.
Dr. Horst found that potassium bicarbonate keeps fungus at bay, although it doesn’t completely eliminate it. It’s useful on early blight, powdery mildew (I’m keeping an eye on my squash for that) and other common leaf problems.
Green Cure is a wettable powder – you mix a couple of tablespoons in a gallon of water and spray it on the plant. As with ALL pesticides, organic or not, read and follow the lable. I like to spray early in the morning, before breezes kick up and the sun becomes intense on the leaves. With this product, coverage of upper and lowersides of leaves is important, and will have to be reapplied every two weeks until I decide I’ve had enough tomatoes.