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I’ve already had several questions about how to avoid problems in vegetable gardens, so thought it seemed timely to repost this blog on preventing and/or treating problems.
Our garden vegetables are prone to certain diseases. Our best defense is knowledge and good cultural practices.
Despite our best efforts, sometimes we still have problems. So what can we do? If we are fairly certain it’s a fungal disease then garden sulfur may help. A fungus is common early in the season, particularly when we’ve had a cool, damp start. It’s also common in later summer when the humidity has been off the scale. Since so many diseases start with brown and/or yellow spots, however, try to go online and look-up tomato diseases to see if your particular problem looks more like blight, Septoria, Verticillium or Fusarium.
One more thought—even a fungicide can kill a honeybee or butterfly if sprayed directly on them. Spray just before dark for best results—this gives pollinators a change to go home first. Even though copper sulfate is listed as an organic fungicide, there is evidence that it is more toxic to bees than is sulfur.
For most diseases, the only thing we can do is to remove the infected plant as soon as possible and dispose of it. DO NOT compost it. Put it in a plastic bag, tie it up and toss it before it has a chance to spread. And don’t plant another member of that same vegetable family there again for several years.
Here is a brief description of some of the more common garden diseases—for a better diagnosis, check online for a picture of your problem.
Blight (Early or Late): Circular or irregularly shaped dark spots surrounded by yellow on older leaves first. Stressed plants are most at risk. Do not allow plants to wilt. Water thoroughly without over-watering. Do not fertilize until the first flowers appear. Use a lower nitrogen fertilizer (like Tomato-tone). Blight can be easily transmitted when foliage is wet so avoid handling plant. Pick off the affected foliage and treat the plant with a mild organic fungicide.
Fusarium Wilt: Yellowing and wilting of leaves tend to occur on one side of the plant. In early stages, top growth may wilt in sun and recover in the evening, regardless of whether or not soil is moist. Planting in a well-draining spot is essential. Remove and destroy the infected plant.
Verticillium: Yellowing and wilting of leaves will occur all over-usually starting at the bottom. Top growth may wilt in sun, early on, and recover in the evening. Plant in well-draining soil only and remove and destroy infected plants.
Septoria leaf spot: Small spots with darker brown margins appear. Heavily infected leaves will turn brown and fall off. Wet foliage and prolonged spells of wet cooler weather can affect. Do not use overhead watering. Remove and destroy infected plants.
Tobacco Mosaic: Yellowish green and dark green patches. New leaves may be “ferny” and distorted in appearance. Infection of a garden plant can be caused by smoking near tomato family members. Do not smoke or handle tobacco products near tomato or related plants. Mosaic can also show up in cucumber family members.
Powdery Mildew: A grayish white film appears on foliage. Our high humidity is the culprit. Avoid getting water on the plant foliage. When it first shows up, remove the worst of the affected foliage and apply an organic sulfur-based fungicide—spray very early in the morning or just before dark to avoid sunburn. Keep weeds and debris out of the garden to avoid spores wintering over.
Blossom End Rot: Ever gone to pick that beautiful ripe tomato only to find the bottom is black? That’s a disease called Blossom End Rot. Tomato family members are prone to it. It is caused by calcium deficiency. This is why I use Tomato-tone—it has added calcium. Eggshells crushed and added to the soil will help—in several years once they have composted down.
Next week, I’ll talk about common vegetable garden insect pests.