Though I am still singing hallelujahs for the abundant rains earlier this year (lakes are full and, for now, exceptional drought is a faded memory), the moist environment did contribute to an unfortunate outbreak of Alternaria solani, known in gardening circles as early blight, or EB for short.
Early blight is a fungal disease that afflicts members of the nightshade family and though it’s never been a problem on my eggplant or peppers, tomatoes are especially susceptible. The fungal spores can be introduced into the garden in a number of ways – they can arrive on infected transplants, can be carried by wind, rain, people or equipment and can also overwinter in the soil. If you have grown tomatoes for several years you probably have fungal spores in your soil. Infected fruit that is left in the garden can transmit the disease to seeds yielding volunteer seedlings that carry the spores and perpetuate the cycle.
The fungus starts as a small dark spot on the leaf; round or angular in shape and often surrounded by a pale yellow halo. A pattern of concentric rings may be observed as the lesion enlarges.
Symptoms generally appear on the oldest leaves at the bottom of the plant and gradually progress upward. If conditions are favorable, meaning wet leaves and warm temperatures, spores can multiply rapidly and spread.
One of the basic concepts of plant pathology is the plant disease triangle. In order for disease to occur there must be a pathogen, a plant host and a suitable environment. Remove any one of these factors and voilà – no disease. In the case of tomatoes we have a host and most likely a pathogen already present and if the environment is conducive the disease will occur.
Controlling the environment thus becomes our primary way of controlling the disease. If early blight was a problem in your garden this year, here are some steps you can take to minimize its effects in future plantings:
- Space tomato plants 2-3 feet apart to provide adequate air circulation around plants. Fungal spores will germinate and reproduce on wet leaves so the quicker leaves dry out after a rain event the less chance that spores will spread. Also cage or stake tomatoes to encourage air flow and minimize foliage contact with soil.
- Plant in full sun for optimum photosynthesis and to insure that wet leaves dry quickly.
- Mulch around the base of the plants to prevent soil (and potential spores) from splashing up onto the leaves.
- Avoid overhead watering. Use drip irrigation or soaker hoses to minimize wet foliage.
- Rotate nightshades to another part of the garden for a minimum of 2 years.
- Fertilize and water tomatoes as needed to maintain healthy growth; stressed plants are more susceptible to disease.
- Remove and discard infected plant debris and volunteer seedlings which may harbor plant pathogens. Weed the garden regularly as weeds can also harbor disease-producing spores.
- Seek out tomato varieties that have resistance or tolerance to early blight, indicated by the capital letter “A” (for Alternaria) after the variety name on plant tags or seed packet descriptions. A few varieties to look for include ‘Iron Lady’, ‘Jasper’, ‘Mountain Magic’ and ‘Big Beef’.
- Purchase seed and transplants from a reputable source.
- Use a fungicide. Most fungicides work by altering the environment (in this case the leaf surface) to prevent development or spread of disease. They are most effective as a preventive control and should be used as soon as symptoms appear – once the disease takes hold it is dang near impossible to get it under control. Products recommended for control of early blight include Serenade®, sulfur or copper based fungicides, potassium bicarbonate and fungicides containing chlorothalonil. All are considered organic except chlorothalonil. For maximum control continue to treat plants as long as environmental conditions are favorable for disease development. According to Dr. Joe Masabni, Texas A&M AgriLife Extension Vegetable Specialist, chlorothalonil is the most effective; potassium bicarbonate is the least effective. If the thought of using a non-organic control concerns you it may be worth noting that the dilution rate for chlorothalonil concentrate is low; one tablespoon product to one gallon of water. Whether to use organic or synthetic products is your choice, but no matter what you use, read the label and apply according to the directions.
Watering, fertilizing, mulching and otherwise tending tomatoes through the heat of summer can become a full time job, even more so if they have lost their healthy spring vigor. If yours have succumbed to pest or disease it is better to pull them out than to let them fester in the garden. Harvest the healthy fruit, dispose of the diseased foliage, enjoy a plate of fried green tomatoes and start thinking about plant rotation and tomato varieties for the 2017 season.
Fried Green Tomatoes
This is a non-traditional take on a Southern classic from the folks at Baker Creek Heirloom Seed Company.
6 large green tomatoes, sliced ¼” thick
Pat tomatoes dry and dip both sides in flour to absorb moisture. Set aside.
1 package (12-14 oz) silken tofu
2-3 Tbsp water
Crumble tofu in blender and blend, adding water gradually until the mixture becomes creamy. Pour batter into pie plate and set aside.
1 cup panko bread crumbs
½ cup cornmeal
2 tbsp nutritional yeast flakes
1 tbsp onion powder
1 tbsp garlic powder
1 tbsp turmeric
½ tsp cayenne
½ tsp salt
Stir all ingredients together and transfer to a shallow pan. Dip tomatoes in batter then into panko mixture, patting the breading onto tomatoes so it adheres well. Heat about ¼” of oil in a cast iron skillet and fry tomatoes on both sides until browned. Serve warm.