Most tomato plant problems stem from improper planting and care techniques, but with minimal planning and care, tomatoes will reward gardeners with juicy, trouble-free fruits. If, however, a common fungus like early blight, Septoria leaf spot, Anthracnose ripe rot or wilt takes hold, quick and appropriate action can save your harvest.
According to the University of Connecticut, "High soil fertility reduces the severity of this disease (blight), as does maintaining plant vigor." To that end, Ohio State University recommends that gardeners "Apply 2-1/2 to 3 lbs. of a complete fertilizer, such as 5-10-10, 5-20-20 or 8-16-16 per 100 square feet of garden area. Work the fertilizer into the soil about two weeks before planting. An additional sidedressing of a nitrogen fertilizer may be desirable after the first cluster of flowers have set fruit."
Like most tomato fungus diseases, Septoria leaf spot fungus (Septoria lycopersici) spores live in the soil. Splashing rainwater spreads the spores to the lower leaves of the plant and the disease spreads slowly upward. At the first sign of leaf spot--grayish white spots on the lower leaves--trim off the affected leaves and discard. Do not prune or work around your plants after a rain because this can cause reinfection. Mulch or apply landscape fabric around the base of your plants to prevent fungus spores from splashing onto the leaves.
There are a variety of chemical controls available for tomato fungus diseases. For the most effective control, these sprays should be applied before symptoms appear, but they can be used during an outbreak to control or stop fungal spread. Mancozeb/maneb, chlorothalonil and copper products can be used to minimize crop damage. These broad-spectrum fungicides are sold under a variety of brand names and must be applied regularly--usually at 7 to 14 day intervals--for the best results.
Bacillus subtilis is a naturally occurring soil organism that is present in soil. It is recovered from the soil and used in a commercial products that are available in nurseries and garden centers. Known as biological fungicides or microbial fungicides, these products work best when applied before a fungal outbreak occurs. When used properly, Bacillus subtilis products will suppress soil fungi and protect tomato plants from most common fungal diseases.