Black Spots on Tomato Plant Leaves

Question:

I have Roma and Grape tomato plants that have loads of fruit on them, the vines are another story! They were all in good shape until a month ago, when leaves started turning yellow with black spots. I sprayed some insecticidal soap on them a few times, and cut off the bad foliage, but they continued to deteriorate. Again my tomatoes are great, but the vines are nearly bare because the leaves turn yellow and dry up and fall off. What causes this and what can I do in the future to prevent it? Thanks for your help.

Monica from PA

Answer:

Monica,

From your description, it sounds like your plants could be affected by one of three common tomato blights. Septoria leaf spot (or blight) and Early Blight are the two most common, both of which tend to start after the fruit sets. The third is Late Blight, which usually only occurs after unusually cool, wet weather. These are all airborne fungal diseases that require dew or rain to infect the plants. These diseases build up rapidly in wet weather and cause dark leaf spots followed by yellowing and defoliation (leaf drop). They may also produce spots on the fruit.

You did the right thing by cutting off the affected foliage, however these blights are difficult to control once established. This fall, pull up and destroy any remaining vines. Because this fungus can over winter in the soil, rotate your tomato plantings every year (plant in the same place only once every 4 years). Mulch the base of the plants with 1-2 inches of straw, newspaper or other organic materials and water the plants from the bottom. Consider spacing the plants farther apart to increase air circulation and use a fungicide as needed.