Bacterial Spot

• Bacterial leaf spot, caused by Xanthomonas campestris, is indicated by angular spots on tomato leaves. The leaves are also often rimmed with a band of dead tissue. Most of the spread of this bacteria occurs because of infected seeds or transplants. The bacteria can be spread by any water movement. The longer the period of high moisture, the greater the likelihood for infection. Control or prevent it by applying a protective film of copper fungicide before rain events, practicing crop rotation and using only certified seeds and plants.
  
  

Tomato Spotted Wilt Virus

• Tomato spotted wilt virus (TSWV), a disease spread by thrips, causes dark spots on leaves. These spots spread to stems, where they form cankers. The tomato leaves will bronze and young plant tips die back. The fruit will develop patterned yellow spots and rings. Tomatoes infected with this virus must be discarded. To prevent infection, minimize the presence of weeds around the garden that could serve as hosts to the thrips.
  
  

Tobacco Mosaic Virus

• Tomatoes infected by tobacco mosaic virus have crinkled and mottled foliage and fruit suffers from internal browning. Tobacco mosaic virus is easily spread when tomato plants come into contact with tobacco products or tools or hands that have handled tobacco. Infected plants and plant debris must be removed and destroyed. Some varieties are more resistant to tobacco mosaic virus than others.
  
  

Septoria Leaf Spot

• Tomatoes around the world can be attacked by the Septoria lycopersici fungus. The fungus causes small circular spots on the lower surface of older leaves. The spots have gray or tan centers with a dark brown margin. These spots may grow and coalesce. Severely infected leaves can yellow, dry up and drop off. Control it by removing tomato debris and practicing good sanitation; fungicides can also be used to control Septoria.
  
  

Early Blight

• Early blight, a fungal disease caused by Alternaria solani, is easily recognized by 1/2-inch-wide circular lesions within which dark concentric circles develop. This leaf blight typically begins on older, lower leaves and progresses upward, causing leaves to wither, die and drop from the plant. The blight can also cause collar rot, damping off, stem cankers and root rot. The fungus prefers moist conditions and temperatures around 80 degrees Fahrenheit. Alternari fungus overwinters in plant debris or soil and is also seed-borne.