While bacterial speck and spot are not always catastrophic to a crop of tomato plants, these diseases can still be problematic when trying to cultivate high-quality yields. Warm, moist conditions favor bacterial spot, while cool, moist conditions favor bacterial speck. The foliar symptoms of each disease are almost identical, and can be misdiagnosed. However, symptoms that appear on the fruit are usually different and make proper diagnosis easier.
Bacterial spot is caused by the bacterium Xanthomonas campestris pv. vesicatoria, and it can affect both tomato and pepper. The infection starts off as small circular to irregularly shaped spots that are greasy in appearance. A yellow halo may form around the spot. These spots may merge and defoliation can occur. The fruit shows raised black spots, which expand and become sunken scab-like areas.
Bacterial speck is caused by the bacterium Pseudomonas syringae pv. tomato. This bacterium attacks tomatoes, but no other plants in the tomato family. It can, however, survive without causing disease problems on other plants surrounding the tomato fields. As with bacterial spot, small spots form on the leaves, and also can be found on stems and flowers. The immature fruit will have small sunken specks that do not rupture the skin of the tomato.
Both diseases have identical control methods. It is of utmost importance to use disease-free transplants or seed. Properly space your plantings and each year rotate the location of your tomatoes and related plants, such as pepper and eggplant. Keep weeds in check. Remove infected leaves to prevent further infection. Dispose of plant debris in the fall. Water in the early morning without wetting leaves, and avoid working with your plants when they are wet. Water and fertilize to maintain the plants natural defense to disease. Fixed copper sprays plus mancozeb may also be used to prevent spread of these diseases.
This article originally appeared in the 8/8/2003 issue.