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| Figure 1. Leaf symptoms of bacterial speck. | Figure 2. Fruit symptoms of bacterial spot |
DiseaseBacterial speck and bacterial spot normally are not as prevalent as some of the other leaf spot diseases of tomatoes in Kansas, but they can cause serious damage during wet summers. Bacterial spot also may occur on pepper. On tomato, both diseases result in spot formation on the leaves and fruit. Heavy infection can cause defoliation, but the main effect of these diseases is the reduction of fruit quality. Leaf symptoms of bacterial speck and bacterial spot are similar. Both diseases result in small (1/8 - 1/4 inch) black lesions on leaves. These spots usually are surrounded by a yellow halo. The lesions of bacterial spot tend to have a greasy appearance; those of bacterial speck do not. The two diseases are more easily distinguished by symptoms on the fruit. Bacterial spot results in small, slightly raised, water-soaked spots. These spots may enlarge to 1/4 inch in diameter and become very rough and cracked. Bacterial speck lesions also are slightly raised, but typically much smaller (1/16 inch) than those of bacterial spot. Bacterial speck lesions do not crack or become scaly as in bacterial spot. CausesBoth the bacterial speck (Pseudomonas syringae pv. tomato) and the bacterial spot (Xanthomonas campestris pv. Vesicatoria) bacteria can survive on plant debris or on other weedy hosts. The bacteria also may be introduced into a field on contaminated seed or on infested or infected transplants. Driving rain and mechanical injury to plants caused by hail and high winds increase the severity of these diseases. The development of bacterial speck is favored by relatively cool (70° F), wet conditions; while bacterial spot becomes more severe during periods of warm temperatures (75 to 80° F), heavy rainfall, and a high relative humidity. ControlTomato varieties with resistance to bacterial speck are currently available and should be used where this disease has been a continual problem. However, these varieties are still susceptible to bacterial spot. Both bacterial speck and spot can be prevented or reduced in severity by cultural practices. Follow a three year rotation with non-solanaceous crops in commercial production. In home gardens, alter the planting location as much as possible. If you must replant in the same location, fall plow or till under dead plants to hasten decomposition. Start transplants from seed that has been tested for bacterial spot contamination. Inspect transplants or young plantings for evidence of leaf spotting. Keep fields free of weeds by cultivation. Avoid the use of overhead irrigation. Instead, use drip tapes or lines, or soaker hoses for watering. Mulch around plants with plastic or straw. Avoid working with wet plants. Copper-based fungicides, including basic copper sulfate, copper hydroxide, and copper resinate, may be effective in suppressing bacterial speck and bacterial spot. Make applications at the first sign of leaf spotting or at the time of first blossom. Continue applications at 7 to 10 day intervals. Chemical sprays may not completely control the disease during weather favorable for infection. |
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Web updated 9/01/06 |