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Problem: Bacterial Speck - Pseudomonas syringae pv. tomato
Host Plant: Tomato
Description: Bacterial 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 quite 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 are typically much smaller (1/16 inch) than those of bacterial spot. Bacterial speck lesions do not crack or become scaly as in bacterial spot.
Both 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 (75-80 F), heavy rainfall, and a high relative humidity.
Recommendations: Control measures for the two diseases are
similar. These diseases can be prevented or reduced in severity by removal of plant debris
in the fall, cultivation of weeds, rotation, and the use of clean (non-infested) seed and
transplants. If lesions develop on leaves and fruit, spray every 5 to 10 days. Chemical
sprays may not completely control the disease during weather favorable for infection.
References:
1. Leaf and Fruit Diseases of Tomato. K-State Research and Extension, Publication L-721.
2. Bacterial Speck and Bacterial Spot of Tomato. K-State Research and Extension Electronic Publication.
Last Update: 05/06/2003
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