Disease guide

Pseudomonas syringae pv. tomato
Two races (O and 1) have been reported.

This bacterium can attack the leaves, stems, petioles and flowers of the plant. Leaf symptoms appear as dark brown to black spots often surrounded by a yellow halo. Black lesions with yellow borders can also occur on leaf margins where guttation droplets collect. Large areas of leaf tissue are killed as these lesions coalesce. oval to elongated black lesions occur on stems and petioles. Generally, fruit lesions remain small (1mm), speck-like and are superficial, however, they can be larger and sunken. On immature fruit they are surrounded by a green halo.

Disease development is favored by cool (13-25°C, 55-77°F), rainy weather or sprinkler irrigation. Usually one day of leaf wetness is required for the disease to develop. Bacterial speck often occurs in arid areas where sprinkler irrigation is used, but seldom occurs under drip or furrow irrigation in those areas. The organism can survive on the roots or leaves of many crops and weeds. Seed can be infected, however seed transmission is usually of minor importance.

The use of resistant varieties is the most effective way to control this disease. Copper sprays applied early can reduce disease incidence. Sprinkler irrigation will generally increase disease incidence where the bacteria are present, and therefore, furrow or drip irrigation should be used when possible.