Bacterial leaf spot and stem blight of safflower is caused by the bacterium Pseudomonas syringae. Infection occurs when bacterial cells are deposited onto leaves by splashing water, aerosol movement, or from contaminated seed and multiply to form large populations. The bacteria gain entry into plants through natural openings and wounds. Infection occurs most readily during cool (less than 85ºF), wet weather, especially hard, wind-driven rains. Bacteria are disseminated within and among fields by splashing water, aerosols, and on contaminated equipment and workers. The pathogen survives between susceptible hosts in and on weeds such as hairy vetch, infested crop debris and contaminated seed.
Disease initially appears as dark, water-soaked lesions on leaves, stems, and petioles. Lesions become red-brown in color and turn necrotic with age, and often develop a pale yellow margin. Some lesions may have a dark brown to black margin. The terminal bud is often killed, and the interior of petioles may develop a rot that extends below the soil line into roots.
Severe infections can kill plants, but infected plants may recover when hot, dry conditions return. Yield losses can be significant.
No biological control strategies have been developed for bacterial leaf spot and stem blight.
Plant high quality seed free of the bacterial leaf spot pathogen. Varieties with moderate levels of resistance, such as Morlin, are available and should be planted if suitable for local production requirements. As with other diseases caused by pseudomonads, crop rotation to non-hosts, incorporation of crop debris, weed control in and around fields, and furrow irrigation from pathogen-free sources of water such as wells may reduce disease incidence and severity.
Chemical controls are not available for bacterial leaf spot and stem blight.
Categories: Safflower, Disease, Bacterial Leaf Spot, Stem Blight
Date: 3/3/2005