Lettuce, brassicas and other leafy greens are grown year-round in many regions and, while insect and fungal disease pressure may reduce in winter, growers need to watch for bacterial diseases. These can be soil or seedborne, may transfer between crops on plant debris, or be spread by wind, contact or rain splash.
Key bacterial diseases to look out for include:
» Xanthamonas species are often associated with leaf spotting or leaf blight diseases. Lesions are often dark brown or black and commonly spread by rain splash or irrigation. Xanthomonas campestris causes black rot in brassicas resulting in infected V-shaped lesions in brassica leaves. If leaves are split open, the black infection is seen, especially in leaf veins.
» Pseudomonas species are also responsible for leaf spotting symptoms in lettuce, and peppery spot and head rot symptoms in brassicas. These lesions tend to be more light brown or tan in colour.
» Pectobacterium carotovorum infects lettuce, onions, brassica and carrots causing soft rot in all. Symptoms include wilting of plant material and watery-soaked lesions often resulting in a foul smelling, slimy mess.
Effective control of bacterial diseases is challenging. Current best practice is to maintain protective copper sprays through the growing season. Use clean, certified seed to reduce the spread of seedborne bacteria. Three-yearly crop rotation can help minimise the spread of peppery spot in brassicas as it’s relatively short-lived in soil. Avoid working in crops in wet conditions help stop spreading bacteria diseases among plants.
For more information on controlling bacterial diseases, please contact your local Fruitfed Technical Horticulture Representative.