The Disease Doctors: BRASSICAS

There are many diseases that are common and "bother" our brassicas as detailed below:

CLUB ROOT

Pathogen - Plasmodiophora brassicae, a soilborne slime mold-like parasite

Host – most members of the brassica family

Environment – Cool, wet, acidic soils

Signs & Symptoms – Roots will be partially or totally swollen. If severe, water and nutrient uptake will be hindered and the plant will show symptoms similar to water and nutrient deficiency – wilting and yellowing of the leaves. Plants may also become stunted, show reduced head development, or die.

Controls – Awareness of disease presence in the past is important when developing a crop rotation. The parasite can survive in soil for up to 10 years. Ensure soils are well drained and at a proper pH. Select resistant varieties, when available. Remove infected crops from the field and burn them – do not bury or feed to livestock, as the organism will persist and be spread.

BLACK ROT

Pathogen – Xanthomonas campestris, a seedborne bacteria

Host – most members of the brassica family, particularly cabbage and cauliflower

Environment – wet and warm (80-86 degrees Fahrenheit) conditions

Signs & Symptoms – Initially, the plants will display V-shaped lesions at margins of leaves. Leaf veins will become blackened. Leaves will die off and drop. If the disease reaches the stems and affects the vascular system of the plant, the plant will wilt.

Controls - A proper crop rotation of three years between brassicas and planting in areas of good soil drainage and aeration are important for prevention. Avoid overhead irrigation. If plants are infected, remove from the field. Use of copper may help prevent spread to healthy plants.

DOWNY MILDEW

Pathogen – Peronospora parasitica, a fungal-like organism

Host – many brassicas, including cabbages, cauliflowers, Brussels sprouts, radishes, swedes and turnips

Environment – favors cool, wet conditions

Signs & Symptoms – The disease starts with angular, yellow spots on upper leaf surface. Eventually, these spots will turn brown. Cotton-like spots will form on the underside of the leaves. Seedlings may also be affected and will be totally covered in the mildew.

Controls - A proper crop rotation is a starting point. Grow resistant varieties or disease-free certified seeds. Ensure proper air circulation among plants. Remove infected leaves and burn. Copper may reduce spread of disease.

ALTERNARIA LEAF SPOT

Pathogen – Alternaria brassicae & A. brassicicola, seedborne pathogens easily spread by wind

Host – most brassicas

Environment – warm (77-86 degrees Fahrenheit), wet weather

Signs & Symptoms – Leaf spots start as pinpoint yellow areas, expanding to up to 5cm in diameter. As these spots enlarge, the centers display dark concentric rings. Browning of the heads in broccoli and cauliflower may also be seen.

Controls – A proper crop rotation is a good start. Use disease-free seed. Avoid overhead irrigation.