Category : Fungal
Alternaria leaf spot (Black spot, Gray spot)
Alternaria spp.
Alternaria lesions on turnip leaf
Symptoms
Small dark spots on leaves which turn brown to gray; lesions may be round or angular and may possess a purple-black margin; lesions may form concentric rings, become brittle and crack in center; dark brown elongated lesions may develop on stems and petioles
Cause
Fungus
Comments
Management
Plant only pathogen-free seed; rotate crops; applications of appropriate fungicides control disease when present
Anthracnose
Colletotrichum higginisianum
Anthracnose symptoms on turnip leaf
Symptoms
Small circular or irregularly shaped dry spots which are gray to straw in color on leaves; a high number of spots may cause the leaf to die; lesions may coalesce to form large necrotic patches causing leaves to turn yellow and wilt; lesions may split or crack in dry centers; dry sunken spots on roots which enlarge and turn gray or brown
Cause
Fungus
Comments
Management
Control of disease depends on sanitary practices; treat seeds with hot water prior to planting; rotate crops; plant in an area with good soil drainage; remove all cruciferous weeds which may act as a reservoir for the fungus
Black root
Aphanomyces raphari
Symptoms
Small black-blue areas on roots which expand and girdle taproot; roots become constricted at site of lesions; black discoloration extends into root
Cause
Fungus
Comments
Management
Control depends on crop rotation with non-brassica species
Black rot
Xanthomonas campestris
Symptoms
Seedlings develop wilted yellow to brown leaves and collapse; yellow, V-shaped lesions on mature leaf margins; dark rings can be found in the cross section of the stem
Cause
Bacterium
Comments
Management
Primary control methods based on good sanitation; plant disease-free seed; rotate crops every 2 years or less to non-brassica; avoid sprinkler irrigation
Cercospora leaf spot (Frogeye leaf spot)
Cercospora brassicicola
Cercospora lesions on turnip leaf
Symptoms
Angular or circular green to gray spots with brown borders on leaves; plant defoliation may occur in the case of a severe infestation
Cause
Fungus
Comments
Management
Plant only certified disease-free seed; avoid overhead irrigation; rotate crops to non-brassica species for 2-3 years; apply appropriate fungicide if disease emerges
Clubroot
Plasmodiophora brassicae
Deformed turnip roots caused by club root infection
Symptoms
Slow growing, stunted plants; yellowish leaves which wilt during day and rejuvenate in part at night; swollen, distorted roots; extensive gall formation
Cause
Fungus
Comments
Management
Once the pathogen is present in the soil it can survive for many years, elimination of the pathogen is economically unfeasible; rotating crops generally does not provide effective control; plant only certified seed and avoid field grown transplants unless produced in a fumigated bed; applying lime to the soil can reduce fungus sporulation
Downy mildew
Peronospora parasitica
Symptoms
Irregular yellow patches on leaves which turn light brown in color; fluffy gray growth on the undersides of the leaves
Cause
Fungus
Comments
Management
Remove all crop debris after harvest; rotate with non-brassicas; application of appropriate fungicides may be required if symptoms of disease are present
Sclerotinia rot (White mold)
Sclerotinia sclerotiorum
Infections usually begin at the base of the plant and will cause tan water soaked lesions on leaves. Eventually cottony white mycelia will develop and cover infected tissues. From this mycelia black seed like bodies (sclerotia) will be produced
White lesions on turnip stems caused by Sclerotinia rot
Symptoms
Irregular, necrotic gray lesions on leaves; white-gray leions on stems; reduced pod set; shattering seed pods
Cause
Fungus
Comments
Management
Rotate crop to non-hosts (e.g. cereals) for at least 3 years; control weeds; avoid dense growth by planting in adequately spaced rows; apply appropriate foliar fungicides
White spot
Pseudocercosporella capsellae
Symptoms
Small, necrotic, brown spots on leaf tips or margins that matures to light gray or white with the original dark spot in center; margins of lesions may be darker; lesions may coalesce to form large chlorotic areas and cause defoliation
Cause
Fungus
Comments
Management
No known plant resistance to white leaf spot so control relies on cultural practices such as rotating crops and removing weeds; application of appropriate fungicide may help control the disease
Wirestem (Damping-off)
Rhizoctonia solani
Symptoms
Death of seedlings after germination; brown-red or black rot girdling stem; seedling may remain upright but stem is constricted and twisted (wirestem)
Cause
Fungus
Comments
Management
Plant pathogen-free seed or transplants that have been produced in sterilized soil; apply fungicide to seed to kill off any fungi; shallow plant seeds or delay planting until soil warms