Diseases in Oilseed Rape

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Light leafspot

Light leaf spot is the main foliar disease to attack winter oilseed rape in the north of Britain. It can infect leaves, stems, flower buds and pods of winter oilseed rape. Spring oilseed rape is not affected but brassica vegetables can be affected.

About the Disease

The short period of time between harvest and sowing in Scotland results in leaf infection soon after sowing, but initially, plants are symptomless. During November/December, pale green or water-soaked lesions appear on older leaves, these lesions become brittle and crack easily when bent. In December/January symptoms become visible as large (1cm diameter) spots, fawn in colour with a crust appearance.

During wet weather spore masses or spore droplets are produced on both surfaces of the leaf around the outer edge of lesions, often with apparently healthy green tissue. The spore droplets have an appearance of salt grains on the surface of the leaf and are diagnostic of the light leaf spot fungus.

Light leaf spot after 48 hours incubation which brings out the classic ‘salt-like’ white spores

The presence of light leaf spot fungus can slow down the growth of leaves within the area of infection without affecting the rest of the leaf, resulting in the curving of leaves around the point of infection.

Infection of the stem results in small brownish, purple lesions often with black speckling around the edge. This can be confused with bruising caused when stems rub together. As the stems start to extend in spring, the lesions expand and by June can be several centimetres in length.

In severe cases stems split vertically along the lesion and occasionally break. These splits can allow access to other pathogens such as botrytis grey mould and sclerotinia.

Further Information

Managing Light Leaf Spot Risk in Oilseed Rape

Clubroot

Clubroot affects plants within the brassica family. Plants are stunted as a result of tumour like growths on their roots.

About the Disease

Clubroot affects plants within the brassica family. Plants are stunted as a result of tumour like growths on their roots.

It is a soil-borne disease and is becoming more prevalent and problematic in oilseed rape crops with shorter time periods between the rotations.

Crops grown in wet fields, with a low pH are at greater risk of infection. Flooding can cause disease spread. Managing soil structure and drainage can help towards disease management, as can regular soil sampling and pH management.

AHDB Cereals & Oilseeds funded research has reported a yield loss of 0.03 t/ha per 1% of plants infected.

Sclerotinia stemrot

Sclerotinia can attack a wide range of crops, including oilseed rape, potatoes, peas, beans, carrots and lettuce. Crops which are unaffected include grasses and cereals.

About the Disease

Sclerotinia can attack a wide range of crops, including oilseed rape, potatoes, peas, beans, carrots and lettuce. Crops which are unaffected include grasses and cereals.

The disease can be identified from approximately May onwards when the stems become bleached. A hard block of sclerotia forms within the cavity of affected stems leaving the plants more prone to lodging. These are white bodies which later turn black.

The disease favours wet conditions and can be spread via airborne spores from May. The spores can survive within the soil for up to eight years. Lengthening the rotation can help towards controlling the problem, as can ploughing following OSR - this buries the spores to a depth greater than that where they can germinate.

Powdery mildew

This airborne disease causes silvery white patches on the leaves of most brassicas, which eventually causes defoliation. It favours warm and humid conditions and spores can affect both the upper and undersides of leaves. Characteristic silvery patches may be more prevalent on the undersides of leaves where they are protected from rainfall.

About the Disease

Powdery mildew can affect both winter and spring sown oats. The disease, produces a white fluffy fungal growth on the leaf surface. This can cause leaves to turn yellow, leading to a loss in green leaf. High levels of disease at an early crop growth stage can kill out tillers.

The disease is known as a biotroph which means it requires a living host to survive. A typical symptom of powdery mildew is white fluffy superficial fungal growth on the surface of leaves, stems and ears. Fungal spores which develop from these lesions are spread to other plants via the wind. The ideal infection conditions are mild and humid. Very wet conditions can limit the spread of the spores.

The disease can also overwinter in crop trash in black fungal bodies known as cleistothecia. Cereal volunteers are another method of survival. The "Green Bridge" allows powdery mildew to spread from a winter-sown crop in the autumn to the spring sown crop in the spring, to late-developing volunteers before infecting the following winter crop.

Diseases in Oilseed Rape

For the latest updates and information on crops and soils, subscribe to our Crops & Soils Newsletter.

You can also visit our archive for Crop Updates here.

Light leafspot

Further Information

Managing Light Leaf Spot Risk in Oilseed Rape

Clubroot

Sclerotinia stemrot

Powdery mildew

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Sign up to the FAS newsletters

Diseases in Oilseed Rape

For the latest updates and information on crops and soils, subscribe to our Crops & Soils Newsletter.

You can also visit our archive for Crop Updates here.

Light leafspot

Further Information

Managing Light Leaf Spot Risk in Oilseed Rape

Clubroot

Sclerotinia stemrot

Powdery mildew

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Integrated Land Management Plans

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