Light Leaf Spot in Oilseed Rape

Light Leaf Spot in Oilseed Rape

Light leaf spot is the major oilseed rape disease in Scotland and northern Britain. Although the disease occurs in the rest of Britain, Phoma is more dominant in southern Britain. However, the scale of light leaf spot in southern Britain is probably underestimated due to latent or indistinct visual symptoms.

Light leaf spot leaf, flower bud and pod infections often seriously diminish rape yields in susceptible crops, with yield losses of up to 40% in the worst case. Average yield losses range between 0.5 and 1.2 t/ha, depending on the severity of infection.

Leaf lesions	Stem lesions	Pod lesions

Disease symptoms appear from late autumn, often in foci, as pale green or bleached leaf blotches surrounded by a halo of white/pink spore masses.  Lesions can coalesce and the whole leaf may be affected. These leaf blotches can be mistaken for fertiliser scorch.

Often infected plants exhibit no symptoms, but these may be induced to sporulate by placing leaves in polythene bags at 10-15°C for three days.

Stems can develop fawn/pink lesions surrounded by fine darkened and speckled margins. In cases of high humidity these can be surrounded by white spore masses. Lesions are also formed on the lower stem and might be confused with those caused by Phoma lignam.

Affected buds and pods are covered with small white to fawn spots which, if severe, can result in flower abortion. Pod damage can lead to premature ripening and pod shattering.

The light leaf spot fungus (pyrenopeziza brassicae) is able to survive the summer months on debris from the previous oilseed rape crop. Initial autumn infections are mainly derived from wind-dispersed ascospores.

Controlling Light Leaf Spot in Oilseed Rape

Avoiding sowing susceptible varieties, and destroying or disposing of stubble as soon as possible after harvesting, will help to control this disease. Two-spray programmes are recommended to control the disease: a late autumn protectant treatment and a follow-up in early spring, as the crop grows away, to guard against flower and pod infection and limit yield loss.

On oilseed rape Proline 275 can be used throughout your disease control programme, and gives you outstanding performance on light leaf spot and Phoma in the autumn, as well as providing cost-effective activity against Sclerotinia at flowering.

The few resistant cultivars need to be carefully stewarded to protect valuable genetic resource, which is best achieved using an integrated control strategy, including fungicides.