• Philip

Infected and Contagious

Light leaf spot (LLS) is a disease of oilseed rape and some vegetable brassicas, caused by the fungus, Pyrenopeziza brassicae.

The disease appears, after a long period of symptomless growth, firstly on leaves as speckles of white spore.

That sentence tells a partial story. Some of the main damage caused by LLS is when it develops on the flower buds. That “long period of symptomless growth” means the disease is developing systemically within the plant, however everyone talks about and checks for symptoms on the leaf. Rothamsted workers tell us, it will be visually found on the floral parts of the plant in March.

Recently there has been a move not to grow varieties of oil seed rape with an AHDB ratings below “6.”

There are 29 varieties you could have planted in autumn 2021 and only 2 of them are 5’s. No problem then? But what does the rating really mean and how does that help in the field? Well, a rating of 8 or 9 could mean that it is not worth spraying where a system of integrated disease / crop management has been actioned.

However, with a rating of 6 and the fact that not too long ago it was reported that the forecasting system for LLS was “inaccurate,” one could soon be lulled into a false sense of security when a large proportion of autumn spraying is centred around Phoma control not Light Leaf Spot.