West: Autumn, season of mists and rampant oilseed rape

The mild, damp weather continues, with heavy mists this week reducing the opportunities for spray applications onto anything like dry leaves. We shouldn’t be lulled into a false sense of security; last year the really cold weather didn’t start until the last week of November.

Oilseed rape crops continue to grow rapidly and some are now above knee high (depending on the height of your knees!). The first few phoma lesions are just starting to appear, even in resistant varieties, and it’s a good time to get on with a fungicide, provided that the crop leaves are reasonably dry. The addition of a sticker/extender surfactant to the fungicide is beneficial when spraying conditions are less than ideal.

Cabbage stem flea beetle larvae can be found in some crops. A pyrethroid insecticide can be added to the fungicide if necessary.

Many growers are waiting to apply propyzamide or carbetamide to rape but the soil is still too warm on the lower ground and crop density is too great for the chemical to reach the soil. We shall have to wait for frosts to knock back the leaves to have any chance of an even application. On higher ground on the Cotswolds, soil temperature last week was down to 10C so is nearly suitable for spraying.

Dense crops of winter barley are suffering from high levels of mildew but it is unlikely that a fungicide will be of benefit at this stage. Frost will put a stop to the disease and although mildew does affect root development, it is unlikely to be a problem in such well-developed crops.

With rapid crop growth in cereals, manganese deficiency is showing on susceptible soils. This needs correcting as soon as possible as a deficient crop is less winter-hardy and more prone to mildew.

Aphicidal seed dressings will now have run out of steam in early drilled cereals and there have been aphids present in most crops this year. If no aphicide has yet been applied it’s probably a good idea to do so. In high risk areas further south, where an aphicide was applied in early October, it may be necessary to go a second time. Keep monitoring crops for re-infestation while the mild weather continues.

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