Phoma & volunteers are key OSR targets

Check oilseed rape crops for phoma now, particularly those close to rape stubbles from the 2005 harvest, urges ADAS.

Phoma leaf spot is increasing rapidly in most areas and is now the main priority for action, it advises.

New spots from the disease are showing after heavy spore release about two weeks ago, and with recent rain releasing yet more spores the symptoms will increase well into November.

Crops with five to six leaves have reached the 10-20% plants affected threshold for fungicide treatment, and some forward stands have more than half the plants hit.

Syngenta’s SPAWS update (see reports levels in an early September-sown crop at ADAS Boxworth rising from 2.5% to 40% affected during the week to 24 Oct.

Overdue herbicides must also be applied soon, especially where emergence was slow and weeds are filling the patches in the absence of crop shading, adds ADAS.

Dense cereal volunteers are said to be an increasing problem, especially where crops are small, with some untreated crops having cereals 15-20cm tall and tillering.