Crops most at risk are those closely spaced and those with very hairy foliage. Keep tunnel or glasshouse doors/vents open whenever possible. If you can introduce air movement within the crop canopy and not just over the crop, the incidence of Botrytis is dramatically reduced. If you have automatic watering, try to alter the sequence by watering those susceptible species early in the morning rather than late at night. The foliage will dry out in the morning rather than stay wet all night. Aim to have the leaf surface dry at least once every 24 hours.
Choisya Root and stem rotting can be more of an issue in the autumn/winter months for these plants. In the past, laboratory tests have shown Pythium, Phytophthora and Fusarium present so try to keep them on the dry side this winter. Drenching with fosetyl-aluminium, Serenade ASO (SOLA 2009-0246) or Subdue may help to suppress the disease but water control is the main point to watch.
Heaters Remember that if you are using heaters that are direct fired at the moment that you are using paraffin with low sulphur content. If you have snow on glass or tunnels that are shut up for extended periods, then open the doors or vents, just once a day, even for a short time, to give an air change. This reduces the risk of foliage scorch from the build up of sulphur fumes from paraffin or ethylene from gas.
Heathers Erica and Calluna can suffer from Rhizoctonia during this time, particularly protected crops and young over-wintering plugs. Those where no control programme is in place are often most at risk. A spray with Rovral WG or Basilex will give control but do note the restrictions on the Basilex label.
Azalea gall This can be expected during the latter part of December onwards if wet weather conditions continue. Spray with a mix of Croptex Fungex and Serenade ASO (SOLA 2009-0246) when the first signs of this disease are seen.
Weed control Apply residual herbicides to field-grown crops such as Devrinol, Stomp 400SC (SOLA 2008-2923), Flexidor 125 or Butisan S on suitable spraying days. Avoid spraying residual herbicides during periods of heavy rainfall or the herbicide can be washed down into the root zone and cause foliar damage.
John Adlam is managing director at Dove Associates www.HorticultureWeek.co.uk/nursery for recent articles