Fertilisers: Top dress stock plants and trees that do not have longer-lasting CRF products. Use a horticultural grade 1:1:1 fertiliser where the source of potash is potassium sulphate rather than potassium chloride.Certain ornamentals can be chloride-sensitive, resulting in leaf damage. Consider a granular product such as Floranid Permanent, Osmocote Topdress NT, Sincron or Triabon on overwintered container plants. CRF plugs pushed into the growing media work well but can be difficult to insert. Application rates vary, but as a guide use one gram per litre of compost or one 5g plug per two-litre pot. Wet weather will affect outdoor container crop nutrient levels so top dress those crops you want ready later this month. Top dressing can destroy the herbicide layer at the point of application. You may need to reapply around three weeks after top dressing to avoid weed growth.
White blister: Remember to check under leaves of Aubrieta and Arabis and control with Amistar (SOLA 2009-0443) or Signum (SOLA 2009-1842) if seen.
Botrytis: Maintain botrytis control on protected crops. It is still quite active at present so clean up old foliage and trimmings from where infection can spread and keep the tunnel doors open when you can. Check for paeony blight (Botrytis paeoniae) on tree paeonies and other larger varieties. It shows as dark purple blotches on stems near the soil surface. Left untouched, the stems will rot off and fall over. Spray with suitable products such as Amistar (SOLA 2009-0443), Rovral WG, Scotts Octave, Serenade ASO (SOLA 2009-0246) or Switch if seen.
Leaf spots: Maintain leaf spot controls on herbaceous and shrubs this month.
Heater damage: Unvented direct-fired oil heaters can create a build up of sulphur dioxide, while propane-fired heaters can cause ethylene build up in structures. Both can result in damaged foliage of young plant material. It is even more important at the moment to open your tunnel doors or glasshouse vents, even if it is only for half an hour a day, to bring about an air change in the structure. Have your direct-fired heaters regularly checked for correct and efficient operation.
Caterpillars: Consider Conserve, Nemolt (SOLA 2007-2120) or Majestik in integrated pest management (IPM) systems and Toppel 100EC or Decis for non-IPM areas. Tortrix moth caterpillars are around now.
John Adlam is managing director at Dove Associate