Frog hoppers: "Cuckoo spit" is now active on ornamentals, which is a more cosmetic than damaging pest. Spray with Savona or Chess WG (SOLA 2008-2834) and use Decis or Toppel 100EC in non-IPM systems.
Dianthus: Newly-potted Dianthus may need a directed spray to the crown with Cercobin WG (SOLA 2008-1384), Scotts Octave or Switch to control Fusarium spores. Sciarid larvae can damage roots straight after potting so apply nematodes, Hypoaspis or Atheta.
Powdery mildew: Check Acer, Aster, Crataegus, Euonymus, Euphorbia, hops, Lonicera, oaks, miniature roses, Solidago and Verbena. Use Amistar (SOLA 2009-0443), Bumper 250EC (SOLA 2009-0707), food-grade potassium bicarbonate, Nimrod or Systhane 20 EW for control. Emulsifiable formulations have the potential to cause scorch on sensitive young foliage. Outdoor crops will benefit from applications of Cyflamid (SOLA 2007-0512), Stroby WG, Lyric and Folicur for longer-term control.
Fireblight: Most infections occur from the flower spike. Check on fireblight subjects, remove all suspect plant material and burn it - do not compost or recycle. To reduce the risk of infection in hawthorn hedgerows (removing your fireblight buffer zone), trim hedges as soon as they flower to remove flower heads. Only do this if your nursery is not in the ELS scheme.
Caterpillars: Different species are active on trees including Betula, Crataegus, Carpinus and Quercus. The damage can be significant over just a few days so control when seen with Nemolt, Dimilin Flo, Decis, Runner (SOLA 2008-2903) or Toppel 100EC. Install a range of different tortrix lures under protection particularly over plants damaged last year.
Green manures: Order seed now for planting at the end of this month. Mustards are good for quick manuring in between crops. The Caliente range from Plant Solutions will increase soil organic matter levels and also provide additional biofumigation benefits. Manage green manures with additions of fertiliser, as required, prior to sowing.
Dahlias: Watch out for ring spot virus on foliage. It is quite distinctive with yellow spots and dark centres. Advise your supplier as soon as you spot any of these symptoms because it can spread to a whole crop and other genera very quickly by aphids.
John Adlam is managing director at Dove Associates www.HorticultureWeek.co.uk/nursery for recent articles