Bacteria: Acanthus are vulnerable to a bacterial attack causing rot, especially in the plant's crown. Spray with Croptex Fungex and Serenade ASO (SOLA 2009-0246) if seen. Maintain copper sprays on laurels, other Prunus subjects and Magnolia.
Astrantia: Leaf spotting can be caused by a number of different pathogens including Leptotrochila astrantiae, which produces dark-brown/black leaf spots surrounded by a yellow halo. More prevalent in wet, humid conditions, it can be controlled with broad-spectrum fungicides such as Amistar (SOLA 2009-0443) or Bumper 250EC (SOLA 2009-0707).
Whitefly: Rotate sprays, install sticky traps to monitor pest populations and keep introducing Encarsia and Eretmocerus. Remember that spraying three times at five-day intervals to control subsequent generations give the best adult control programmes.
Sucker: On Buxus, curled foliage with a white fluffy growth surrounding the insect inside the curling are signs of infestation. On Crataegus, small white insects colonise growing tips producing distorted rosette-like galls. Spray with Hallmark WZT (SOLA 2008-2944), Gazelle or Dursban WG. For IPM systems, try Chess WG (SOLA 2008-2834).
Biological control: Monitor introductions closely to make sure they have released successfully and are providing effective control. Increase predator numbers weekly to keep pest populations at manageable levels.
Rhododendron bud blast: This can be identified by a distinctive black or silvery colour and black bristle-like spore heads. It is associated with rhododendron leaf hopper feeding, which then lays its eggs in the flower head. A two-pronged attack is needed - control by spraying with Calypso (SOLA 2006-3728) or Chess WG (SOLA 2008-2834) on protected crops or Talstar 80 Flo or Hallmark WZT (SOLA 2008-2944) on outdoor crops. Chlorothalonil or mancozeb will reduce its spread.
Spider mites: Borneo (SOLA 2008-1216) is effective now and can control all moving stages, has an ovicidal effect on female adults and can persist for up to 60 days on foliage. Naturalis-L has some effect on this pest along with aphid, whitefly and thrip.
Spraying: Bees are attracted to honeydew from aphids as well as pollen. You have a legal obligation to advise beekeepers of any spraying activities that may affect their hives.
- John Adlam is managing director at Dove Associates www.HorticultureWeek.co.uk/nursery for recent articles.