16 March - Weevils and mildew

Vine weevil Check containers for larvae and apply nematodes if compost temperatures are at or above 5°C. Adult activity will be rising too. Focus on euonymus, ferns, fuchsia, heuchera, hosta, hydrangea, Taxus, junipers, Pathenocissus, Photinia, pieris, primula, pyracantha, sedum and skimmia. Monitor composts of sacrificial plants such as euonymus or primula weekly for signs of larval activity. Control adults more effectively using late-afternoon applications of Chess WG (EAMUs required) or Steward (EAMU 2008-2905). Non-IPM systems can use Hallmark WZT (EAMU 2008-2944) too.

Downy mildew Check for yellow patches, usually on young foliage, followed later on by grey fungal growth on leaf undersides. Protect crops using Bravo 500 (EAMU 2011-1130), Dithane 945 (EAMUs required), Karamate Dry Flo Neotec or Proplant (EAMU 2016-0785) on buddleia, Cirsium, Digitalis, geum, hebe, impatiens, osteospermum, pansy, rose and others. Control any infections seen using Amistar (EAMU 2009-0443), Fenomenal (EAMU 2013-1990), Fubol Gold WG (EAMU 2013-2288), Invader (EAMU 2012-0109), Paraat (EAMU 2011-2585), Signum (EAMU 2012-2141) or Valbon (EAMU 2014-2325).

Aphids Check protected, evergreen crops regularly. Use short-term, contact-acting products including Chess WG (EAMUs required), Majestik, Movento (EAMU 2011-1987), Pyrethrum 5EC or SB Plant Invigorator. Avoid frost before, during and after applications. Aphidius colemani will more effectively control the round species — melon cotton and peach potato aphids. Aphidius ervi prefer elliptical species — glasshouse potato aphid.

Predators Start predator introductions now for whitefly, aphids, mites and thrips in protected, frost-free structures.

Leaf crinkle Cold nights and warm days can affect large-leaved shrubs and some herbaceous crops. It is essentially cosmetic but may affect sales. Ventilate protected structures on warmer days. Fleece vulnerable crops at night to reduce extreme day/night temperature fluctuations.

Gleditsia and oaks Get ready to apply Gazelle SG or Hallmark WZT (EAMU 2008-2844) to outdoor crops at leaf emergence to prevent midge egg-laying — particularly for oaks, where the midge will go for the central bud.

Plane anthracnose The best approach is to apply preventive fungicides such as Bravo 500 (EAMU 2011-1130) or Dithane 945 (EAMUs required) to outdoor crops just before foliage emerges. Check for small, brown patches that develop underneath leaf buds in the next few weeks. It can be more of an issue in cool, wet springtime weather.

John Adlam, managing director, Dove Associates

HorticultureWeek.co.uk/nursery


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