27 May - Watch out for whitefly

Willow anthracnose: Small purplish spots are produced on leaves and shoots that enlarge causing leaf and twig death. Control with Amistar (SOLA 2009-0443), Signum (SOLA 2009-1842) or Switch. Apply at bud break and through the summer if it is hot and dry. Salix matsudana 'Pendula' is reported to be resistant.

Pearlwort: Effective pre-emergent herbicides for container-grown nursery stock were identified in HDC project HNS 139. New project HNS 139a will look closer at Dual Gold and Sumimax. Coarse pot surfaces reduce weed germination so a bark mulch or coarse peat growing media help in reducing weed growth.

Bed space: Use it wisely and, while you have the opportunity, implement a strategic plan for setting down new potting.

Whitefly: Control active populations on IPM non-edible crops with rotational sprays of Chess WG (SOLA 2008-2834), Intercept 70WG, Majestik, Mycotal, Naturalis-L, Nemolt (SOLA 2010-2131), Oberon (SOLA 2004-1718), Savona and SB Plant Invigorator. Other products include Actara (SOLA 2009-2801), Calypso (SOLAs required), Decis, Gazelle, Spruzit or Toppel 100EC. Some products have edible crop approvals. Couraze, Exemptor or Imidasect 5GR provide longer-term control for non-edible ornamentals. Spray three times at five-day intervals to control all subsequent generations.

Thielaviopsis (black root rot): Symptoms include wilting, leaf yellowing and blotching due to patchy root death - roots have black tips or blackened areas on them. This disease is water spread so hygiene is a key control. Apply drenches of Prestop, Scotts Octave or Switch to affected crops. If you have the disease under Mypex then drench Prestop, Revive or Serenade ASO (SOLA 2009-0246).

Buddleja: Black sticky spots on leaves and stems of protected crops of Buddleja, Digitalis or Phygelius are a natural plant response to high day and low night temperatures. No damage occurs underneath the spot and irrigation or hand watering usually removes it.

Craneflies: Adult activity suggests leatherjackets will be present soon. Liners and small pots are at most risk with damage to the base of the plant at ground level. Control with nematodes or, for outdoor crops, Dursban WG, Decoy Wetex or Draza Forte.

John Adlam, Managing director, Dove Associates


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