Buddleja - Black sticky spots on leaves and stems of protected Buddleja, Digitalis or Phygelius are a natural plant response to high day and low night temperatures. There is no damage to the leaf underneath the spot and irrigation or hand watering will remove it.
Downy mildew - Symptoms include death of lower leaves and yellow blotches on the top surface. Spray Aliette 80WG or Fubol Gold WG (protected SOLA required) this week on Digitalis, pansies, roses, Buddleja, hops and Hebe if seen.
Blister mites - These can sometimes be seen on pears and currants in May - check susceptible species including Sorbus and Fraxinus. Spray with Hallmark WZT (SOLAs required for ornamentals and currants) or Talstar 80 Flo if seen.
Aphids - Under protection, use Aphidius colemani to control melon cotton and peach potato aphids and Aphidius ervi for the potato aphid, glasshouse potato aphid and others. Bamboo aphids are best sprayed. Along with Majestik, Savona and SB Plant Invigorator, include Aphox, Chess WG (SOLA 2008-2834), Decis (SOLA 2007-1693), Gazelle and Calypso (SOLAs required) in your programme, rotating to avoid resistance build up. Intercept 70WG, Gazelle and Calypso have an IRAC code of 4A - do not use in succession. Avoid Decis if using predators.
Western flower thrip - Check bedding plants, roses, Fuchsia and Clematis. Use blue traps with pheromone lures to monitor populations. Biological control is effective if temperatures are stable under protection. Control larvae with Amblyseius spp. Pupae can be controlled with Hypoaspis, nematodes or Atheta. Establish a breeding colony of Atheta in your glasshouses for lasting control of sciarid and shore fly larvae and thrip. Relatively predator-friendly insecticides include Conserve, Dynamec, Naturalis-L and Nemolt (SOLA 2007-2120).
Bifenthrin - Brigade 80SC, Starion Flo and Talstar 80 Flo lose their approval for advertisement, sale and supply on 30 May. Storage and use is approved until 30 May 2011. Gyro and UPL Bifenthrin are no longer available to buy but can be stored and used until 31 July 2010.
Lupins - The seed-borne disease Colletotrichum causing spiralling foliage with darkened and fallen stems should be kept under close observation and controlled with alternate sprays of Cercobin WG (SOLA 2008-1384), Scotts Octave and Switch.
- John Adlam is managing director at Dove Associates www.HorticultureWeek.co.uk/nursery for recent articles.