These can start to pupate this month, making them difficult to control - active larvae may also be found in untreated containers. Nematodes can be applied to saleable edible and ornamental crops but will not control larvae in 24 hours.
Large blue flea beetle: Often seen outside on container plants in May, they are small, blue/purple and seen on ornamentals as well as willowherb and bittercress. Spray with Decis (SOLA 2007-1693), Hallmark WZT (SOLA 2008-2944) or Talstar 80 Flo if seen (non-IPM) and Chess WG or SB Plant Invigorator if using predators. Other similar beetles can attack iris, heathers, willow, poplar and alder.
Two-spotted spider mite: Keep Phytoseiulus applications going on vulnerable crops this month. Add in Amblyseius californicus for warmer days.
Bees: Notify beekeepers near your nursery if crops are sprayed in flower. Damage to colonies can be costly and involve court action.
Leaf miner: Adults lay their eggs inside the leaf tissue. They then burrow under the leaf, leaving distinctive meandering trails. Biological control is effective on protected crops - sprays of Calypso (SOLA 2006-3728), Decis (SOLA 2007-1693) or Dynamec (non-IPM) can be used.
Rose leaf rolling sawfly: This pest usually appears on more mature roses than newly-potted ones. Eggs are laid down the main vein on a leaf causing the leaf to roll up in a tube for protection. Control on outdoor crops with Decis, Toppel 100EC, Hallmark WZT (SOLA 2008-2944) or Talstar 80 Flo.
Despatching plants: Make sure any plants left over are still included in your pest and disease control programmes. They can act as a "sink" for transfer of infection onto new crops if left untreated.
Liquid feeding: If you liquid feed, switch to a high N feed now, using a 2:1:1 for overhead irrigation systems or 2:0:1 for drip systems applied weekly at 1:200. Avoid scorch on warm days by not liquid feeding during the heat of the day or in direct sunlight.
Thuja: Needle cast disease caused by Didymascella is now active, causing fronds to go brown. Close inspection shows dark brown spots on the upper surface of the foliage that spread down through the tree. Control with Cercobin WG (SOLA 2008-1384) or Scotts Octave at three-weekly intervals between now and the end of July.
John Adlam is managing director at Dove Associates www.HorticultureWeek.co.uk/nursery for recent articles