Phytophthora - Consider drenching products such as Aliette 80WG, Previcur Energy (SOLA 2008-2667), Proplant or Subdue to Chamaecyparis species to suppress Phytophthora in the growing media or field. These plants are very susceptible and treatment now will give them some protection from the disease, which may colonise on any dead roots resulting from the winter period. Drenches of Revive, Serenade ASO (SOLA 2009-0246) or Trianum P give added security to these susceptible crops. Cytisus also benefit from a drench to control Pythium root damage, which can sometimes be the cause of yellow emerging foliage.
Vine weevil - Larvae are active in untreated containers now. Low-temperature nematodes can be applied to crops and are available in 50- or 250-million packs. If a non-edible crop is ready, the only approved insecticide you can drench with is Intercept 70WG. Incorporating Suscon Green or one of the granular neonicitinoid products into plugs and liner compost (ornamentals only) is important to ensure full protection when potting on.
Broad mite and tarsonemid mite - These can cause stunting and distortion of buds on ornamental crops. They are also hard to see without a hand lens. Dynamec, Oberon (SOLA 2004-1718) or SB Plant Invigorator are available for control but check their persistence if you have an integrated pest management programme in place for other pests.
Blossom wilt - Check for dead buds on ornamental Malus and spray with Cercobin WG (SOLA 2008-1384) to control Botrytis (or blossom wilt) infections of opening buds. Warm days during bud opening can often trigger this disease.
Midge - Check Crataegus (particularly 'Paul's Scarlet' Award of Garden Merit) for the gall tip midge (Dasineura crataegi). Eggs are deposited in April/May and infected tips fail to grow normally with distorted rosette-like galls. Products such as Gazelle, Hallmark WZT (SOLA 2008-2944) or Dursban WG give control.
Ronstar granules rates - When applied by motorised knapsack applicator, try to get the granule to drop from above onto the pot. Good weed control is hard enough without putting low rates of herbicide on.
- John Adlam is managing director at Dove Associates www.HorticultureWeek.co.uk/nursery for recent articles.