On a recent visit to Hidcote, one of our most well-know National Trust gardens, I was disappointed to see day lilies (Hemerocallis) with buds swollen and destroyed by big bud mite. Even worse, plants for sale out in the plant centre were similarly infected. Why is the National Trust, of all people, selling and distributing this cursed pest to all parts of the country?
I am given to understand that the Dutch use neonicotinoids to effectively control this pest. But leading UK growers, alert to possible bee damage from spraying, are looking to breed big bud mite-resistant cultivars as the long-term answer.
Where this leaves National Collections of heritage day lilies is another matter. Do they need to be grown under Enviromesh, which keeps out bees and allows the use of systemic insecticide?
At the very least, National Trust staff must pick off and destroy swollen and infected buds from plants that are on sale. It would be a sensible approach to do the same for plants that are growing in the garden, although after a wet June the garden maintenance staff obviously have more than enough to do already.
Is the sensible compromise here to use systemic insecticide specifically on clumps of Hemerocallis early on in the year so the dose is much reduced come flowering and bees working through mixed borders have any residues diluted yet again?
Trying to control lily beetle by either treating the bulb or spraying new shoots with systemic insecticide works pretty well, although attack can start again as plants come into flower, presumably indicating that the pesticide is so diluted it no longer has an effect.
A second spray after flowering retains foliage as well as helping to build up bulb strength for the next year’s flowering. Are the organic dictators going to see the loss of day lily flowers from gardens until we develop big bud mite-resistant cultivars?
Peter Seabrook is a gardening writer and broadcaster