LETTER OF THE WEEK

HOW DOOMED ARE MARGARET’S LILIES?

It is, I think, fair to say that Margaret Dudley is consumed with anxiety about her potted lily bulbs, over which she kept a watchful eye all summer, waging what she thought was a successful war on a mild invasion of scarlet lily beetles by squashing any she saw. She was horrified, subsequently, to see dozens of them on the foliage.

Are her bulbs doomed? Should she repot them? Are the beetles lurking ready to pounce next year? Questions, questions… so here are some simplified lily beetle life-cycle facts that might help Margaret to form a strategy for the coming year.

1

Adult lily beetles overwinter in soil and in leafy, messy, sheltered places – and not necessarily near where lilies actually grow. Only the worst, repeated summer attacks weaken the bulbs.

2

Beetles emerge in very early spring in sunny weather (before lilies are even “up”), making a beeline for a related source of food, commonly fritillaries. If Margaret can catch/eliminate these, she will perhaps be able to see off this first wave, who are the troublesome breeders.

3

Adults move on from fritillaries to young lily stems and, on the backs of leaves, lay clutches of tiny eggs, which hatch into very visible, brownish, lumpy, greedily leaf-shredding grubs, which then drop off, replete, to pupate in the soil. The following generation of scarlet beetles that emerges feast heavily, and then hibernate – to breed the following year.

Nobbling the beetles emerging from hibernation in spring is clearly a good (but imperfect) way to control them. Apart from squashing them, various organic sprays containing natural pyrethrins and synthetic pyrethroids may be helpful, but have to be used repeatedly.

Sprays containing the neonicotinoid active ingredient acetamiprid, such as Bug Clear Ultra, are more effective (visit the RHS website for detailed advice on garden pesticides).