MY sister wrote to me recently about a plague of tiny, shiny black flies living in her bonsai trees. Nature had lobbed one of those well-aimed and peculiarly personal pranks at her that makes us begin to doubt all we learned in science class. Just before the black flies moved in, she wrote, there had been a distressing visitation of head lice, brought home from her sons school. It had been dealt with vigorously and thoroughly: "extinguished in clouds of poison".
When the black flies arrived on the scene, even my loose traumatised sister could appreciate that the black flies were black flies - and not head lice. But then how to explain that one of these black fly egg-cases, a "tan, slightly woody `filing'" had been discovered attached somehow to her neck at the height of the loose emergency?
What she needed at that time of crisis was the Royal Horticultural Society's new guide, Pests And Diseases, an authoritative volume just published by Dorling Kindersley. Like all of DK's gardening books, it is a pleasure to hold and to browse through, well-designed and well-printed on good paper, and filled with clear photographs, diagrams and line drawings.
Pests And Diseases is written by Andrew Halstead, the senior etymologist at the Royal Horticultural Society and Pippa Greenwood, the good-humoured plant pathologist who regularly appears on BBC television and radio. Her bright countenance will be familiar to viewers of the programme, Gardeners' World, on which she cheerfully tackles the likes of woolly aphid, mealy-bugs or parsnip canker.
The book is divided into a number of easy-to-use, cross-referenced sections. The first part, "The Gallery of Symptoms" is illustrated with luscious colour photographs of blighted, bitten, rotten, rusted, infected and otherwise disfigured plant parts, the idea being that by comparing your own afflicted plants with those in the pictures, you identify the problem. Another section, "The A-Z of Pests, Diseases and Disorders" gives more information about the malady, and possible solutions. Later, a catalogue of "Individual Plant Problems" gives lists of all the troubles a particular species might run into.
But perhaps the most useful pages are those on "Garden Health and Problems" . He're, the miniature ecosystem which is the garden is explained, and the need to maintain that fragile balance is emphasised. The authors encourage readers to follow good practices such as companion planting, crop rotation, weed control, proper pruning and - most importantly - vigilance. Refreshingly, the book on the whole advocates building a healthy horticultural environment and using preventive measures to deal with potential problems, rather than the routine slaughter of creepy-crawlies and extermination of possible pathogens that was once the norm.
There are hours of ghoulish enjoyment to be had trawling through the catalogue of Shakespearean-sounding ailments, thanking your lucky stars your plants don't have slime flux and wet wood, fomes root and butt rot, carrot motley dwarf virus or sweetcorn smut.
Many of the pests are delicately illustrated by fine line drawings, although not, I note with disappointment, either the New Zealand flatworm, an earthworm-destroying terror - or the adult narcissus fly, the larva of which hollows out the centre of daffodil bulbs, filling it with its abominable excrement.
And my sister's shiny black-flies? I'm not sure, probably fungus gnats or black aphids - or perhaps a new super-race of tree-dwelling head lice.