5 September 2018

Don’t sit and watch your fruit turn brown – get in early and wage war on the spores

Gardeners must prevent the initial damage that allows the decay fungi to enter.

As sure as night follows day, every year – around this time – at least one anguished gardener will ask me what can be done about the soft brown rot that is affecting a large proportion of his or her apples, pears and plums. And equally as sure, I shall tell them there is very little – unless they can prevent the initial damage that allows the decay fungi to enter.

This very thought was brought to my attention early this morning as I sat drinking the first cup of tea of the day. For there was the initial damage being created in front of my eyes: one of our largest apple trees was playing host to a veritable avian flock that seemed to comprise most of the native bird species of Warwickshire, although with blackbirds and starlings in the greatest numbers.

Their activity appeared almost premeditated in its vindictiveness, as they hopped from branch to branch, taking a peck here and a peck there until they must have visited most of the apples on the tree. Those single bird pecks – or commonly, the even smaller holes caused by wasps – are more than adequate to allow the spores of the brown rot fungus, forever flying around in the air, to gain a foothold and begin the debilitating progress that finishes with the fruit becoming a useless pulp.

And so it is with countless other garden ailments that seemingly arise as if by magic. Because the air around us is full of fungal spores, their numbers and species fluctuating with the seasons and the temperature and relative humidity on an almost hourly basis. It is a state of affairs that has spawned the science of aerobiology – over the years, its practitioners have charted the passages of vast clouds of spores of cereal rust fungi over inter-continental distances.

In gardens, it is partly aerobiological knowledge that has formulated, if not control, then at least methods of avoiding two of the most destructive of all fungal pathogens – those causing honey fungus and silver leaf disease of plums and other fruit trees.

There was once an apparently arcane piece of legislation called the Silver Leaf Order. This required all dead wood of apple and plum trees to be burned before 15 July each year. The logic behind this stricture was that roughly after that date the causal fungus, which may have been growing on the dead wood, begins to disperse its spores in the damper, late-season weather. And for the same reason, all pruning of plums and related trees should ideally be performed in spring – not now, in autumn or in winter, when the pruning cuts will lay bare the succulent woody tissues on which the fungus will thrive.

The situation with honey fungus is slightly different and there has never been any corresponding legislation, but as the toadstools may be produced at any time in the second half of the year, it can be deduced that this is when its spores are drifting in the air currents over our gardens. The normal way for the honey fungus to gain admission to a hitherto uncontaminated garden is by the spores alighting on the newly cut surface of the stumps of recently felled trees. Thus, tree stumps should always be dug or ground out with specialist equipment to remove this potential source of new infection. I should perhaps add, however, that an alternative source of honey fungus involves no spores but is spread through the soil from already diseased stumps on neighbouring land.