Your gardening questions answered: How can I deal with a troublesome pest?

Q: I have a pyracantha that in the last year has developed woolly aphid on the leaves and trunk. It was particularly bad during the summer and I tried hosing it off, but it was quite extensive, so difficult to get rid of completely, and kept coming back. The plant has also not flowered properly and has very few berries. Is there any non-chemical treatment I can use? TR

A: While I try my best to respect most forms of life, I admit to a deep loathing of woolly aphid, a garden pest with an ick factor to the power of a thousand.

Properly known as Eriosoma lanigerum, this sap-sucking insect overwinters deep within the bark of the plant. Then in spring-summer it emerges to form dense colonies of brown-black aphids that excrete a white, waxy, protective material (see what I mean about the ick factor?) that from a distance looks like some form of nasty mould.

A common pest of pyracantha and cotoneaster as well as fruit trees, woolly aphid can quickly disfigure the host plant and leave it vulnerable to damaging diseases including mildew and canker.

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Nature lovers will point out that it’s an important part of the food chain (true) and of garden ecosystems (true), and that because of this its presence in our gardens should be tolerated (also true). Sadly none of the above makes it any less repulsive.

As regards controlling or eradicating woolly aphid, unfortunately the standard organically-acceptable options are limited. Conventional advice includes selectively pruning out any very badly affected branches and using a stiff bristled brush in spring/ early summer to dislodge early infestations, not a realistic task when it comes to something as fiercely thorny as pyracantha.

The environmentally acceptable, contact-only, non-residual, biodegradable spray known as Uncle Tom’s Soap (fruithillfarm.com) can also be used to help control infestations. A natural soft soap containing fatty acids that works by washing off the insect’s protective waxy covering and then stopping it from breathing. You’ll probably need several applications spread out at fortnightly intervals .

By gardening organically and avoiding the use of conventional insecticides, fungicides and herbicides, you can also encourage this pest’s natural predators, a list which includes earwigs, ladybirds, lacewings, hoverfly larvae, and a parasitic wasp called Aphelinus mali.

All of the above aside, pests and diseases are almost always a sign that a plant is stressed and struggling as a result of its growing conditions, making it much more vulnerable to attack.

Natural, health-boosting, disease-fighting products such as liquid seaweed feeds and nettle feeds will help but truly sustainable plant health starts from the ground up. So, do everything you can to support soil health with the yearly addition of organic mulches (well-rotted manure, home-made compost, or proprietary products such as Gee-Up.ie and Mulch.ie) to help to boost soil fertility and soil structure.