The cypress aphid, sucks the sap out of the prolific evergreen, leaving it the rusty colour characteristic of dead foliage.
The spread of unsightly brown patches instead of the usual rich green hue can certainly spoil landscaping on industrial parks and ornamental and residential gardens. And the aphid can kill specimens in one season if infestation is heavy enough.
The problem is not an easy one to diagnose, says Alan Abel, technical director of Complete Weed Control (CWC), which operates a 50-strong franchisee network throughout Britain and Ireland.
“We were receiving calls from our council contacts who were passing on reactions from residents blaming pesticide spraying for their brown hedges. At first, we believed we were at fault, even replacing hedging to compensate for the loss. Then we realised where the true source of the trouble lay – with the Leylandii aphid – and knew we could counteract attack by the insect.”
In fact, CWC operate a tightly controlled method of spraying pavements, using a device called Weed-IT which only treats vegetation and operates under a protective hood to avoid the possibility of pesticides drifting on to unwanted greenery. That fact alone alerted CWC to the likelihood that the problem had arisen from another source.
Now they know the real culprit, CWC is keen to alert councils and to roll out its spray programme for Leylandii that it says will eradicate the aphid and return brown to green again as next season’s growth begins.
An application in March or April, when the growing season gets underway and aphids begin their sap-sucking, followed by another treatment in May usually sees off the problem.