Leylandii hedges being killed by Aphid Attack

What might be killing your Leylandii hedge? with large brown patches. - X Cupressocyparis leylandii

Cypress Aphid Spider

Cypress Aphid Spider

The scourge of neighbours and gardeners alike is seemingly under attack - literally, from a small bug - The Cypress Aphid!

It is causing severe damage and even death to Leylandii hedges throughout the UK.

Love them or hate them, the Leylandii conifer is under threat - certainly for the short to medium term. Prolonged spells of mild weather has led to a dramatic increase in population of this insect, and as many will be aware, there is a plentiful food source, with Leylandii hedges aplenty!

X Cupressocyparis leylandii - is under severe threat - not from suffering neighbours with weedkiller or axes, but from a small aphid which has found a great place to feed - totally unhindered in the dense cover of a well cared for Leylandii hedges.

Now the problem is, by the time you discover that you have an infestation of Cypress Aphid it can be too late.

Prevention of an Infestation

Prevention of an Infestation is key and the least expensive way. From the images below, you can see the unrepairable damage that can be caused by Aphids. We recommend a treatment of 'Provado Ultimate Bug killer', this 30ml is concertrated and mixes up to 6 litres of Bug Killer. One application in the spring or early summer will do the job for the season. Leylandii hedges are thick so make sure you give the insides and outsides a spraying. Replacing the whole hedge can be expensive, as detailed below.

Badly infected by Leylandii Aphids, this Leylandii Castlewellan Gold, may yet still recover.

Badly infected Leylandii

Our own observations would seem to suggest that they prefer a good feed on the golden form of Leylandii - Castlewellan Gold being the most common.

A good specimen of Leylandii can grow as much as 3ft (1 metre) in a year - and onwards and upwards after that. Thoughtlessly planted - and often miss-sold - they have become a fighting ground for neighbours after being recklessly planted by un-knowledgeable owners. True - as a screening plant, or dense hedge - they have been a boon for those wanting a bit of privacy in their garden, but all too often the Leylandii has been neglected, resulting in out of control hedges, or worse, sixty feet high trees which do little to endear neighbours to each other!

Well cared for green Leylandii hedge, with no visible signs of aphid damage. This particular hedge forms part of the Broadview Gardens - attended by students at the Hadlow College, so maybe the skilled maintenance regime is resposible for the good condition

Perfect Leylandii

The 'perfect' Leylandii hedge on left shows no signs of damage. The Clipped hedge in the image at the top is showing severe infestation symptoms. There is sufficient re-growth on this to look for at least partial recovery.

Irresponsible planting and aftercare, has even resulted in legislation. Legislation aimed at curbing the problem, but made cumbersome by stupid drafting, and little thought to implementation. Where Leylandii is a problem, a quick remedy is required, not procrastination by local officials as is often the case.

However, the little Cypress Aphid has come to the rescue - maybe only temporary - by sucking the sap out of these loathsome trees. 'Death by bug' may not become a complete reality, for a cold winter may kill or reduce the Cypress aphid population. However, this 'fright' may do much to deter people from planting x Cupressocyparis in the future.

As with all aphids, it can be controlled if not killed by insecticide sprays. Herein lies a problem for would-be 'DIY pest control enthusiasts!

  • Firstly, it is not proven that old brown growth will re-grow. Very doubtful! And in any case this is a little like closing the gate after etc etc etc.... The brown patches mean dead plant tissue. The aphid will have had its fill and moved either further along the Leylandii hedge, or of to a neighbouring stand of fresh foliage.
  • There would be considerable cost involved in most cases. The little 'Ready to Use' Bug gun will not go far in this particular fight.
  • There is a considerable problem with the actual spraying of a large hedge - not least from the health point of view of yourself - and also your neighbours!

Maybe at last, the solution has been found to this problem. And, it is a problem of considerable magnitude to those neighbours who are not 'owners' - yet are almost helpless to do anything to stop their own garden being used as a reservoir for the thirsty and hungry Leylandii.

Substantial damage from Leylandii Aphids means that this hedge will have to be replaced

Substantial damaged Leylandii

No hope of any re-growth on this Leylandii hedge.

The RHS has concluded that this might be the worse outbreak for 25 years! Not a bad conclusion considering that there are now many thousands more Leylandii in existence than there were 25 years ago!

Aphids are normally found once gardening proper starts! Easter is the normal time for gardening activity. It is also the time when gardeners everywhere are amazed to find aphids sucking away at young plant growth. Those aphids are normally quite visible. However, for the aphid sucking away in the dense confines of the Leylandii hedge, no problem of being found out. In any case, the feast may have been going on for a couple of months with the mild winters we have experienced. So the damage is first noticed with the brown patches on the Leylandii hedge. Too late for insecticide - the bug has flown!

SE UK seems to be the main problem area, but it won't be long until the aphids find their way up the M1 - especially if the milder weather continues.

An insecticide containing imidacloprid and thiacloprid would be our suggestion. Don't worry about the chemical name - Provado Ultimate Bug killer contains the ingredients and is available at any good garden centre. It has a systemic action, so is taken up into the sap of the Leylandii, not simply used as a 'contact' killer. (It does have a contact effect, but it is the ability to be taken into the plant's sap system which is the important aspect.) BUT not on hedges where you cannot control the spray or drift. Get a professional to do the work - or start afresh with a new type of hedge! Some say that the Leylandii will perhaps recover from all but the worse attack.

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