Conifer Hedge Query

Answered by Harrod Horticultural Posted in Category Pest Control & Nature

Dear Martin

My conifer hedge has plenty of brown patches and isn't looking its best.

I've got a nasty feeling spider mite could be responsible; please could you let me know what you think could be causing the problem and how I can go about dealing with it?

Thanks

Alan

Dear Alan

Many thanks for your enquiry and before beginning any treatment, it’s essential to identify the cause of the problem. Brown areas on conifer hedges can be caused by numerous factors – heavy trimming or pruning, aphids, phytophthora and growing conditions - but as you’ve already mentioned spider mite as a potential culprit, we’ll start with them...     

There are various species of spider mite but all have one thing in common – they love warm weather. At this time of year, most species overwinter in the egg stage but the greenhouse spider mite may spend the winter as hibernating adults so the best time to launch a control programme us in the spring when they spark back into life and eggs begin to hatch.

As we follow an organic approach to gardening, naturally occurring predators and organic sprays form a large part of our range. Biological control (the introduction of predatory mites and insects) is arguably the most environmentally friendly method of controlling spider mites and early season measures are based on the predator Amblyseius andersoni, a greedy little mite which feeds on all stages of spider mite and can be introduced once temperatures reach 10°C. The predatory mites are supplied in weatherproof sachets of 250 and hung in the hedge; they slowly make their way from the perforated sachet and begin feeding.

The summer months represent the halcyon days for spider mites and a tell tale-sign of a serious infestation is the appearance of webbing on affected plants. Another predator is available for these warmer conditions – Phytoseiulus persimilis – but only if temperatures remain at or around 20°C. These mites are capable of completing their lifecycle twice as fast as the spider mites and their sheer numbers and appetite for the mites provide effective summer control. Again, you need only introduce the predators to the plant and sit back and watch!

For a more hands-on approach, the organic Savona and Insect Killer Sprays allow you to get an early handle on this pest and these sprays also have the advantage of controlling cypress aphids, another cause of brown patches in conifer hedges. Don’t use these sprays as well as introducing the predators though as the latter will also be killed.     

Finally, for an instant remedy try spraying the affected trees with a winter tree wash. Usually applied to fruit trees, this natural spray will kill any hibernating pests and their eggs on contact.

As for the other possible reasons mentioned earlier, try following the advice below:

•    Trimming – only trim lightly as conifers are poor at producing green growth once wood has been cut into. From the image provided, I think your trees may be Chamaecyparis lawsoniana, a species susceptible to browning so make sure you trim them lightly between April and August and not when the trees are under stress eg. in very dry or warm conditions

•    Phytophthora and Growing Conditions – there’s not a great deal you can do about Phytophthora root rot apart from improve the drainage around the roots of the hedge. Making the trees as comfortable as possible by regular watering in dry spells, feeding with a general purpose fertiliser and mulching with well rotted compost should all help them recover from any pest and diseases problems

It’s always notoriously difficult to accurately identify problems with plants at this time of year but I hope the information above proves to be of help. Of course, this advice is only my opinion and a close-up inspection of the trees is necessary to find the cause, but this should be something to go on.

Thanks again for your enquiry and if I can do anything else to help, just ask! 

Kind Regards and Season’s Greetings
Martin

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