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• Complex Shapes & Figures • Problem Solving • Growing Topiary

• Problem Solving

Introduction
Generally speaking, topiary being in the main created from hardy, often
native tree and shrub species, is relatively little troubled by pests and diseases. That is not to say they do not suffer from them, but like most plant populations in nature, there will be a balance between pests and their predators, diseases and the plants in-built resistance and defence mechanisms. The goal should be to have physically thriving specimens well suited to their environment which can then naturally resist attack from any source.

Pests
Here generalisations must be made as each plant species will have its own range of very specific pathogens. The problems generally occur from sap sucking insects - aphids, scale, leaf miner and gall-forming midges.
When the problem is limited, hand picking (or clipping off) affected parts may help achieve control. Chemical methods may also be tried as a last resort, but very often the insects are well hidden or defended or may not even be present by the time the damage is seen. Note too the damaging imbalance they can cause to the pest¹s predatory populations. Often it is better to help the plant and let nature take its course.
Ensure the plant is not under cultural stress and in particular do not be tempted to overfeed it... Excessive stimulation of soft growth will be the result, leaving the plant little able to defend itself from attack and an easy target for pathogens.

Diseases
Again, particular plant species will have their own highly specific
diseases, so some generalisations must be made...
Plants under stress will succumb to disease readily whereas those growing with strength, vigour and hard growth have a natural resistance.
Diseases affecting topiary can broadly be split into two classes, those affecting foliage and those affecting the root systems. Unfortunately the dense surfaces we encourage and strive for in topiary create close humid atmospheres within that encourage the spread and growth of many diseases.

Perhaps the most devastating disease affecting Box topiary are the Box
Blights... these provoke the yellowing/browning or blackening of foliage, shoot die-back and possible eventual death of the plant. Volutella, the causal agent for the traditional form of Box Blight was and is very serious, but plants can recover. Now though there is a new disease - Cylindrocladium, which can and does kill Box topiary and Box hedging. The most likely way it will infect your garden is on bought in plants. You have been warned!
As far as diseases affecting the root systems are concerned, Phytopthora is the most important. Yew in particular is highly susceptible to this pathogen. Although bronzing, yellowing and eventual death of the foliage are the symptoms, the actual cause lies below ground level. Here the root system is being slowly killed. This disease (like many others) is encouraged by wet and waterlogged conditions at the roots. It is therefore particularly prevalent in new plantings, where the soil structure has been damaged by cultivation, or where drainage has been detrimentally altered or is not yet settled. This disease can be a killer, but this is not always so. If poor drainage can be remedied and the soil structure improves, the plants can after a time grow out of it.
There may be chemical controls available in the trade but, in a garden
situation, with large or extensive collections, the chemical quick fix is no real answer to problems. Here, good drainage is definitely the cure in the long run.

Cultural disorders
This is a general heading which covers many symptoms where the cause cannot be pinned down directly to a specific pest or disease causing pathogen.
Poor growth in this case may be one of many things... environmental factors may play their part - Too little light or too much light; Too cold or too hot; Extreme or fast temperature fluctuation; Being under the drip of trees; Being in a localised severe wind turbulence; Or locally dank, still, humid conditions.

Soil nutrient levels may play a part. Are some essential elements missing or perhaps locked to plants because of unfavourable pH for that species? Soil testing kits are widely available and should be used.
Drainage has one of the greatest bearings on a topiary specimen¹s general health. If this is at fault, then the plant is sure to suffer. Bear in mind too, local drainage and root conditions can alter as a result of compaction - by vehicles, machinery or people¹s feet and may change following nearby building work.
Competition from other plants also needs to be taken into account - for
light, water and nutrients. This may grow slowly as a problem and perhaps remain unidentified. Local plantings may start small but will grow in time and slowly alter the balance in any area.

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thanks and credits to Chris Crowder, Head Gardener at Levens Hall