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JAPANESE MAPLE PESTS & DISEASE IN THE UK

WATER AND WEATHER
By far the most common causes of damage to Japanese maple trees are incorrect watering, frost and sun. Especially when Japanese Maples are grown in containers they require even watering.

Planting them in the correct position should avoid much of the damage caused by high winds, extremes of cold and high heat.

Article and pictures by .

APHIDS AND JAPANESE MAPLE TREES


IDENTIFICATION


Aphids are tiny insects about 3mm long with the most common types being black fly and green fly. Other types do exist but are rarer. The first appear on juicy, tender young shoots. As the colony increase in number they spread to the underside of young leaves.



They cause damage in two ways. Firstly, they cause leaves to curl up and eventually fall off. Aphids also excrete a gooey liquid often referred to as 'honey dew'. This attracts lots of diseases which becomes clearer when the 'honey dew' changes colour often going black.

TREATMENT OF APHIDS


Overfeeding, especially in spring, encourages aphids. The plant will quickly produce lots of soft new shoots which are readily colonised by aphids. So, avoid overfeeding your plants especially in the spring.

Early action when greenfly are first noticed or anticipated will enable more successful organic treatment of aphids. Roses are particularly affected by by aphids so the minute you see aphids on roses in your garden or area inspect other shrubs and trees for signs of an aphid attack.

If you aren't particularly squeamish many of the aphids can be killed by running your forefinger and thumb over leaf and shoot surfaces. This will simply squash them to death! Water over the leaves after doing this will wash many of the dead aphids away. A spray is even more effective.

Preventative treatment that works is a spraying with 2 litres of water containing a teaspoon of washing up liquid. It is thought that the diluted washing up liquid clogs up the aphids and causes them to die. It has no ill effects on the plants themselves. Concentrate spraying on new shoots and the undersides of leaves.

Encouraging other beneficial insects which eat aphids is also another approach which works well. The main 'consumers' of aphids include ladybirds, hoverflies and lace wings. Encourage them into your garden by planting marigolds and calendula. Strangely, a patch of nettles is also an excellent way of attracting aphid eating insects. They attracted to the aphid species which colonise nettles but which affects no other garden plants.

CHEMICAL SPRAYS ON JAPANESE MAPLE TREES


Use only as a last resort but often it is the only solution when an aphid attack has become out of hand. There are lots of systemic insect sprays on the market which work well. Check the label to ensure they are good for controlling aphids. Systemic sprays used for roses are excellent.

VERTICILLIUM WILT


IDENTIFICATION

Verticillium Wilt affects lots of plants, shrubs and trees. Most commonly affected are Japanese Maples, chrysanthemum, carnations, cotinus and catalpa. Strangely, strawberries are also affected.

The main sign of infection is leaves turning brown, especially near the base. Plants begin to wilt in warmer weather although they may temporarily recover if the weather turns colder.

Woody plants such as acers and chrysanthemums will have brown marks on the wood immediately below their bark. Branches may die completely in parts of the plant.

VERTICILLIUM WILT DAMAGE


This is a disease which is first spread in the soil. It enters the plant through damaged or weakened roots. Once the Verticillium Wilt fungus infects the roots of the plant it spreads upwards. The plant's natural defence system attempts to isolate the fungus but in the process it prevents water being passed around the plant internally. This causes parts of the plant to die.



TREATMENT OF VERTICILLIUM WILT


There is no treatment for Verticillium Wilt. Managing an infection is a matter of damage control because the disease can be passed to other plants. One common source of infection is the soles of your boots transferring infected soil from one part of the garden to another.

The plant or tree should be dug up with as many of the roots as possible and burnt completely. Be careful when transferring the plant and roots to the point of burning, do not allow any possibly infected soil to come into contact with any other soil or plant.

Unfortunately, the disease can remain in the soil for up to 15 years so do not plant any susceptible plants on the area for many, many years. Sometimes a new plant will appear to grow successfully for two or three years before it also shows signs of the disease. Don't waste your time cleansing the soil with Jeyes Fluid or similar preparations, they do not get rid of Verticillium Wilt in soil.

Ideally the area should be grassed over and left. However there some plants which have immunity to Verticillium Wilt and these should grow successfully on an infected site. Apple and pear trees both do well but not plum trees. Conifers are resistant and these come in a variety of forms and sizes. Other plants and trees to consider with excellent immunity include, beech, ginkgo, hawthorn, hornbeam, mountain ash, sycamore and walnuts.

VINE WEEVIL AND JAPANESE MAPLES


Adult vine weevil
Vine Weevil

IDENTIFICATION


Vine weevils have two distinct appearances depending on the stage in their life cycle, When they are grubs / larvae in the soil a vine weevil is about 2cm / 5/8in long when fully grown, white at first but turning brown. Their bodies are "C" shaped and they can be found under the soil near the main stem of the plant.

When they emerge from the larvae the adults are 1cm / ┬╝in long. They look like small beetles, browny black coloured and pear shaped, the heads are a dark black. The top part is pitted with lots of little indentations. They have what appear to be wings but in fact they are unable to fly.

VINE WEEVIL DAMAGE


As adult "beetles", vine weevils will eat the edges of leaves. This attack disfigures the leaves but healthy plants, trees and shrubs will recover from this damage. However the grubs eat the roots and even sometimes the main stem of plants which, if left untreated, is often fatal.

Note that plants, trees and shrubs grown in open ground are not affected, attacks occur on plants grown in containers. Understanding the life cycle of the vine weevil is essential to minimising the damage they do to plants.

VINE WEEVIL LIFE CYCLE


July to August
The adult lays eggs near the surface of the soil. If the soil is mulched the eggs will most likely be laid in the mulch. Each adult will lay about 200 eggs which take about 3 weeks to hatch. Immediately the eggs hatch the emerging larvae begin feeding on the smallest roots of the affected plant. as the larvae grow in size they will 'upgrade' to feeding on larger roots and in some cases the main root.

September to November
As the temperature of the soil begins to cool the larvae will gradually stop eating and burrow down lower into the soil where they hibernate over the winter.

March to June
The larvae start feeding on larger roots as the soil temperature increases, In May to June they transform ('pupate') into adults.

PLANTS AFFECTED BY VINE WEEVILS


Vine Weevils prefer container grown plants and small trees. Almost any shrub or small tree can be affected although vine weevils do have a preference for camellias and rhododendrons. Japanese Maples are also a plant of choice.

TREATMENT OF VINE WEEVILS
First attack the adult vine weevils and this can only be done manually. When an adult vine weevil is attacked by a predator it's natural reaction is to fall to the ground and play dead. Their browny /black colour makes them very difficult to spot on soil. The plan of action should be to lightly shake the shrub which will cause the bugs to fall off - an upturned umbrella will catch many of them. Another method is to lay white paper around the plant so all the Vine weevils to be seen more clearly.



The next treatment is to encourage wildlife which enjoy eating the vine weevil at all stages of their lives. This includes birds, hedgehogs, frogs and toads. One particularly good method is to encourage birds into your garden by providing them with food and water. Position the bird feeder as near to the affected plant(s) as possible.

Biological control of the larvae stage stage of the vine weevil is a good method of interrupting their life cycle. There are a few nematodes readily available from garden centres or online which will attack vine weevils. Our favourite is Steinernema kraussei mainly because it remains active at lower temperatures compared to other nematodes. This allows it to be applied from mid-March through to September.

There are chemicals which can be applied to the soil but they should not be used for edible plants although they are fine for Japanese Maples. Search on the internet for "vine weevil chemical control" if you wish to use the chemical route but the previous suggestions will work as well if not better.