Hi, welcome to Taiga Bonsai, in this article we continue our discussion on ‘Plant husbandry’ dealing with more harmful pests and disease.

Introduction – during World War II (1939 – 1945) many governments mandated that more produce be grown to feed those at the front line and rationing was introduced which lasted until 1954. Meadows and wildlife havens were turned into arable land and although the effects of this were not apparent at the time; it was the beginning of the end for the bug world.

The birth of the EEC – on March 25th, 1957 France, West Germany, Italy, the Netherlands, Belgium and Luxembourg signed the Rome treaty establishing the European Economic Community (EEC), also known as the Common Market. Later other countries joined and soon there was an abundance of food.

This excess including butter mountains, milk and wine lakes, gluts of potatoes, apples and other crops could have been given away to the poor, or countries facing drought and famine. Instead what could not be poured away was disposed of in disused mine shafts. The politicians and agricultural heads wanted to maintain ‘economic stability’ – ‘nothing is for free’.

The green and pleasant lands are now a bygone era, forests have and are being cut down. An area the size of Wales 20,779 km² (a country in southwest UK) is being removed on a daily basis in the Amazon.

The meadows that existed are now under housing estates, rivers are polluted and the air quality is deteriorating. The friendly bugs have gone and it is doubtful they will return. The crop harvests GMO or organic will devastated by marauding invaders many whom are immune to pest control.

A never ending battle – according to CABI News digital library (09 February 2022) they conclude there are approximately 73,000 different tree species on Earth, of which around 9,000 are thought to be undiscovered. In addition, there exist more than 80,000 known plant diseases worldwide.

All plants are vulnerable to attack by disease, including crop plants which are frequent victims. The result is enormous agricultural, horticultural and economic loss. Now due to the relaxed regulations pest and disease are able to infect countries that were free of this devastation.  

The problem with disease – is that it cannot in reality be detected until there is visible evidence, by insect damage or that of fungi. Science has told us that microorganisms can exist in a single-cell form or a colony like bacteria and fungi. Although they are often associated with dirt and disease, most microbes are beneficial. But as we are aware there exist those microbes, fungi and pathogens that have lethal potential; here a few examples.

Armillaria mellea is a parasitic fungus doing immense damage to forests, it attacks both coniferous and deciduous species. By the time the fruit bodies are in evidence, the damage done internally is usually so great that the tree is doomed.

It is widespread in northern temperate zones including North America, Europe, Northern Asia and in South Africa. Trees that are attacked become parasitized. The foliage becomes sparse and discoloured, twig growth slows down and branches die back. There are no known fungicides or management practices that can kill Armillaria mellea after infection without damaging the infected plant.

Canker is a small area of dead tissue, which grows slowly, some of these are of only minor consequence, but others are ultimately lethal and therefore, can have major economic implications for agriculture and horticulture.

They are caused by a wide range of organisms including fungi, bacteria, mycoplasmas and viruses. The majority of canker-causing organisms are bound to a unique host species or genus, but a few will attack other plants. Fungicides or bactericides can treat some cankers, often the only available treatment is to destroy the infected plant to contain the disease. The Butternut canker (shown below) is a lethal disease affecting Butternut trees for which there is no cure.

This is a deadly bacteria that attacks economically important crops such as olive, citrus, plum trees and grapevines. Since 2015, it’s been rapidly spreading from the Americas to Europe and Asia. Once the disease infiltrates a plant, it is there to stay, it starves the plant of water until the plant dies or becomes too weak to grow fruit. 

Xylella fastidiosa – is another deadly disease the bacterium (shown below)

X. fastidiosa costs $104 million per year in wine losses in California and in Italy. The bacteria has led to the decline of 180,000 hectares of olive groves destroying many centuries-old trees; a loss of €390 million over three years. X. fastidiosa constitutes a threat not only to Italy but to all the Mediterranean region’s economy.

X. fastidiosa is not known to be in the UK however, there have been outbreaks of the disease in mainland Europe in France, Italy and Spain. Portugal confirmed its first case in 2019 on lavender.

The UK Government is concerned about how to prevent the disease being accidentally brought into the country on imported plants. In 2020 Lord Framlingham a Conservative peer asked the Government what the UK’s regulations are regarding X. fastidiosa.

UK regulations were to introduce measures to strengthen the protection of plants from certain pests and diseases, including Xylella. They were made under article 52 of the EU Plant Health Regulation, allowing the UK to take additional temporary national measures. Providing they inform the European Commission and put forward a technical case to request EU measures against a specific pest.

However, those measures have not or will not be introduced in time to mitigate the risk concerned. Moreover, the UK Government has argued that current EU emergency measures on Xylella, do not address risks highlighted in the UK’s pest risk analysis on the disease.

In particular, it is not clear if or when the EU emergency measures will be reviewed to address these risks and ensure a greater degree of assurance of disease freedom, in relation to plants of those species being moved in the EU and introduced from third countries.

As such, there remains an unacceptable level of pest risk and this instrument introduces national measures under article 52, in the absence of EU requirements.

Verticillium– is a genus of fungi in the division Ascomycota, which is an anamorphic form of the family Plectosphaerellaceae. The genus used to include diverse groups comprising saprobes and parasites of higher plants, insects, nematodes, mollusc eggs and other fungi.

The genus, currently thought to contain 51 species, may broadly be divided into three ecologically based groups – mycopathogens, entomopathogens, plant pathogens and related saprotrophs. At least five species are known to cause a wilt disease in plants called verticillium wilt: V. dahliae, V. longisporum, V. albo-atrum, V. nubilum, and V. tricorpus. A sixth species, V. theobromae, causes fruit or crown rot, a non-wilting disease.

Verticillium wilt is a disease that can affect over 400 different plants and trees, many of which are economically important worldwide. Several characteristics of Verticillium make it difficult to manage: prolonged survival in soils without the presence of a host plant.

The fungus survives in the soil principally in the form of microsclerotia and invades the plant through the root system, colonising the vasculature eventually leading to plants demise.

The main mechanisms of it’s pathogenesis are xylem vessel blockage and toxin production. When the fungus propagates within a host plant, the mycelium blocks the xylem vessels, impairing the transport of water and nutrients in the host.

Thus forces of transpiration and respiration in leaves combined with blocked xylem transport, cause water imbalances in leaves that result in leaf yellowing and wilting, contributing to plant death.

In addition, Verticillium produces mycotoxins within the plant that can cause necrosis in leaves and impair metabolism in the plant’s body. In some systems, toxin production has been shown to be the main cause of plant wilting.

The diseases discussed here (Armillaria mellea, Butternut canker, Xylella fastidiosa and Verticillium) are very serious not to be taken lightly, they can infect other plant types within the vicinity. However, there are many more to be found within the 80,000 diseases that we know of. In the next article we look at the borers, until next time, BW, Nik.

Hi welcome to Taiga Bonzai, we continue our discussion on pests and disease as it is an important topic that effects all aspects in the world of flora including bonsai.

Introduction – being mindful of the pests and disease affecting horticulture, especially temperate species which are vulnerable.

All flora are susceptible to attack from pests and diseases whether grown naturally or cultivated. In an attempt to eradicate these unwanted problems most fruiting and flowering specimens are sprayed with a fungicide or repellent.

Chemical protection – does in many respects produce the results intended, but some will argue that it also destroys those creatures that eradicate the unwanted. Moreover, it can be said that when winter arrives many pests will die due to loss of foliage and the coming cold.

Nonetheless, there are such pests whom are able to survive cold conditions via hibernation hidden beneath a tree’s bark, in it’s seed pods or in the soil medium.

For example, the Oak – genus Quercus, a favourite of the Tortricid Moth caterpillar – Family Tortricidae that destroys acorns. Carpenter Ants – Genus Camponotus hibernates under pine tree bark. The spruce beetle, Dendroctonus rufipennis its larvae bores into the phloem of conifers and feeds on the live tissue.

The Asian longhorn beetle Anoplophora glabripennis a native of China and the Korean peninsula excavates 1cm diameter holes in the main trunk causing sap bleeding. Eventually the affected tree dies.

Diseases – include; ‘Red band needle blight’ Dothistroma, needle blight affects conifers most commonly pines. It causes needle loss, which eventually kills the tree. Ash die-back Fraxinus excelsior affects ash trees it is caused by the fungus Hymenoscyphus fraxineus, that blocks the tree’s water transport system causing leaf loss and ultimately die-back of the tree’s apex or crown.

Horse chestnut canker a bacterium species known as Pseudomonas syringae pv. Aesculi. It causes extensive bleeding areas on tree stems. Phytophthora austrocedri affects junipers causing die-back of foliage, stem and collar lesions and eventually death.

The above mentioned pests and diseases are but a few of the 80,000 that we know of, attacking many species of tree both deciduous and coniferous. Arguably such devastation is due to climate change and infestation via unwanted importation of packaging material. For example wooden boxes and crates and although authorities do much to enforce regulations, it is difficult to stem the invasion.

We like to assume that our indoor environment is free from pests and disease, nothing could be further from the truth. The ‘greenhouse’ or home is riddled with invaders and no matter how vigilant we are, eradication is virtually impossible.

Arguably, the cause why the latter are able to thrive is due to the temperate conditions plus abundance of food and water. Here are a few of the most common that devastate plant life.

Mealybugs – quite visible to the naked eye are related to scale insects and congregate on leaf joints and the undersides of leaves. They damage plants by sap sucking, which causes the leaves to wilt, turn yellow to brown and eventually fall from the plant. Removal of this pest(s) can be achieved either by spraying them with water or via a chemical spray designed for Aphid treatment. The plant then should be isolated from others until the treatment is successful and the plant has recovered.

Aphids – normally a pale green in colour can be found in other shades such as grey and black. Having arrived on a plant their numbers rapidly increase infesting the plant in great hordes with a preference for the underside of leaves. As with the Mealy bug they also suck the sap from the leaves and if not removed quickly, the plant may become infected by disease and viruses.

Aphids can be removed relatively easily by the use of warm soapy water directly sprayed on them. Alternatively a chemical application designed for this pest can be used, but the plant should be isolated until the treatment is completed and the plant is free from infection.

Scale Insect – there are more than 25 species of these limpet-like creatures, which makes identification difficult due to their well camouflaged appearance. They devastate a wide variety of plants by sucking the sap and as a result the plant is severely weakened distorting growth.

Evidence of their existence can be seen as the growth of black, sooty moulds and or a sticky substance (honeydew) on foliage. Another sign of scale infestation is leaf blemish. Scales have hard shells and removal can be difficult hence the use of chemical application such as an Aphid spray, which softens the shell eventually killing them. The plant has to be isolated until the treatment is successful.

Sawfly Craesus septentrionalis – can be a real nuisance for those whom have Betula species (Birch) as bonsai specimens because, the tender young leaves are prone to be ravaged by the Sawfly larvae running rampant all over the tree. As do the larvae of a large number of species of butterflies, moths and other insects. Female sawflies are so called because of the saw-like appendage at the tip of their bodies, which is used to cut slits into the leaves where the eggs are laid.

There are different species of sawfly and the damage cause by their larvae is peculiar to each species for example. Some will leave notches or holes in leaves or devour the leaf leaving just its skeleton, others spin webs, leave galls and some will roll up a leaf completely.

Sawfly are commonly found in bonsai for example. Conifer sawflies feed on needles and bore into buds and shoots. On Salix (Willow) the sawfly leaves distinctive red/brown galls, fruit and flowering – Prunus,(Cherry) Pyrus, (Pear) and Malus (Apple) are all affected by the sawfly.

The most common way to eradicate sawfly larvae is either removal manually or by using a horticultural soap as used for Aphids and Mealybugs, but the plant should be isolated so as not to infect others and to allow for the treatment to work.

Sciarid flies – often called Dark-winged fungus gnats – are commonly found in moist environments including areas where house plants are situated. They thrive on damp soil conditions and can be seen scurrying over the soil, flying around and landing on stems, branches and leaves. Although they are known to be a pest in mushroom horticulture, they present no threat to bonsai plants nonetheless, they can be extremely irritating especially in a home environment.

This large Diptera genus is one of the least studied mainly due to its small size 2mm and the difficulty in specific identification. It is said that more than 1,700 species have been described with an estimated 20,000 awaiting further study.

Springtails – Collembola form the largest of the three lineages of modern hexapods the other two being Protura and Diplura these creatures are not classed as insects, because they are omnivores having internal mouth parts.

They are small white or grey in colour and feed off the soil’s dead organic matter. When plants are watered and springtails are present, they are agitated and move rapidly and look unsightly. Springtails pose no threat to bonsai or other house plants, it is their very presence which can be irritating.

If the desire is to eradicate these creatures, one can water the plants from the bottom by immersing the container in water and/or reduce the amount of water. But water reduction may not be conducive to some plant species, hence a careful balance should be maintained.

The above mentioned pests and diseases are common to bonsai horticulture, they are but a few of the many thousands that are in existence. Nevertheless, over the past decades horticulturists and scientists have done much of the spade-work, hence it is not that difficult to find the answer one is looking for a particular problem. But it pays to be vigilant and inspect your bonsai specimens on a regular basis; ‘Prevention is better than cure’.

Soil – another factor to consider is the soil composition, because bonsai are confined to a relatively small quantity of soil and this growing medium has to fulfil its needs. It must be able to retain water yet have good drainage and have the ability to allow for air circulation.

Soil contains a multitude of living organisms that consume, digest, and cycle nutrients. These living organisms include archaea, bacteria, actinomycetes, fungi, algae, protozoa, and a wide range of insects for example. Mites, nematodes, earthworms and ants, all of which are important to the vitality of a soil composition.

Soil in a bonsai pot does not last indefinitely, it decays over a period of time due to the absorption of minerals therein and once expired it is unable to support the tree in order to sustain health and growth. This is when the tree is most vulnerable and attack from pests and disease can quickly take hold.

Having said this one may think that a bonsai has to be re-potted every year – not only is this a misconception, it is unnecessary. A tree in a pot or container planted in year one will take at least 2 to 4 years to establish itself although much depends on the species and its growth rate.

This can be assessed by teasing the tree out from its container and checking the root ball. If the roots are densely packed with little soil in situ, then it will probably need re-potting. Alternatively if what is seen is the opposite, then it can be re-placed and left for another season or two. Until next time, BW, Nik.