Hi, welcome to Taiga Bonzai in this article we discuss some of the many reasons why plants give the appearance of health and vitality one moment, then suddenly show signs of decline. A problem scientists and horticulturists have been trying to solve for eons.

Introduction – there are countless reasons why plants die and to attempt to explain the cause and effect would result in volumes of the written word. Therefore, we look at some of the most common and uncommon. These include the seed or plant, soil medium, water table, pests and disease.

It can be argued that seeds are delicate in their form and their is evidence to support this theory for example. In (commercially grown) vegetables and various fruit species, due to their short ‘shelf life’.

However in the main seeds collected from the wild are robust and hardy, able to withstand high and low temperatures. They can be stored in the right conditions for long periods of time; providing they have not been attacked by pests and disease.

Soil mediums – are prepared to suit the plant be it ericaceous (coniferous) or organic. (deciduous) It should be a composition with good drainage allowing the roots especially feeders to travel in search of nutrients and moisture. (see article 06 – ‘The pH factor (Part I)’ which discusses the acidity/alkaline levels for a range of plants.

A question often asked is “does the soil have to changed on a regular basis” in short the answer is no. Because a teaspoon of soil is estimated to contain up to a billion bacteria cells, that work to maintain the soil condition. Adding a small amount of fertilizer occasionally helps and the plant can survive for years in the same medium.

However, much depends on the type of plant regardless of the species. If growing from seed then the plant will require a soil medium to help the initial growth stage for example, John Innes no. 1 or similar brand.

When the plant has developed sufficiently i.e. a few pairs of true leaves it is re-planted in a soil medium that is more appropriate. This is done to slow the growth rate, otherwise the plant/s become ‘spindly’ tall, or thin. Hence, the result is usually stress and vulnerability to attack because it’s defences have yet to be developed.

Water table – in the main most trees dislike their roots soaking wet nonetheless, there are exceptions to this consensus for example, the following permanently reside in wet conditions.

Pumpkin genus Cucurbita, Ash, Fraxinus profunda Sweetbay Magnolia, Magnolia virginiana Willow, Salix Mangrove, Rhizophora mangle Bald Cypress, Taxodium distichum Water Tupelo, Nyssa aquatica River Birch, Betula nigra and Pin Oak Quercus palustris. The water pH ranges from acidic to saline and plants living in such conditions are able to thrive. Whereas other species cannot tolerate these extremes.

Rain water is always preferable, alternatively if you rely on the household tap, the water condition will depend on the supplier and the chemicals used to treat it for example. Chlorine (CI) a strong disinfectant added to drinking water as a purification technique. Moreover, tap water needs to stand for a couple of days before use.

Pests and disease – the most common of pests and disease derive from insects including: Aphids Aphidoidea, Scale Coccoidea, Mealybug Pseudococcidae, Sawfly Septentrionalis and Red spider mite Tetranychus urticae. The latter difficult to see with the naked eye as it resides in the soil, the only immediate way of detection is via the very fine webs they weave.

The above mentioned pest are just an example and can be dealt with accordingly using horticultural soap not insecticide. Unfortunately the predators that usually protect our plants are disappearing at breakneck speed due to loss of habitat caused by the idiosyncratic lust for urbanisation.

The decline – over the last few decades there has been a decline in the insect population. Disappearing are many helpful predators including, Ladybugs Coccinellidae, Green Lacewings Chrysopidae, Honey Bees genus Apis, Praying Mantis family Mantidae, Spiders family Arachnida, Ground Beetles family Carabidae, Soldier Beetles family Cantharidae, Assassin Bugs family Reduviidae and Robber Flies. Asilidae

These insects are part of the food chain they eradicate unwanted pests including aphids, scale, mealy bugs and saw fly and in turn are the main resources for many birds, small mammals, fish, reptiles and other creatures.

Moreover, they are an important key for human food production because, many crops depend on insects for pollination leading to fruit and seed production. Insects play a very important role in decomposing organic matter allowing nutrients to return to the soil. Therefore, in terms of insect ecological importance, a sharp decline in their abundance is of great concern.

The arguments – here are the points view from others whom are mindful of this issue. Will de Freitas asks if we are facing insect Armageddon he states that, “A recent study found that German nature reserves have seen a 75% reduction in flying insects over the last 27 years.”

The researchers involved made stark warnings that this indicated a wider collapse of the general insect population that would bring about an ecological catastrophe if left unchecked. (article – October 25, 2017 – The Conversation)

Damian Carrington Environment editor for ‘The Guardian’ in his article (10th February 2019) argues that “The world’s insects are hurtling down the path to extinction, threatening a catastrophic collapse of nature’s ecosystems.” “More than 40% of insect species are declining and a third are endangered. “The rate of extinction is eight times faster than that of mammals, birds and reptiles; the total mass of insects is falling by a precipitous 2.5% a year, according to the best data available.”

In the February 2020 journal ‘Biological Conservation’ no, 242 (a leading international body of scientists in the discipline of conservation science) Editor in chief Vincent Devictor of the Institut des Sciences de L’Evolution de Montpellier, France stated that.

“We are causing insect extinctions by driving habitat loss, degradation, and fragmentation, use of polluting and harmful substances, the spread of invasive species, global climate change, direct over exploitation and co-extinction of species dependent on other species.”

Devictor goes on to say that “With insect extinctions, we lose much more than species. We lose abundance and biomass of insects, diversity across space and time with consequent homogenisation, large parts of the tree of life, unique ecological functions and traits and fundamental parts of extensive networks of biotic interactions. “Such losses lead to the decline of key ecosystem services on which humanity depends.”

The blame game – these are but a few of the arguments from scientists and conservationists from the many we have researched and from these points of view, it appears we have a major situation on our hands.

There are many theories as to the decline in insect populations they include, habitat destruction by intensive farming and urbanisation, pesticide use, introduced species, climate change, eutrophication from fertilisers, pollution and artificial lighting; the latter used in huge polyethylene tunnels for intensive crop production.

Yet, despite the scientific evidence provided, globally our performance in instigating effective insect conservation is below par, we need to realise this fact and act accordingly.

This would involve more inclusive education, better decisions with land managers and government officials in maintaining unique habitats, across the globe. To have more expansive sustainable agriculture and forestry, improved regulation and prevention of environmental risks and greater recognition of protected landscapes.

Insects are a major component of the tapestry of life and failure to protect them will have dire consequences. Because without them a void will appear allowing unwanted pests to multiply to plague proportions.

As we go through our discussions on ‘Plant husbandry’, we reveal more facts that have disastrous effects on horticulture including bonsai. 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.