Hi, welcome to Taiga Bonzai, many of the questions we receive are mostly related to ‘Plant husbandry’ for example, “why do seedlings and young trees have their foliage turn brown then die?”

Introduction – to summarise the above question would not be helpful, because this is a lengthy subject with many connecting factors. These will be discussed in the coming articles.

Germination – is defined into two categories Epigeal (above ground) and Hypogeal. (below ground) As a seed germinates the first structure to emerge from most seeds is a root from the embryonic called a radicle. This primary root referred to as a taproot has smaller lateral roots (secondary roots) sprouting from the taproot. These in turn produce even smaller lateral roots, (tertiary roots) which serve to increase the surface area for water and mineral absorption.

The above images show the stages of germination from the radicle to the first true set of leaves and needles respectfully. Cotyledons are the first leaves produced by plants, but are not considered true leaves. They are sometimes referred to as ‘seed leaves’, because they are actually part of the seed or embryo of the plant. These seed leaves serve to access the stored nutrients in the seed, feeding it until the true leaves develop and begin photosynthesising.

Root growth – roots grow in length from their ends only, the very tip of the root is covered by a thimble-shaped root cap called the calyptra, which protects the growing tip as it makes its way through the soil.

Behind the root cap lies the apical meristem, here cells are produced some are added to the root cap. But the majority are added to the region of elongation, which lies just above the meristematic area.

Above this lies the region of maturation where the primary tissues of the root mature, completing the process of cell differentiation that actually begins in the upper portion of the meristematic region. (shown below)

Aerial roots – called adventitious roots arise from an organ other than the root, for example from a stem or leaf. These adventitious roots often referred to as aerial roots can hang long distances before coming into contact with the soil or remain dangling in the air.

Some of these including the Screw pine and banyan do assist in supporting the plant in the soil. Aerial roots are the primary means of attachment to non-soil surfaces such as buildings, rocks and other plants for example. The Ficus watkinsiana family Moraceae (strangler fig) named for their pattern of growth upon host trees, which often results in the host’s death.

A number of other specialized roots exist among vascular plants for example. Pneumatophores an aerial root specialising in gaseous exchange are commonly found in mangrove species that grow in saline mud flats. These are lateral roots that grow upward out of the mud and water to function as the site of oxygen intake for the submerged primary root system.

Other root systems – the roots of certain parasitic plants are highly modified into haustoria, a rootlike structure that grows into or around another structure to absorb water or nutrients. Mistletoe and members of the broomrape family are good examples of this.

Many plant roots also form intricate associations with mycorrhizal soil fungi, a number of non-photosynthetic mycoheterotrophic plants including the Indian pipe Monotropa uniflora rely exclusively on these fungi for nutrition.

Root functionality – the primary tissues of the root are from outermost to innermost, the epidermis, cortex and vascular cylinder. The epidermis is composed of thin-walled cells and is normally only one cell layer in thickness.

Water absorption and dissolved minerals occur through the epidermis, a process enhanced in most land plants via the presence of root hairs. These slender tubular extensions of the epidermal cell wall are only found in the region of maturation.

The absorption of water is achieved via osmosis process, because (a) water is present in higher concentrations in the soil than within the epidermal cells. Here salts, sugars and other dissolved organic products are contained.

(b) The membrane of the epidermal cells is permeable to water, but not to many of the substances dissolved in the internal fluid. These conditions create an osmotic gradient, whereby water flows into the epidermal cells. This flow exerts a force called root pressure, that helps drive the water through the roots.

The cortex conducts water and dissolved minerals across the root from the epidermis to the vascular cylinder, then transported to the rest of the plant. The cortex also stores food transported downward from the leaves through the vascular tissues. The innermost layer of the cortex consists of a tightly packed layer of cells called the endodermis, which regulates the flow of materials between the cortex and the vascular tissues.

Why no tap root? – In bonsai many practitioners remove the ‘tap root’, but the ‘tap root’ enables stability and water absorption so why remove it? The following species have rather large tap roots Oak Quercus, Black Walnut Juglans nigra, Silver Fir Abies alba and White Mulberry Morus alba.

Coniferous species contrary to popular belief do not have long tap roots. Their lateral roots and tertiary roots spread outward and grow downward which gives stability. However, there are some exceptions including the Long Leaf pine Pinus palustris that have large tap roots.

In order for these and many other species of tree to become bonsai the roots have to be pruned and the more vigorous the root growth the more pruning is required. In Japan and China young trees are planted in deep pots to encourage root growth and after a few seasons they have their tap roots removed to allow the lateral and tertiary roots to develop and thicken; these roots if near the base of the trunk are the potential nebari.

Root damage – many plants will survive and recover from root damage providing the damage does not exceed 1/4 of the total root zone. Most of the important feeder roots of trees or shrubs are within the upper six inches of the soil and if damaged, uptake of water and nutrients is restricted reducing growth.

In addition, root damage may take months or even years to progress, and it is during this period where problems begin which can cause symptoms of decline or demise depending on the situation and how much damage occurred.

One of the biggest problems when root pruning bonsai is the lack of care taken, we have witnessed countless instances where the root ball is attacked with 2, 3, and 4 pronged instruments. The roots are basically ripped apart causing irreparable damage and as stated if more than 1/4 of the total root ball is damaged chances are that the tree’s health will diminish for some considerable time and this is where pests and disease can attack.

This brief discussion on germination and in particular the functionality of a plant’s root system may lead to a better understanding of its importance. But there are many other factors to consider, these include the wrong type of soil medium, incorrect pH (see article 06 ‘Soil Biology 1.’

Over and under watering, inferior lighting conditions, climate, stress, and worst of all the hidden menace. Which are pests and disease either within the soil medium, meaning fungal or insect attack above the soil level. (see article 26 ‘Plant Husbandry 1.’

A final thought on the root system especially with bonsai is root protection. Bonsai are confined to shallow pots and are vulnerable to extreme cold conditions. Any moisture in the soil will freeze preventing the root system from functioning properly to the point of demise. Therefore, some form of protection is required because in winter time trees still need water.

Of course much depends on the species, hardy species from colder climes do not need protection as they are endemic to the region and are used to extreme conditions. But species from temperate zones will not, our experiments using the Aleppo pine Pinus halepensis, native to the Mediterranean region as an example proved our theory to be correct.

Nonetheless, if in doubt take precautions and move vulnerable trees to cold storage. In the next article on ‘Plant husbandry’ we turn our attention what happens above the soil, until next time, BW, Nik.

Hi, welcome to Taiga Bonzai, we have written much on pests and disease, which cause problems for bonsai enthusiasts and horticultural communities worldwide. In this article we discuss a candidate that not only kills trees, but is able to create serious problems to humans and domestic animals.

Introduction – the ‘Maritime pine‘ or ‘cluster pine‘ Pinus pinaster is native to the Mediterranean basin covering a large area that includes, Portugal, Northern Spain, Southern and Western France, Western Italy, Croatia, Tunisia, Algeria and Northern Morocco.

It is a hard, fast growing pine containing small seeds with large wings and favours this region’s climate of cool rainy winters and hot dry summers. Pinus pinaster is closely related to Pinus halepensis commonly known as the ‘Aleppo pine‘, because both species share many of the same characteristics and pests.

Pinus halepensis also grows in the Mediterranean region in Malta, Montenegro, Albania and east to Greece, Syria, Lebanon, Southern Türkiye, Palestine, Jordan and Israel.

Both these species are subject to attack from Dioryctria sylvestrella, commonly known as the ‘Pine knot-horn‘ or ‘maritime pine borer‘. It is a member of the Pyralidae family, which occurs naturally in Europe, much of Asia and North Africa. This pest has been discovered as far north as the Arctic Circle, but is more common at lower latitudes where it does the most damage.

D. sylvestrella – is a small mottled brown and white insect with a wingspan of 28 to 35 mm, which flies in a single generation from June to October. The female chooses fast-growing, vigorous host trees on which to lay its eggs. The larvae attack buds, shoots, cones and young stems.

Damaged tissue attacked by the rust fungus Endocronartium allow the larvae to enter the tissues and tunnel under the bark into the phloem. The larvae usually remain close to where they were hatched, but occasionally migrate to other parts of the tree.

Larvae pupate inside a mass of resin mixed with frass (shown below) which they produce and continue to feed within. Their boring activity causes large quantities of resin to flow from the wounds weakening the tree, allowing fungi and other pathogens to gain entry eventually threatening the trees health.

D. sylvestrella was first detected in the UK in 2001 and is different from the three other species in the genus, by the fact that the subterminal line is generally smooth with a single waved kink at its midpoint. In the other three species this line is dentate from the mid-point to the dorsum.

Efforts to control – these species of pine are under threat, young trees have no defence and eventually succumb, older more mature trees are able to withstand the onslaught but are severely weakened.

In Italy the powers that be have thought of several methods to control D. sylvestrella for example, chemical usage. But horticulturists are against such practice, their arguments are that there is little or no control and many claim that an effective chemical solution has yet to be found.

In addition, it is argued that a chemical approach would have serious consequences to the horticultural industry. Because if used its properties become airborne resulting in contamination of other crops including, olive, fruit and vegetable production rendering such unmarketable.

Hence loss of income not only to the horticulture fraternity, but also to the state. Moreover, no one in their right mind would consume contaminated food produce, because of the possible side effects if they are unsure of its origin, which is a stringent mandate of the EU.

Finding a solution – the agricultural sector meaning the farmers and growers are of the consensus that it is virtually impossible to prevent the onslaught of D. sylvestrella. Due to its abundance in the Mediterranean region and its ability to invade.

However, studies on D. sylvestrella behaviour indicate that larvae when ready to metamorphosize are compelled to descend the tree and conceal themselves in the litter at the tree’s base. Therefore, preventing the larvae from doing so seems a logical solution in stemming the birth of the next generation of moths.

Traps have been manufactured that can encircle the trunk capturing the larvae as they descend, which are then disposed of. Although these traps are efficient they cost approximately 30 to 50€ each depending on the region. To some this may appear inexpensive; but in reality it is the opposite because much depends on the amount of trees one has on the land. Hence farmers and growers are designing and constructing their own versions. (shown below)

This homemade version consists of plastic base and wall with a layer of foam affixed to the inner diameter to fit snugly against the contours of the trunk. A hole is drilled into the base where a tube protrudes downward to which a plastic bag containing tree litter is tied on.

The larvae walk around the trap eventually falling down the tube into the bag, when the bag is full the larvae are disposed of. This homemade trap costs approximately 3€ to construct. It can be argued that sometimes even the most simplest of inventions are more effective than expensive chemical alternatives.

D. sylvestrella – is harmful to humans and domestic animals due to its ability to shed toxic hairs (called setae or spines) from its body, which it is apt to do when disturbed. According to James H. Diaz of the National Centre for Biotechnology Information; (NCBI)

“Caterpillars bear highly specialized external nettling or urticating hairs and breakaway spines or setae to defend against attacks by predators and enemies“. “These can inflict serious human injuries ranging from urticarial dermatitis and atopic asthma to osteochondritis, consumption coagulopathy, renal failure and intracerebral hemorrhage.”

There are approximately 12 families of lepidoptera worldwide that are able to inflict serious injuries to humans and D. sylvestrella a member of the Pyralidae family is one of them. Andrea Seldeslachts, Steve Peigneur, and Jan Tytgat in their paper published online 2020 May 30. ‘Caterpillar Venom: A Health Hazard of the 21st Century’ states that;

“Depending on the family and species involved, some toxins provoke local urticating dermatitis, a burning sensation, allergic reactions, respiratory system problems and/or ophthalmia nodosa, whereas others cause systemic effects, including hemorrhagic syndrome, acute kidney injury and/oral phalangeal periarthritis.“

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7345192/

With domestic animals, being inquisitive is their natural bent, prone to sniffing or licking: The effect of the toxic venom from the hairs (setae or spines) of D. sylvestrella has what only can be classed as a devastating tragic misfortune, in that there being no antibiotic treatment available at this juncture.

These animals are at risk with the most vulnerable part being the snout a wet fur less surface around the nostrils of the nose called the rhinarium. If this is infected by venom the consequences are severe; hence contact with D. sylvestrella larvae should be avoided at all cost.

As we have stated pests and disease are a major problem in today’s world which have been highlighted through our recent articles. Not all can be attributed to mankind’s actions, but many can – we have problems of varying degrees that require urgent attention; failure to address it will only lead to escalation. Until next time, BW, Nik.