Winter is waining, the long dark days and nights are drawing to a close, the once crisp white snow now wears a dirty grey/black mantel of dust as it slowly melts away, but let us not be too hasty to shed those warm layers needed to combat the cold for the weather can change its mind as it is apt to do.
It is reassuring to know that winter’s demise is imminent here in Scandinavia (although its return is inevitable) but, with the coming of spring the problems begin again for example, Biotic and Abiotic disease. The following is an extract from the new book…. Taiga Bonsai (Simplifying The Art)
Biotic diseases are caused by living organisms, fungi, bacteria and pathogens left by viral infected insects for example, the ‘Red band needle blight’ (Dothistroma) that affects conifers mostly pines, causing needle loss eventually killing the tree. Ash dieback affects Ash trees and is caused by the fungus (Hymenoscyphus fraxineus) which blocks the tree’s water transport system causing leaf loss and ultimately dieback of the tree’s apex or crown.
Horse chestnut canker a bacterium species known as (Pseudomonas syringae pv.) causes extensive bleeding areas on tree stems. (Phytophthora austrocedri) affects Junipers causing dieback of foliage, stem and collar lesions and eventually death.
Biotic diseases usually appear on random plants but, can effect different plants with various levels of severity often with visible signs of disease for example, fluffy masses of mould, orange pustules and round leaf spots, wet or water-soaked lesions and irregular shaped leaf spots. Viruses often cause cankers and irregular colour changes such as mosaic patterns on leaves or unusual foliage colours for example, reddening of the leaves. Nematodes, a microscopic worm are also classified as a biotic disease causing root rots and irregular root growth. Arguably biotic diseases are part and parcel of nature’s rich tapestry something we have to accept.
Abiotic diseases are the result of non – living causes, the result of human activity – herbicides, pollution, an excess or lack of nutrients that plants require for growth. For example, Chloride (C1-) and Magnesium (Mg+2) are both essential nutrients important for normal growth. However, excessive concentrations of these nutrients may harm a plant with chloride being responsible for foliage damage as opposed to magnesium.
High concentrations of MgC12 ions in the soil may be toxic insomuch that they are able to effect and alter water relationships meaning the plant can not accumulate water and nutrients naturally. The effect of chloride in the conducting system causes an accumulation of necrosis in leaves or needles and where dieback first occurs, leaves are weakened or killed, which can lead to the death of of a tree.
A common cause of necrosis is brown, dead or wilted leaf tips and yellowing of older leaves. If this is the case, then the plant should be removed and cleaned immediately by washing the whole tree including the root ball with distilled water and the decaying foliage removed; the container or pot should also be cleaned and the plant re-potted in a fresh soil medium.
When dried out particles of (MgC12) become airborne they travel great distances, contaminating all they come in contact with especially trees and shrubs be they of natural proportions or bonsai and also back into the soil where they react causing chloride toxicity. Remember the line in the opening paragraph “the once crisp white snow now wears a dirty grey/black mantel of dust” this is the residue of (MgC12).
Symptoms associated with exposure to de-icing, salt sprays, aerosols or road dust differ from root absorption, the side of the tree facing the road may exhibit more damage and foliage will have surface deposits of salt crystals or dust. These usually appear in a distinct pattern affecting other plants that are in close proximity.
One of the major causes of excessive concentrations of (MgC12) is due to the de-icing of highways, streets, roads and pavements via the use of granulated magnesium chloride (MgC12) applied during the winter months that is different to halite road salt. (sodium chloride NaC1) Liquid (MgC12) solutions are also applied to non-paved roads during spring and summer months for dust suppression.
Pest and disease problems in bonsai are often the result of more than one cause, these are referred to as complexes for example, aphids and leafhoppers often spread various plant diseases in the process of feeding. Weak plants in abiotic conditions (nutrient deficient soils) are more susceptible to attack by various diseases and insects. In such cases it is not enough to simply treat a tree with pesticide or fungicide, all cases of the complex should be addressed to ensure good health and vitality in the tree’s development.
Magnesium chloride according to the powers that be, this chemical be it in granulated or liquid form is mandatory for de-icing and suppression of dust. But, when the snow has gone and the roads and pathways have dried, (MgC12) still remains on the surfaces and when the machines start sweeping these areas, the dust as stated becomes airborne – an ill wind. The area where my bonsai trees are housed is open to the elements and prone to (MgC12) residue; to say that it is a pain in the neck to have to be constantly cleaning, is an understatement. Arguably there should be a consultation regarding (MgC12) usage; until next time BW, Nik.