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 the next; 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 those uncommon. These include the seed or plant, soil medium, water table, pests and disease most of which can be found in our articles and we will point them out as we proceed with this discussion.
Seeds – in nature plants have various ways of dispersing their seeds on the wind, by animals and birds that consume and dispense them through their digestive system. Such seeds released from the parent plant are in what is termed as a dormancy stage and dormancy is a natural state of being in many plants, its function is to ensure that the seed will germinate at an appropriate time. However, seeds can remain in a dormant state and fail to germinate although conditions, temperature, water and light are in ample supply.
Why this phenomena occurs can be attributed to a seed’s morphological and physiological requirements, because seed dormancy is able to originate in different parts of the seed for example, within the embryo or its coating – the shell or husk. Dormancy is deemed not as a constant, but as a variable because it is a common phenomenon encountered in a large variety of trees. However, it should be noted that not all seeds have embryos hence they will never germinate.
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, because their ‘shelf life’ is short. However in the main seeds collected from the wild are robust and quite hardy able to withstand high and low temperatures and can be stored in the right conditions for long periods of time; providing they have not been attacked by pests and disease. See article 60 ‘Germination! – no guarantee’
Soil mediums – are prepared to suit the plant beit ericaceous (coniferous) or organic (deciduous) and should be a composition with good drainage allowing the roots especially feeders to travel in search of nutrients and moisture; compacted soil mediums are detrimental to the plants well being. See articles 27 and 28 ‘The pH factor’ which discusses various soil compositions. 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 leaves it is re-planted in a soil medium that is more appropriate, this is done to slow the growth rate otherwise the plants becomes ‘spindly’ tall, or thin and will take some considerable time to gain girth. Plants in this condition are easily stressed and susceptible to attack because it’s defences are weakened, the first signs are chlorosis (yellowing of the leaves) and leaf drop.
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 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 quite well, but the majority of others species cannot tolerate these extremes.
If you have the ability to harvest and store rainwater this is 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. Fluoride (F) banned in many countries is a neurotoxin and endocrine disruptor, able to damage the thyroid gland and interfere with bone formation. Chlorine (CI) a strong disinfectant added to drinking water as a purification technique. Other chemicals can include Mercury (Hg), Arsenic (As) used in a multitude of industrial processes, Lead (Pb) a major toxin that still exists due to corroded piping systems. To read the problems with tap water and how to treat it see articles 35 and 36 ‘A teaspoon of vinegar’.
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. Plants infected with red spider mite often fail to survive yet they can be saved. Remove the plant from its container and discard all traces of soil, the whole plant is sprayed with horticultural soap; re pot the plant, water, isolate and keep a watchful eye out so the problem does not reoccur.
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. Farmers and land holders are being paid not to produce crops but to turn their fields into wildlife havens to encourage the return of the predators. This is akin to ‘shutting the stable door after the horse has bolted’ a ludicrous policy considering the present world crisis.
(a) During World War II (1939 – 1945) many governments mandated that more produce be grown to feed those at the front line, those unable to enlist for whatever reason were forced to endure rationing 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. Evidence of this can be substantiated in article 56 ‘Bug apocalypse’
(b) On March 25th, 1957 France, West Germany, Italy, the Netherlands, Belgium and Luxembourg signed a treaty in Rome establishing the European Economic Community (EEC), also known as the Common Market. As the years rolled by other countries also signed up and soon there was an abundance of food including butter mountains, milk and wine lakes, gluts of potatoes, apples and other fruits. Did they give it away to the poor or countries facing drought and famine – NO – what could not be poured away was disposed of in disused mine shafts
(c) 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 and the crop harvests GMO or organic will devastated by marauding invaders many whom are immune to pest control see article 20 ‘Pests and diseases’
(d) Remember covid 19 where 6.3 million needlessly lost their lives, the world’s governments could not solve that problem and the disease is still apparent; what are they doing now, placing sanctions that are a reaction of mass childish hysteria; which has backfired. In the immortal words of ‘Ja Ja Binks’ the Gungan outcast in ‘Star Wars’ (plated by actor Ahmed Best) “Weesa in deep do do” and the level is rising. Is it not high time the bungling cretins of the EU and others be held accountable for their stupid mismanagement and decision making. We leave you with this thought; “The folly of the mindless maketh the intelligent weep.”
The problem with disease is that it cannot in reality be detected until there is visible evidence, either insect damage or that of fungi and canker. Science has told us that microorganisms can exist in a single-cell form or a colony like bacteria and fungi and 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 broadleaf trees. 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 and Northern Asia also in South Africa. Trees that are attacked become parasitized. The foliage becomes sparse and discoloured, twig growth slows down and branches may die back. There are no known fungicides or management practices that will kill Armillaria mellea after infection without damaging the infected plant.
A 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.
Image courtesy of wikipedia
Borers are perhaps the most harmful to trees, The Asian Longhorned beetle Anoplophora glabripennis native to eastern China, and Korea has been introduced into the United States, where it was first discovered in 1996, and in Canada and several countries in Europe including, Austria, France, Germany, Italy and UK. This beetle is believed to have been spread from Asia in solid wood packaging material. A. glabripennis primarily infest maple, poplar, willow, and elm trees. In the United States it has attacked birch, katsura, ash, planes and Sorbus; In Canada on maple, birch, poplar and willow and in Europe on maple, alder, birch, hornbeam, beech, ash, planes, poplar, Prunus, willow and Sorbus.
The Bronze Birch borer Agrilus anxius is a wood-boring Buprestid beetle native to North America numerous in warmer parts of the continent where it thrives. It is a serious pest on birch trees Betula frequently killing them and if this insect came to Europe there would be no hope for Birch forests as the trees have no resistance against this species of insect; hence the effect on Scandinavia’s Birch industry would be devastating.
Sirex woodwasp Sirex noctilio a species of horntail native to Europe, Asia and North Africa is an invasive species in other realms including Australia, New Zealand, North and South America and South Africa where it has become a significant economic pest of pine trees especially Pinus radiata. The wasp can attack a wide variety of pine species, although some species seem to be more susceptible than others and stressed trees often are attacked. It is believed that this insect was introduced on unprocessed pine logs imported from Europe.
Sirex woodwasp Sirex noctilio
There are many other pests and disease to contend with several of which we have discussed in the articles 62 to 66 ‘Unseen enemies’, but one that is now devastating the horticulture industry is Xylella fastidiosa. 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.
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 hence, 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 if they inform the European Commission and put forward a technical case to request EU measures against a specific pest, but 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.
It would appear from the above debate that various governments cannot not find common ground to solve the problems of pest and disease control, they are only concerned with their own interests instead of working for the good of all. The problems are out there and they need to be addressed as science has told us, failure to do so will result in dire consequences for all. In the last part of this series ‘plant husbandry’ 5 we conclude this topic with some unanswered questions, until next time, BW, Nik.