Hi, and welcome to Taiga Bonzai, in this post we continue our journey bringing to light the catastrophic failures of mankind’s idiosyncratic actions.

Introduction – according to the Botanical Gardens Conservation International (BGCI) and its network of 500 member organisations, there are 60,065 species of trees in the world; Many are rare and threatened with extinction.

If we multiply the number of tree species with the number of known pests and disease all with different triggers, the statistics would not only be bewildering but also incomprehensible. Here we highlight more increasing problems the world has to face beginning with a few examples of the many deadly diseases, for which at this juncture there is little or no control.

Disease – Armillaria Root, according to Guido Schnabel of the Clemson University School of Agricultural, Forest and Environmental Sciences. “Armillaria root rot caused by the fungus Armillaria tabescens wreaks havoc on rootstocks, killing young and old peach and cherry trees before spreading to neighbouring trees.” “Between 1987 and 1992 Armillaria root rot caused an estimated $3.86 million to the peach industry and between 2000 and 2002, more than $1.5 million in damage to the Georgia peach industry.”

The first symptoms of an Armillaria infection are chlorotic leaves, stunted growth and sudden collapse of shoots. An obvious sign that infection is there due to the presence of clusters of mushrooms around the base of an infected plant. Fungi sprouting from an A. mellea infection are honey-coloured to dark brown and have a domed cap. “Depending on species, the mushrooms may or may not have an annulus around the stalk or caps that are more disc-shaped.”

This devastating disease can be caused by other Armillaria species including, A. mellea a the primary pathogen in northern states causing premature peach tree decline. The potential for significant annual losses in Michigan, is due to the predominant fungus A. ostoyoe found in tart cherry orchards. There is no ‘silver bullet’ solution to protect trees and Armillaria infections have taken many prime orchard sites out of production causing a huge loss of revenue.

Anthracnose – high on the list of devastation is widespread and considered an important disease in most countries. It is caused by a group of fungi in the genus Colletotrichum, that attacks leaves, twigs, flowers and fruits of a great number of tree and shrubs.

Apple scab is a common disease of apple and crab apple tree varieties, as well as Mountain ash Sorbus and pear. It is caused by a fungus Venturia inaequalis that infects leaves and fruit, leaving the latter unsuitable for consumption. Leaf spots are olive green at first, later turning dark brown to black. Infected fruit turns colour in a similar fashion, ending up brown, corky and deformed.

Thousand canker disease – affects many plants including walnuts Juglans sp. It is mainly found in the Western United States however, black walnuts trees in Tennessee were found to be infected in the summer of 2020. It is vectored by walnut twig beetles Pityophthorus juglandis and forms small cankers around their galleries.

As time progresses these small cankers coalesce to girdle branches and stems, trees can be infected for years before symptoms become visible for example. Foliage in the upper branches of declining trees wilt and become yellow. Once a tree begins to decline it is often dead within a few years and at present there are no chemical management solutions to control the disease.

Thus far we have given examples (albeit in brief) of the devastation caused by some of the many thousands of insects and disease. Adding more examples would probably substantiate the argument further, but this task has already been accomplished. In the book ‘Taiga Bonzai – Simplifying The art’ (Revised Edition), where 2 chapters reveal extensive information on these subjects, c.13 concentrates on ‘Pest and Disease’ and c.14 discusses ‘Toxicity’.

We now turn our attention to plants required for our consumption namely fruit and vegetables starting with one of the world’s oldest fruits the humble apple. The bureaucracy over production and the controversy surrounding it including the diseases that attack various species of this particular fruit.

The apple – Malus domestica, its ancestor Malus sieversii originated in Central Asia 4 thousand years ago. Today there are 7,500 apple varieties throughout the world – 2,500 of which are grown in the United States. In the 2019/2020 crop year, China was the leading producer of apples, it’s production amounted to 41 million metric tons. The European Union came in second place with approximately 11.48 million metric tons.

The UK has been producing apples since the Roman occupation (AD 43 to AD 410) however, production is now in serious decline due to bureaucracy and trade problems with the EU. Hence growers are given payments to burn their orchards.

Natural England and the National Trust claimed 60% of England’s orchards had disappeared since the 1950s and have launched a £500,000 project aimed at halting the decline. The crisis has been even worse in some areas such as Devon, which has lost almost 90% of its orchards.

According to David Bullock, the head of nature conservation at the National Trust, “Traditional orchards have been disappearing at an alarming rate. We are in real danger of losing these unique habitats.” (https://www.theguardian.com April 2009)

The orchard – apple trees need space to grow, dwarf varieties require a minimum of 5m, standard trees need a distance of 9 to 11m. But this distance is inadequate because, as the trees mature they spread out, thus the risk of cross contamination from bacterium and fungal spores increases.

In 2017 the total area harvested in the world for apples was 4,933,841 hectares. But, apples are not the only fruit produced, other varieties include apricot, pear, peach, plum and damson. Hence the land mass required increases – these varieties predominantly cultivars are also susceptible to attack, thus the orchard becomes the playground for disease.

Such diseases include: Fire Blight a contagious disease affecting apples, pears, and some other members of the family Rosaceae. It is a serious concern to apple and pear producers and is believed to be indigenous to North America, from where it spread world-wide.

Powdery mildew Podosphaera leucotricha a fungus that forms a dense white fungal growth (mycelium) on the host tissue affecting leaves, buds and shoots. Black Rot and FrogEye Leaf Spot Botryosphaeria obtusa attack fruit, leaves and bark of apple trees. Phytophthora Rot a soil-borne fungal disease by the pathogen Phytophthora sojae causes seed rot and attacks roots and stems; trees infected by such pathogens are usually destroyed.

However, there are apple tree varieties that are said to be disease resistant for example, Liberty, Freedom, Dorsett Golden, Enterprise, Goldrush, Pristine, Arkansas Black and Williams Pride which are American cultivars. European apple trees include, Topaz, Herefordshire Russet and Otava, but can the claims of being disease resistant to all insects and pathogens be substantiated – in short the answer is probably not.

Arguably much depends on a particular climate zone; arid, humid, wet and cold. Moreover, these zones harbour other pests for example, the Round headed apple tree borer, European red mites, Red banded and oblique banded leaf rollers, Rosy aphids, Woolly aphids, Green fruit worms, Leafhoppers and Japanese beetles. Until next time, BW, Nik.