Apart from old age, some times trees die unexpectedly, even at a young age.
The death of fruit trees can be caused by several factors:
1) Collar rot
2) Armillaria root rot
3) Soil contamination with aggressive chemical substance
4) Tree canker
5) Tree trunk restriction
Drought is often the cause if the trees are not cared for and the competition of grass and weeds is too severe, combined with a long dry period. If this is not the case, then a careful examination of the tree will need to be carried out.
Examine the tree trunk very carefully. Is there an obstruction that has grown into the tree trunk and is causing severe restriction? If this is the case some new and healthy-looking young shoots will appear below the restriction. This will also be the case if tree canker is girdling the tree. Next, use a sharp knife to peel back a portion of the bark on the trunk. If no healthy yellowish cambium under the bark is present and the wood is brown and dead, then points 1, 2 or 3 , as mentioned above, are the most likely causes of the tree trouble. An example of Point 3 is when a chemical substance such as concentrated weedkiller has been poured onto the ground next to the tree.
If this is not the case, we will then be left with points 1 and 2 as the most likely cause. In both cases, the chance of the trouble spreading to other trees becomes an issue, because the fungus remains active on the tree roots. If it is the armillaria fungus, the toadstools will appear around the trunk in the late autumn period. However the bootlace-like fungal threads will then already have arrived around the roots of your nearest fruit tree or ornamental tree. In that case grubbing the tree in total is the only option.
Summarising, if after a detailed examination, you find that the likely cause of tree death is armillaria, then you will have to grub the tree immediately, remove it off the site, roots and all, and burn it, as soon as you can. Armillaria fungus is very active in finding and infecting its next victim.
Whatever the outcome of your examination, my advice is to always use new, clean soil if you want to replant a fruit tree this coming autumn. Taking in consideration crop rotation principles, do not plant apple after apple or pear after pear etc. Vary the tree types. So, for example, apple after pear will be fine.
The illustration above is from “The Book of gardening: a handbook of horticulture”, 1900, edited by William D. Drury. It is accompanied by the following text:
“Armillaria mellea (Agaricus aielleus) This is a most destructive fungus found upon living ornamental trees, such as Conifers, as well as upon orchard trees. It is responsible for the disease known as Tree Root Rot. The fungus is most abundant, and is found both as a saprophyte and as a parasite. The clusters of Mushrooms at the base of trees are very familiar; they are, moreover, conspicuous alike as to size and colouring. The cap is of a pale yellow, with darkish scales upon it; the stem is also yellow. The fungus finds access to healthy trees either by means of its spores, which germinate on an injured part of the bark; or by means of the very peculiar mycelium, which is black and stringlike, and always endeavouring to penetrate the roots of healthy trees. The only thing that can be said in favour of this fungus is that its sporophores, or Mushrooms, are edible, though not particularly rich in flavour, being somewhat strong. Care should be taken to carefully remove and either eat or burn all specimens of the fungus, so that the danger of trees being infested by the spores which are shed is minimised. The mycelium found under the bark is white and felted. Once a tree has been badly attacked nothing can save it from destruction, as the mycelium spreads under the bark with considerable rapidity. Preventive rather than remedial measures should be adopted. These may well consist in the removal of all dead stumps on which the fungus is growing as a saprophyte; and in isolating the infected live trees.”