LACK OF COMMUNICATION IS THE REAL CAUSE OF TREE DECLINE

Added on 29/12/2011

Article

By Bill Kowalczyk

Gallileo's real problem was that he couldn't get his critics to look through his telescope and thereby grasp what he was telling them. The trees in this country are declining and dying as a result of the refusal of Horticulturists, Gardeners, Nurserymen, Landscape Architects and Planners to listen to and heed the views of Arboriculturists. The case of 'Cherry die-back' as reported in the News on 22 August is a perfect illustration of the lack of respect, or at least communication with, the highly trained, qualified and skilled professionals who have daily contact with the trees in our community.

In my capacity as a Consulting Arboriculturist in Hampshire, a general decline of Cherry trees has been noticeable for more than a decade. Whilst it may well be correct to say that the disease is likely to be caused by a bacterial canker such as Pseudomonas, the real cause of the problem is more fundamental and of course much more complex. It is my view that it is a combination of cultural and chemical conditions that results in increased levels of stress, and therefore weakness, for plants in general and Cherry trees in particular. An holistic approach is required, looking at the whole issue, before any progress can be made.

Stress has become a buzzword of the eighties and nineties, but is no less the relevant because of that. As with humans, and I suspect with any other living organism, increased levels of stress leads to increased susceptibility to disease. The immune system becomes dysfunctional. As with motor cars, the closer one gets to operating at critical levels of stress, the more likely there will be a breakdown or failure of the system.

With cherry trees their phenology, or timing, of their processes must be understood. They are amongst the earliest flowering trees in the spring. This means that they have to draw on stored energy reserves to expand their flowers which cannot be replaced until their leaves are expanded and can photosynthesise. This is a critical time of low energy reserves. The fungal disease which causes Blossom Wilt, and is now also widespread, affects the newly emerging flowers and shoots and results in the tree needing to draw further on already depleted energy reserves in order to produce a second flush of leaves. Any passing Pseudomonas is going to have a field day under such conditions and is simply another symptom of the decline rather than the cause.

By the time the tree owner notices that there is a problem, very often the symptoms of shot-hole effect, cankerous lesions, and gum exudations are already well established. At this stage pruning is probably too late as it will inevitably entail the removal of green tissue which is essential to the plant to produce the energy required to cope with or to contain the disease. To add insult to injury, towards the end of summer just as the tree appears to have made it through the season, along comes another fungal disease causing Cherry leaf Scorch probably preventing the tree from entering the winter season armed with a full complement of stored energy. Then the whole process starts again the following spring. It is only a question of time before Honey Fungus or Phytophthora Root Rot finishes the job once and for all.

It is my belief that Horticulturists and plant propagators have to take a share of the responsibility for this. They are forever selecting earlier and more showy flowering varieties which require a greater demand on stored energy reserves and thereby getting closer and closer to the critical tolerances of stress levels before failure of the system, without any regard for the future of that system. Nurserymen too, have to take some of the blame. Too often I feel that the 'quantity rather than quality' ethic shows itself to be their most important criteria. I regularly find badly pruned trees with series of flush cuts on stems, the supposed rationale to produce straight and smooth stems. In reality the columns of damaged tissue are more likely to produce strip cankers or internal cracks in later life. Furthermore, modern lifting techniques and plant handling methods often leave trees with desiccated, split, broken, crushed or otherwise damaged roots. Such conditions start the young trees out on a cycle of stress and weakness.

For years, especially in the 1940's and 50's there was massive overplanting of Cherry trees almost to the exclusion of any of the other 1000 or so species or variety of trees available. Landscape Architects, Planners and Consultants may be responsible for making things worse by specifying these poor plants for a totally inappropriate situation. The site conditions may be such that plants are too exposed or shaded, subject to local waterlogging or drought, or overcrowded by other plants. More often than not an expensive development is followed by an expensive planting scheme with a skimping on the provision for site preparation. This leaves the poor landscaper with a 'bomb-site' of surface sub-soil, mud pools, concrete, building rubble and all manner of other assorted detritus in which to plant what should be regarded as a considerable long-term investment. I have seen specifications which require the addition of fertilisers at this point. So we have genetically weak choice of plant species, possibly weak, damaged and stressed plant material, being introduced to an inhospitable or inappropriate site (more stress), and all this before having a chance to recover from the shock of transplanting, then being forced into rapid growth by the use of chemical fertilisers. This takes more energy from reserves. The 'Defense Budget' is seriously depleted and so the tree's ability to respond to pathogens is compromised.

Increasingly mulch is being specified (how did this positive benefit slip through the net?) but this is often spread too thinly to have much effect either for weed suppression, moisture retention or soil conditioning.

Add to all this climatic changes with summer droughts and winter flooding, and atmospheric pollution, especially low level Ozone, Nitrous Oxides, and Particulates, and we have a complex and potentially lethal cocktail of chemical and physiological conditions which are destroying our trees (and probably our planet!).

I am not a scientist or researcher, I do not have the answer to these problems. However, I will listen to other professionals, from whatever field of expertise and who may have some of the answers. No-one is entitled to wash their hands of responsibility once that plant has been selected, once it is out of the nursery gate, once it is stuck in the ground. Looking at one small symptom or condition and devising a treatment is like Yossarian in Catch 22 making an exemplary job of dressing poor Snowden's leg wound without noticing most of his insides have spilled out of a gaping hole in his back!

If no-one is prepared to ask the Arborist what is happening out there in the big wide world 10, 20, 50, 100 or even 250 years after everyone else has ceased to claim any responsibility, then we have no chance! We must speak to each other. We must adopt a more holistic approach to our chosen field.

Regards, Bill