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Saturday 10 December 2016

More knowledge of nature can tackle disease in trees

Sowing mixes of species to replicate the natural world may solve the issue

Joe Barry

Published 12/04/2011 | 05:00

Perhaps we need to avoid monocultures of single species in order to reduce our vulnerability to disease outbreaks
Perhaps we need to avoid monocultures of single species in order to reduce our vulnerability to disease outbreaks

We are all familiar with potato blight or Phytophthora infestans, the disease that caused the great famine of the mid-1800s. Most of us would also be aware of Sudden Oak Death, which caused serious damage to oak in the US and some further limited damage in Europe.

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Phytophthora diseases are very much in the news right now because of the infection of one lone Sitka spruce following the recent outbreaks of Phytophthora ramorum (P.ramorum) in Japanese larch.

Extensive surveys have been undertaken by our Forest Service since 2003 and while P.ramorum had been detected in woodland on wild rhododendron, there had been no instances of it attacking commercial tree species. However, in July last year it was discovered in Japanese larch and also in a few stands of Noble fir, beech and Spanish chestnut that were growing close to the infected larch.

When I saw a photograph of the lone, infected Sitka spruce, which was found growing under a canopy of diseased rhododendron, it reminded me of someone sitting in a doctor's waiting room surrounded by flu victims coughing their lungs out. In that situation it is hard to imagine how one could escape infection.

As I write, no further evidence of P.ramorum has been found in Sitka and the area in question is in strict quarantine.

But we must remain on our guard and the Forest Service is recommending vigilance and asking that woodland owners report any suspicious signs of disease.

My guess is that, in time, many more species will be added to the already extensive list of trees and shrubs that are vulnerable to Phytophthora attacks and maybe fresh, and, as yet, unknown pathogens will emerge to cause further damage in our woodland.

We will just have to learn to live with them as we have with all other blights and diseases, and cope with outbreaks while continuing to add to our store of knowledge of what is required to grow strong, healthy trees.

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Nature favours those species that are adaptable and which can survive under changing circumstances. There are already elm trees evolving that are resistant to Dutch elm disease and despite its known vulnerability to Phytophthora alni, we still manage to successfully grow alder.

There may be a lesson to learn here from the practices of organic grain growers who sow mixes of corn species to 'confuse' diseases. This actually works and perhaps we need to more closely mimic nature in the layout and species mix of our plantations.

Trouble

Growing large areas under monocultures of any species is asking for trouble and we should learn from the way in which continental European countries with a traditional woodland culture have practised the planting of a broad mix of species for centuries.

Our Forest Service has been widely criticised in the past for introducing the compulsory planting of some diverse species and the inclusion of 10pc of broadleaves in all new plantations where appropriate. The wisdom of this is now becoming apparent, as is the old saying, "never have all your eggs in one basket".

For many millions of years, plants, animals and insects have been gradually evolving and taking advantage of all available niches in the natural world. The fittest survive and prosper and the weakest become extinct. Most species are extraordinarily adept at meeting the challenges posed by alterations in their habitat and their normal food supply.

It's tough out there in the wild but nature is incredibly resilient, and plant, animal and insect species survive through their amazing ability to develop defences against predators, climactic changes and diseases and ensure their own safety.

We need to look closely at how we have been imposing unnatural conditions on many species of crops simply to facilitate ease of management and the use of large harvesting machinery. P.ramorum is just one of thousands of fungal diseases that are out there waiting to find yet another species to invade.

Constantly having to update the mixes of sprays and chemicals we use to ward off such diseases is uneconomic and cannot be a long-term solution. I earn my living from the land and certainly don't want to sound like some fanatic preaching an unrealistic 'back to nature' approach.

However, common sense demands that we continually question the ways in which we grow our crops and rear our livestock. Growing trees, pigs or chickens or whatever intensively, creates the conditions whereby diseases thrive.

Perhaps we need to learn more from the natural world rather than trying to bludgeon it into submission.

Indo Farming



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