Injections and soil amendments "can boost trees' resilience"

A range of available products can enhance trees' resistance to pest and disease attack, according to Dr Glynn Percival, who manages Bartlett Tree Experts' laboratory at the University of Reading.

Percival discussing biochar amendments to ash trees with chief plant health officer Nicola Spence on BBC's Countryfile last year
Percival discussing biochar amendments to ash trees with chief plant health officer Nicola Spence on BBC's Countryfile last year

He told the recent Arboricultural Association amenity conference: "When we go abroad, we get vaccinated with a weak strain of the disease. Sometimes once is enough, as with tuberculosis."

Disease resistance can similarly be induced in plants, he argued, and indeed studies have already shown levels of control comparable with conventional chemistry in fireblight, Phytophthora root rot, powdery mildews and spruce wilt - "all very different types of organisms", he noted.

"You can buy injection equipment but it's illegal to use it. I don't know why there's such resistance. But it's an option for the future."

Meanwhile at Bartlett's laboratory, "we have shown you can treat the trees' roots, and we are now doing a trial with the London Borough of Barnet on newly-planted street trees", he said.

Using a mulch of chipped willow, which contains salicylic acid, is also effective against apple scab, he added. "That's just one compound that can switch on the tree's defence systems."

A soil amendment of biochar has also been found to boost trees' resistance against Phytophthora ramorum, acute oak decline and horse chestnut leaf miner, he added, while phosphites added as bark spray "also boosts their immune system".

Chitin, a by-product of the seafood industry, "is another product you have access to", and which can be air-spaded around the roots of apple against scab, he said.

"Over the last two years we have also trialled these products in combination at various trial sites using various modes of application," he said, adding that the efficacy of different forms of biochar also need to be compared.

But he pointed out: "Trees only have a certain amount of energy and you will get 15-20% less growth - it's a trade-off."

Percival was later presented with the Arboricultural Association Award 2017 at conference awards dinner on 12 September.


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