FIREBLIGHT CONTROL IN CRATAEGUS HEDGES BY CLIPPING

In May 1972 experiments were started to prove the value of cutting and trimming of hawthorn hedges in the control of fireblight.

At that time hawthorn was a very common constituent of hedges around the gardens and orchards in the fruitgrowing areas and no. less common as shelterbelts in the windexposed agricultural areas of our country.
As it was also considered to be the most important host plant under Danish conditions its presence seemed to imply an enormous risk, encouraging the spread of fireblight.

On account of energetic appeals to farmers and fruitgrowers many hawthorns were removed around nurseries and fruitplantations but in spite of this appeal some people did not want to grub their shelter-belts, before they had been able to plant and see grow up a new hedge of a resistant species.
Therefore in some places attempts were made to kill the hawthorns and to keep the dead hedge as a windbreak.

With flame-throwers a fairly good result was obtained, but a better effect was achieved by spraying the hedges with hormone compounds.
For instance spraying in summer with the weed killer 2, 4, 5, – T (Tormona) was effective, but there was much damage to surroundings and so the treatment cannot be used on a large scale.
It was also tried to scorch the green parts of the hedges by means of spraying with blue vitriol (CuSO₄) and green vitriol (FeSO₄), but these treatments had no effect at all.

In England it had been experienced that hedges which have only a few flowers were not so susceptible to fireblight as the uncut ones which have many flowers and where we often see the primary infections.
With that knowledge we started experiments with some hawthorn hedges in fireblight-areas according to the following plan:

1. Untreated

2. Cut down to a height of 2–3 m and clipped on both sides.
   In subsequent years the sides and top were clipped in the summer.

3. As for 2, but the clipping in subsequent years was done in winter.

4. Cut back to ground level in 1972 and the regrowth was not clipped afterwards.

The results have on the whole been as we expected considering the very weak infection which has taken place in these trials.
In the first year we found a few shoot infections in the untreated bushes and in one of the winterclipped bushes.
The following year we only found infections in the untreated bushes.

In 1974, when the conditions for fireblight evidently were better, we found comparatively many blossom- and shoot infections in the untreated bushes and a few shoot infections in the winterclipped bushes.
The bushes which had been cut at ground level and also the summerclipped showed not yet infections.

Symposium on Fire Blight

H.A. Jorgensen

https://doi.org/10.17660/ActaHortic.1978.86.12