Articles
NATURAL INFECTION OF HOST PLANTS IN THE DANISH “FIREBLIGHT GARDENS”
A host plant is furthermore able to overwinter the disease and will remain infected after a period of conditions unfavourable for the spread and survival of the pathogen.
Since 1972 the susceptibility of host plants under field conditions has been investigated in two areas in Denmark, the so-called "Fireblight Gardens". Both areas lie near the sea and so are exposed to humid air and both are in areas were fireblight occurs naturally.
They are also in close proximity to elderly hawthorn-hedges, which were already infected by fireblight when the experiment started.
One "garden" is situated at Bøtø on the island Falstria in the south-eastern part of Denmark in the neighbourhood of The Baltic.
The other is located at Vester Gammelby in the south-western part of Jutland near The North Sea.
About 4 000 specimens belonging to 40 species within 16 genera were planted in the first two years of the experiment.
Generally 50–75 plants of each species were planted.
Crataegus monogyna was planted in between the test plants so as to gradually increase the infection pressure.
The plants are listed in table 1. They fall into four groups.
- Ornamentals which are frequently planted in Danish gardens.
- Plants received from Holland, which are more common there than in Denmark.
- A group of Malus of especial interest to bee-keepers on account of their yield and quality of their pollen.
- A collection of 10 clones of Crataegus which have been chosen and propagated because they apparently show resistance to fireblight under natural conditions.
From the list it appears which plants have been naturally infected during the past 6 years.
In the first summer fireblight was found in the Crataegus monogyna catch-plants and in Crataegus oxyacantha ‘Paul’s Scarle’ as also in two of the Cotoneaster species, namely C. lucidus and C. moupinensis.
Fortunately the apprehension that the disease might devastate the plantations turned out to be unfounded.
In southern Jutland the conditions for infection seem to be somewhat better than in Falstria, where the plants after 5 years now appear to be very healthy.
This summer we have had great difficulty in finding new infections even in the catch-plants and also in the old hawthorn-hedge along the plantation.
Cotoneaster divaricatus was only found to be infected by fireblight in one year of the trial, while C. lucidus was found to be infected in four years.
For both species it was a question of a few small tipinfections.
Cotoneaster moupinensis has shown the diseases every year but seems to have a quick recovery, while C. salicifolius was infected in