Apple canker control

Apple canker, caused by the fungus Nectria galligena, is a serious problem for many Northern Ireland Bramley growers. The fungus enters the tree in the autumn through leaf scars and in the spring-summer through bud scale scars and other damage points. As well as causing cankers, N. galligena can infect fruit, producing eye rot in fruit stored long-term.

Research is in progress to find out if nursery stock also has a role in transmitting infection as seems to be the case in dessert apple varieties.

After the very wet weather this summer, which will have encouraged spread of canker, it will be particularly important for growers to take measures to protect their trees at leaf-fall.

Trials over a ten year period at Loughgall highlighted the benefits of autumn copper in preventing leaf scar infection.

Two sprays of copper oxychloride ('Cuprokylt') applied at 5 percent and 50 percent leaf-fall reduced the number of new cankers by nearly 70 percent.

Benzimidazole fungicides (carbendazim, thiophanate-methyl) applied in the spring-summer have a dual action. They help to protect the tree from infection and also inhibit spore production by N. galligena on existing cankers. This reduces contamination of fruit and so less eye rot develops in store.

Where there's severe canker in an orchard and the fruit is to be stored long-term, spring-summer benzimidazoles may be worthwhile. However, significant reductions in canker and eye rot are only achieved if they're used for most of the treatments in the spring-summer programme from bud-burst to the end of June. Because of the risk of selecting for benzimidazole-resistant apple scab, benzimidazoles should be applied as a tank-mix with another approved scab fungicide.

Work in the 1980's showed that existing cankers can also be treated. The most effective measure is to prune out and burn the affected branches, but where this isn't feasible, the canker may be cut out and treated with a fungicide paint. Only octhilinone ('Pancil T') is currently approved for canker treatment.