Wet weather raises threat of apple scab disease

Fruit consultant warns that heavy rain in summer and last week of September have provided ideal conditions for disease.

Long spells of heavy rain in summer and the last week of September have provided ideal conditions for the establishment of apple scab, the crop's worst disease, according to senior Agrii fruit consultant Colin Bird.

"Scab is worse this autumn than for a number of years," he said, explaining that growers who timed their sprayings well during summer's poor weather conditions have kept on top of the scab problem.

"But when the weather was against them it was easy to spray at the wrong time, with fungicides washed off the leaves, allowing infection to get established. Where it wasn't well controlled earlier this year it's tending to show up now. If it gets in next spring it can't be eliminated and you've lost the battle."

Apple scab is caused by a fungus, Venturia inaequalis, whose inoculum overwinter in leaf litter before releasing spores the following spring that then re-infect the tree. But taking prompt action now can avert later problems, Bird advised.

"If buds have not yet sealed, a preventive fungicide spray programme will protect them until they have completely closed and make them safe from infection."

Just as important is the application of five per cent urea spray at the start of leaf senescence and during leaf fall, followed by the pulverisation of fallen leaves.

Bird said a timely application of urea "supercharges the leaves with nitrogen", making them more palatable to earthworms and soil micro-organisms that digest the inoculum. Pulverising the leaves helps, but first they should be blown or swept into alleys from under trees.

"Weeds in the herbicide strips will need to be got rid of because they trap fallen leaves, making it difficult to blow or sweep them into the alleys," Bird warned. "If the urea is applied too early, it will feed the fruit bud but have no effect on scab."

Chlorpyrifos use - Feedback being sought

Growers who applied the insecticide chlorpyrifos this year are being urged to provide feedback to the Say No to Drift stewardship campaign at the National Fruit Show (Kent Showground, 17-18 October).

"We are very interested in individual grower experiences with using the Albuz TVI Anti-drift nozzles in 2012 and also with implementing a 50m buffer zone around watercourses for orchard treatments," said Lindsay Fogg of ADAS, which coordinates the campaign.


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