North Cumbria Orchard Group

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Apple Scab

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Apple Scab

Postby MarkEvens » Mon Apr 11, 2011 11:38 am

Scab is very common in Cumbrian orchards, owing to our wet climate. Arguably it is mainly a cosmetic fault as apple trees appear to survive even the worst attacks. However, if it affects the fruit as well as the leaves, then cracking and subsequent spoilage can occur. There are a number of ways of avoiding or reducing scab:
1) Plant scab-resistant varieties suitable for Cumbria (see the Fruit Database page).
2) Practice good orchard hygiene. Scab spores overwinter in fallen scabby leaves. Break the cycle by removing dead leaves from the ground.
3) Spray. If you are "organic" then you can use an (inorganic!) sulphur spray (but note that certain trees are intolerant of sulphur, e.g. Belle de Boskoop, Lane's Prince Albert, Lord Derby, Newton Wonder). If you are not "organic" then you can use an (organic!) spray such as Myclobutnil (e.g. Systhane).
Now (mid-April) is the time to be alert for scab infection. The spores need a certain amount of warmer weather to "wake up", after which a mild wet spell can trigger their release. This week (w/b 11/4) is forecast wet but fairly cool, so it may be another week or so yet. Sprays only have a limited period of effectiveness, so timing is important (Myclobutnil will treat infection incurred within the previous 4 days and continue to protect for 6 to 9 days after spraying).
Actions:
Clear up last year's dead leaves, if you haven't already done so.
Spray at the critical time (watch replies to this post for further comments on timing). This is usually around the "pink bud" stage.
Alternatively, don't worry and pour yourself another glass of cider.
Please reply to this post with your views, comments and questions on the subject of scab.
MarkEvens
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Re: Apple Scab

Postby MarkEvens » Thu Apr 14, 2011 8:39 am

April 14th: We are now in the "accelerated" phase for scab spore development. Around half the spores which have overwintered will be mature. All that is needed for infection to occur is a mild damp day. In milder parts, this may have occurred this week, but I suspect most of North Cumbria was too cold so the next wet spell is the one to look out for.
MarkEvens
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Posts: 207
Joined: Sat Nov 20, 2010 5:34 pm

Re: Apple Scab

Postby MarkEvens » Sat Apr 23, 2011 8:28 am

Significant risk of infection today (23rd April), as we have a mild wet day after a warm spell. Those who wish to spray should do so now (following the manufacturer's guidance and avoiding spraying open flowers).
MarkEvens
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Posts: 207
Joined: Sat Nov 20, 2010 5:34 pm


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