Ap­ple ails

Sunday Tasmanian - Tassie Living - - FRONT PAGE - Peter Cun­dall

AP­PLE scab is among the dead­li­est of all ap­ple dis­eases. It is caused by a par­a­sitic fun­gus, the spores of which arise from partly- de­com­posed de­bris from last sum­mer’s dis­eased fruit and fallen leaves.

The fun­gal spores set­tle on the leaves and then quickly move on to the fruit. We can see it de­vel­op­ing at first with slightly- shriv­elled, dirty­look­ing leaf- clus­ters.

Later, as it moves on to ap­ples, we can see lop- sided, dis­torted young ap­ples form­ing with dark, some­times cracked, scabs on one side.

I’ve long- since learned to con­trol ap­ple scab with rig­or­ous hy­giene around vul­ner­a­ble va­ri­eties – mainly Granny Smith, Pink lady and Mutsu.

It is es­sen­tial to spring- prune all sus­cep­ti­ble ap­ple trees to al­low a free flow of dry­ing air through canopies

This in­volved rak­ing up and cart­ing away ev­ery fallen fruit and all fallen leaves.

I also closely mow, right to the ground, any grass or weeds with a grass- catcher at­tached, es­pe­cially in early win­ter and spring.

In May, this is fol­lowed by a wide sprin­kling of builders’ lime be­neath and around the trees.

Lime helps to speed up de­com­po­si­tion and en­cour­ages earth­worm ac­tiv­ity dur­ing win­ter to get rid of any re­main­ing dis­eased ma­te­rial.

In late win­ter, a good scat­ter­ing of blood and bone fur­ther ac­cel­er­ates de­com­po­si­tion while help­ing to fuel growth.

It is es­sen­tial to spring- prune all sus­cep­ti­ble ap­ple trees to al­low a free flow of dry­ing air through canopies.

This should be fol­lowed by spray­ing all leaf sur­faces with a mix of builders’ lime and wa­ter when the first blotchy leaves in­di­cate disease is at­tempt­ing to move in.

Scab or­gan­isms pre­fer acidic con­di­tions, so the lime cov­ers the leaves with a pro­tec­tive, al­ka­line coat. It works bril­liantly to keep this disease at bay. Luck­ily builders’ lime is an ex­tremely cheap form of pro­tec­tion so the over­all cost is low.

If the lime spray goes on too early, scab or­gan­isms will at­tack all new, un­pro­tected leaves which emerge af­ter­wards, so it may be nec­es­sary to spray again. This is what I’ve been do­ing.

Ap­ple scab can only pen­e­trate leaves that re­main wet for sev­eral hours un­der rel­a­tively cool con­di­tions. Un­for­tu­nately, th­ese con­di­tions have hap­pened many times in Tas­ma­nia, es­pe­cially at night- time dur­ing spring and early De­cem­ber. This is why this disease has be­come par­tic­u­larly preva­lent this year.

How­ever, the lime coat­ing is not eas­ily washed off and usu­ally re­mains for sev­eral weeks, de­spite per­sis­tent rain.

In most home gar­dens we can give vul­ner­a­ble ap­ple trees this type of close at­ten­tion. It also means go­ing over the trees reg­u­larly to pick off any dis­eased ap­ples and to prune out all dirty- look­ing leaf- clus­ters.

If we can con­trol ap­ple scab dur­ing early sum­mer there is lit­tle chance of re- in­fec­tion hap­pen­ing once tem­per­a­tures rise above 25C.

Once the disease is elim­i­nated, the trees will not be re- in­fected, un­less ne­glected ap­ple trees are grow­ing nearby.

I should add that lime sprays also pre­vent cal­cium de­fi­ciency, the main cause of ‘ bit­ter pit’ dis­or­der in ap­ples, while spring prun­ing and fruit thin­ning also helps con­trol brown- rot disease.

Lime sprays ap­plied dur­ing De­cem­ber and early Jan­uary are also an ef­fec­tive means of con­trol­ling pear and cherry slug.

This is a slug- like grub that at­tacks and skele­tonises the leaves of cherry, pear, Ja­panese plum, quince, hawthorn and re­lated plants.

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