Peter Cun­dall: Guru’s ad­vice for foil­ing fun­gal prob­lems

Re­cent heavy rain­falls are caus­ing many prob­lems for gar­den­ers from leafcurl in nec­tarines to more se­ri­ous fun­gal dis­eases such as ap­ple and pear scab, writes PETER CUN­DALL

Sunday Tasmanian - Tassie Living - - NEWS -

Fun­gal dis­eases of ev­ery kind are now caus­ing se­ri­ous prob­lems in all parts of our Tas­ma­nian gar­dens

Let’s face it, this spring’s per­sis­tent rains have pro­duced pos­i­tive re­sults. Farm dams are now brim full, the growth in most gar­dens has been phe­nom­e­nal and many mois­ture-lov­ing fruit trees, es­pe­cially pear, ap­ple, plum, cherry and apri­cot have clearly been thriv­ing be­cause of ex­tra mois­ture in the soil.

Un­for­tu­nately many neg­a­tive as­pects of heavy rains and sat­u­rated soils are also ap­pear­ing and the re­sults can be dev­as­tat­ing. Fun­gal dis­eases of ev­ery kind are now caus­ing se­ri­ous prob­lems in all parts of our Tas­ma­nian gar­dens.

Any­one grow­ing peach or nec­tarine trees will al­ready be see­ing the de­struc­tion caused by leafcurl. Once fo­liage has been in­fected it is too late to spray for con­trol. All we can do is pick off all dis­torted leaves on which the leafcurl fun­gus has started to bloom, leav­ing the youngest, healthy leaves un­touched.

Other se­ri­ous fun­gal dis­eases now in­fect­ing some fruit trees have been en­cour­aged by rain­falls late in the day or at night. They cause leaves to re­main wet for hours, al­low­ing dis­ease or­gan­isms to gain ac­cess to fruit and even young shoots.

Ap­ple and pear scab are se­ri­ous fun­gal dis­eases and both op­er­ate the same way. Par­a­sitic spores arise from the dis­eased re­mains of last sum­mer’s leaf and fruit de­bris, still ly­ing be­neath trees.

The spores set­tle on leaf sur­faces but can­not pen­e­trate un­less con­di­tions re­main wet for sev­eral hours. That’s why evening and night rain­falls can be so deadly. Later the dis­ease or­gan­isms move on to im­ma­ture, de­vel­op­ing fruit caus­ing un­sightly scabs, which in turn make ap­ples or pears be­come dis­torted and ined­i­ble.

Dur­ing the day, even an odd shower does lit­tle harm be­cause leaves dry off

dur­ing warm, sunny pe­ri­ods mak­ing it dif­fi­cult for the dis­ease to pen­e­trate.

Dis­ease con­trol is also why we prune trees, shrubs and roses to open up over­crowded canopies to al­low dry­ing air to cir­cu­late freely, pre­vent­ing in­fec­tion.

Scab dis­eases pre­fer the slightly acidic sur­face of leaves in or­der to sur­vive and thrive. I’ve found rea­son­able con­trol can be achieved by mak­ing leaf sur­faces al­ka­line and unattrac­tive to scab or­gan­isms.

I do this by spray­ing all the fo­liage with lime wa­ter – noth­ing more than a big, dou­ble-hand­ful of fine, white builders’ lime mixed into a large bucket of wa­ter.

When sprayed over the trees, the mix­ture dries off so leaves be­come heav­ily spot­ted with white lime. To get the spray over the tops of large tree canopies I slide a 2m long piece of con­duit over part of a hose to stiffen it. A spray­ing de­vice is then at­tached with a tube linked to the bucket of lime wa­ter. This al­lows me to use nor­mal wa­ter pres­sure from a tap which also sucks up the lime mix­ture to ef­fec­tively cover all leaves.

The builders’ lime does no harm to the trees, but even pro­vides cal­cium while also help­ing con­trol pear and cherry slug, also a se­ri­ous pest of hawthorn, quince and Ja­panese plums,

The other fun­gal dis­ease spread by rain is quince ‘fleck’. This too re­sults from spores aris­ing from last au­tumn’s de­bris. The fun­gus first shriv­els leaves, then at­tacks the fruit caus­ing it to turn black and split.

Quince trees pre­fer acidic soils so I avoid us­ing lime wa­ter. In­stead I prune off all leaves and small branches show­ing early signs of in­fec­tion. It also helps to pre­vent the dis­ease spores from ris­ing if thick lay­ers of over­lap­ping newsprint are spread be­neath quince trees, ex­tend­ing from the trunks to well be­yond drip-lines.

The newsprint is wet­ted and weighed down with sheep ma­nure, blood and bone or pel­letised poul­try drop­pings.

Fi­nally they are cov­ered with a heavy mulch of straw. This or­ganic ma­te­rial seals in mois­ture, then grad­u­ally rots away dur­ing sum­mer to grad­u­ally en­rich the soil.

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