Big wet ups risk of canola dis­ease

Narrogin Observer - - News - ■ Peter Milne

Cool wet con­di­tions have placed canola at higher risk of Sclero­tinia stem rot this year and grow­ers are urged to mon­i­tor early flow­er­ing crops.

Depart­ment of Pri­mary In­dus­tries and Re­gional De­vel­op­ment plant pathol­o­gist Ravjit Khangura said Sclero­tinia apothe­cia, the minute fun­gal fruit­ing struc­tures of the dis­ease, and basal stem in­fec­tions had been re­ported in the north­ern and south­ern re­gions.

Stu­art Slade, who has about 700ha of canola across three prop­er­ties in Mount Barker, Ko­jonup and Mood­i­ar­rup, has been look­ing for Sclero­tinia for a cou­ple of weeks but is yet to find any.

He finds the fun­gus about every sec­ond year and all his va­ri­eties of canola ap­pear equally sus­cep­ti­ble.

“A lot of it is pad­dock his­tory,” he said.

“We do a lot of trash man­age­ment in burn­ing and try­ing to smash up that stub­ble to kill the schlero in­side.”

Dr Khangura said the best con­di­tions for Sclero­tinia spore re­lease oc­curred three weeks be­fore flower if more than 40mm of rain­fall oc­curs with greater than 75 per cent hu­mid­ity.

“For a sig­nif­i­cant level of stem in­fec­tion to oc­cur, th­ese favourable con­di­tions should con­tinue at least for the next two to three weeks,” she said.

She said canola that had started flow­er­ing or was about to flower was most at risk and may re­quire fungi­cide treat­ment.

Mr Slade said he would use a heli­copter if he needed to spray his canola. He said the most sig­nif­i­cant cost was the chem­i­cals, not the ap­pli­ca­tion, and the down­ward draft of the he­li­copters helped force the fungi­cide down into the canopy.

Dr Khangura said tim­ing was cru­cial to an ef­fec­tive re­sponse; how­ever the risk re­duced if dry weather was fore­cast through­out flow­er­ing.

“If wet and hu­mid con­di­tions pre­vail a few weeks be­fore flower and the fore­cast is for con­tin­u­ous show­ers for the next two to three weeks, grow­ers are ad­vised to spray their crops at 20-50 per cent bloom, if there is a his­tory of Sclero­tinia in the pad­dock and the sur­round­ing pad­docks,” she said.

Two spray ap­pli­ca­tions should be con­sid­ered if grow­ers have high-risk pad­docks, such as those with tight ro­ta­tions, heavy soil types, a dense stand of canola or high rain­fall ar­eas where con­tin­u­ous wet con­di­tions were fore­cast dur­ing flow­er­ing.

Dr Khangura said the re­turn on in­vest­ment from a sin­gle ap­pli­ca­tion of fungi­cide had var­ied be­tween $40-$225 per hectare.

“How­ever, late ap­pli­ca­tions past 50 per cent bloom are off-la­bel and not ef­fec­tive in con­trol­ling dis­ease in most years,” she said.

Depart­ment of Agri­cul­ture and Food canola pathol­o­gist Dr Ravjit Khangura has un­der­taken re­search that shows that the tim­ing of fungi­cide treat­ments to con­trol Sclero­tinia stem rot in canola is cru­cial to pro­tect­ing yields.

Sclero­tinia stem rot.

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