Ap­ply best prac­tice to sti­fle sep­to­ria

Irish Independent - Farming - - Front Page -

THE dif­fi­culty in con­trol­ling ce­real pathogens should not be un­der­es­ti­mated. These or­gan­isms are com­plex and found ways to sur­vive in the wild long be­fore we de­cided we didn’t want them in our cul­ti­vated fields.

Part of any pathogen’s sur­vival mech­a­nisms is to change in re­sponse to an out­side in­flu­ence that stops it de­vel­op­ing and re­pro­duc­ing. These out­side in­flu­ences could be cold, wet con­di­tions, change of cul­ti­var or the ap­pli­ca­tion of a fungi­cide.

Fungi­cides, once dis­cov­ered and in­tro­duced, have a de­fined life of prac­ti­cal use be­fore the pathogen de­vel­ops ways around the fungi­cide’s mode of ac­tion. The use­ful­ness of any fungi­cide is de­pen­dent on how of­ten it is used and how it con­trols the pathogen, ie a fungi­cide re­ly­ing on one mode of ac­tion will have a shorter life than one which con­trols the pathogen in sev­eral dif­fer­ent ways (Stro­bil­urins ver­sus Chlorothalonil).

As an ex­am­ple, if a fungi­cide had a life cy­cle of, say, 40 ap­pli­ca­tions, then if it was ap­plied on av­er­age three times a year, its use­ful life in the field would be around 13-14 years.

Sep­to­ria con­tin­ues as a mov­ing tar­get and it ap­pears the pathogen has shifted again this year. Oak Park duo Dr Stephen Kildea and Dr Eu­gene O’Sullivan have been mon­i­tor­ing changes in sep­to­ria pop­u­la­tions for the past few years and they were among the first sci­en­tists to spot changes and iden­tify trends in sep­to­ria de­vel­op­ment.

The ge­netic trends that oc­curred over this pe­riod es­tab­lished that sep­to­ria had de­vel­oped mech­a­nisms to tol­er­ate more fungi­cide (be­fore, the fungi­cide con­trolled them) and these strains have been classed as mu­ta­tions (S524T, V136A, Y461S). The mu­ta­tions make these sep­to­ria strains harder to kill (or in­sen­si­tive) by pro­th­io­cona­zole and epox­i­cona­zole, there­fore both these fungi­cides are grouped into Group 1-type tri­a­zoles. How­ever, these sep­to­ria strains are eas­ily con­trolled with both tebu­cona­zole and met­cona­zole (Group 2).

The de­vel­op­ment of these mu­ta­tions have not, so far, re­sulted in poor disease con­trol but the most likely ev­i­dence grow­ers will see in the field is re­duced per­sis­tence, ie fungi­cides not con­trol­ling the disease for as long as it nor­mally did.

Sep­to­ria pop­u­la­tions mon­i­tor­ing last year have shown that about half were of the in­sen­si­tive type (or less eas­ily killed by fungi­cide). There­fore, these pop­u­la­tions are in ev­ery field and each grower must ap­ply best prac­tice to min­imise the im­pact of this sep­to­ria. In a high disease year, a grower who only uses a one fungi­cide type (Pro­line, Opus, Rubric, etc) is highly likely to lose yield in com­par­i­son to us­ing al­ter­na­tive groups or adding SDHIbased chem­istry to the mix.

Last year turned out to be a low disease year, thus fungi­cides were not put un­der pres­sure and, in gen­eral, fungi­cides worked well.

The Tea­gasc ad­vice for con­trol­ling sep­to­ria and man­ag­ing in­sen­si­tive strains in win­ter wheat is out­lined in ta­ble 4 (right). The strat­egy is based on keep­ing pop­u­la­tions of in­sen­si­tive sep­to­ria to a min­i­mum through the sea­son.

Ad­di­tional ac­tives may be needed for other dis­eases.

Tri­a­zoles: Group 1: Epox­i­cona­zole; Pro­th­io­cona­zole;

Group 2: Tebu­cona­zole; Met­cona­zole.

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