Managing Brownrot/Blossom Blight Resistance in Stone Fruit
The discovery overseas of Brown Rot (Monilinia fructicola) resistance to propiconazole has some very important implications for Australian stone fruit growers.
Over the last three years, Clemson University in the USA has been collecting Monilinia fructicola samples in an effort to determine whether propiconazole resistance has developed in the field.
Resistant isolates were obtained in the last two years of collection from Georgia.
So why is Georgia observing resistance? In general, the number of propiconazole applications in an orchard determines the sensitivity level of the pathogen population.
This means that the more often you spray propiconazole, or related products, the less effective these sprays are likely to become.
The key message for Australia’s stone fruit growers is, DO NOT depend too much on propiconazole. Have a robust integrated approach to managing disease.
Use propiconazole (a DMI fungicide) as just one element in a program that includes rotation with products from other fungicide groups, and use label rates.
Reduced rates may not provide adequate control, and such practices may actually encourage resistance development.
Attention to good hygiene practices in the orchard and packing shed and other cultural techniques such as removal of infected fruit and pruning out diseased twigs is now even more crucial than ever.
Last season, stone fruit growers received a major boost to their spray programs with the introduction of Agnova’s Chorus. Chorus is a Group I fungicide and controls both Brown Rot and Blossom Blight (Monilinia laxa) in apricots, peaches, plums and nectarines.
Before Chorus, the stone fruit industry only had 2 major effective chemical groups to chose from – the Group B Dicarboxamides (e.g. Roval and Sumisclex), and Group C DMIs (e.g. Tilt and Saprol).
John Read, AgNova Managing Director, recommends that in order to get the best out of this new chemistry, growers should apply Chorus at pink to early bloom and again early to late bloom .
He suggests following up with Tilt or Saprol sprays at Petal fall to shuckfall then again 3 weeks preharvest.
Rovral just pre harvest and then again post harvest would be ideal.
“This program uses the major three chemical groups available to their technical strengths and fits in with
recommendations by AVCARE and industry researchers,” he said.
“Chorus is systemic and rainfast within two hours of application. It rapidly penetrates leaves and flowers and also shows good persistence on plant surfaces.
“Stopping disease at two sites, it helps prevent the fungus from penetrating the plant and also from growing within the plant. Defence from inside creates weatherproof disease protection.
“Chorus is also IPM friendly and rated as harmless to beneficial insects such as earthworms, predatory mites, ladybirds, parasitic wasps and predatory bugs.
“This fungicide is particularly suited to use early in the season because it provides reliable control during periods of high disease pressure, low temperatures or adverse weather conditions.
“The bottom line is that we have to take a very proactive resistance management approach for brown rot control. Resistance status in Australia is at this point in time unknown,” Mr Read said.
He advised Chorus SHOULD NOT be used on cherries.
17-Aug-2006