Fungal and bacterial plant pathogens can develop resistance to certain fungicides or bactericides applied for their control. Resistance management guidelines are used to delay resistance development for products that have a high likelihood of selecting resistant pathogen strains.
If resistance develops to a particular product, then other products containing active ingredients in the same mode of action (MOA) group will also be affected.
Eight years ago, Dr Phil Elmer from Plant & Food Research was contracted to assess the efficacy of certain fungicides, with a key finding in his 2019 report stating that there were high levels of botrytis resistance to Prolific®, Pristine® and Rovral® in Central Otago cherries. In addition, there was indications of a shift in efficacy of copper in Hawkes Bay on summerfruit. From this work, resistance management guidelines for the use of fungicides on summerfruit were developed.
If you suspect resistance in your orchard there are testing guidelines on the Summerfruit NZ portal or contact Summerfruit NZ for assistance.
Stephen Ogden (Summerfruit NZ Market Access Manager) monitors changing regulations worldwide to the fungicides and bactericides that we currently use. Seven of the 24 products listed on the Summerfruit NZ PHI chart have a high risk of being removed from use due to global reassessments. Only eight products are rated a low risk.
This season we are facing lower maximum residue limits (MRL’s) for iprodione, (sold as Rovral Aquaflo®, Ippon 500SC® and Rapid 500TM), in some countries as a result of lower Codex MRLs being set. Please see the Portal for the updated PHI's.
Last season Summerfruit NZ’s Fungicide Resistance Management Guidelines were updated and sent to growers as a physical wall chart. This chart and the NZ Market PHI chart detail which FRAC group, read activity group, the fungicides belong to. The Resistance Management chart has information on the appropriate use of each product as does the product label. This chart can be found on the Summerfruit NZ Portal under On Orchard / Resistance Management.
In simple terms the key products should be used at only one part of the season, bloom or pre-harvest, should be mixed with another product from a different activity group, and used in strict alternation. A discussion with your spray representative is highly recommended. As an industry we cannot afford to lose product efficacy, as new control chemistry is slow to be approved through the NZ regulatory pathway.
The R&D programme is testing several biofungicide products for efficacy against the main summerfruit diseases. The programme is also continuing to test fungicides that do not have efficacy label claims, with a view to generating label claim extensions or off-label use guidance for growers.