Although resistance to metalaxyl-M has yet to be demonstrated in the main causal organism, Pythium violae, the sustainability of using a single fungicide with a single mode of action is a cause for concern.
HDC project FV 391 focused on quantifying the extent of enhanced degradation of metalaxyl-M at crop sites currently monitored for cavity spot, carrying out initial screening and evaluations of new fungicides and biological treatments for P. violae control, determining optimum timings and doses for promising products, investigating the use of pre-planting calcium applications and determining rates of application and effects on pH and calcium availability.
In year one, low rainfall resulted in low incidence of cavity spot and no control with metalaxyl-M even at the site where no enhanced degradation of metalaxyl-M was observed. But wetter weather in 2012 contributed to cavity spot in more than 55 per cent of roots.
Metalaxyl-M gave good control at one site (64 per cent) although disappointingly none of the novel coded products were effective at the standard rate of application and will be investigated at higher rates in the coming season.
Calcium treatments showed trends for decreased cavity spot at higher rates, with Limex incorporated before sowing giving control at one site.
Horticultural Development Company
For details on all HDC activity, visit www.hdc.org.uk