Carrots the biology and control of cavity spot

Five replicated trials were conducted on commercial farm crops during the period 1987-1989. In four trials, carried out in the first 2 years of the project, cavity spot developed at moderate-severe levels. In the remaining trial in 1989 symptoms consistent with those of cavity spot were not recorded, perhaps a reflection of the low soil moisture levels in this very dry season.

Treatment with metalaxyl as Fubol 58WP or Favour 600FW was very effective in controlling the disease at all sites where the disease occurred. Only when the rate of application was reduced to 3 kg(l) product/ha did control deteriorate significantly. There was no advantage in increased water volumes above 500 1/ha or split application treatments. The timing of fungicide application appeared not to be critical. Treatment with metalaxyl immediately post-drilling in February-March or on removal of the polythene cover in May appeared equally effective.

Control of cavity spot with such a late fungicide application conflicts with results from trials on maincrop carrots where treatment 8-12 weeks after drilling is usually ineffective. This aspect of fungicide timing on early crop warrants further investigation as it may offer an opportunity to more fully understands the aetiology of the disease.