, Volume 20, Issue 1, pp 21-26

Effect of metalaxyl and phosphonate on incidence of cavity spot in carrots

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A single application of metalaxyl to commercial carrot beds at rates between 0.43–2.14 kg/ha from 4 to 14 weeks after sowing, consistently reduced incidence of cavity spot. A single spray of phosphonate on beds at rates from 8–16.5 kg/ha up to 10 weeks after sowing had no effect on incidence of cavity spot. In one trial, phosphonate at 25 kg/ha applied 12 weeks after sowing reduced incidence of cavity spot. Seed dusting with 1.5–6.0 g metalaxyl/kg seed increased seedling survival but reduced root weight at harvest, probably due to increased competition between plants. Pythium ultimum was the most commonly isolated Pythium species from soil and Phytophthora megasperma was also isolated from field soil at the experimental site. Both these fungi were relatively insensitive to phosphonate in vitro.