Effects of benomyl, carbendazim, fluazinam and thiophanate methyl on white root rot of avocado

Benomyl, carbendazim, thiophanate methyl and fluazinam were tested in vitro and in vivo for their effects on Rosellinia necatrix. Benomyl, carbendazim and thiophanate methyl at ⩾0.5 μg ml−1 totally inhibited R. necatrix mycelial growth on PDA medium. At 0.1 μg ml−1, carbendazim and fluazinam inhibited growth by 97% and 84%, respectively, in comparison with fungicide-free medium. Benomyl and thiophanate methyl had less effect (53% and 22%, respectively) at this dose. Mycelia treated with fungicide were tested for their capacity to grow when transferred to fungicide-free medium one month after treatment, demonstrating the fungistatic effect of fluazinam in comparison with the other systemic fungicides assayed.The in vivo effects of fungicides on white root rot (WRR) control in avocado plants was studied in two greenhouse experiments with eight sequential applications of fungicides at doses of 0.1% (w/v) and 1% (w/v). Plants were inoculated once with R. necatrix or inoculated twice when plants received an additional dose of inoculum 30 days after the last application of fungicide.Fluazinam was highly effective in the control of WRR as measured by aerial symptoms, plant height increase, dry weight of secondary roots, percentage isolation of R. necatrix from secondary roots and R. necatrix populations in soil. Carbendazim, benomyl and thiophanate methyl were less effective.