Protectant and postinfection activity of triforine against ascospore infections of Monilinia vaccinii-corymbosi in lowbush blueberries

The protectant and postinfection activity of triforine against ascospore infections of Monilinia vaccinii-corymbosi was examined in lowbush blueberries. Potted plants were sprayed with a commmercial tractor-mounted air assisted sprayer at rates of 266, 418, and 570 g a.i./ha. Plants were incubated at varying temperatures and inoculated with 5X10(5) ascospores/mL at appropriate times after or before spraying. Time of disease onset and final disease incidence were determined as measures of fungicide efficacy. When plants were sprayed and then challenge-inoculated 1 h later, only trace amounts of disease developed. However, when plants were challenge-inoculated after 4, 8, and 12 d, disease onset occurred earlier and final disease incidence increased markedly, indicating poor protection by triforine. When plants were inoculated and sprayed with triforine 24, 48, 72, and 96 h later, disease onset was delayed and disease incidence was low in the 24- and 48-h treatments, indicating excellent postinfection activity of triforine. Postinfection activity diminished slightly at 72 and 96 h at 12/5 degrees C, but diminished significantly more at 20/5 degrees C. Disease was less in all fungicide treatments compared with the unsprayed controls, and disease control improved with increase in rate of triforine. A trial with simulated rainfall indicated that some of the fungicide was washed from tissues, but a sufficient amount was absorbed even within the first hour after application to give significant disease control. By monitoring infection periods growers should be able to schedule postinfection applications of triforine and likely reduce the number of sprays required in some years.