Efficacy of registered and unregistered fungicides for control of Phytophthora root rot of azalea, 2006

摘要

Evaluation of fungicides with potential for control of Phytophthora diseases has been a priority of the IR4 Ornamentals Program. Registered and unregistered fungicides that included several phosphite salts were compared forcontrol of Phytophthora root rot on nursery grown, potted azaleas grown under 55% shade cloth and sprinkler irrigation (0.9 in. /day). Azaleas were trimmed and transplanted from 2-in. pots on 18 May into 0.75 gal plastic pots containing potting mix (8 pine bark : 1 sand, amended with 5 lb dolomitic limestone/yd3), and allowed to establish. A 6 to 9 moslow release fertilizer (18-6-12) was applied at 0.08 oz/pot. The phosphite salts were applied as foliar sprays to run-off on 1 Jun, 5 days prior to inoculation. On the morning of 6 Jun, two rice grains colonized by P. cinnamomi were placed in each of three holes around the circumference of the pot at a depth of 1.6 in. and covered. In the afternoon, drench applications of the remaining fungicides so listed in the table were made at the rate of 8.5 fl oz/pot. There were seven replications of each treatment arranged in a randomized complete block design. All fungicides were re-applied on a 28-day schedule for a total of three applications. Disease severity was assessed at regular intervals over the season with top weight and root rot ratings taken on 7Sep.