Chemical control of Phytophthora cinnamomi in potted Leucospermum plants
The efficacy of fosetyl-Al (soil drench), metalaxyl-M (soil drench), fluazinam (soil drench) and potassium phosphonate (foliar spray) in controlling Phytophthora cinnamomi root infections of Leucospermum cvv. High Gold, Sunrise and Spider was compared. The Leucospermum plants were potted, placed in a fibreglass tunnel and inoculated. Fungicide treatments began 4 weeks after inoculation. Stem lesion length was measured and the degree of leaf chlorosis as well as root rot were rated at the conclusion of the experiment The pathogen was re-isolated from the root and crown of each plant, and soil baiting and dilutions were done to monitor soil populations of P. cinnamomi. During the 1997 season, metalaxyl-M gave the best control compared with the other treatments. The combination of metalaxyl-M with cv. Spider completely suppressed symptom development. However, during the 1998 season when climatic conditions were favourable for disease development, no differences were observed between the treatments and the control. Cv. Spider had higher tolerance against the fungus even with the most aggressive isolate and during the warmer 1998 season, indicating the importance of combining chemical control with plant resistance. None of the treatments showed any phytotoxicity.