Abstract
Phytophthora wilt, caused by the root-infecting fungus Phytophthora cinnamomi, is a serious disease of rhododendron. The symptoms of this disease include wilt, dieback, and death of nursery cuttings as well as large plants. The effects of two soil additives, Supersorb (a hygrogel) and Aquagro (a wetting agent), with and without Metalaxyl (Subdue 2E), were assessed on decreasing the incidence of Phytophthora wilt in container grown `Nova Zembla' rhododendron. Rooted cuttings grown in amended or non-amended mix were inoculated with P. cinnamomi. Metalaxyl treatments were applied once at the full label rate of 4 fl oz/100 gal at planting, or twice (at planting and 8 wks later) at 1 or 2 fl oz/100 gal. Trials were conducted from June to September in the greenhouse (1990) and outdoors (1991). Plant growth and disease incidence were evaluated weekly. In both trials, the Supersorb and Aquagro treatments did not affect disease incidence, although they did significantly affect plant growth. All metalaxyl treatments reduced disease incidence significantly when compared to controls.
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