Evaluation of fungicides and a biocontrol agent against powdery mildew disease of apple

摘要

Ambri apple, an indigenous and highly prized cultivar of delicious apple (Malus domestica) is moderately resistant to apple scab but is highly susceptible to powdery mildew disease.The disease caused by Podosphaera leucotricha (Ell. & Ev.) Salm, is present in all apple-growing regions of the world, where it requires as many as 10 applications of fungicides for control in some countries (10). The disease creates considerable problems because it reduces the photosynthetic area of leaves in young plants, which can severely stunt the growth, and can diminish yield in mature plants. Infected young trees are seriously damaged or become poorly shaped because of retarded vegetative growth or loss of terminal buds. P. leucotricha is an obligate parasite thatoverwinters on apple as mycelium in dormant buds infected during the previous growing season (4). The "primary infection phase" of the disease is initiated by conidia produced on overwintering mycelium at bud break, which infect young leaves, flowers and shoots. Newly formed conidia from these sources are inoculum for the "secondary infection phase", which is the infection of healthy leaves during the growing season (2).