Chrysanthemum White Rust
Chrysanthemum White Rust  The chrysanthemum white rust fungus is encouraged by a moist, humid atmosphere. It may persist from year to year on overwintering plants.Susceptible Plants- Chrysanthemum in greenhouses and outdoors. Symptoms- The symptoms of chrysanthemum white rust are very distinct. Light green to yellow spots up to 5mm in diameter appear on the upper surface of the leaf. These spots become brown and necrotic with age . Raised beige to pink pustules form on the underside of leaves beneath the spots. Pustules become white with age. Pustules are most common on young leaves and flower bracts but may form on any green tissue or the petals. Symptoms usually occur during cool, wet weather.
Life Cycle- The disease is brought into the greenhouse on infected plant materials. Infected plants may look normal until correct environmental conditions encourage symptom development. Hot and dry weather may delay onset of symptoms for up to eight weeks. Fungicide applications may suppress disease development.
Chrysanthemum White Rust can also be spread to uninfected plants on contaminated soil, litter, dead leaves, gardening equipment, clothes, shoes, and hands. The fungus only grows and reproduces on susceptible host plants. Chrysanthemum White Rust produces two types of spores. Teliospores are in the pustules on the underside of leaves and remain on the pustule unless they are aggressively brushed off. Teliospores can persist up to 8 weeks on pustules attached to leaves. Teliospores produced basidiospores under moist conditions (96-100% relative humidity for at least three hours). Basidiospores are fragile and short-lived (1 hour or less depending on the humidity) but they are responsible for explosive epidemics under the correct environmental conditions. Infection can occur when temperatures are cool (between 40-73F (5- 23C) with an optimal temperature of 63F( 17C)) and relative humidity is high (96-100%). A film of free water on the leaves is required for infection. Symptom development usually occurs in 5 to 14 days. Prevention and Control- Choose less susceptible cultivars and destroy affected plants. Do not propagate from plants inflicted with chrysanthemum white rust. Oxidate
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