Symptoms and Control Methods of Spruce Leaf Rust
Spruce leaf rust is distributed in Sichuan, Yunnan, Gansu, Qinghai, **, Taiwan, China and other places. The disease damages Picea likiangensis, Picea asperata, Picea crassifolia, Picea brachytyla var. complanata, Picea linzhiensis, Picea schrenkiana and Picea obovata, etc.
Symptoms: When buds are infected, the needles on the newly grown tender shoots turn yellow or orange-yellow, short and thick; orange-yellow cushion-like telia or blister-like aecia are produced on the diseased leaves; the diseased buds resemble a yellow flower, and soon the diseased leaves turn black and die. On infected 2-year-old leaves, parts turn yellow, and blister-like aecia or orange-yellow cushion-like telia are produced on them.
Pathogen: The pathogen is fungi of the genus Chrysomyxa spp., belonging to Basidiomycotina, Teliomycetes, Uredinales.
Occurrence pattern: The life cycle of the disease varies with different pathogens. Chrysomyxa ledi, Chrysomyxa rhododendri, Chrysomyxa succinea and Chrysomyxa expansa have a long-cycle life history, while Chrysomyxa deformans and Chrysomyxa weirii have a short-cycle life history, with only the telial stage. For spruce leaf rust caused by Chrysomyxa expansa, at the turn of spring and summer, aecia are produced on the needles; after the peridium ruptures, aeciospores are released, and the aeciospores are spread by wind to the leaves of rhododendrons, germinate or invade through stomata, and produce telia on the underside of the leaves. Teliospores do not overwinter; in cloudy and rainy weather, they can germinate to produce basidia and basidiospores. The basidiospores are spread by airflow to the tender shoots of spruce, germinate and invade, and overwinter in the host buds. In the second year, spermogonia and aecia are produced on the needles. Spruce leaf rust in ** has only the telial stage, and the pathogen overwinters in the buds as latent mycelium. In the second year, all needles growing from diseased buds are infected. When teliospores encounter cloudy and rainy weather, they germinate to produce basidia and basidiospores. The basidiospores overwinter latently in the overwintering buds of spruce.
Control: 1. Reduce infection sources: Eradicate intermediate hosts such as rhododendron, Ledum and Camellia plants around the spruce. Prune diseased buds and destroy them in a centralized manner. 2. Chemical control: In late spring and early summer, spraying with fenaminosulf, hydroxyquinoline, sulfur suspension concentrate, 75% chlorothalonil wettable powder and other agents gives relatively good efficacy.