How to prevent and control sclerotinia rot in fingered citron? Detailed explanation of prevention and control methods
Symptoms:It damages the fruit buried in sand during storage. Diseased fruit usually starts at wounds, initially water-soaked, light brown, rapidly expands, soft rot, finally rotting into a pile of mush, and the diseased part produces a large number of black particles, namely the pathogen's sclerotia.
Pathogen:Sclerotinia sclerotiorum (Lib.) de Bary, called sclerotinia, belongs to the Ascomycota fungi. The sclerotia produced on the diseased part are oval to irregular in shape, initially white, later turning black on the outside, measuring 2-5 x 1-3 (mm). On PDA the colony is white, felt-like, with mycelium flat, rough, and growing rapidly. The hyphae are colorless, branched, and produce conidiophores; at the tips of the conidiophores or their branches, small phialides are irregularly clustered, densely bearing colorless, single-celled, minute conidia, measuring only 1.5-3 x 1-2 (μm); after one week, large irregular sclerotia gradually form, initially white and later black on the outer layer.
Transmission routes and disease conditions: It overwinters as sclerotia in the soil, on diseased residues, or mixed in compost. The overwintering sclerotia germinate under suitable conditions to produce apothecia; after the asci mature, when air humidity changes, they shoot the spores from the asci, which spread with the wind and infect surrounding plants. In addition, sclerotia sometimes directly produce hyphae. The hyphae on diseased plants have strong infectivity and become a source of re-infection that expands the spread. The hyphae develop rapidly, causing the diseased part to rot. When nutrients are consumed to a certain extent, sclerotia are produced, and the sclerotia germinate without dormancy. The disease occurs under cooler and humid conditions, with an optimum temperature of 5-20°C, and 15°C being the most suitable. Ascospores can germinate at 0-35°C, with 5-10°C being most favorable. Hyphae can grow at 0-30°C, with 20°C being the most suitable. The temperature for sclerotium formation is consistent with that required for hyphal growth, and sclerotia are killed at 50°C after 5 minutes. The pathogen has strict humidity requirements: in moist soil, sclerotia survive only 1 year; if the soil is waterlogged for a long time, they die within 1 month; in dry soil they can survive more than 3 years, but are not easy to germinate. Sclerotium germination requires high temperature and cool conditions, and after germination the development of the asci requires sufficient moisture for 10 consecutive days. At 70% relative humidity, ascospores can survive 21 days; at 100% relative humidity, they survive only 5 days. In Guangdong it occurs from October to December, causing relatively severe damage.
Prevention and control methods:At the early stage of disease onset, begin spraying 40% carbendazim·sulfur suspension concentrate at 600-700 times dilution, or 70% thiophanate-methyl wettable powder at 500-600 times dilution, 50% carbendazim·sulfur suspension concentrate at 600 times dilution, 80% carbendazim wettable powder at 600-700 times dilution, or 50% iprodione wettable powder at 1000-1500 times dilution, once every 7-10 days, for 2-3 consecutive applications.