Apple brown spot

Apple brown spot is a fungal disease that primarily affects the leaves of apple trees, but it can also infect fruits and petioles. The disease is caused by the pathogen *Spilocaea pomi* and can significantly impact tree health and fruit quality. **Symptoms:** The disease typically begins on the lower, inner parts of the canopy. Initially, small brown spots (0.2–0.5 mm in diameter) appear on the leaves. These spots are often solitary or clustered. As the infection progresses, the lesions expand into round, dark brown areas with a yellow margin and a green halo. In the center, black spores (conidia) form in a rosette-like pattern. Some lesions may take on a lance-shaped or irregular form, spreading radially from the initial spot. Over time, the infected leaves turn yellow, while the underside remains green and brown. The lesions are generally smaller than lenticels, making them easy to distinguish. **Infection Cycle:** The pathogen survives the winter in infected fallen leaves on the ground. In spring and summer, it produces conidia and ascospores, which are spread by wind and rain. The spores usually enter the leaves from the underside, with an incubation period of 6–12 days. In dry years, this period can extend up to 45 days, and higher temperatures tend to shorten it. From infection to leaf drop, the process takes about 13–55 days. The disease typically starts in May–June, peaks between July and August, and declines by October. **Favorable Conditions:** The disease thrives in winters that are not dry and in springs with early, heavy rains. Years with advanced and prolonged rainy seasons see more severe outbreaks. Younger trees of the same species are more resistant than older ones. Fruit-bearing branches tend to be more susceptible than non-fruiting ones, and the lower part of the canopy experiences earlier and more frequent infections. This is likely due to poor air circulation, low light, and high humidity in the inner canopy. **Control Methods:** 1. **Cultural Practices:** Improve tree vigor through proper cultivation, including good drainage for heavy soils and maintaining appropriate soil moisture. Prune trees to improve air circulation and light penetration, reducing disease risk. Remove and destroy fallen leaves in autumn and winter to eliminate overwintering sources of the pathogen. 2. **Chemical Control:** Apply fungicides such as 1:2:200 Bordeaux mixture, 30% mancozeb wettable powder at 500–600 times dilution, 70% mancozeb WP at 500–600 times, or 50% thiophanate-methyl suspension at 500 times. Other options include 64% fosetyl-aluminum WP, 80% antibacterial agent 402 EC, and 60% carbendazim ultrafine powder. Spraying should begin after flowering, with applications every 20 days for 3–4 times. Adding adjuvants like 0.5–1% soy milk or "6501" adhesive at 1000 times dilution can enhance spray coverage and effectiveness. By combining cultural and chemical strategies, growers can effectively manage apple brown spot and protect their orchards from significant losses.

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