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Apple anthrax
Apple anthracnose, also known as bitter rot or late rot, primarily affects the fruit but can also infect branches, twigs, and other parts of the tree. This disease is widespread in apple-growing regions across the country. In summer, high temperatures combined with heavy rainfall—particularly in provinces like Jiangsu, Anhui, Henan, and Hubei—lead to severe outbreaks, significantly impacting both yield and fruit quality. In areas where the trees are highly susceptible, the damage can be devastating. For example, Shandong, Hebei, and Liaoning have suffered major losses in rainy years, while the disease tends to be less severe in Shanxi, Gansu, and Jilin.
Symptoms of the disease typically appear on the fruit surface as large, dark, round spots that start small and gradually expand. The lesions have clear edges and become soft and brown as they develop, causing a bitter taste and deepening into the fruit. Over time, the affected area forms concentric rings of dark and light coloration. When the lesion reaches about 2 cm in diameter, it develops conidial discs—initially dark brown and later turning black, arranged in a circular pattern. These black spots eventually break through the skin, especially during wet weather, when bluish-red mucus containing spores emerges. As the conidial discs form, the inner flesh turns dark brown. A single lesion can cover up to one-third to one-half of the fruit's surface. Infected fruits may have several to dozens of lesions, with dry spots ranging from brown to dark brown. Lesions grow slowly at first but accelerate as the fruit approaches maturity, often reaching half the fruit size within 7–8 days, leading to significant fruit drop.
On branches, the disease usually starts at the base of pests or thin branches. Early symptoms show irregular dark brown spots that enlarge, causing ulcers, cracking, and exposure of the xylem. Severe cases lead to the death of branches above the infected area. Black protrusions and small particles also appear on the diseased surface. Under controlled indoor conditions, red conidial masses can develop within 7–9 days. In orchards, infections often begin from the top of the tree, spreading downward. Severely affected fruits lose their ability to produce new shoots, resulting in drying and death.
The main pathogens responsible for anthracnose are fungal hyphae that remain dormant on pests, stems, and dead fruits. The optimal temperature for mycelium growth is 28°C, with a maximum of 40°C and a minimum of 2°C. Due to the latent nature of the infection, the incubation period varies by species and season, sometimes lasting up to 50–60 days. In Zhengzhou, Henan, the incubation period for the most vulnerable red-wringed variety is 9–11 days in May, 6–8 days in June, 4–5 days in July, and just 2–3 days in August.
During the next growing season, when suitable temperature and humidity conditions occur, conidia are produced and spread via rain and insects, becoming the primary source of infection. Conidia can directly infect the fruit, and high temperatures promote spore germination. Under favorable conditions, spores can penetrate the fruit flesh within 5 hours and complete the invasion process in 10 hours. The disease continues to spread throughout the growing season and persists until late autumn. The pathogen can infect fruit before harvest and continue developing during storage, transportation, and sale, though it rarely spreads during storage. The latent infection characteristic means that early fruit invasion occurs during the fruit-filling stage. High temperature and humidity are key factors in disease outbreaks, making the disease more severe in hot and rainy regions.
Control methods include strengthening cultivation practices such as deep plowing, timely drainage, increasing organic fertilizer, avoiding excessive nitrogen, and enhancing tree vigor to improve resistance. Regular weeding and pruning help reduce humidity and improve air circulation and light penetration. Removing diseased material—such as dried branches and fruits—is essential. Applying fungicides before bud emergence helps eliminate overwintering pathogens. Experience shows that trees treated with a shovel-removing agent can delay disease onset by 15–30 days, effectively controlling its spread.
During the growing season, protective fungicides like Bordeaux mixture and tetramycin are commonly used. In areas with severe outbreaks, Bordeaux mixture is applied early, followed by tetramycin in mid-season and Bordeaux again later. Application timing typically includes 1–2 sprays of 1:2–3:200 Bordeaux mixture 5–6 months before harvest, 1–2 sprays of 50% wettable powder at 600–800 times dilution from mid-June to early July, and 2–3 sprays of Bordeaux solution after mid-July. If heavy rain occurs between May and June, fungicides should be applied earlier. Proper storage management is also crucial, including removing diseased fruits before storage and controlling temperature. Regular inspections are necessary when temperatures rise to quickly identify and remove any infected fruits.