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Large crystal pears against black spot
Big fruit crystal pear is a new late-maturing sand pear variety introduced into the city in recent years. However, in cultivation, we found that large fruit crystal pears, such as poor management and vulnerability to melasma, often cause early defoliation and weaken the tree vigor. This in turn affects the quality of the fruit and causes great losses. Therefore, the majority of farmers should attach great importance to it. The disease mainly harms the large fruit crystal pear leaves, new shoots, and pear fruit on the leaking bagging. The earliest onset of young leaves, began to produce brown to dark brown 1 to 2 mm round spots, the edge is obvious, after the spot gradually expanded into a nearly round or irregular shape, the center gray or gray brown, dark brown edges, sometimes with a roulette . The lesions merged into irregularly shaped large lesions for a long time, causing the leaves to scorch and deform, causing early defoliation. When the weather is wet, the surface of the lesion is covered with black mold. When the shoot is damaged, the lesion is oval, black, and slightly concave at the beginning of the lesion, and then expands to a lesion with a long ellipse, light brown, and obvious depression. Diseases and health departments often have cracks at the junction, and the diseased skin is easily broken or dead. Damage to young fruit, initially produced on the surface of the fruit one to several black round spots 1 ~ 2 mm, gradually expanded into a round or near-circular, the color becomes light brown to dark brown, lesions slightly concave. Late fruit deformities, cracks, fruit often fall early. When the grown fruit is sick, its early symptoms are similar to those on the young fruit, but the lesions are larger, dark brown, and the latter is shed. Severe disease, a constant lesion merged into a large lesion, the late dark green surface mold. The highest temperature and the smallest rainfall have the greatest impact on the occurrence and development of melasma. The general temperature of 24 °C ~ 28 °C, while continuous rain, is conducive to the occurrence and spread of black spot. Temperatures above 30°C and continuous sunny days, the disease stops spreading. According to the research of plant protection experts of Hebei Agricultural University, the distribution of conidia in the field is closely related to temperature and humidity. When the temperature reached above 20°C, spores in the field were the most abundant. The peak period of sporulation was from June to July. When the temperature dropped below 20°C after autumn, the amount of spores in the field decreased. Spring spores appear early, while spores appear late. The rainfall and rainy days in the central and southern parts of the province during the period from May to June are relatively low, and the air humidity is relatively low. However, after the wheat harvest, with the increase of rainwater, especially after the rainy season from July to August, it began to have a lot of black spot disease. The conditions that occur. In addition to the above-mentioned meteorological conditions, the author also found through investigation that the severity of the occurrence of large fruit pear pear black spot is closely related to the strength of the tree vigor. The tree vigor is strong and the incidence is lighter; the weaker tree vigor causes more severe disease. In addition, the lack of fertilization in the orchard, partial application of nitrogen fertilizer or excessive amount of results are all conducive to the occurrence of this disease. In order to prevent black spot disease in large crystal pears, comprehensive measures must be taken. 1. Clean orchards reduce the source of overwintering bacteria. The pathogens mainly overwintered with conidia and mycelium on the damaged leaves, diseased fruits and branch shoots. Therefore, the deciduous and fruit drop in the orchard should be removed before the fruit tree sprouts, the diseased shoots should be cut off, the burned ones should be concentrated, and the shoveling agent should be sprayed before germination. 2. Strengthen cultivation management and increase tree vigor. Green manures or organic fertilizers can be added in orchards. Low-lying, poorly-drained orchards should be drained. 3. Spray protection. Before the pears germinate, spray 200 times the mixture of sodium pentachlorophenol and 5 Baume degrees lime sulfur mixture. In order to protect the fruit, it must be sprayed 1 to 2 times before falling into the bag, and immediately after spraying, bagging. In late June (early stage diseased leaf stage) to mid-late August, 5 to 6 fungicides were sprayed to control the disease development. The agent can be used for 1500 times for 50% acetaminophen, 8 times for MDS 80%, 3 times for 3% polyoxin, and 1 :2 to 3:240 Bordeaux mixture. In order to delay the development of drug resistance, acetaminophen and Bordeaux mixture should be used interchangeably.