Cause Analysis and Countermeasures of Baisha Loquat Disease

Cause Analysis and Countermeasures of Baisha Loquat Disease

Jiangsu Province has a long history of loquat cultivation, with more than 40 loquat varieties and obvious advantages in germplasm resources. in 2016, the province covers an area of more than 28000 mu of loquat, of which Dongting Mountain in Suzhou is 23000 mu, accounting for 82% of the total area of the province. Historically, it is one of the four key loquat producing areas in China, mainly varieties Baiyu, green seed, Guanyu, etc., excellent varieties, rich experience of fruit growers.

Loquat is evergreen all the year round, blossoms in winter and lasts as long as three months. the fruit is ripe in late spring and early summer, which is the off-season of fresh fruit, so it is a characteristic fruit tree in leisure agriculture. In recent years, through the adjustment of fruit industrial structure in Wuzhong District of Suzhou City, loquat has become the largest fruit in Wuzhong District, with rising industrial benefits, accelerated industrialization process and continuous expansion of industrial functions.

However, with the rapid development of loquat in the past two years, the whole adult tree has died sporadically, and the disease is becoming more and more serious. After the author's in-depth study, the causes are analyzed and the prevention and control countermeasures are put forward.

1 the invasion of bad weather

The first was the extreme low temperature of-.6 ℃ on January 24-26, 2016, which, according to meteorological data, was the lowest in nearly 30 years (the lowest temperature recorded in 1969 was-8.7 ℃), which dealt a fatal blow to old loquat trees. Secondly, natural disasters such as Rain Water in the Huangmei season in early July and 40 days of high temperature and drought from July to August occurred frequently, resulting in serious disasters to fruit trees in our region, especially in Dongshan and Jinting towns. if the tree is weak, the tree will die, and the most serious one is loquat (figure 1). The main reasons are: Rain Water, water in the soil is saturated for a long time, the root system is anoxic for a long time, resulting in fibrous root (absorbing root) necrosis, tree potential is extremely weak, coupled with the continuous high temperature and drought in August, aggravated the death of the tree. Among them, the old loquat areas such as Bingchang, Luo Hanwu and other old loquat areas in the national one-village and one-product loquat demonstration village are prominent due to the aging of trees, the ability to resist waterlogging, drought and high temperature is obviously weakened, and the phenomenon of loquat tree death is more prominent.

Fig. 1 the whole loquat tree died

2 harm of two major diseases of loquat

Loquat has a variety of diseases and insect pests, the main diseases causing loquat tree death are white feather disease and white silk disease, these two diseases are soil-borne diseases, the disease site is in the root and root neck, the first formation of white hyphae in the root neck, the mycelium invaded the xylem, resulting in the whole root rot, and then led to the death of the whole plant. The two diseases spread closely in the orchard, mainly by sclerotia transferred with Rain Water or irrigation water, but also by hyphae (figure 2) [Jishan Huayao]. When the tree is weak, it is easy to be infected and cross-invaded, and it is easy to get sick in the high temperature and rainy season and poor ventilation, resulting in the death of the whole plant and even causing devastating losses to the loquat planted in pieces. it is one of the urgent problems to be solved in loquat production at present.

2.1 White stripe disease

Loquat white stripe feather disease is widely distributed and occurs in both new and old producing areas. It mainly harms the root and the root neck. after the bacteria infect the root, white hyphae are formed at the root tip, and brownish mycelium and mycelium are formed on the old root or main root, which can sometimes fill the gaps in the soil (figure 3). Black sclerotia can grow on the mycelial layer. The hyphae penetrated through the cortex and invaded the xylem, causing the whole root to rot. The aboveground parts of diseased trees are as follows: delayed germination, thin new shoots, slow growth, and easy to wither in sunny days. In severe cases, the old leaves yellowed and fell off until the whole plant died.

Disease regularity: bacteria are mainly transmitted by soil contact, which is usually caused by soil bacteria. In orchards with poor drainage or loquat trees planted too deeply, the disease is more common in old trees than in young trees, and the disease is more common in orchards with heavy soil than in sandy soil.

Fig. 2 mycelial spread around the diseased plant

Fig. 3 soil infection mycelium of loquat tree root

2.2 White silk disease

White silk disease, also known as stem base rot, occurs mainly in the root neck of adult trees or seedlings, and the most common disease is 5cm to 10cm from the ground. In the early stage of the disease, white hyphae formed on the surface of the root neck, and the epidermis showed water-stained brown spots. The hyphae continued to grow until the root neck was completely covered with a silk-like white mycelium layer. As the disease develops further, the cortex of the root and neck decays and spills over brown juice. The aboveground parts of diseased trees are as follows: the leaves become small and yellow, the branches shorten, and the fruit is more and smaller; after the disease spot surrounds the trunk, the diseased tree will suddenly die in summer.

Disease regularity: the pathogen overwintered with mycelium in the neck of diseased tree root or in soil with sclerotia. Under natural conditions, sclerotia can survive in the soil for 5 to 6 years. The bacteria spread in close range in the orchard, mainly by sclerotia transferred with Rain Water or irrigation water, but also by hyphae. Long-distance transmission is through infected seedlings. The incidence of loquat trees is higher in orchards with heavy clay and poor drainage and loquat trees planted too deeply. It is easy to get sick in the hot and rainy season.

(3) improper cultivation methods

Improper cultivation is also one of the root causes of tree decline and death, mainly as follows: first, do not pay attention to pruning. Without pruning for a long time, the tree structure is disordered, the tree potential is weak, and diseases and insect pests are easy to occur. Second, the cultivation density is too high. Cultivation is too dense in many places, especially in the old areas, such as the Luohanwu area of Bingchang Village. High-density cultivation will inevitably affect the ventilation and light transmission of the tree, resulting in closed trees and vulnerable to diseases and insect pests. Once some adverse climatic conditions are encountered, it is very easy to weaken or even die; third, it is related to the long-term application of chemical fertilizer. Many fruit growers do not pay attention to the application of organic fertilizer and often use some chemical fertilizers repeatedly, resulting in the change of soil pH value. In addition, it is also related to the long-term use of herbicides in the soil; fourth, improper fertilization methods, due to labor reasons, fruit farmers plan to save trouble and directly spread on the surface of the soil, autumn and winter also lack of soil deep turning this link, resulting in loquat root floating, drought resistance and other abilities weakened.

4 prevention and control countermeasures

4.1 strengthen cultivation management

To increase the application of organic fertilizer to promote the growth of trees, promote the development of roots and improve the disease resistance of plants, orchards should do a good job in lowering the groundwater level and drainage.

4.2 when replanting, do a good job of soil disinfection or soil replacement

It is best not to plant loquat in the pit of newly cut diseased plants. if you want to plant, you must clear the rotten roots, mix the soil with lime, spray carbendazim, exposure and other thorough disinfection before planting, and the conditional roots should be planted with new soil to prevent soil-borne diseases. Deep furrow and high border cultivation should be carried out in flat orchards.

4.3 reasonable shaping and pruning to enhance ventilation and light transmission

Keep a reasonable spacing between plants. Reasonable shaping and pruning, increase the ventilation and light transmission conditions of the tree, and reduce the humidity in the orchard.

4.4 dig up the diseased tree and destroy it in time

To avoid bark trauma as far as possible, diseased trees should be dug up in time and concentrated burning or deep burial, and trench isolation to prevent infection.

4.5 Chemical control

When symptoms appear in the upper part of the tree, remove the soil near the main root at the base of the trunk to dry, look for the site of the disease, scrape off the spot on the neck of the root thoroughly with a knife, disinfect the wound with 1% copper sulfate solution, and then cover it with Bordeaux pulp. then cover the new soil, at the same time in the periphery of the diseased tree, dig isolation ditches, isolate the disease area, and prevent spread to the outside. 50% methyl topiramate wettable powder 300 × 500 times was used to drench the roots of trees that had and may be affected by the root.

4.6 change the way of fertilization

The surface layer is ditch or ring-shaped deep application. The whole garden is turned deep in autumn and winter, combined with the application of mature organic fertilizer.