Causes and control techniques of kiwifruit root rot disease

Causes and control techniques of kiwifruit root rot disease

Wang Xiaoshuang

The root system of kiwifruit is fleshy, and its water content is high and the respiration is strong. Kiwifruit root rot is usually caused by high soil moisture content or compaction, heavy sticking and disease. In this regard, the majority of growers should attach great importance to it and take effective measures to prevent and control it.

1. The soil water content is too high

(1) Causes

Kiwifruit is a vine fruit tree, compared with other fruit trees, its leaves are thinner and larger, the leaf area is larger, the respiration is stronger, the water transpiration is also larger, and the water content of fleshy roots is more than 80%, so it has a higher water demand. However, due to its shallow root system and fleshy roots, it likes water and avoids stagnant water, and is a fruit tree that is not tolerant to moisture. Under normal circumstances, the soil moisture content of the orchard is about 65%, which is suitable for the normal growth and development of kiwifruit trees; if the soil moisture content is less than 65%, the growth of its roots will slow down or even stop; if the soil moisture content is higher than 65% and continues for a considerable period of time, the water will block the capillary pores of the soil, which will make the root water content in a saturated state, block the normal respiration of the root system, and make the root cells lack oxygen, resulting in root rot, leaf yellowing, Wilting, even a large amount of shedding and branches dry up, the fruit often stops growing or falls off early, and in severe cases, the whole fruit tree can die.

The groundwater level is high or low-lying, the drainage is not smooth, the irrigation is too frequent, the water volume is large, the soil is too sticky, the permeability is poor, and when the rain and water accumulation are serious after autumn, the kiwifruit tree is more prone to root rot and even dead trees.

(2) Main management techniques

1. Scientific irrigation. It is necessary to ensure that there is sufficient water supply after the application of basal fertilizer and top dressing, before and after germination and fruit expansion, and also to ensure that the soil of the orchard is moist in other normal growth periods and cannot be affected by drought. In summary, irrigation must normally be in place by June to meet the soil moisture needs without saturating the orchard soil for a long time. After June, water should be controlled as appropriate. Flood irrigation is prohibited, and it is best to water in batches. Water-saving irrigation methods such as sprinkler irrigation and drip irrigation are recommended to help you know the right amount of water and avoid waste.

2. Ensure that the orchard has a smooth drainage system, so that the orchard will not be waterlogged due to stagnant water, resulting in rotten roots and dead trees.

Second, the soil compaction is serious

(1) Causes

1. Some fruit farmers are still using a large number of chemical fertilizers and ignoring the application of organic fertilizers and biological fertilizers, resulting in a serious lack of organic matter and beneficial microbial flora in the soil, blocked soil pores, and poor air permeability, which in turn causes root rot due to poor root respiration and lack of oxygen.

2. If the kiwifruit seedlings are planted too deeply, it will also cause their roots to rot.

(2) Main management techniques

The sandy loam soil with pH of 7~8 and good permeability, fertile and loose and rich organic matter content is suitable for planting kiwifruit. Kiwifruit is a fleshy root, therefore, its root system has poor soil penetration and large respiration, at this time, the soil compaction is serious, low-lying plots prone to water accumulation, and the groundwater level is high, are not suitable for cultivating kiwifruit. Based on this, the following points should be done:

1. When building a garden, you must choose a sandy loam plot with fertile soil, loose soil, high organic matter content, neutral slight acidity and drainage and irrigation conditions.

2. Pay attention to the application of organic fertilizer and biological fertilizer, and avoid blindly applying a large number of chemical fertilizers, so as to improve the organic matter content of the orchard soil and ensure that it is loose and breathable.

3. Implement the high ridge cultivation mode, when planting kiwifruit trees, it must not be too deep, and the suitable planting depth should not exceed 20 cm, and the grafting joint part should be 5~10 cm higher than the ground.

3. Disease and rotten roots

The diseases that cause the root rot of kiwifruit are generally transmitted by the soil, and some of these diseases are carried by the seedlings purchased when the orchard was established, and if they are not strictly quarantined and disinfected, these seedlings themselves may carry a variety of soil-borne diseases; In addition, if the stubble of the kiwifruit orchard is a nursery or other orchard, and the soil is not disinfected before the kiwifruit is planted, there are a variety of soil-borne diseases that can also cause root rot in the kiwifruit.

(1) Root rot

1. Harmful symptoms. The disease is a fungal disease, the pathogen is a small dense ring fungus, which occurs in various kiwifruit producing areas in the mainland, which can cause rot of rhizomes and underground roots, and if the disease is severe, it can make the whole fruit tree die. Normally, in the high temperature and rainy season, small mushrooms with light yellow umbrella-shaped clusters can often be found on the ground near the rhizomes and diseased roots of infected kiwifruit, which are the fruiting bodies of their pathogenic bacteria. Most of them start from the cortex of the rhizome of kiwifruit trees, and at the beginning of the occurrence, water-stained yellow-brown lesions can be seen, and then gradually turn into brown rot as the disease progresses. If it is not properly controlled, it will quickly spread to the main root and lateral roots, causing the root system to rot and overflow brown sap, smell like distiller's grains, and often grow a white hyphae between the cortex and xylem. The aboveground part is characterized by slender branches, small and yellow leaves, and weak growth, if the disease is severe, it can cause the leaves of kiwifruit to turn yellow and fall off, and the tree body wilts and dies.

2. Regularity of occurrence. The pathogen overwinters in the root tissues of infected fruit trees with mycelium and fungal cords, or in orchard soil with diseased residues, and can infect healthy roots in the following year. Healthy roots can also be infected if they come into contact with diseased roots or diseased tissues, and the germs can be spread through labor tools, underground pests, and irrigation and rainwater. In the high temperature and rainy season from July to September in Piyang County, the peak period of the disease occurred. The disease is often more severe in sandy loam orchards, orchards with unscientific fertilizer and water management and extensive management.

3. Prevention and control technology. First, to build a kiwifruit orchard, it is necessary to choose a plot with rich organic matter content and strong permeability, and complete drainage and irrigation facilities; avoid too deep when planting seedlings; if there are residual stumps and stumps, they must be properly disposed of in a timely manner. Second, because root rot is a soil-borne disease, it is recommended to apply sodium pentachlorophenol 150 times solution to disinfect the soil before kiwifruit planting. In the early stage of the disease, it is recommended to apply 200 times of 4% pesticide resistance 120 water solution or 200~400 times of 80% zebsen zinc wettable powder for root irrigation.

(2) Rhizobia

1. Harmful symptoms. Rhizobia, also known as root cancer, is the pathogen of soil tumemocarcinoma, which is mainly harmful to the rhizomes and roots of kiwifruit. When the root system is first infected with the disease, the epidermis can produce milky white fleshy tumors the size of soybean grains, and as the tumors swell, their color tends to gradually darken to brown to black-brown, the surface is rough or uneven, and the texture gradually changes from fleshy to woody. The diseased kiwifruit plant can not develop normally due to the root system, fewer capillary roots, and weakened function, resulting in the gradual weakening of the tree, the leaves are yellow and small, and the leaf and fruit fall are serious.

2. Regularity of occurrence. The root of rhizobia usually overwinters in the cortex of diseased root tissues, and can also overwinter in the soil of orchards with diseased residual tissues (which usually survive for more than one year), and the roots and bacteria in the soil of kiwifruit infection are the main sources of infection in the second year. Farming operations, wounds caused by pests, and grafting joints are the main channels for the invasion of pathogens, which are generally transmitted through underground pests, rainwater, and irrigation water. The disease is often more severe in orchards with alkaline soils, serious soil compaction, poor drainage due to poor management, rampant underground pests, and more tree wounds caused by orchard farming.

3. Prevention and control technology. The first is to try not to use the previous crop for the forest nursery or other fruit trees as an orchard, do not use the seedlings in the diseased area, and find the infected plants in the seedlings, which should be destroyed in time, and disinfect other seedlings in the same batch (the seedlings can be soaked in 2% lime solution for 1~2 min or 0.1% mercury water for 3~5 min). Second, once the fruit tree is found to be susceptible to the disease, the disease can be completely removed after the root soil is picked up, and then the wound is evenly smeared with 5% bacterial poison water agent 30~50 times or 3~5 °Bé stone sulfur mixture or 100 times of bacterial water killer and other agents;

(3) Phytophthora disease

1. Harmful behavior. The pathogen of the disease is Phytophthora phytophthora, a variant of fungi, mainly for the root system of kiwifruit, usually from the wound of the rhizome into the invasion infection, kiwifruit susceptibility in the early stage, its rhizome appears a week like a water-soaked lesion, gradually expand and become dark brown irregular, can cause the cortex rot and necrosis of the rhizome week, its xylem will also become dark brown, with obvious distiller's lees smell. Due to the damage of the transport tissue, the growth of the aboveground part is retarded due to malnutrition, and the leaves are yellow and small, which can eventually cause plant death.

2. Regularity of occurrence. Phytophthora overwinters in the soil of orchards. The disease is more likely to occur in orchards with severe soil compaction, poor permeability, high water content, high humidity or waterlogging, and in high temperature, high humidity and rainy seasons. If the seedlings are planted too deeply, the root respiration is obstructed and the lack of oxygen is also easily induced due to poor soil ventilation. Production tools and rainwater are the main routes of transmission of Phytophthora fungus, and can also be transmitted through wounds after root bites by underground pests such as grubs and ground tigers, as well as wounds from frostbite near the ground. Normally, the disease begins to occur in late spring and early summer, and the peak of the disease occurs from July to September during the hot and rainy months, and the disease stops in autumn due to the gradual decrease in temperature and humidity.

3. Prevention and control technology. The first is to choose fields with high organic matter content, loose and fertile, low groundwater level, not easy to accumulate water and good drainage and irrigation conditions to build gardens. Second, when planting seedlings, the grafting joint must be 5~10 cm higher than the ground, and it is advisable to adopt a high ridge shallow planting method, and the watering must be uniform to avoid the orchard soil from drying out and wetting suddenly. Thirdly, at the initial stage of the disease, the root soil of the fruit tree was removed to dry and the diseased tissue was completely scraped, and then 0.1% mercury solution was applied for disinfection. Fourth, when applying base fertilizer in autumn, it is forbidden to apply sheep manure, cow manure, pig manure and human feces that are not completely decomposed, because these undecomposed manure contains more miscellaneous bacteria and will become the source of infection of the disease.