Occurrence Patterns and Control Methods of Major Diseases of Atractylodes macrocephala
Ningguo City, Anhui Province is a traditional main producing area of Atractylodes macrocephala, with a planting history of more than 40 years. Because its products are large, thick and of good quality, they are deeply loved by merchants from all over the country. The city's annual planting area of Atractylodes macrocephala is about 90 hectares, with an output value of about 2 million yuan, making it one of the main sources of income for the city's medicinal herb farmers. In recent years, with the continuous expansion of the planting area of Atractylodes macrocephala, the diseases of Atractylodes macrocephala have shown a trend of increasingly severe occurrence year by year, especially damping-off at the seedling stage; root rot and southern blight of the roots and rhizomes at the adult plant stage; and leaf spot disease of the leaves, which has a high incidence rate and causes the most serious damage, bringing relatively large economic losses to medicinal herb farmers.
I. Occurrence patterns and damage characteristics
1. Damping-off: also called stem rot blight, it is the main disease of Atractylodes macrocephala at the seedling stage. The pathogen is Rhizoctonia solani. The pathogen overwinters in the soil or host residues as mycelium or sclerotia, and can live saprophytically in the soil for 2-3 years. When it encounters a suitable host, it can invade and cause damage. Mycelium can also be produced on the diseased part, quickly spreading and expanding to damage neighboring plants. This disease is a low-temperature and high-humidity disease. If low-temperature and rainy weather occurs after early spring sowing, the Atractylodes macrocephala seedlings grow slowly, the tissues have not yet become suberized, and disease resistance is weak, making them highly susceptible to infection. Ungerminated buds, small seedlings and transplanted seedlings can all be affected, resulting in rotten buds and rotten seeds. After the seedlings emerge, water-soaked dark brown lesions appear at the base of the young stems near the soil surface, and quickly extend around the stem. The stem tissue necrotizes and contracts into a thread-like "wire stem". Brown sclerotia resembling small soil particles often adhere to the diseased part. The aboveground part wilts, and the seedlings lodge and die. This often causes seedlings to die in patches, leading to destruction of the crop. Moist leaves close to the ground can also be affected, with water-soaked dark brown large spots appearing at the edges and quickly spreading over the entire leaf.
2. Root rot: also called dry rot, it is one of the important diseases of Atractylodes macrocephala. Soil-borne and seed-tuber-borne pathogens are the sources of infection. During storage of seed tubers, exposure to heat reduces seedling disease resistance, which is the main cause of disease occurrence. When the soil is flooded, the soil texture is heavy, undecomposed organic fertilizer is applied, or nematodes and underground pests cause damage, resulting in poor root development or wounds, the plants are highly susceptible to pathogen infection and disease. The pathogen requires high temperatures, and the disease often suddenly occurs during the middle and late stages of plant growth when the temperature rises and continuous rainy days turn sunny. The disease generally begins to occur in late April, with peak occurrence from June to August. The diseased plant rate is about 20%, and in severely diseased fields it can reach more than 60%. After late August it gradually decreases and tends to stabilize. The symptoms are browning and rotting of the fine roots of the rhizome. It then spreads to the upper fleshy rhizome and stem, forming dark brown sunken rotten spots, and the aboveground part begins to wilt. On the cut surface of the rhizome and stem, the vascular bundles show an obvious discoloration ring. In the later stage, the entire rhizome becomes spongy black dry rot, and the plant dies, being easy to pull out of the soil. It occurs commonly in both new and old producing areas, causing dry rot, stem rot and wet rot, seriously affecting yield and quality.
3. Southern blight: commonly known as "white sugar rot", it damages the rhizome. Contaminated soil, fertilizer and seed tubers are the sources of infection. In the early stage of disease, reinfection occurs through mycelial spread or sclerotia carried by water flow. Diseased plants are first seen in the field in late April, with peak occurrence from June to August. High temperature and rainy conditions easily cause an epidemic. The incidence rate in general fields is about 15%, and in severely diseased fields it reaches more than 20%. After August, the incidence rate gradually declines and the disease tends to stabilize. The symptoms are that the fibrous roots and rhizome on the rhizome turn brown, and the surface of the rhizome is covered with white mycelium, within which milky white or light brown sclerotia can be seen. Sometimes white mycelium can also be seen on the soil surface around the base of the stem of diseased plants, with sclerotia among it. As the disease progresses, the stems and leaves of the aboveground part of the diseased plant gradually wither and die, and the underground rhizome begins to rot, with the rotten rhizome appearing like a "rotten tuber".
4. Leaf spot: called "iron leaf disease" by medicinal herb farmers, it is an important leaf disease commonly occurring in Atractylodes macrocephala producing areas. The leaves prematurely wither due to the disease, leading to reduced yield. The pathogen mainly overwinters as pycnidia and mycelium on diseased residues and seed tubers, becoming the primary infection source for the initial infection the following year. In the following spring, the pycnidia release conidia after encountering water droplets, which invade through stomata and cause primary infection; new conidia are produced on the lesions and continuously cause reinfection, expanding and spreading. Seed-borne infection causes long-distance spread, while rain splash is the main route of short-distance spread. Insects and farming operations can also cause spread. The disease has a long occurrence period, and its epidemic requires high humidity. It mostly begins in late April, with peak occurrence from June to August. When there is more rain and the temperature rises and falls sharply, the disease is severe. The symptoms are that small yellow-green spots first appear on the leaves, then become polygonal or irregular due to the limitation of leaf veins, dark brown to black, with a gray-white center bearing small black dots. In severe cases, the lesions merge with each other and cover the entire leaf, appearing iron-black. Similar brown spots also appear on stems and bracts.
II. Control measures. Because soil, seed tubers, fertilizer and diseased residues carrying pathogens are the fundamental causes of Atractylodes macrocephala diseases, the control of Atractylodes macrocephala diseases must adhere to the policy of "prevention first, prevention more important than treatment, integrated control". On the premise of insisting on soil disinfection and seed and seed tuber treatment, strengthening field cultivation management and improving plant disease resistance can inhibit the occurrence of diseases; once diseases occur, chemicals can be used to seal off and kill the diseased area, control the spread and transmission of pathogens, and reduce losses caused by diseases.
1. Site selection and land preparation: It is advisable to choose virgin land or land where Atractylodes macrocephala has not been planted for more than 4 years, with deep soil layers, facing north from a south-facing position, and well-drained sandy loam mountain land as the seedling and cultivation fields for Atractylodes macrocephala. The selected plot is best a sloped plot with a slight gradient to facilitate water permeability and drainage. For the seedling field, a relatively barren shady slope virgin land or abandoned land with a slope of 10-15 degrees is preferable. If the land is too fertile, the young leaves of Atractylodes macrocephala seedlings are too tender and have weak disease resistance. After the previous crop is harvested, winter plowing should be carried out in time, which is beneficial to soil maturation and can also reduce weed, disease and pest damage. Before sowing, apply sufficient base fertilizer and then plow once more. According to the requirements for seedling or transplanting land, make fine, broken and level beds.
2. Soil disinfection: In order to effectively prevent the occurrence of diseases such as damping-off, before land preparation, spread 50 kg of quicklime powder per mu on the seedling and cultivation land, then plow and harrow finely; before sowing and transplanting, treat the soil with 50% carbendazim or 50% ridomil granules at 1-2 kg per mu; avoid raising seedlings or planting in diseased soil.
3. Seed treatment: Before sowing, select fresh, plump, uniformly mature, disease-free seeds and soak them in warm water at 25-30°C for 24 hours, then remove them, and then dress the seeds with 50% dexon at 0.3% of the seed amount or 50% carbendazim at 0.5%. This can both cause the seeds to absorb water and swell and play a sterilizing role, reducing the occurrence of diseases during the growth period.
4. Narrow-bed seedling raising and timely sowing: First dig perimeter ditches and waist ditches in the seedling field that are 60 cm deep with a bottom width of 40 cm; then make seedbeds 80 cm wide. Between two adjacent seedbeds, dig drainage ditches 30 cm deep with a bottom width of 25 cm, connected with the waist ditches and perimeter ditches. Make the bed surface turtle-backed to facilitate drainage. Sowing is best done from late March to early April. Too early makes the seedlings susceptible to late frost damage; too late, due to higher temperatures, the early suitable growth period is short, the seedlings grow poorly, and they are susceptible to diseases, pests and weeds, resulting in low seed tuber yield. Using narrow-bed seedling raising and short-term sowing can reduce the occurrence and spread of damping-off and other diseases and lower the number of pathogen-carrying Atractylodes macrocephala seed tubers.