How to prevent and control soybean root rot? Detailed prevention and control techniques for Heilongjiang
Root rot occurs commonly in the soybean-producing areas of Heilongjiang Province. In the field, the usual rate of diseased plants is 30%-40%; in low-lying land and continuous-cropping land, the rate of diseased plants can reach more than 70%, and the highest seedling death rate is more than 15%. The eastern region is more severely affected than the western region, with the most severe occurrence in the moist-soil areas of the east. In an ordinary year, the rate of diseased plants in the early growth period of soybean (before the flowering stage) is about 75%, and the disease index is 35%-50%; in rainy years, the disease index can reach more than 60%.
The occurrence of soybean root rot mainly depends on conditions such as the amount of inoculum in the soil, the soil's physical and chemical properties, soil temperature and moisture, and the resistance of the plants. To better prevent and control soybean root rot, prevention and control must be carried out according to these disease-occurrence conditions. Change the previous approach of using chemical agents alone for control, and adopt comprehensive control measures that combine agricultural measures with biological agent control.
1. Avoid continuous cropping and rotate crops scientifically. Because the root rot pathogen is a soil-inhabiting fungus and can live saprophytically in the soil, under continuous cropping conditions the pathogen grows well and reproduces quickly, the amount of inoculum in the soil increases, and the disease is severe. In addition, changes in root exudates, decomposed root stubble, and rhizosphere microorganisms in continuously cropped soybean fields worsen the soil environment, disrupt the normal physiological activity of soybean roots, reduce root physiological vigor, destroy the symbiotic nitrogen-fixing system, inhibit the root's absorption capacity, weaken plant metabolism, and cause the plants to grow slowly. Therefore, the longer the continuous cropping period of soybean, the more severe the occurrence of root rot.
At present, the fundamental way to address the harm of continuous and alternating soybean cropping is to adhere to a system of rotating with gramineous crops for more than 3 years. However, under the current conditions in which farming households are the units of production and operation, continuous and alternating soybean cropping is unavoidable. Therefore, continuous cropping and alternating cropping should be distinguished, continuous cropping should be minimized, and alternating cropping should be used appropriately. When continuous or alternating cropping is used, flatland and second-class lowland with high organic matter content can be selected for planting soybean; continuous cropping can also be only for one year, and corn, hemp, or flax as the previous crop is best for soybean.
2. Select land scientifically according to the soil's physical and chemical properties. Loose-textured soil with good permeability, such as sandy loam, light loam, and black soil, has milder disease than heavy-textured, poorly permeable albic soil and clay soil; fertile soil has milder disease than poor soil.
3. Adjust the sowing date according to soil temperature and moisture. The optimum temperature for soybean seed germination and seedling growth is 20-25°C; when the temperature is below 9°C, emergence is severely affected. Therefore, when the soil temperature at sowing is low, the disease is severe. When soil water content is high, especially in low-lying, moist land, soybean seedlings grow weakly, have poor disease resistance, are easily infected by pathogens, and the disease is severe.
4. Adopt scientific cultivation and tillage methods. Generally, ridge-cultivated soybean has milder disease than flat-cultivated soybean, and soybean cultivated on large ridges has milder disease than soybean cultivated on small ridges. The reason is that ridge cultivation allows intertillage and hilling, making the soil loose, improving permeability, and lowering soil water content; flat land, because the soil becomes compacted and is prone to waterlogging, has high soil water content, which favors pathogen reproduction and root infection, resulting in more severe disease.
5. Choose an appropriate sowing depth. The sowing depth of soybean directly affects the speed of seedling emergence. If sowing is too deep, and especially if the soil temperature is low, seedlings grow slowly, the tissues are tender, and the underground root system is elongated, making the roots easily infected by pathogens and worsening the disease.
6. Adopt a balanced fertilization method. The level of fertilization also has a great influence on the occurrence of root rot. Heilongjiang generally emphasizes phosphate fertilizer while neglecting nitrogen fertilizer, potassium fertilizer, and the application of trace elements, and rarely uses farmyard manure. In continuous and alternating cropping fields, the content of available nitrogen and potassium nutrients in the soil decreases, and the content of trace elements such as boron, zinc, and molybdenum decreases, causing nutritional imbalance and reducing crop disease resistance. Through scientific soil testing and formula fertilization for balanced fertilization, rationally supplementing nitrogen, phosphorus, and potassium fertilizers as well as trace element fertilizers can significantly improve soybean's resistance to root rot. Applying 1000 kg of organic fertilizer per 667 sq m can increase soybean yield by more than 10%.
7. Control insect pests and reduce opportunities for pathogens to invade through insect wounds. Generally, root maggot damage to the roots favors the occurrence of root rot; the higher the rate of insect-infested plants, the more severe the disease, and vice versa.
8. Use reasonable chemical herbicides. If chemical herbicides in soybean fields are applied well, they can play a good role in weed control in soybean fields, but some chemical herbicides, due to improper application methods and doses, can cause herbicide injury to soybean seedlings, hinder seedling growth, and at the same time worsen the occurrence of root rot.
9. Select disease-resistant varieties. High-yield, high-quality varieties with strong stress resistance and mild disease occurrence can be selected. Practice has proved that selecting disease-resistant or disease-tolerant varieties is an effective measure to reduce the impact of continuous and alternating cropping on soybean yield and quality. In addition, different varieties should be reasonably combined, and varieties should be rotated to reduce the harm of continuous and alternating cropping. In particular, varieties such as Suinong 14, Suinong 15, Hefeng 25, and Hefeng 35 have relatively severe occurrence of root rot and cyst nematode disease; varieties such as Suinong 10, Xinhefeng 25, and Kenjiandou 23 can be selected.
10. Increase the sowing rate. For continuous and alternating cropping fields, it is necessary to ensure the number of soybean seedlings, give play to the yield-increasing role of the population, and thereby reduce the extent of yield reduction; the sowing rate should be appropriately increased, generally by 8%-10% more than normal soybean sowing rate, and sowing quality should be improved to increase the number of retained seedlings.
11. Fine tillage. Continuous and alternating soybean cropping fields, especially those continuously cropped year after year, cause the soil to become compacted and hardened, lack a reasonable aggregate structure, and decline in fertility. Fine soil tillage can break the compacted layer, create good soil conditions for the growth and development of soybean roots, and effectively reduce disease and pest damage. In soil tillage, we must adhere to a soil tillage system combining subsoiling, plowing, harrowing, and rotary tillage, with subsoiling as the main measure, and vigorously promote the subsoiling tillage method to improve the soybean growth environment. In addition, after ordinary soybean seed coating agent is used for seed dressing, the efficacy can only last 15-25 days, so intertillage and hilling must be carried out in time. Especially when the underground roots are damaged and even die, intertillage and hilling measures are even more important, in order to promote the formation of new lateral roots at the base of the aboveground stem and to replenish fertilizer and water in time; otherwise, the lack of lateral roots will cause seedling death.
12. Chemical control. Through seed dressing with chemicals, delay the infection period. 35% Duokefu seed coating agent has a short effective period of only 25-30 days; because fungicides have a short effective period, seed coating agents made from multiple fungicides can only protect the main root, protect seedlings, delay infection, and reduce damage. Commonly used methods: (1) Dress seeds with a soybean seed coating agent containing carbendazim, thiram, and insecticide, using 1000-1500 ml of seed coating agent per 100 kg of seeds. (2) Dress seeds with 150 ml of 2.5% Raxil suspension seed coating agent plus 40 ml of 20% Apron seed dressing agent per 100 kg of seeds. The control effect of biological agents is better than that of chemical agents. First, biological control breaks the balance of the microbial community environment in the soil and reduces infection of the roots by harmful fungi; second, the duration of action is long, with an action time of more than 70 days; third, it is highly targeted and has extremely strong inhibitory effects on the main obstacle factors to continuous and alternating soybean cropping - Penicillium purpurogenum and the toxins it secretes, and the soybean root rot pathogen - Fusarium F6. In 2006, a biological seed dressing experiment was conducted on a soybean field with many years of continuous cropping in the Hulin area of Heilongjiang Province over 133 hectares. The seedling death rate with seed coating agent dressing was more than 10%, while the seedling death rate with biological seed dressing was less than 5%. In particular, in a field continuously cropped for 7 years, the seedling death rate with seed coating agent dressing was about 30%, while the seedling death rate with biological seed dressing was about 3%. The method is to dress seeds with 1000-1500 ml of 2% Junkeduke (ningnanmycin) aqueous solution per 100 kg of seeds,