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1. Symptoms and Pathogenesis of Asparagus Stem Blight 1. Infected stems of pathogenic bacteria in the early stage of onset of symptoms, forming a spindle-shaped dark brown spot, spotted spindle-shaped or short-lined, surrounded by hydrophilic edges, showing edema. Subsequently, the lesions spread irregularly and gradually expanded. The center was sunken and auburn. The spots finally turned gray and white, and many small black spots were spotted on them, namely the conidia of pathogens. One week after the diseased spot passes around the stem, the infected stems and branches will die and die.
2. Pathogenesis The pathological pathogen of Asparagus stem blight is Asparagus stem mold. The pathogenic bacteria lived on the diseased plants or in the soil as conidiospores. In the following year, spores fly out of the spores through rainwater, tillage tools, and other means of transmission. After the initial infringement of the tender, the spores released from the mature conidia are flushed out by the rain, and are splashed with rain and rain. A secondary infection of the base of asparagus stems. The pathogen is most likely to invade when the stem is young, and the infection rate is generally highest within 10 days after the stem is grown. Asparagus can undergo more than 10 repeated infections during the entire growing season of asparagus.
The disease can be divided into two stages in a year: First, the disease expansion period, which is 30-40 days after the onset of disease. The disease rate in this period is still low, the condition is developing slowly, and the second is a serious disease period, that is, 40 days after onset. The disease rate in the field reached more than 40%. This period started from about the end of July or August, when the bamboo shoots gradually became denser. Together with the onset of the rainy season, a very favorable condition was created by the occurrence of diseases, thus depressing the disease in the early stage. Control of late onset has a great effect.
Second, the incidence of stem blight of asparagus
1. F2 generation varieties with poor resistance to large areas:
At present, more than 80% of the asparagus we plant is poor quality seeds of the F2 generation. Asparagus cultivation of the main varieties of UCl57F2, UC800F2, UC72F2 and so on. The disease resistance of these varieties is very poor. Once the environment is suitable, it is easy to have a large area of ​​disease.
2, Qingyuan is not thorough:
At present, most rural households clean their gardens in time, but some farmers still do not understand whether the park or the clear garden is not completely timely. According to the investigation, ashes were scavenged and cleared out of the ground and burned, and the garden was completely cleared. The incidence of the disease only accounted for only 5% in the second year. Unclear gardens, the incidence rate of 58%.
3, suitable climatic conditions:
The suitable temperature range for the growth of pathogens is 23-26°C. Above 35°C or below 10°C, conidia do not germinate. The temperature in the spring is closely related to the onset of the disease sooner or later. In July, August and September, high temperature and high humidity are the vegetative growth stages of asparagus, which is also the peak period of pathogenic infection. The rate of diseased plants basically increases with the increase in the number of rains. Ten days after each rain, the incidence peaks in the field.
4. The timing of the stem of the mother is not suitable:
One of the main conditions for the occurrence and prevalence of asparagus disease is rain, and if the stem is kept in the rainy season, the chance of pathogen infection is greatly increased.
5, management is not timely, fertilization is unreasonable:
In the rainy season, the asparagus field should pay attention to drainage in time to reduce the water table and the humidity in the field. Excessive use of nitrogen fertilizer, excessive nutrient growth, most farmers in pursuit of immediate interests, reapply N fertilizer or only N fertilizer, so that shoots grow densely, stem cell wall is tender and thin, the bacteria easily into the dip. According to the survey Apply N, P, K three-element compound fertilizer, the incidence of strains only accounted for 10%, only urea, the incidence of disease strains accounted for 58%.
6, excessive dependence on pesticides and unreasonable application:
Since stem blight can be repeatedly infested, the control of the pesticide must be early, and the pathogen base must be strictly controlled. At present, most of the rural households are treated lightly and recklessly. When they see the disease, they are ruled and disease-free. As a result, many drugs are used for prevention and control, which increases the cost, and the effect is not very satisfactory.
There are two main problems in the use of pesticides: First, a single drug, so that the disease resistance. The problem of drug resistance caused by a single application of a single agent for a long period of time has become increasingly serious, resulting in a significant reduction in the control effect, or even completely ineffective. Second, the use of drugs is not timely, although the number of drugs used a lot, the control effect is poor. As soon as the test rain stopped, it was immediately sprayed. The field was basically disease free. After the rain, it was not sprayed in time. The resulting diseased plant accounted for 37%.
Third, Asparagus stem blight comprehensive control measures
1. Agronomic measures Pharmacy control is one of the important measures for disease control, but now field conditions have deteriorated, asparagus has low disease resistance, and disease is rampant. It is sometimes difficult to be effective only by drug defense. The use of agronomic practices is indeed a very effective method.
(1) Clearing the garden and reducing the number of pathogenic bacteria is a fundamental and thorough way of clearing the garden and reducing the number of pathogenic bacteria can play a control effect of more than 60%. The practice is: In November of each year, when the asparagus pods begin to turn yellow (do not wait until the stalks are dried), use an iron shovel or hoe to remove the asparagus stalks from the ground by about 5 centimeters, and remove the asparagus pods from the asparagus fields for treatment ( For feed, fuel, etc.). Before pouring the frozen water, pick up the dead branches scattered in the asparagus field. This is a very important task and must not be taken lightly.
(2) Keeping the stems of the mother's stem during the rainy season to reduce the chance of infection. Staggering the tender stems of the mother's stem during the unearthed period and the rainy season. Sticking to shoots in the July and August rainy seasons to prevent tender stem infections and increase the source of bacteria. One of the main conditions for the occurrence and prevalence of asparagus disease is rain, so the production generally requires the maternal stem to stay in the early days of fine weather for more than 5 days, so that the occurrence and spread of pathogenic bacteria have lost the conditions, not easy to infect the disease.
(4) Strengthen management, enhance resistance, timely cultivating and weeding, timely removal of diseased stems, and control of stem stalk volume in shoots. In the rainy season, the asparagus field should pay attention to drainage, reducing the water table and the humidity in the field. Balanced fertilization is an important measure to ensure that asparagus grows robustly and resists various diseases. In the fertilization should follow the organic, inorganic, biological fertilizer three combinations, nitrogen, phosphorus, potassium three matching the basic principles. Precipitating and fertilizing N increased by P, K, N, P, and K of the rejuvenation fertilizer, and N light weight and P and K in the autumn. According to the survey, the percentage of diseased plants that were formulated according to the formula was lower than the N, P, and K ratios by 60%, and the yield was increased by 50%.
(5) Ingeniously stop the infestation and prevent the spatter from splashing, and apply grass straw or mulching film in the field to avoid raining. The test showed that: to prevent the bacteria splash, blocking the infection. Tests have shown that: the cultivation of composite membranes to avoid rain can produce 72.7% to 77.1% of disease, and the disease index is 60.1% to 62.2%.
2, the prevention and treatment of pharmaceuticals should be more important than prevention, must be early prevention, strict control of the pathogen base, fight for disease or less incidence. At present, most of the farmers relied on light prevention, treatment, disease prevention, and prevention and control, resulting in more medication, more work, increased costs, but the effect is not very satisfactory.
(1) Seed soaking and seedlings are used to eliminate seeds and bacteria are soaked. 16% antibacterial net 2000 times soaking can be used for 1 day. The soil used for seedbed must be soil-sterilized with 500 times the inhibitory net (120 g/mu). In addition to the tender young seedlings, the characteristics of low resistance and susceptible to disease, after the seedlings can be unearthed, the net can be hung and antibacterial net space for fumigation sterilization, 1 point to 30 grams, 5-7 days to replace once.
(2) When the Stem of Stem and Stem Nursing Stem is on the stem of the mother, the root disc and the surrounding soil are usually sterilized with 500% liquid of 16% for 3 to 5 days prior to the stem of the mother to kill the pathogen in the soil and protect the stem of the mother. Infringed. After unearthing, the individual stems that have just appeared signs of disease are treated with pesticide and stem. When the reserved female stem grows to 5cm in height, the stem is applied with 2% bacteriostatic net 5-10 times, and the stem is applied every other day. , Apply 3-4 times.
(3) Diligent use is often replaced by the growth of bamboo shoots in the growing season. The poor ventilation conditions of the shoots, coupled with the onset of the rainy season and high humidity in the field, are the peak period of pathogenic infection, and are also the key protection period, regardless of the disease. Disease should be prevented and treated. After the branches of the mother stems are sprayed, they are sprayed with 1000 times antibacterial liquid, sprayed once every 2 days, sprayed 3-4 times, and sprayed with 1000 times antibacterial liquid before spraying, 3-5 days in advance. Spray once every 5-7 days. Generally, disease-free plots can be sprayed to protect therapeutic agents. To obtain anti-drug effects, it is necessary to:
1 Be sure to take the drug during the period of easy infection when the tender stem is withdrawn.
2 spray should be uniform and thoughtful, the interval should be short 3 best prevention and treatment time should be sprayed immediately after the rain stopped. 4 Avoid drug resistance, use different dosage form of pesticide rotation. 5 It is best to use a 16% antibacterial net that has three functions of prevention, treatment, and eradication.
(4) To disinfect the whole soil in the dormant period before the spring sprout in the Qingyuan Garden, 16% antibacterial net soluble powder 500 times, 75% chlorothalonil 500-800 times liquid, 50% carbendazim wettability Powder 500-600 times liquid. One spray.
The prevention and control of asparagus stem blight must thoroughly implement the guiding ideology of "prevention and control of integration, monitoring throughout the process". It is the foundation to reduce the number of bacterial sources and timely prevention is the key. Disease prevention is not sick, increase production and increase income.
Asparagus stem blight is a devastating disease. It is called "asparagus cancer." Once it gets stem blight, it cuts production, destroys the crop, and causes huge losses to farmers. Due to the impact of SARS in 2003, the price of asparagus was low, many farmers quit management, and the incidence of stem blight was more serious. At the same time, asparagus fields accumulated a large number of germs. In 2004 and 2005, there were more rainy days and more rainfall. As a result, there was a large outbreak of stem blight in asparagus. According to statistics, asparagus production was reduced by about 40% in these two years.