Cucumber downy mildew is caused by the infection of Pseudopeuonospora crbensis (Berk. et curt.) Rostsv. The mycelium is inseparable and colorless, grows and develops between host cells, and extends into the host cells to absorb nutrients through an ovoid or finger-like branching sorber. The occurrence and prevalence of downy mildew has a great relationship with temperature and humidity. When the relative humidity is above 85%, the temperature can be affected by downy mildew in the range of 10-26°C, and the greater the humidity is, the more severe the disease is. Due to the high humidity in greenhouse cultivation, this disease is more likely to occur. In the seedling stage can be susceptible to disease, the majority of adult disease after entering the flowering melon. At the beginning of the disease, water-stained light green spots appear on the leaves. After being expanded, the veins are limited by polygons. The color changes to yellow-green, yellow, and finally to brown. In wet conditions, the spots on the back of the leaves grow. Black mold layer. Due to the rapid spread of the disease and serious harm, the prevention and treatment must be timely and rational. In recent years, the majority of vegetable farmers often do not pay attention to rotation and intermittent use of drugs in the prevention and treatment of the disease, and rely too much on a high-efficiency pesticide and use it for consecutive years, resulting in a certain degree of drug resistance. In order to screen out pharmaceuticals that have both protective activity, therapeutic activity, and long-lasting efficacy, the author conducted a field efficacy trial on six fungicides in the first half of 2002 and achieved preliminary results. The results are summarized as follows: 1 Materials and Methods 1.1 Tested pharmaceuticals and treatment trials Six agents were marketed. The test consists of 7 treatments: (1) 60% extinction Grams WP (active ingredient: flumorph, mancozeb, Shenyang Chemical Research Institute) 1000 times; (2) 52.5% fasting net WG (active ingredient: oxazole (3) 72% Kelu WP (active ingredient: cymoxanil, DuPont) 500 times; (4) 64% virgin WP (active ingredient: cacao) (5) 70% Mancozeb WP (Liyang Chemical Factory, Xinyi City, Jiangsu Province) 500 times; (6) 40% Triethyl Aluminate WP (Zhejiang Lanxi Pesticide Factory) 300 times; (7) Clear water control (ck). 1.2 Test Method The test was set up in Wang Jianjun's greenhouse in Wangfen Village, Wangfu Township, Xiangyang District, Shangqiu City. The greenhouse was built in 2001 and the cucumber was planted in the early spring. This year is the second year. The cucumber variety is Jinyan No. 2, which is planted in wide and narrow rows. The width is 80cm, the narrow row is 50cm, and the plant spacing is 25cm. The garden soil is a moist soil sandy loam soil, the pH is 6.7, and the cultivation and management is at the middle and upper levels. The downy mildew began to appear in the early stages of melons. The experiment was set up with 7 treatments, 3 repetitions, a total of 21 plots, a plot area of ​​10.8 m2, and random arrangement. After the investigation of the condition base before spraying, spray once on March 29, April 5, and April 12, spray with a constant spray of Gongnong-16 Knapsack sprayer, and the leaves are fully wet on the front and back surfaces. Evenly distributed, spraying 1kg for each plot. When spraying, try to avoid liquid scattering between adjacent treatment to reduce human error. 1.3 Investigation of the effect The 6 plants were fixed in each plot, and the entire plant was investigated. Each survey was conducted before the first application and 7 days after each application. The number of diseased leaves was investigated according to level 5 criteria, and the disease index, disease index growth value and actual control effect were calculated, and the test results were checked for significance (DMRT method). The disease index, disease index growth value and actual control effect were calculated according to the following formula: disease index (%) = [∑ (level of diseased leaves at the disease level) / (check the total number of leaves of the highest value)] 100, disease index Growth value = condition index after application - condition index before application, control effect (%) = [(incremental value in control area - increase in disease index in treatment area) / increase in index value in control area] 100. The grading standards used in the survey were: Grade 0 - leaves without lesions; Grade 1 - Lesions accounted for less than 10% of the area of ​​the leaves; Grade 2 - Lesions accounted for 10% - 20% of the area of ​​the leaves; Grade 3 - Lesions accounted for the area of ​​the leaves 20 %-50%; Grade 4 - Lesions account for more than 50% of leaf area or dead leaves. 2 Results and analysis From the test results, it can be seen (Table 1) that the field condition of the test was more serious when the drug treatment was performed, and the weather was more foggy and humid throughout the application period, prompting the rapid spread of the disease. After administration of each agent, the condition was controlled to varying degrees. In the six drug treatments, the control effects of treatment (1) and treatment (2) have been very good, being 86.01%-90.87% and 88.44%-94.10%, respectively. The difference between these two agents was not significant; treatment (3) and treatment ( 4) The drug efficacy is good, which is 74.37%-78.39% and 71.07%-77.22%, respectively. The first 4 treatments have relatively stable efficacy and long duration; the latter two treatments are slightly less effective at the later stage, which is similar to the greenhouse. It is related to the long-term use of such agents. 3 Summary and discussion (1) Among the six fungicides, the main components of fasting are fluconuterone and cymoxanil. Famoxadone has strong systemic absorption, protection, healing, and eradicating effects; Local systemic absorption can inhibit sporulation and spore invasion, control the spread of pathogens, and accelerate the concentration of their advantages have a dual role of efficient sterilization and long-lasting protection, the best control effect, the average control effect of 91.87%; Gram is a combination of flumorph and mancozeb, flumorph is a cinnamamide fungicide with strong systemic absorption, both protective and therapeutic effects, mancozeb is mainly inhibited copper copper propionate body Oxidation is a protective bactericide, and the protection and bactericidal effects are more prominent after the two are mixed. The average control effect is 87.75%. Kelu is made from cymoxanil and mancozeb. It has both bactericidal and protective effects. The average control effect is 76.16%. Antivirus is a compound of oxazapine and mancozeb. It is a highly effective fungicide with both sex absorption and contact toxicity. It has a preventive and therapeutic effect and performs well. The average control effect is 73.45%. The above four kinds of drugs are all compounded drugs, which overcome the singleness of the effect, and can not only be bactericidal but also have protective activity. The control effect is ideal. (2) Mancozeb is a protective bactericide. Triethylaluminum phosphonate is a systemic organophosphorus fungicide. Even if the two are used at higher concentrations, their efficacy is not ideal. The old Vegetables use these two kinds of medicines for a long time, and cucumber downy mildew has different degrees of resistance to them. In order to improve the control effect, the above-mentioned four new fungicides can be used alternately. (3) Downy mildew has a greater impact on cucumbers in greenhouses. Chemical control is performed before or at the onset of disease. If you miss the best period of prevention and treatment, you can apply 52.5% fast net WG1500 times or 60% kill WP1000 times, spray 7 days or so, spray 2-3 times, combined with reducing greenhouse humidity, can effectively control the development of the disease .
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