Integrated Control Methods and Technical Key Points for Cucumber Downy Mildew
Cucumber, a plant of the genus Cucumis in the family Cucurbitaceae. Also called huanggua or qinggua. The fruit is oily green or emerald green, with soft small spines on the surface. It is commonly cultivated throughout China, and is now widely grown in temperate and tropical regions. Cucumber prefers warmth and cannot tolerate cold, and is one of the main greenhouse products.
Morphological characteristics of cucumber
Annual trailing or climbing herb; stems and branches elongated, with ribbed grooves, covered with white stiff hairs. Tendrils slender, undivided, with white soft hairs. Petiole somewhat rough, with stiff hairs, 10-16 (-20) cm long; leaf blade broadly ovate-cordate, membranous, both length and width 7-20 cm, both surfaces very rough, covered with stiff hairs, 3-5 angled or shallowly lobed, lobes triangular, toothed, sometimes ciliate at the margin, apex acute or acuminate, basal sinus semicircular, 2-3 cm wide, 2-2.5 cm deep, sometimes the base connivent backward. Monoecious.
Male flowers: often several clustered in leaf axils; pedicel slender, 0.5-1.5 cm long, puberulent; calyx tube narrowly campanulate or nearly cylindrical, 8-10 mm long, densely covered with white long soft hairs, calyx lobes subulate, spreading, nearly equaling the calyx tube; corolla yellow-white, about 2 cm long, corolla lobes oblong-lanceolate, acute; stamens 3, filaments nearly absent, anthers 3-4 mm long, connective exserted, about 1 mm long.
Female flowers: solitary or rarely clustered; pedicel stout, pubescent, 1-2 cm long; ovary fusiform, rough, with small spine-like protuberances. Fruit oblong or cylindrical, 10-30 (-50) cm long, yellow-green when ripe, surface rough, with spiny-tipped tuberculate protuberances, very rarely nearly smooth. Seeds small, narrowly ovate, white, without margin, both ends nearly acute, about 5-10 mm long. Flowering and fruiting period in summer.
Growing environment of cucumber
Temperature: Cucumber prefers warmth and cannot tolerate cold. The suitable temperature for growth is 10-32°C. Generally, 25-32°C during the day and 15-18°C at night give the best growth; the most suitable soil temperature is 20-25°C, with a minimum of about 15°C. The most suitable day-night temperature difference is 10-15°C. At high temperature of 35°C, cucumber photosynthesis is poor; at 45°C, high-temperature damage occurs; at low temperature of -2 to 0°C, it freezes to death; if hardened at low temperature, it can withstand a low temperature of 3°C.
Light: South China type varieties are relatively sensitive to short-day conditions, while North China type varieties have no strict requirements for day length and have become day-neutral plants. Their light saturation point is 55,000 lux, and the light compensation point is 1,500 lux. Most varieties grow well under short-day conditions of 8-11 hours.
Water: Cucumber has high yield and a large water requirement. The suitable soil moisture is 60-90%; during the seedling stage, water should not be excessive, with soil moisture of 60-70%; during the fruiting stage, sufficient water must be supplied, with soil moisture of 80-90%. The suitable relative air humidity for cucumber is 60-90%; if the relative air humidity is too high, disease is very likely to occur, causing reduced yield.
Soil: Cucumber likes moisture but cannot tolerate waterlogging, and likes fertilizer but cannot tolerate excessive fertilizer. Fertile soil rich in organic matter should be selected. It generally prefers soil with a pH between 5.5 and 7.2, but a pH of 6.5 is best.
Integrated control of cucumber downy mildew
Downy mildew is one of the main diseases of cucumber. It can occur from the seedling stage to the mature plant stage, and the most susceptible period is after fruit setting. High air humidity and the presence of pathogens can cause a major outbreak.
Symptoms of cucumber downy mildew: Downy mildew is a high-temperature and high-humidity disease. Because it develops rapidly, it is also called "paomagan". Generally, the disease is severe from March to April in spring, with chlorosis of leaf mesophyll and angular brown lesions restricted by leaf veins, and gray-black (purple-black) mold layers on the underside of leaves. This causes the leaves to dry up and fall off quickly, until the plant dies.
Integrated control methods for cucumber downy mildew:
Downy mildew should be mainly prevented. Select disease-resistant varieties; control field humidity, promptly remove old and diseased leaves, and provide ventilation and light.
In the early stage of the disease, foliar spraying can be done with 72% Kelu wettable powder at 600 times dilution, 72.2% Previcur water agent at 400 times dilution, 68.75% Yibao at 1000 times dilution, or 25% Amistar at 1500 times dilution. Anke, Yinfuli, Pinrun, Baitai, etc. can also be used. Apply once every 7-10 days, rotating products, for 2-3 consecutive times.
1. Use high-temperature greenhouse sealing. This is one of the important means of disease control in greenhouses, and this method can be used to control downy mildew, powdery mildew, angular leaf spot, gray mold, scab, and many other diseases. The specific method is: around noon on a sunny day, after watering thoroughly, seal the greenhouse to raise the temperature; when the temperature reaches 45-46°C, maintain it for 1.5-2 hours, then ventilate slowly to lower the temperature. Note that when sealing the greenhouse, the mercury bulb of the thermometer should be at the same level as the highest point of the plants. You can also water one day before sealing the greenhouse, and water again after sealing is finished.
2. Chemical control: use 66.8% Meiduoke wettable powder at 700-800 times dilution, 75% Kekangling at 1500 times dilution, plus white sugar and vinegar at 300 times dilution to control downy mildew; when angular leaf spot occurs mixed in, add 77% Kocide wettable microgranule powder at 400 times dilution. New types of pesticides in recent years, such as 10% Kejia suspension concentrate, whose active ingredient is cyazofamid, are a new imported pesticide used for the prevention of downy mildew in cucumber, melon, and grape. Generally, after planting and seedling recovery, spray 2-3 times at 2000 times dilution, with an interval of 7-10 days. It can also be used as a therapeutic agent; in the early stage of the disease, use 1000-1500 times dilution, for 2-3 consecutive applications, with an interval of 7-10 days. The duration of this pesticide is 10-14 days; rainfall 1 hour after application does not affect its efficacy. It can be mixed with most insecticides and fungicides, such as mixing with 53% Jinlei at 500 times dilution to increase systemic conductivity.
In addition, a pesticide promoted in recent years is 42% trichloroisocyanuric acid soluble powder, also a new type of eradicant for controlling downy mildew in vegetables. The trade name is Kejunjing. It is a broad-spectrum, systemic, therapeutic fungicide. For cucumber downy mildew, spray at 3000-4000 times dilution. There is also 0.5% amino-oligosaccharin water agent (Shiteling) at 1000 times dilution, which not only treats the disease but can also improve the plant's immunity. When spraying the solution, it must be sprayed evenly and thoroughly so that the underside of the leaves receives the pesticide. After application, check whether the mold layer on the lesions on the underside of the leaves has dried and died. Generally, it should be used 2-3 consecutive times.