How to prevent and control cucumber phytophthora blight? Recognizing the damage symptoms is key

Cucumber phytophthora blight can infect plants from the seedling stage to the mature plant stage. When seedlings are infected, dark green, water-soaked rot first appears on the tender tips, which gradually dries up and forms bald tips. At the mature plant stage, it mainly damages the base of the stem and the nodes of tender stems, starting as dark green water-soaked areas, then becoming soft and markedly constricted, and the leaves above the affected part gradually wither. Now let us take a look at the prevention and control methods for cucumber phytophthora blight!

Occurrence pattern of cucumber phytophthora blight

Cucumber phytophthora blight is a fungal disease. The pathogen overwinters in the soil or in manure along with diseased plant residues. In the following year, under suitable conditions, it produces sporangia that spread through wind and rain, irrigation water and water droplets. The optimum temperature for disease development is 28 to 30 degrees Celsius. When rainfall is heavy, rain occurs frequently, or shallow water is abundant and in large amounts, the disease occurs easily and spreads quickly. Therefore, under conditions of low-lying terrain, poor drainage and high humidity, the disease is severe.

Conditions for the onset of cucumber phytophthora blight

The pathogen mainly overwinters as mycelium, oospores and chlamydospores in the soil or in manure along with diseased plant residues, and spreads through wind, rain and irrigation water. The optimum temperature for disease development is 28-30 degrees C, and soil moisture is an important factor affecting the degree of epidemic of this disease. In years with high summer temperatures, heavy rainfall and many rainy days, phytophthora blight tends to become epidemic and causes severe damage. In addition, low-lying terrain, poor drainage and continuous cropping make the disease more likely to occur. In protected cultivation, at the turn of spring and summer, after the ventilation openings at the front of the greenhouse are opened, the disease tends to develop rapidly.

Prevention and control methods for cucumber phytophthora blight

1. Agricultural measures: Choose disease-resistant varieties, such as Jinchun No. 3, Jinza No. 3, Jinza No. 4, Zhongnong 1101, Longzahuang No. 5, Zaofeng No. 2, etc. Use Yunnan black-seeded pumpkin as rootstock for grafted seedling production. Adopt high-ridge cultivation and cover with plastic film to reduce opportunities for the pathogen to infect the plants. Avoid flood irrigation and avoid excessively high soil and air humidity. In open-field cultivation, drain accumulated water from the field in time during the rainy season, and promptly pull out

central diseased plants.

2. Disinfection treatment: An effective method for seed disinfection is to soak seeds in a 800-fold solution of 25% metalaxyl wettable powder for 30 minutes, then germinate and sow. For soil disinfection of seedbeds or greenhouse soil, mix 8 grams of 25% metalaxyl wettable powder per square meter of seedbed with soil and spread it on the seedbed. In protected cultivation, before planting, spray the ground with a 750-fold solution of 25% metalaxyl wettable powder.

3. Chemical control: The key to controlling cucumber phytophthora blight in open fields is to start spraying one week before the rainy season arrives, once every 7 days for 3 consecutive sprays. Optional agents include a 600-fold solution of 64% Sandofan wettable powder, a 1000-fold solution of 25% metalaxyl wettable powder, a 1200-1600-fold solution of Yemeishaxing wettable powder, and a 600-fold solution of 50% metalaxyl-copper wettable powder, etc. Practice has shown that spraying a 500-fold solution of 70% mancozeb wettable powder or a 1:0.8:200 Bordeaux mixture before disease onset for protective spraying gives very good control efficacy.

Damage symptoms and prevention and control methods of bitter melon phytophthora blight

Bitter melon phytophthora blight damages stems, leaves and fruits, with more occurrences at the base of the vines and the nodes of tender vines. The pathogen is Phytophthora parasitica, a fungus of the Mastigomycotina. In the north, autumn cucumbers are more affected, while in central and southern China, spring cucumbers are more commonly affected. Besides cucumber, it also damages winter melon, wax gourd, zucchini, snake melon, pumpkin, watermelon and other crops. Now let us take a look at the prevention and control methods for bitter melon phytophthora blight!

Damage symptoms

Bitter melon phytophthora blight mostly shows symptoms before flowering, and both stems and vines and fruits can be infected. When leaves are infected, they first lose their luster, with initial dark green water-soaked lesions that are irregular in shape and have indistinct edges. When humidity is high, a very thin layer of white mold can be seen growing on the diseased area; when dry, it appears greenish-white and breaks easily. Petioles and vine nodes show dark green water-soaked soft rot, and the affected parts constrict easily. When fruit is affected, dark green sunken lesions appear; when humidity is high, the fruit quickly softens and rots, and sparse white mold grows on the affected part, with the rot giving off a foul odor.

Occurrence pattern

The pathogen mainly overwinters in the soil as mycelium, oospores or chlamydospores along with diseased plant residues, and seeds can also carry the pathogen. The temperature range for pathogen development is 5-37 degrees C, with the optimum temperature 28-30 degrees C. Within the optimum temperature range, the length of the rainy season and the amount of rainfall are the decisive factors for the occurrence and epidemic of the disease. If the rainy season comes early, rainy days last long and rainfall is heavy, the disease occurs early and is severe. In addition, poor field drainage and high soil moisture easily induce phytophthora blight.

Agricultural control

For agricultural control of bitter melon phytophthora blight, a crop rotation of more than 3 years can be implemented, and high-ridge (bed) cultivation with plastic film mulching can be adopted to reduce pathogen splashing from the ground. Irrigate reasonably and control field humidity. During the rainy season, appropriately control watering, drain water promptly after rain, and ensure the ground dries after rain. When drought occurs, water in time; when watering, strictly prohibit flood irrigation, and it should be done in the afternoon or evening on sunny days. Apply more organic fertilizer to promote robust plant growth, deep roots and lush leaves, and improve resistance. Adjust the plants in time to prevent excessively dense growth and poor ventilation and light penetration. Remove diseased leaves at any time and burn them.

Chemical control

For chemical control of bitter melon phytophthora blight, alternately spray agents such as a 800-1000-fold solution of 25% ridomil wettable powder, a 600-800-fold solution of 80% zineb wettable powder, a 500-600-fold solution of 64% Sandofan wettable powder, a 300-400-fold solution of 40% fosetyl-aluminum wettable powder, a 500-600-fold solution of 80% Xinwansheng wettable powder, a 400-600-fold solution of 72.2% Previcur aqueous solution, and a 600-fold solution of 50% potassium copper phosphonate wettable powder, once every 5-10 days for 3-4 consecutive times. Spraying should be thorough and meticulous, covering all leaves, fruits and the nearby ground.

Causes and prevention and control methods of greenhouse cucumber phytophthora blight

What symptoms does greenhouse cucumber phytophthora blight have? Recently, many vegetable growers have reported that gumming began to appear on the stems and vines of cucumbers grown in greenhouses. At first the gum was clear, then turned slightly yellow, and the gumming cucumber vines quickly rotted and broke. After gumming appears on cucumber stems and vines, in severe cases the fruit also exudes gum. These are the symptom manifestations of cucumber phytophthora blight. Below, the editor shares the prevention and control methods for greenhouse cucumber phytophthora blight.

Causes of greenhouse cucumber phytophthora blight

There are many causes of gumming on cucumber stems and vines, but judging from the recent phenomenon of gumming on cucumber stems and vines in greenhouses, it is mainly caused by cucumber phytophthora blight, which should receive special attention from cucumber growers. Cucumber phytophthora blight mainly damages leaves, stems and fruit, with young stems and tender tips suffering the most severe damage. When leaves are infected, dark brown water-soaked spots appear and then expand into nearly round large lesions. When moist, the lesions expand very quickly and often cause the entire leaf to rot; when dry, the lesion edges are dark green and the center is light brown. When stems are affected, the diseased part is water-soaked, dark green and rotting, and markedly constricted, producing gum, causing the branches and leaves above the affected part to wilt and die, but the vascular bundles do not discolor. When fruit is affected, water-soaked dark green nearly round sunken lesions appear. When humidity in the greenhouse is high, the disease develops rapidly, and in the later stage the diseased part secretes milky white gum that gradually turns amber, then softens and soft-rots.

Prevention and control methods for greenhouse cucumber phytophthora blight

For agricultural measures, black-seeded pumpkin can be used as rootstock for grafted seedling production. Adopt high-ridge cultivation and cover with plastic film to reduce opportunities for the pathogen to infect the plants. Avoid flood irrigation and avoid excessively high soil and air humidity. After discovering central diseased plants, pull them out in time.

For chemical control, a 600-fold solution of 64% Sandofan wettable powder, a 1000-fold solution of 25% metalaxyl wettable powder, or a 800-fold solution of 58% metalaxyl mancozeb wettable powder can be used for root drenching, once every 5-7 days for 3 consecutive drenches.