Bitter gourd mainly damages the leaves. The primary foliar was pale yellow and then expanded. The lesion was limited to a polygonal or irregular shape by the veins. The color gradually changed from yellow to tan to brown. In severe cases, lesions merged into plaques. When the humidity is high, a white moldy material grows on the back of the leaf, sometimes the white mycelium is seen on the leaf surface, and the mildew layer is rarely seen when the weather is dry. The field symptoms resemble the powdery mildew of bitter gourd. Bitter gourd powdery mildew also damages the leaves, petioles and stems. The first time there are white moldy spots on the leaves or tender stems, and then it expands into mildewed spots. In severe cases, the leaves appear chlorotic yellow spots, and some even form large patches or cover the entire leaf. Front or back. In the fall, many small black spots grow on the stains, namely the ascospora of the pathogen, which is different from downy mildew. If necessary, determine the pathogen by microscope.

Pathogenic characteristics

The cyst stem protrudes from the stomata by 1 or 2 or 3 to 4 branches, and is 165 to 420 microns in height. The major axis is 105 to 290 microns in length, accounting for 2/3 to 9/10 of the total length, and 5 to 6.5 microns in thickness. The base is slightly enlarged, the upper part is bifurcated branches 3-6 times; the end branches straight or slightly curved, long 1.7-15 microns; the sporangia are light brown, oval to oval, papillary, size 15, 31.511.5 to 14.5 micron, aspect ratio 1.2 to 1.7, resulting in zoospores, invading after germination; oospores in leaf tissue, globose, pale yellow, 28 to 43 microns in size .

Transmission routes and conditions

In cold regions, germs can survive in living plants in greenhouses or greenhouses, spread infections from greenhouses or greenhouses to open field plants, and it is unclear whether or not ovum spores survive in winter. In warm areas, there are melons in the field at the anniversary, and the spores can be spread by wind and rain. There is no obvious overwintering period. The germination temperature limit is 4～32°C, and the optimum temperature is 15～19°C. The disease is easily induced by low temperature and rain. Occurs in South China and Yunnan from May to June and September. Occurrence occurs from July to October in Beijing and Inner Mongolia. Generally, the damage is lighter. It seems that bitter gourd has strong resistance to downy mildew, but it should be considered when growing in the north or in the off season. Prevention.

Control methods

(1) Pay attention to the selection of disease-resistant seed varieties in serious cases. Such as Xia Feng 3

(2) The use of compost made from fermented bacterium strains will reduce the humidity in the field and reduce the damage.

(3) From the perspective of avoiding diseases, the humidity in the shed is preferably maintained at 90% to 95%, and in particular, the time for dew condensation on the leaves must be shortened or controlled in an intermittent state. Because the surface temperature of crops is due to radiation heat radiation at night, the body temperature of the plants is sometimes lower than the temperature in the shed. When the humidity in the greenhouse is saturated, the temperature at the same temperature as the condensation temperature (dew point temperature) will produce knots on the surface of the plants. In addition, after the sunrise, the temperature of the surface of the crop has risen at a slower rate than the temperature. When the relative humidity on the soil surface evaporates and the relative humidity is close to saturation, the plant surface temperature is lower than the dew point temperature. Dew condensation may also occur in this case. It seems that condensation can occur in two situations, but its frequency varies depending on the region, season, and facility conditions. Management seeks to reduce the duration of foliar condensation.

(4) 70% ethidium phosphine sprayed at the beginning of the disease; Mn-Zn wettable powder 500 times, or 58% ledomil; Mn-Zn wettable powder 500-600 times, 64% antivirus WP 500 times, 50 % of Amethyst Copper or Methacrylate Aluminium Copper 600 times, 72% of Frost Urea Manganese Zinc (Ke Kang Ling) WP or 72% of DuPont Ke Lu WP 800 times, 700 times the amount of water can be sprayed when the disease is severe , Or switch to 69% Anke manganese zinc wettable powder or water dispersible granules 1000 times or 47% Garnett's WP 800 to 1000 times liquid, 56% backing water dispersed micro granules 700 to 800 times, Bitter gourd is sensitive to the sensitive seedlings of copper, and the amount and concentration must be strictly controlled during the growth period to prevent phytotoxicity. Bitter gourd mixed with powdery mildew can be sprayed 69% Anke manganese zinc wettable powder 1600 times plus 20% Triadimefon EC 2000 times, every 10 days or so, continuous control of 2 or 3 times. The drug was stopped 4 days before the harvest.

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