Watermelon downy mildew disease 17/12/2021

Ph.D Nguyen Minh Tuyen

Watermelon is a crop with high economic value, because watermelon is loved and consumed regularly by society. However, in the process of producing watermelon, farmers often face many diseases. In particular, downy mildew is one of the dangerous diseases for watermelon plants in particular and cucurbits in general. Late blight has seriously reduced the yield and quality of watermelon, increasing production costs of farmers.

Symptoms and effects:

The disease can appear on all parts of the melon plant, but the most typical lesions are on the leaves. The disease usually appears on the underside of leaves, at first it is pale green and polygonal in shape, limited by leaf veins, then the lesions are gradually darkened, and then gradually destroyed. When there is high humidity, the disease will appear a layer of white mold. On the upper surface of the leaves, the lesions are light in color at first, then turn yellow-brown, and finally dry. The disease can spread to other parts of the plant. When the disease is severe, the lesions can coalesce, causing the leaves to burn in patches and fall prematurely. The fruit of diseased melon plants will be small and pale in taste, reducing the commercial value.

 

Pathogens and conditions for the development of the disease:

The disease is caused by the Pseudoperonospora cubensis fungus

Conditions for the development of the disease:

- Before planting, the garden has not been cleaned of the remnants of the previous crop, especially cucurbits.

- The garden is planted with melons and cucurbits continuously without rotation, or planted near the garden is planted with cucurbits, melons...

- Planting with infected varieties, planting with high density, unbalanced fertilization and excess nitrogen, lack of microelements, so the garden is dense, with high humidity. The plant is weak, so the resistance is poor.

- Poor water management, making the garden often too wet.

- Winter-Spring crop, usually with cool or slightly cold temperatures, high air humidity, little sunshine, and foggy nights are optimal conditions for disease development.

Effective preventive measures:

- Sanitize and destroy disease remnants on the garden before planting, especially in the previous crop when plants with the same gourd family were planted.

- Do not use infected varieties.

- Plant with appropriate density, avoid planting too thick, easy to cause dense, damp in the garden.

- Balanced NPK fertilization, enhanced micro-organic fertilizers, supplemented with semimacro and trace elements to help increase plant resistance, such as POLY FEED 15-15-30 foliar fertilizer at the fruitting stage

- Raise high beds, cover with nylon film and water appropriately so that the garden is not wet regularly.

- Rotate with other crops if the garden regularly grows melons and cucurbits.

- In cloudy weather with little sunshine, lots of fog, cool and humid air, the following precautions should be taken: CLEARNER 75WP, with a dose of 1.5 kg/ha. The amount of water sprayed is 400-500 liters/ha.

- Check the melon garden regularly, when the disease appears in the field, it should be sprayed twice 7 days apart.

 

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In recent years, the area of citrus has been expanded because it is a fruit tree with high economic efficiency. However, in order to sell at a high price, not only in quality but consumers also require the external beauty of the fruit, so pest management on citrus is a matter of great concern to farmers. The hot season is a favorable condition for thrips to develop and cause damage, affecting the commercial value of fruit.

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