How to prevent and control powdery mildew? These methods you need to master

Powdery mildew mainly damages wheat leaves, and also damages stems and ears. It can occur from the seedling stage to the heading stage. On the leaves, it first produces small yellow spots, which then expand into round or oval lesions. A white powdery mold layer forms on the surface, interfering with normal metabolism, causing premature aging and reducing yield. Let's take a look below at how to prevent and control powdery mildew!

Symptoms of powdery mildew damage

Powdery mildew occurs on leaves, tender stems, flower stalks, flower buds, petals and other parts. In the early stage, it appears as irregular yellow-green small spots with indistinct edges. Subsequently, the lesions continuously expand, white powdery spots form on the surface, and finally numerous black dots grow in that area. The infected parts turn gray, spreading in patches to cover the surface, with indistinct edges, appearing dirty white or pale grayish white. When the damage is severe, the leaves shrink and become smaller, the tender shoots become twisted and deformed, and the flower buds do not open.

Agricultural control of powdery mildew

1. Choose disease-resistant varieties. When purchasing seedlings, strictly remove infected plants to eliminate the source of disease. When propagating, cut disease- and pest-free cuttings or root suckers as asexual propagation material. When seedlings leave the nursery, apply pesticide treatment to strictly prevent diseased seedlings from being introduced into new areas.

2. Rotate with non-host flowers and trees for 2 to 3 years to reduce the source of disease. Thoroughly clean the nursery, sweep up dead branches and fallen leaves, and prune diseased and pest-infested branches and destroy them in a centralized manner. During the growing period, promptly remove diseased branches and leaves, thoroughly remove fallen leaves, prune diseased and pest-infested branches and overly dense branches in the middle and lower parts, and destroy them in a centralized manner. Do not plant too densely. Strengthen ventilation in greenhouses to reduce humidity.

3. Promptly drain accumulated water in fields and flower pots. Do not water too much. Water from the edge of the pot, and do not splash water on stems and leaves, to reduce the spread of pathogens and the chance of disease. Apply more phosphorus and potassium fertilizer and less nitrogen fertilizer, so that the plants grow robustly. Apply more fully decomposed organic fertilizer to enhance the disease resistance of the plants.

4. When flowers and trees in greenhouses develop the disease, before raising seedlings and planting in the greenhouse, thoroughly remove all plants in the greenhouse, clean the greenhouse, and strictly disinfect by means such as fumigation with chemicals. Strictly prevent diseased seedlings from entering the greenhouse. As far as possible, plant a single variety of flowers and trees in the greenhouse, and avoid mixed planting to prevent cross-infection. Before buds sprout on open-field flowers and trees in early spring, the greenhouse can only be opened after thoroughly destroying the diseased plants inside, to prevent pathogen spores from spreading outside the greenhouse.

Chemical control of powdery mildew

1. During the overwintering period, spray or brush branches and trunks with a diluted lime-sulfur mixture of 3 to 5 degrees Baumé. Note that flowers susceptible to pesticide damage, such as cineraria, cannot be treated with it. Spray sulfur powder on the ground, generally using 25 grams to 30 grams per 70 sq m, to eliminate the overwintering sources of infection.

2. During the growing period, protective agents can be sprayed before the disease occurs, and systemic agents should be sprayed after the disease occurs. According to the disease symptoms, the growth of flowers and trees, the climate conditions and the characteristics of the pesticide, apply once every 5 to 20 days, for 2 to 5 consecutive applications. For flowers and trees grown for one season, one systemic agent can only be applied 1 to 2 times. Frequently change the types of pesticides to avoid the development of pesticide resistance in pathogens.

3. When the disease is severe, spray 15% triadimefon 1000-fold solution, 2% agricultural antibiotic 120 water solution 200-fold solution, or 10% polyoxin 1000- to 1500-fold solution. Traditional drugs, due to repeated use, cause pathogens to develop antibodies, and their effectiveness drops sharply, so alternating use is recommended. In addition, white liquor (35% alcohol content) 1000-fold solution can also be used, sprayed once every 3 to 6 days, for 3 to 6 consecutive sprays, washing the leaves until there is no white powder.

4. For flowers and trees planted in protected areas such as greenhouses and conservatories, in addition to spraying the various agents mentioned above, fumigants and dust agents can also be applied. Before planting or after finishing, carry out empty-greenhouse disinfection. For every 100 sq m, use 250 grams of sulfur powder and 500 grams of sawdust, mix evenly, divide into 10 piles, ignite with red-hot coal balls or charcoal, and do not use open flame. Keep the greenhouse closed for one day and night. During the fumigation process, strictly guard against fire. Fumigation during the growing period of flowers and trees is prone to cause pesticide damage and should be used with caution. During the plant growing period, use 45% chlorothalonil smoke agent before the disease occurs.