What are the latest control methods for apple powdery mildew?

Apple powdery mildew occurs commonly in apple-producing areas in China. Besides harming apples, it also damages pears, sand apples, crabapples, binzi and Malus baccata, and causes severe damage to Malus baccata seedlings, small apple types such as binzi and sand apples, crabapples, and apple cultivars such as Wojin, Zhu, Hongyu and Guoguang. Now let us take a look at the control methods for apple powdery mildew!

Disease conditions

When winter buds sprout in spring, overwintering mycelium produces conidia that spread through airflow and cause infection. The disease period is from April to September. In April and May, temperatures are relatively low, which is the peak period for powdery mildew occurrence. From June to August, the disease develops slowly or stalls, and when autumn shoots sprout in September, a second disease peak begins. Warm and dry springs, rainy and cool summers, and clear autumns are favorable for the occurrence and spread of this disease, while continuous rain will inhibit the occurrence of powdery mildew. In orchards with high planting density, closed tree canopies, poor ventilation and light penetration, excessive nitrogen fertilizer application, and weak branches, the disease is severe. When pruning, if branches are not headed back, are left long, and retain a large amount of overwintering diseased buds, the disease is severe.

Damage symptoms

1. Young shoots: Young shoot growth is inhibited, internodes are shortened, and the leaves growing on them become narrow and long or do not open, becoming hard and brittle with upward-curling leaf margins. In the early stage, the surface is covered with white powder, which gradually turns brown later. In severe cases, the entire shoot dies.

2. Leaves: Sparse white powder first appears on the underside of leaves. New leaves are slightly purple, shrunken and deformed. Later, the white powdery layer gradually spreads to both sides of the leaf. The color on the upper surface of the leaf is uneven in shade, and powdery disease spots appear on the underside. Diseased leaves become narrow and long, with wavy shrunken margins or uneven surfaces. In severe cases, diseased leaves gradually turn brown from the leaf tip or margin, and finally the entire leaf dries up and falls off.

3. Flowers: When apple flower organs are damaged, white powdery spots appear at the calyx depression or pedicel depression. The sepals and pedicels become deformed, and petals are narrow and long and pale green. The pistils and stamens of damaged flowers lose their function, cannot pollinate and set fruit, and finally dry up and die.

4. Young fruit: Damage to young apple fruit mostly occurs near the calyx. White powdery spots appear at the calyx depression, and the diseased part becomes hard. After the fruit grows, the white powder falls off, forming net-like rust spots, and the hardened tissue later forms cracks or fissures.

Control methods

1. During winter pruning, thoroughly prune out diseased shoots. Check carefully in spring and summer, promptly prune out diseased shoots when found, seal them in plastic bags, take them out of the orchard, and burn them in a centralized manner or bury them deeply. Plant at a reasonable density, improve ventilation and light conditions, and reduce the probability of disease occurrence. At the same time, appropriately control the amount of nitrogen fertilizer applied, pay attention to the combination of nitrogen, phosphorus and potassium, and increase the application of phosphorus and potassium fertilizers.

2. Before apple trees sprout, the orchard must be cleaned, using lime sulfur mixture, Guoguang xinjunamine, thiophanate-methyl, etc. Apply the first treatment at the pink bud stage of apple and after petal fall, spraying 15% Guoguang triadimefon 1000-1500 times solution or Guoguang Baixiu 1000-1500 times solution.

3. Before apple tree buds, in combination with the control of other diseases, spray 5 times Baume lime sulfur mixture. At the bud stage, spray 1 time Baume lime sulfur mixture. In spring, at the early stage of disease occurrence, spray 25% triadimefon wettable powder or 20% triadimefon emulsifiable concentrate 2000 times solution, or 12.5% tebuconazole 2000 times solution, once every 10-20 days, for a total of 3-4 times.

4. Before apple flowering, at the young fruit stage, and at the fruit enlargement stage, spray “Guaguo Zhuangdiling” once each time. By thickening the nutrient transport ducts of the fruit tree and increasing the amount of nutrient transport, it improves the fruit enlargement vitality and nutrient matching function, achieving the goals of protecting flowers, protecting fruit, strengthening fruit, and setting more fruit.

5. Spray 15% triadimefon wettable powder 3000-5000 times solution or 15% triadimefon wettable powder 1500-2000 times solution. If powdery mildew occurs severely and the rate of diseased shoots reaches 15%, spray 15% triadimefon 1000-1500 times solution or 70% thiophanate-methyl 1000 times solution.