Detailed Explanation of Control Methods for Apple Alternaria Leaf Spot

Apple alternaria leaf spot is an important disease of apple. This disease can cause early defoliation of apple trees, weaken tree vigor, and not only affect the yield of the current year, but also affect flower bud formation and reduce the yield of the following year.

1. Symptoms

It mainly damages young leaves, especially young leaves within 20d. In the early stage of the disease, small brown spots appear on the leaves, surrounded by purple-red halos. When conditions are suitable, the lesions connect and form patches, and finally the leaves scorch and fall off. When the weather is humid, black mold grows on the reverse side of the lesions. After young leaves are infected, the damaged parts stop growing, causing the leaves to shrivel and become deformed, and some lesions rupture and perforate. After the petioles and young twigs are damaged, oval brown sunken lesions are produced, the leaves are prone to falling off, and diseased branches are easy to break and easy to wither. Fruit damage mostly occurs near maturity, with brown spots 1-4mm in diameter produced on the fruit surface. When the fruit core is damaged, brown to dark brown mold is produced, and in severe cases it expands into the flesh.

2. Control Methods

① In late autumn and early winter, collect diseased fallen leaves and burn them in a centralized manner, and prune off diseased branches.

② From mid-June onward, the disease on apple water sprouts and leaves intensifies, and this is the main source of infection for later-stage disease. Pruning off these useless water sprouts in time and improving ventilation and light transmission conditions in the orchard can reduce disease occurrence.

③ Apple alternaria leaf spot generally only damages young leaves within 20d after leaf unfolding, while apple trees have 2 new shoot growth periods in 1 year, among which spring shoot leaves play a decisive role in the tree's nutrition for the whole year, fruit quality, yield, and flower bud formation. Therefore, the principle should be adopted of focusing protection on spring shoots and reducing later-stage inoculum sources. After spring shoots emerge and the diseased leaf rate reaches 5%-10%, begin spraying 10% Polyoxin wettable powder or 50% iprodione wettable powder 1000-1500 times diluted solution, 80% Daconil or Sporgon wettable powder 800 times diluted solution, or 60% mancozeb wettable powder 500 times diluted solution 1-2 times. When autumn shoots emerge, spray once, and the purpose of controlling the disease can be achieved.