How does crape myrtle grow black leaves?

It is not crape myrtle that grows black leaves, but the black spots that cause it.

Sooty blotch, also known as soot disease, is widespread among garden plants in China. The invasion of Lagerstroemia speciosa is mainly due to the harm of Lagerstroemia speciosa and Lagerstroemia speciosa, that is, the mucus secreted by them is used as nutrition to induce a large number of bacteria polluting coal to multiply. After the disease, the leaves of diseased plants are covered with black mold layer, which not only affects the ornamental value of Lagerstroemia indica, but also affects the photosynthesis of leaves, resulting in the weak growth of plants and early defoliation.

Symptoms:

The pathogen of Lagerstroemia indica in sooty blotch also belongs to fungi, but there are many kinds of pathogens in sooty blotch. The same plant can be infected with a variety of pathogenic bacteria, and its symptoms are slightly different, but the black mold layer or black pulverized coal layer is an important feature of the disease. Sooty blotch mainly attacks leaves and branches. The disease first occurred along the main vein on the front of the leaf, and then gradually covered the whole leaf surface. In severe cases, the surface of leaves, branches and even petioles will be covered with a layer of black pulverized coal. These black powders will block the stomata of leaves and hinder normal photosynthesis.

Occurrence law:

Sooty blotch pathogens overwinter in diseased leaves and branches in the form of mycelium or ascomycetes. Because the mucus secreted by Lagerstroemia indica and Lepidoptera Lagerstroemia indica will provide nutrition for pathogenic bacteria in sooty blotch, generally, after the occurrence of these two pests, a large number of them occur in sooty blotch. The damage peak of Lagerstroemia indica and Lagerstroemia indica is from late June to early September, and the high temperature and humidity at this time are also conducive to the occurrence of the disease, so spring (caused by wintering bacteria) and autumn (caused by Lagerstroemia indica and Lagerstroemia indica) are the peak periods of the disease.

Prevention and control methods:

1) horticultural prevention and control, strengthen cultivation management, and rationally arrange planting density; Pruning diseased branches and redundant branches in time is beneficial to ventilation and light transmission, thus enhancing the potential number and reducing the incidence rate. Before taking medicine in potted Lagerstroemia indica at home, the diseased leaves can be removed or the moldy layer on the leaves can be washed with clear water, which can play a certain preventive role.

2) The key to chemical control of sooty blotch is to control aphids and scale insects. For plants with serious diseases last year, lime-sulfur mixture with Baume degree of 3-5 can be sprayed before germination in spring to eliminate the source of overwintering diseases. For the plants damaged by sooty blotch in the growth period, 70% thiophanate methyl wettable powder, 50% carbendazim wettable powder and 600% 77% Kede wettable powder can be sprayed 1000 times.