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What to Do When Lilac Leaves Turn Black? Causes and Solutions

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Its leaves turning black is actually related to bacteria. For prevention and control, there are still two approaches. The first is the horticultural one: we cannot plant it in relatively low-lying spots, we need to drain rainwater promptly when it rains, and we must not let infected plants mix in. The second is the chemical one: generally we use Bordeaux mixture, spraying initially at a concentration of 0.1% to 1.0%; of course, fungicides such as Xiaojunling also work.

1. The pathogen

The blackening is mainly caused by a pathogen, a type of Pseudomonas bacterium. It is rod-shaped, with one to two flagella growing out of one side, and it can swim in water and has no capsule. Its metabolic type is respiratory, and its requirements for nutrients are not very high either; as long as there are simple organic compounds and some inorganic salts, it can grow very quickly.

2. Transmission patterns

Generally this organism overwinters on diseased branches and diseased leaves, and when the temperature and humidity suit it the following year, it can reproduce by fission. In addition, its transmission and invasion both depend on water, so it can develop very quickly in relatively humid environments.

Therefore, in relatively low-lying places or places with more rain, lilacs are very prone to the disease, and the leaves very easily turn black. But generally speaking, purple ones are less susceptible to the disease than white ones.

3. Improvement methods

Generally there are two improvement methods: the first is the horticultural one, and the second is treatment through chemicals.

1. Solving it horticulturally also counts as solving the problem at the root: that is, not planting it in relatively low-lying spots, so that water does not accumulate; in addition, if it rains, the rainwater still needs to be drained promptly, and when introducing seedlings we must inspect them carefully and must not bring infected plants in.

2. Treating it with chemicals, we generally use Bordeaux mixture. Initially it is sprayed at 0.1% to 1.0%; of course, there are also some other agents such as Xiaojunling. In addition, we can also sprinkle some bleaching powder or sulfur powder under its shrub layer.

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