What is the pimple on the elm leaves?

"The answer.

1. The small pimple on the elm leaf is a gall, which is a deformed tumor that grows after the elm is stimulated by insect pests.

2. Once infected with galls, it will seriously hinder the absorption of water and nutrients. If the number of galls is large, it may lead to the decline of plant seed setting rate, destroy root tissue and even die after a long time.

3. Once the scabby leaves are found, they should be treated as soon as possible, completely destroyed and sprayed with drugs for thorough prevention and control.