welcom to the site Birks' we could be more help if we knew what plants and a photo would be helpfull or a least a good discripton of the problem. the more you give us the better we can help you. just put the info in the answer box as if you were ansuring

Cliffo's right, we need more info - which plants, any insects present, any spotting of the leaves, any white mould, rust, etc., there are myriads of questions we could ask, and photos would certainly help