This section is from the book "Commercial Gardening Vol2", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
While the plants are still young they are often troubled with greenfly, which should be eradicated at once, or deformed foliage soon presents itself and spoils the sale of the plants. They are sometimes attacked with thrips and even Red Spider; the last-named occurs through keeping too dry an atmosphere, and can be avoided. In the ground the plants are troubled with Aphis in dry weather, and if the stock be valuable the plants should be sprayed. The Frog-hopper or Spittle-fly is often a plague in the summer months, causing the plants to lose their tops. They are best caught during the evening, when they are not quite so wary as during the daytime. Earwigs are sure to be a pest in a dry season, and should be caught by any of the numerous devices adapted for the purpose.