How to Fight the Pests?
Gladioli are relatively free of insect pests. The major insect pest of glads is the gladiolus thrips. This pest is very small and it is difficult to see it with the naked eye. It does considerable damage, especially to the flowers. It "works" on the buds before they emerge from the sheaths and causes malformed and spotted flowers. Thrips can overwinter on stored corms and will injure them at that time.
Usually written sources say that it is very difficult to fight against thrips. A. Verinsh, a famous Latvian selectionist, claims that it is easy if a flower-grower is attentive. If you find thrips on your corms in winter or spring there is an easy way to annihilate them. Put your corms into plastic bags (one sort per bag), inject them with any insecticide and tie up the bags. Be careful to avoid poisoning. In 2-3 days you can take the corms out and put them in their place.
A non-chemical method of controlling thrips build-up is to soak the corms in very hot water (not boiling - about 160° F (80° C)) for about 2 minutes. Try to plant them in a different location each season to help control thrips populations.