Gladiolus is commonly attacked by gladiolus thrips. The minuscule thrips are difficult to see but feed on the shoots and flowers, leaving behind silver-streaked foliage, stunted plants, and flowers that fail to open. The thrips most likely nested in your gladiolus corms and will appear again next year if you don't take action. Winter is the best time to control gladiolus thrips. Dig the tender gladiolus corms in autumn as usual and store them in an unheated garage or shed where the temperature remains at 35-40 F; thrips will be eliminated in these near-freezing temperatures. Control thrips during the growing season with an insecticide spray formulated specifically for thrips or with an insecticidal soap. Follow application directions carefully, and be sure to continue treatment as recommended.