Gladiolus thrips can cause serious damage

Gladiolus thrips (Taeniothrips simplex) is one of the most serious pests affecting gladiolus, report Tina Smith and Bess Dicklow at Univ. of Mass. Severely infested plants have a spotted, bleached appearance. Fed-on leaves and petals appear withered. Seriously damaged flower buds fail to open. The entire plant may become stunted.

The thrips are introduced into greenhouses or fields by infected corms and can overwinter in any stage on corms or on greenhouse grown plants. In the spring, the thrips are carried into fields on corms and start a new cycle of infestation.

As new stems appear, thrips crawl into the leaf sheath where they are protected. When flower spikes develop, the thrips crawl into the bud sheath where it is virtually impossible to contact them with insecticide sprays.

To reduce populations, remove and destroy affected plants. These thrips are best controlled by treatment of corms in the winter.

Before digging corms for winter storage, remove all plant parts and bury them or remove them from the field. Remove dug corms from the field and cure them in a different location to reduce thrips populations. Corms should be kept at 35°F-40°F for at least 4 months to kill the thrips. Avoid freezing the corms.

Monitor for thrips early in the growing season. Inspect sheaths carefully for silver flecking on the foliage. To reduce populations, treat thoroughly when the flower spikes begin to form with abamectin or spinosad.