Shriveled blossoms on gladiola

Asked September 3, 2018, 3:02 PM EDT

Gladiola grew normally until blossom time when the buds began to shrivel. Is the problem in the bulbs or in the soil? Solution? Thank you.

Pennington County South Dakota

1 Response

This appears to be damage from thrips, minute insects with rasping-sucking mouth parts. Gladiolus are one of their favorite foods, particularly the tender flowers. They are very small, almost too small to see with the unaided eye. But you might catch a glimpse of them scurrying around in the flowers, especially down in the crevices. Try pulling apart one of the shriveled flowers and if you don't see any the of the cigar-shaped, usually tan to yellow insects, try gently blowing into the flower. (See image of a thrips below.) That will often encourage them to move around a bit. Look for the small, pale streaks in the flower petals where the insects have been feeding. The feeding causes the flowers to be malformed and not open properly. In heavy infestations the foliage will also turn brown prematurely and the whole plant will look like it is dying.

Thrips are very hard to control. They hide in spots in the leaves and flowers where insecticides will not often reach them. They have become resistant to some of the common insecticides as well. Heavily infested plants should probably be dug out, removed from the garden area and bagged or destroyed. They will often over-winter in stored corms that are dug up in the fall. The gladiolus thrips can be controlled in the growing plant as well as in the harvested corms. To protect the plants, spray or dust the gladiolus when they reach 6 inches in height and continuing treatment every 7 to 10 days until flowering. Diazinon should be used for control. Other insecticides labeled for thrips such as Tempo can also be used, but only for plants listed on the label. The active ingredient in Tempo is available in Bayer Advanced Garden Multi-Insect Killer. When using insecticide, mix and apply according to label directions. After harvesting and curing the gladiolus corms, shake them in a sack with a small amount of 5% Sevin dust (1 - 2 teaspoons for each 100 corms) and store as usual. This procedure will control the thrips in the over wintering corms.