Glads Look Sickly

Question:

Some of the leaves on my glads are deformed and stunted, and are producing no flowers even though it is late summer. I cannot find any small insects on the plant. Thrips, or something else?

Minnesota Master Gardeners say:

 Thrips seem like a good guess, although we are not likely to see them; their damage is the only evidence we usually have. To quote the Yard and Garden brief "Growing Gladiolus:"
"If the leaves appear streaky, or if flowers fail to open or are misshapen or streaked and discolored, the problem is probably thrips. Thrips are tiny insects that overwinter on stored corms. They use rasping mouth parts to feed on gladiolus foliage and flowers, often while the flowers are still in the bud. Spray the plants when you first see damage, using a product containing the active ingredient acephate (Orthene and others) or carbaryl (Sevin). Repeat according to label directions if damage continues."

Always check the label on any pesticide to be sure the plant and insect you intend to use it for are listed.

Thrips damage can resemble virus damage. Here's a quotation from the Extension publication Gladiolus Diseases:
"Light streaking on leaves and flowers produced by feeding of the thrips insect can be confused with a viral disease. Thrips damage usually occurs uniformly in a planting, while viral symptoms generally are on scattered plants only."

Another remote possibility is that there was some sort of herbicide drift that has affected your glads. If this is the case, then there's not a remedy other than preventing it from happening again. The plants will likely either die from it, or grow out of it.

Finally, aster yellows is a phytoplasma disease that can infect glads. It is spread by leafhoppers that have fed on infected plants. Glads with aster yellows may have thin, weak, yellow leaves, and the flower spikes may be twisted and deformed, while the flowers remain green. The whole plant is generally stunted and spindly, and the top is often killed.

Although thrips can be managed with pesticide applications, viral diseases and aster yellows can not be eradicated. If any glad plants look abnormal, stunted or discolored dig them up and destroy them in the trash (not the compost) early in the season if you suspect a virus. Be sure to rotate your glad planting to a new bed if you had disease problems the previous season. If you frequently have problems, you may choose to discard your corms and start with new glads each year for the best results.

For thorough information on growing glads and dealing with these issues, read further:

Growing Gladiolus
http://www.extension.umn.edu/projects/yardandgarden/ygbriefs/h149gladiolus.html

and Gladiolus Diseases
http://www.extension.umn.edu/distribution/horticulture/DG1154.html