DDT AS A CONTROL FOR GLADIOLUS THRIPS 
By M. D. FARRAR, Research Entomologist 
Illinois Natural History Survey 
(Prepared at the request of the Illinois G. S.) 
The new war insecticide DDT (dichloro - diphenyl - trichloroethane) has found a 
place in the control of Gladiolus thrips on stored Gladiolus corms. Early work indicated 
this thrips was very susceptible to DDT. Later tests show those findings to be correct. 
The new method has its greatest use where corms are stored at temperatures that 
permit Gladiolus thrips to breed on corms over winter. Many growers are forced to 
store their corms at such temperatures favorable to the thrips. For these growers, DDT 
will protect their stock from damage without the labor of bagging, airing, or special 
cleaning of the stock. Where corms can be stored at cold temperatures unfavorable to 
development of thrips, use of DDT dust may not be of great value. In Illinois, experi- 
ments carried on during the last two years indicate that DDT will completely handle 
the thrips problem on stored corms. Corms should be dried before treatment, but they 
need not be cleaned. 
The powder containing DDT can be scattered onto the corms at any time after 
they are thoroughly dry. Treating after rough cleaning may be most satisfactory, al- 
though many growers may prefer to clean stock first and then treat it before storing the 
cleaned corms until spring. 
The dust should be worked into the trays sufficiently to coat all corms. For corms 
stored in bags, a small amount of dust may be added and the bag shaken to distribute 
the dust. 
Treated corms need not be disturbed until planting time. The exposure to DDT 
over winter in storage apparently has no adverse effects on either the keeping quality 
or germination after planting. Treated corms are pleasant to handle as a result of the 
talcum used as carrier for the DDT. 
Table 1 gives the Illinois results of tests in 1945. The corms used were dried as they 
came from the field and not cleaned in any way until just before planting. The dusts 
were applied at the rate of 1 ounce of dust to 40 pounds (1 bushel) of dry corms. In these 
tests dusts containing between 1 and 10 per cent of DDT completely prevented any 
injury to the corms by thrips. These tests indicate that a dust which contained more 
than 1 per cent DDT would be satisfactory for this purpose. A wide variety of commer- 
cial dusts containing 1 to 3 per cent DDT are now on the market and are available 
from dealers in insecticides. 
The amount of dust applied is not particularly important provided sufficient dust 
is used to coat the dry corms. Excess dust can be shaken out and used on additional stock. 
Caution: Liquid sprays containing DDT should not be used on corms until tests 
indicate that they do not cause injury. 
Notes on the Life History of Gladiolus Thrips 
Taeniothrips Simplex (Morison) 
In the northern states, where corms are harvested and stored during the cold 
months, Gladiolus thrips apparently do not survive out of doors. Leaving tops in the 
field, exposed to the weather, will cause all thrips on the foliage to die. Piles of foliage 
or clearing shucks should be scattered or burned to insure the destruction of all thrips 
attempting to over-winter in Gladiolus trash piles. 
Thrips carried on the corms to storage will breed at temperatures above 50° F. 
Unless treated, corms stored in basements where winter temperatures are generally 
60° F, or above are almost sure to be injured by thrips before spring. Several generations 
may develop in warm basements during the winter months. Feeding of thrips on the 
corms will cause discolored, hardened areas on the corms. Severely injured corms dry 
abnormally, resulting in shrunken, misshapen planting stock. Such stock is slow to 
start growth and may not produce satisfactory spikes. 
Published by permission of the New England Gladiolus Society in the Gladiolus Magazine, 
December 1945 
