HOW TO CONTROL GLADIOLUS THRIPS 
By MERTON G. ELLIS 
__/ 
While people were bemoaning the depres¬ 
sion, it remained for tiny insects, not more 
than a sixteenth of an inch in length and known 
as thrips, to slip in and do more damage to 
Glads than the depression ever did. In fact 
for a year or so it looked as if the Glad busi¬ 
ness were doomed. 
However, in the spring of 1933 it was dis¬ 
covered that thrips have a sweet tooth and 
since then several sprays have been used which 
have proved very effective on the growing 
plants, and very certain in their results, and 
yet quite inexpensive. We now feel certain 
that anyone who will carefully follow the 
simple methods herein given can again grow 
fine blooms and with no fear of loss from 
thrips. 
And your blooms will be worth more, for a 
lot of your friends will, no doubt, fail to take 
the necessary precautions. The thrips may 
prove to have been a blessing in disguise by 
doing away with a lot of those blooms which 
have been selling at five cents per dozen spikes. 
The adult thrips are black, with a yellowish 
or grayish white band at base of their wings. 
The young are yellowish orange in color. The 
adults are about a sixteenth of an inch in 
length. They increase in numbers very rapidly. 
If you had no good blooms the past season, 
the florets simply withering up, you probably 
had thrips. 
First, before planting, let us free the bulb 
of any thrips. The smaller growers will find 
the use of Napthalene flakes an inexpensive 
and most efficient treatment. Use Napthalene 
flakes at the rate of about an ounce, or a 
tablespoonful, to 100 No. 1 bulbs, or their 
equivalent. If the bulbs are in sacks the 
flakes may be placed in the sacks with the 
bulbs. Or if the bulbs are in crates the flakes 
may be sprinkled over the bulbs and then 
covered with a newspaper for about three 
w«~eks and at a temperature of over 60 degrees. 
Keeping this amount of warmth will allow the 
eggs to hatch, so that the resulting thrips may 
be killed by the fumes from the flakes. Ex¬ 
periment stations have tested this method and 
say it is sure death to all thrips and their eggs. 
As a matter of precaution we are putting 
Napthalene flakes in with all bulbs as they are 
shipped. 
It may be safest to remove the Napthalene 
flakes after about three or four weeks. Some 
growers claim the flakes may injure the bulbs, 
causing some of the blooms to come clubbed 
and causing the new bulbs to make but few 
roots. However, we have seen this happen to 
some varieties in gardens where there were no 
thrips and where no Napthalene had been used. 
Thus far we have seen no bad results from the 
use of Napthalene even where it had been left 
with the bulbs nearly all winter and till plant¬ 
ing time. 
Large growers may find the use of some 
fumigant such as Cyanogas more convenient 
for the treatment of bulbs. This is a dangerous 
gas and is best used under the supervision of 
the local inspector. 
Others may prefer the lye treatment. The 
bulbs may be soaked from eight to twelve 
hours in a solution made of one can of con¬ 
centrated lye mixed with 20 to 25 gallons of 
water. To be entirely sure of getting the 
thrips’ eggs it might be necessary to keep the 
bulbs warm for a few days and give a second 
brief treatment. The same might be true in 
use of the Bichloride of Mercury treatment, 
which consists of the use of an ounce of this 
to about eight gallons of water, and soaking 
about four hours. 
Some growers have found that by keeping 
bulbs in winter storage at a lower temperature 
than 40 degrees the thrips are killed. In order 
to get the eggs it might be necessary to warm 
the bulbs for a few days so they would hatch, 
and then by keeping the bulbs cold again these 
thrips would also be killed. Hard freezing 
weather will apparently kill whatever thrips 
might be trying to winter over in the garden. 
But in warmer climates this would not hold. 
Anyhow, whatever you may do, your neigh¬ 
bors will probably have plenty of thrips and 
some of them will fly or drift with the wind 
into your garden, where, if left unmolested, 
they mav soon increase to millions. To be 
sure of having good blooms you must count 
on that taking place, and without waiting to 
see if it is going to take place, you must begin 
spraying the young plants when they are four 
to six inches tall. This is most important. If 
you delay too long you may have no blooms. 
Many sprays have been used which did not 
prove very effective. The first spray that we 
learned of as being most effective consisted of 
a pint of black molasses and a teaspoonful of 
Paris Green mixed in a gallon of water. Some 
use a larger quantity of Paris Green. However, 
the Paris Green does not mix well with water 
and has to be stirred while spraying. We 
passed this formula on to the florist of the 
State Hospital. They had a very bad in¬ 
festation of thrips, the plants being almost 
black with them. This florist got tired of 
stirring the Paris Green and hit on what ap¬ 
pears to be a much better formula. He just 
leaves out the Paris Green and puts in that 
much Arsenate of Lead instead. This dis¬ 
solves and is a much more deadly poison and 
is also inexpensive. He cleaned the thrips off 
in a hurry with it. However, he got at the 
job too late and the damage was already done. 
The thrips like to lay their eggs in the leaf 
sheaths and in the unopened florets and buds. 
Thus the spray gets only the older thrips. 
Hence the necessity of beginning the spraying 
before the spikes show. That way the thrips 
are killed before they can lay their eggs in the 
flower buds. 
The spraying should be done every week or 
ten days tili the blooms begin to show color. 
It need be only a fine mist with this spray. 
Some growers have used other sprays, using 
considerable force trying to dislodge the thrips, 
but that is a hard thing to do and we recom¬ 
mend instead the method above given. 
We feel absolutely certain that by use of 
the Napthalene treatment of the bulbs and the 
Arsenate of Lead spray for the growing plants 
that the thrips will do no appreciable damage. 
Many growers have reported fine blooms 
this past season, where the year previous they 
had no blooms at all. So, folks, the Glad busi¬ 
ness will soon go on as usual in spite of the 
thrips. 
