PRESS BULLETIN 190
UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
THE CONTROL OF THRIPS ON TOMATOES
BY J. R. WATSON
There is now over most of the State an outbreak of thrips. Complaints
came first from the lower East Coast early in March, and they are coming in
now from sections farther north. Although thrips have been common this
year on such plants as roses and guavas, the most serious damage has been
done in the tomato fields and citrus groves.
The thrips (Euthrips tritici,) called the Grain Thrips because it was first
noticed on wheat in New York, is a minute insect, only one twenty-fifth of an
inch long. It is soft-bodied, with orange-colored head and thorax, and yellow
abdomen. The adults fly readily for considerable distances. When disturbed,
they can spring two or three inches. They are active creatures and crawl
about a good deal. The young (or nymphs) are nearly like the adults, but lack
The life cycle of the thrips is short, a generation occuri-ing every two or
three weeks under favorable conditions. The eggs are laid just beneath the
skin of the plant in a shallow slit.
The young, upon hatching, at once attack the tenderest part of the blos-
som or bud. The stamens seem to suffer first, but as there is always much
more pollen produced than is needed, no particular harm is done here. If
there are only a few of the insects present, say one or two to each blossom,
they usually find enough food in the stamens and do no further harm to the
crop. It is even possible that they may be of service in cross-pollinating the
blooms. But where there are a dozen of them in a single bloom (the writer
has counted as many as twenty) they attack other parts, including the pistil.
This turns black and shrivels up. Soon afterwards the whole flower turns
yellow and falls off. If this is repeated for all the blossoms on the first three
May 4, 1912
or four hands (as was often the case this year,) the crop is ruinously short-
Tobacco decoctions are very effective against these insects. The only
difficulty is in reaching them with the spray, as they are under the stamens
and protected by them. But they are active creatures and when the blossom
is disturbed they at once come out and attempt to get away. It is this habit.
which enables the grower to reach a large proportion of them with the spray.
In spraying, therefore, care must be taken to thoroughly cover the blossoms
or buds so that the thrips cannot get out without being wetted by the solution.
By pausing and letting the spray play for a second or two on each cluster or
"hand," one not only ensures the thoroughness of the spraying, but also
gives the insects time to crawl out where the spray can hit them. For the
same reason one should use as much pressure as is possible, for the double
purpose of driving the liquid into the blossoms and frightening out the insects.
The different tobacco decoctions, of which there are many on the market,
vary much in the amount of nicotine present, and consequently in the propor-
tions in which they should be diluted. Black Leaf "40" should be used in
about the proportion of one part to from 1000 to 1800 of water. The weaker
solutions, such as Black Leaf (two and one-third per cent nicotine,) should be
used at about one part to 100 of water, while one part of home-made tobacco
extract needs about ten parts of water. It is of advantage to put into the
-solution something to give it better sticking qualities. The writer used the
following on tomatoes during April, 1912, and killed about 75 per cent of the
thrips present. (This solution was previously found effective against the or-
ange thrips in California.)
Commercial lime-sulphur......................two and one-third quarts
Black Leaf "40".......................three and one-half fluid ounces
Water ...................... ....... .........................fifty gallons
If one wishes at the same time to kill the tomato worms or other leaf-
eating insects, lead arsenate or zinc arsenite should be used in place of lime-
State papers please copy.