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PRESS BULLETIN 183 February 3, 1912
UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
SPRAYING AND THE CITRUS PURPLE SCALE.
By H. S. Fawcett and O. F. Burger.
A Spraying Experiment.
During an experiment in which orange trees were sprayed three times
with Bordeaux mixture there were found, on an average, 10,000 scale-
insects per orange on the Bordeaux-sprayed trees, as compared with only
30 per orange on unsprayed trees near by. On other trees sprayed three
times with commercial lime-sulphur, in the same grove, there were found
115 scale-insects per fruit, and on neighboring trees sprayed three times
with Yothers' Formula IV, only 5 scales per fruit. On leaves nearest the
oranges an average of 240 scale-insects per leaf was found on Bordeaux-
sprayed trees, as compared with only 10 scale-insects per leaf on the un-
sprayed trees. On the trees sprayed with lime-sulphur, there were 20
scales per leaf, and on trees sprayed with Yothers' Formula IV there was,
on an average, only 1 scale to each leaf.
These counting of scale insects were made at the beginning of Decem-
ber. The spraying were, one in May, one in July, and a third in September,
each in three different localities. The red-headed, white-headed, and black
fungi were present, as parasites on the scale insects. The Bordeaux mixture
was made up of 3 pounds of rock lime and 3 pounds of copper sulphate to
50 gallons of water. The lime-sulphur was diluted at the rate of one gallon
to 25 gallons of water. Others' Formula IV was made up of 3 gallons
of Junior Red engine-oil and 2 gallons of whale-oil soap to 200 gallons of
Scale-insects in September.
Two other counts of the numbers of scale-insects had been made earlier
in the season, one at the beginning of September, and the other at the
beginning of November. In all, the scale-insects on 360 oranges and 1800
leaves were counted for these records. On September 1, there were, on
an average, 390 scales per fruit on the Bordeaux-sprayed trees, 31 per fruit
on the unsprayed trees, 18 per fruit on the trees sprayed with lime-sulphur
and 2 per fruit on the trees sprayed with Yothers' Formula IV. On the
leaves, the average numbers at this time were, 190 per leaf with Bordeaux,
15 per leaf on the unsprayed trees, 5 per leaf with lime-sulphur, and one-half
of one scale per leaf with Yothers' Formula IV.
Scale-Insects in November.
Two months later (November 1) the average numbers were, 3190 scale-
insects per fruit on the Bordeaux-sprayed trees, 29 per fruit on the un-
sprayed trees, 26 per fruit on the trees sprayed with lime-sulphur, and
one scale per fruit on the trees sprayed with Yothers' Formula IV. The
average numbers per leaf were, 190 with Bordeaux, 10 on the unsprayed
trees, 6 with lime-sulphur, and an average of three-tenths of one scale with
Others' Formula IV.
Bordeaux, Lime-Sulphur, and Yothers' Formula IV.
Combining these three counts, and taking the unsprayed trees as the
standard, we have for the Bordeaux an average of 15 times as many scale-
insects on the leaves, and 150 times as many on the fruits, as on the un-
sprayed trees. For lime-sulphur, we have about the same number on the
leaves, and one-half as many on the fruits, as on the unsprayed trees. For
Others' Formula IV, we have one twenty-fifth as many on the leaves, and
one-tenth as many on the fruit, as on the unsprayed trees.
Bordeaux Mixture and Scale-insects.
While it has been recognized that a rapid increase of scale-insects fol-
lowed Bordeaux treatment, accurate numerical data have hitherto been
lacking. The evident cause for this increase of scales is the killing by the
Bordeaux of the scale fungi (red, white and black) which hold the scale-
insects in check. The large totals from the Bordeaux-sprayed trees, in
comparison with the unsprayed trees, indicate what we may expect to
happen when the fungi are not present. When it is absolutely necessary
to use Bordeaux mixture on orange trees, one must always be prepared to
follow it up with a good insecticide. Otherwise the harm done by the in-
creased number of scale insects will often more than counterbalance the
good done by the Bordeaux in killing injurious fungi.
State papers please copy.