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Rahmlow, H. J. (ed.) / Wisconsin horticulture
Vol. XXX (September 1939/July-August 1940)

Wisconsin horticulture, vol. 30, no. 6: February, 1940,   pp. [145]-176

Page 152

Can Apple Dropping Be Controlled 
                           By New Spray? 
A N article in a recent issue of 
     this magazine on results of 
 experiments using one of the 
 new "Growth substances" to stop 
 the dropping of apples just be- 
 fore harvesting created consid- 
 erable interest. 
 At the meeting of the Ameri- 
 can Association for the Advance- 
 ment of Science, held at Colum- 
 bus, Ohio, Dr. F. E. Gardner, 
 Paul C. Marth, and L. P. Batjer 
 of the U. S. Horticulture Experi- 
 ment Station described the new 
 method as follows: 
 Growth    substances, such as 
 napthaleneacetic acid and napth- 
 aleneacetimide, when applied in 
 the form of a spray promise to 
 prevent to a large degree the 
 dropping of apples immediately 
 before harvesting. 
 Growth substances came into 
 practical use a little more than 
 three years ago when it was dis- 
 covered that root cuttings which 
 were difficult to root could be 
 induced to produce g r o w i n g 
 shoots when soaked in a solution 
 containing the substance. Two 
 years ago the same substances 
 were used in sprays to produce 
 parthenocarpic fruit. 
 In carrying out the experiments 
 for the first two uses, the Bureau 
 scientists report, they observed 
 that petiole stubs remained at- 
 tached to the cuttings abnormal- 
 ly long. In a similar manner, the 
 parthenocarpic fruit showed a 
 persistence in staying on the 
 plant. These and other experi- 
 ments, served as a background 
 for starting experiments to pre- 
 vent dropping of apples.. 
 The tendency for apples to drop 
 is, in general, a characteristic of 
 early varieties. It is also a fre- 
quent occurrence with midseason 
and late varieties. As the fruit 
approaches the proper maturity 
and color for harvesting, the 
danger of loss from dropping in- 
creases. Each day that the apples 
remain on the tree to attain these 
desirable market qualities be- 
comes more of a gamble. With 
some varieties, such as Stayman 
Winesap, a disastrous drop may 
occur overnight. On the other 
hand, McIntosh, a notorious drop- 
per in many fruit sections, may 
fall steadily for several weeks 
prior to harvest time or in some 
cases drop very suddenly. 
    How Spray Was Applied 
  The experiments were conduct- 
ed on an orchard scale during the 
past summer and fall. Power 
equipment was used and the 
trees were sprayed thoroughly, 
using from 7 to 8 gallons of 
spray for small trees and as much 
as 25 gallons for large trees car- 
rying 20 or more bushels of fruit. 
Some individual fruits also were 
sprayed with   hand  atomizers. 
Some 21 different varieties were 
included in the study. 
  Using various strength sprays, 
it was found that .0005 per cent 
of the growth substance was suf- 
ficient. This amounts to one part 
of the substance to 200,000 parts 
of water, or about one-half tea- 
spoonful to 100 gallons of water. 
Some better results were noted 
when Y8 of 1 per cent of oil was 
added to the spray. No ill effects 
were noted when the spray was 
applied with the codling moth 
spray of lead arsenate and lime, 
which suggests the possibility of 
combining the anti-drop treat- 
ment with the regular spray pro- 
gram in the case of early varie- 
  As examples of effectiveness of 
the sprays, when 8 Stayman 
Winesap trees were sprayed with 
a .0005 solution the average drop 
18 days after the spray was ap- 
plied amounted to 23.4 per cent. 
On unsprayed trees the drop 
came to 61.4 per cent. With York 
Imperial under the same condi- 
tions, the sprayed trees dropped 
only 14.1 per cent compared to 
40.7 per cent for the unsprayed 
  On most varieties effect of 
  sprays persist for two or three 
  weeks. With the McIntosh va- 
  riety, however, the effect dimin- 
  ishes after 8 or 9 days. Best 
  results were obtained with this 
  variety when the spray was de- 
  layed until drop started. Then, a 
second  spray  can   be applied 
when the first runs out. 
         Timing Spray 
  With most varieties, the best 
results were obtained when the 
spray was applied just as the 
drop begins. This utilizes the 
greatest period of effectiveness. 
The effectiveness also is influ- 
enced by the thoroughness of 
the spray, and to some degree, 
by the temperature immediately 
following the spray. The spray 
takes effect more readily under 
warm temperatures. 
  There is no visible residue left 
on the fruit, and tests with labo- 
ratory animals prove that the 
spray material is not toxic even 
it, large amounts. 
  "The only observable effect on 
the fruit," said the scientists, "is 
the  excellent color developed 
which is so notable that it leads 
one to wonder if there may be 
some more direct color effect 
than can be explained by the fact 
that the fruit hangs longer on 
the tree." 
Editor's Note: This article is pub- 
lished for the information of our 
members only. No recommenda- 
tions are implied. 
February, 1940 

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