SPREADERS FOR SPRAY MATERIALS, AND THE RELA¬ 
TION OF SURFACE TENSION OF SOLUTIONS TO THEIR 
SPREADING QUALITIES 1 
By R. H. Robinson 
Chemist , Oregon Agricultural Experiment Station 
INTRODUCTION 
For many years efforts have been made to improve the spreading 
and adhering qualities of spray materials by the addition of some 
harmless substance that would cause the spray to form a continuous, 
even film over the plant surface covered. At present our greatest 
need in orchard practice, aside from the development of certain 
more effective sprays, is to overcome the difficulty attending the 
application of sprays in which the surface can not properly and 
easily be covered. 
The continual increase in severity of infestation and the appear¬ 
ance of some insect pest or fungous disease into a new section of the 
country emphasizes the necessity of either heavier and more careful 
applications of the poison whereby all of the plant surface will be 
covered, or the use of a more effective spray. Since most of our 
important sprays are effective to the extent that fair control has 
been obtained with them when care is exercised to obtain complete 
coverage, it is obvious that the main factor contributing to the 
ravages caused by insect pests and fungous diseases is the inability 
to cover with comparative ease the entire surface. If the addition 
of a spreader to a spray improves the covering and assists in more 
easily obtaining a protective coating of the poison on those surfaces 
to which the sprays adhere with difficulty, then an important advance 
has been made in spraying. 
An ideal spreader should cause a continuous film of the poison to 
be deposited on the surface covered instead of collecting m drops, 
it should increase adherence, it should not react chemically with the 
poison to form by-products that would cause foliage injury, it should 
not diminish the toxic properties of the poison, and it should not 
cost too much. The difficulty in selecting a spreader with these 
requirements is increased by the fact that the plant may have several 
different kinds of surfaces. For example, the apple tree has the 
smooth upper leaf surface, the hairy under leaf surface, and the 
waxy surface of the partially developed fruit; and in addition it may 
have the smooth bark and the wrinkled bark of spurs and the young 
and old leaves which may offer resistance in various ways to the 
spray. Ruth and Kelley 2 state that the behavior of the surfaces 
toward sprays changes very rapidly, in some cases markedly within 
a week or 10 days. It may be impossible to find a spreader that will 
f ulfill all of the requirements. Investigations, however, may reveal 
materials or combinations of materials that will prove beneficial 
on certain plants at different periods of growth. 
1 Received for publication Aug. 24, 1924; issued September, 1925. ^ A 
2 Ruth, W. A., and Kelley, V. W. recent advances in spraying. Unpublished data. 1922. 
Journal of Agricultural Research, 
Washington, D. C. 
( 71 ) 
Vol. XXXI, No. 1 
July 1, 1925 
Key No. Oreg.-lO 
