May 12,1933 Injury to Foliage by Arsenical Spray Mixtures 511 
Occasionally there would be some combination of injured leaves other 
than those listed above, as, for example, a few leaves badly injured and 
the others practically all sound, and judgment had to be used in desig¬ 
nating the degree in such cases, but these definitions will, in general, 
serve to place the authors and readers on common ground, 
CONDITIONS AlfF^CTlNG THE) AMOUNT OF INJURY 
It is a well-recognized fact that arsenic and its compounds tend to 
injure all forms of life with which they come in contact, but the degree of 
injury varies with several conditions, some of which are more or less 
under the control of the entomologist, the horticulturist, or the farmer, 
who makes use of these compounds for destroying insects upon growing 
crops. A study of these conditions constitutes the most important part 
of this investigation. 
DIFFERENCE IN SUSCEPTIBILITY OF PLANTS 
It has been found that different species of plants vary greatly in their 
natural resistance to arsenical action. Confining ourselves to the higher 
plants and especially to those that for economic reasons are likely to 
receive applications of arsenical insecticides, we find that some will be 
almost or quite killed by applications that will injure others but little. 
difference in genera AND SPECIES 
Numerous spraying tests were made on a rather wide range of plants, 
including some that were only distantly related. Table I, which records 
the results of a test made on August 2, 1915, is fairly typical of the results 
obtained with these plants. It should be added, however, that in other 
tests sugar beet has not usually proven quite as susceptible as here indi¬ 
cated, being about the same as potato. Also, squash has usually proven 
a little more susceptible, being in about the same class as apple. Cabbage 
is distinctly the most resistant of the plants we have tested, though in the 
experiment recorded in this table cucumber was injured but little more. 
Table I.— Plants in field plots sprayed with calcium arsenite, J.2 gm., and soap, y.2 
gm. per liter of water, to show the relative susceptibility of different species 
Name of plant. 
Injury. 
Apple, Wealthy. 
Bad. 
Very bad. 
Slight. 
Do. 
Moderate. 
Bad. 
Moderate. 
Do. 
Bad. 
Moderate. 
Do. 
Bean, White Navy. 
Cabbage, Late Flat Dutch. 
Cucumber, Improved Long Green. 
Potato, Early Ohio.. 
Pea, Senator. 
Rutabaga, Monarch.. 
Squash, Yellow Crookneck. 
Sugar beet, Klein Wenzlebener. 
Tomato, Enormous. 
Turnip, White Globe.. 
We suggest a table of susceptibility of plants we have sprayed, as shown 
in Table II. In using this table one must keep in mind that different 
varieties of the same crop vary somewhat among themselves in this 
respect. In this table an attempt is made to range the plants from the 
most resistant to the most sensitive. 
39363—23-6 
