Missouri Botanical 
Garden Bulletin 
Vol. VII St. Louis, Mo., February, 1919 * No. 2 
SPRAYING 
Spraying is the practice of protecting cultivated plants 
from the attacks of insect and vegetable parasites by cover- 
ing them with substances which have either a toxic or 
physiologically injurious effect upon the parasitic organism. 
The damage which is inflicted annually by various injurious 
insects and fungi is very great and is alleviated to a large 
extent through spraying. Neglect of this precautionary 
measure often causes irreparable injury to plants. 
Every portion of a plant—root, stem, leaf, flower, fruit, 
bark, wood—is subject to disease which may be manifested 
in a number of parts at once. The symptoms of disease are 
rots, blight, wilt, spots, scab, mildew, rust, smut, yellowing, 
and canker. To eradicate the diseases indicated by any of 
these symptoms fungicides are used. A satisfactory fungi- 
cide is one that causes no injury to the plant but is effective 
against the parasites. In addition, it should not be dis- 
solved readily by rain; it should adhere well to plant parts; 
and in some cases it should be colorless. The various spray- 
ing methods employed are: (1) killing of the causal organ- 
ism as it rests upon the seed; (2) killing of superficial fungi 
by applying a fungicide to the green parts of the plant; (3) 
killing of superficial fungi which hibernate upon the bark 
of dormant plants; and (4) the use of protective sprays. 
Killing of causal organism on seed.—For this oe 
disinfecting chemicals are applied long enough to kill the 
organism but not long enough to kill the seeds. Chief 
among such disinfectants are corrosive sublimate (2 quarts 
to 15 gallons water) ; formalin (40 per cent formaldehyde) 
in the ratio of 1 pint to 30 gallons of water; and copper 
sulphate. 
Killing of fungi on green parts of plant.—This method 
is applicable to tee purely superficial fungi, since internal 
parasites cannot be reached without injury to the plant. 
Powdery mildews are the most common examples of such 
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