. Bulletin of the Department of Agriculture. Agriculture. \ 0NTR0L OF ROOT FOEM OF WOOLLY APHIS. 33 INJURY TO THE TREE. Apple trees in the first year of growth were treated at the height of the growing season with varying dosages of carbon disulphid in One ounce of carbon disulphid to 4 gallons of water caused considerable injury, as evidenced by the drying of the foliage, but did not kill the tree, while 2 ounces to 4 gallons of water killed the tree in three Since one-half ounce of carbon disulphid to 4 gallons of water is ample for control there is no necessity for incre
. Bulletin of the Department of Agriculture. Agriculture. \ 0NTR0L OF ROOT FOEM OF WOOLLY APHIS. 33 INJURY TO THE TREE. Apple trees in the first year of growth were treated at the height of the growing season with varying dosages of carbon disulphid in One ounce of carbon disulphid to 4 gallons of water caused considerable injury, as evidenced by the drying of the foliage, but did not kill the tree, while 2 ounces to 4 gallons of water killed the tree in three Since one-half ounce of carbon disulphid to 4 gallons of water is ample for control there is no necessity for increas- ing the strength. In the same way apple trees in their second year of growth were treated with varying dosages of carbon disulphid in One ounce carbon disulphid to 4 gallons of water caused no injury, 1J ounces caused con- siderable injury, and 2 ounces killed the tree outright in 10 The increased re- sistance of the older trees is ex- plained by the greater area in- volved by the root mass, a large part of which was not subjected at all to the fumes of the carbon disulphid. During the ex- tended field tests about 500 apple trees of varying ages were treated at the rate of one-half ounce of carbon disulphid to 4 gallons of water and no apparent injury resulted. Injury to the tree by carbon disulphid in large doses is first in- dicated by a drying of the foliage. This, however, is merely direct evidence that the small roots and rootlets have been injured, thus cutting off the normal supply of water to the leaves and causing them to turn brown. With medium doses rootlets killed by carbon disulphid are rapidly replaced by the otherwise unimpaired root system. With the dosages of one-half ounce to 4 gallons of water the rootlet injury is negligible, and no killing of the foliage or check in growth will Fig. 1.—Diagram illustrating method of determining the lateral diffusion through the soil of carbon disulphid in water. For explanation see p. 32. (Orig
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