Diseases of economic plants (1910) Diseases of economic plants diseasesofeconom02stev Year: 1910 104 DISEASES OF ECONOMIC PLANTS Fig. 43. — The blight showing exudate from bark, much enlarged. This teems with the causal bacteria. After Whetzel. With the flow of sap in the spring these infested limbs become centers of reproduction. From these a milky fluid teeming with the bacteria exudes. This attracts insects which then carry the infection to other twigs and to flowers. Two additional forms of this disease, according to the part affected, are recognized: (1) flower blight, (2) body bligh
Diseases of economic plants (1910) Diseases of economic plants diseasesofeconom02stev Year: 1910 104 DISEASES OF ECONOMIC PLANTS Fig. 43. — The blight showing exudate from bark, much enlarged. This teems with the causal bacteria. After Whetzel. With the flow of sap in the spring these infested limbs become centers of reproduction. From these a milky fluid teeming with the bacteria exudes. This attracts insects which then carry the infection to other twigs and to flowers. Two additional forms of this disease, according to the part affected, are recognized: (1) flower blight, (2) body blight and canker. Neither of these differs essentially from the twig blight, though the body blight or canker is es- pecially worthy of men- tion on account of its peculiar destructiveness. This form occurs where the disease is led by a spur, shoot, or sucker into the cam- bium under the bark of the body or main limbs of the tree, or where primary infection occurs through a wound so as to lead to disease in such parts. The result of such in- fection is a diseased area more or less circular, which may even girdle the tree or branch, and which in any event causes serious injury. The susceptibility of the tree is largely influenced by external conditions. In general, anything which leads to rapid growth, resulting in tender shoots, favors the devel- opment of the disease. There is also much difference in resistance offered by different varieties. The Anjou, Kieffer, Angouleme, and Seckel possess more resistance than the Bartlett, Clapp, or Flemish Beauty. Based on the facts as stated above, the following direc-
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