Diseases of economic plants (1910) Diseases of economic plants diseasesofeconom00stev Year: 1910 VEGETABLE AJSIJ FIELD CROPS 251 ticularly destructive in New York, causing a loss of half the yield, or more in some instances. The attack in the field occurs first upon a few plants during warm, damp weather. Examined while the dew is still present, these plants, seen from considerable distance, display a pecul- iar violet tint especially easy to discern through the dewy covering. Close examination shows the affected part to be covered with a furry coating. On the second day these parts lose the
Diseases of economic plants (1910) Diseases of economic plants diseasesofeconom00stev Year: 1910 VEGETABLE AJSIJ FIELD CROPS 251 ticularly destructive in New York, causing a loss of half the yield, or more in some instances. The attack in the field occurs first upon a few plants during warm, damp weather. Examined while the dew is still present, these plants, seen from considerable distance, display a pecul- iar violet tint especially easy to discern through the dewy covering. Close examination shows the affected part to be covered with a furry coating. On the second day these parts lose their green color, turn pale, or even yellow. On the third or fourth day the plant is entirely collapsed. The diseased spots in the field may each cover an area of only a few feet in diameter, enlarging slowly. If the weather favors the fungus, the disease may sweep rapidly across the whole field. Affected plants, under suitable weather conditions, brilliant, dry at- mosphere, slowly recover, putting out new leaves to replace the dead and lost. Subsequent attacks may occur if the weather favors the growth of the fungus. The injury from this dis- ease is through the loss of leaf surface, thus reducing the growing power of the plant. Usually little or no increase in the size of the bulb occurs after a severe attack. Fig. 112.—Onion plant illustrating manner of death of leaves affected with downy mildew. After Whetzel.
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