UNITED STATES DEPARTMENT OF AGRICULTURE 
DEPARTMENT BULLETIN No. 1288 
Washington, D. C. 
December 19, 1924 
THE CONTROL OF 
AF-SPOT 
By Fred J. Pritchakd, Physiologist, and W. S. Porte, Junior Pathologist, 
Office of Cotton, Truck, and Forage Crop Disease Investigations, Bureau of 
Plant Industry 
CONTENTS 
Page 
Introduction 1 
Natural methods of overwintering 2 
Possibilities of overwintering on 
dead weeds, grasses, and remains 
of various crops 2 
Effect of soil on the viability of the 
fungus 4 
Control measures 5 
Fse of early plants 5 
Prevention of overwintering 7 
Page 
Control measures — Continued. 
Destruction of other hosts 9 
T7se of clean seed beds 10 
Rotation of crops 11 
Use of manure and fertilizers 12 
Spraying and dusting 12 
Development of resistant varie- 
ties 15 
Summary 16 
Literature cited 18 
INTRODUCTION 
Leaf-spot, or blight {Septoria lycopersici Speg. ; PL I, A to 6'), of 
tomato plants causes an average annual loss of approximately 250,000 
tons of tomatoes in the United States. 1 In addition to this loss in 
yield it also causes considerable reduction in quality of fruit. Be- 
cause of the defoliation of the plants the fruits do not mature proper- 
ly, but remain small, yellow, water) 7 , and deficient in solids and flavor- 
ing materials. As they have no protection from the sun by the leaves, 
many of them also become sun scalded (figs. 1 and 2) . Such fruits are 
therefore deficient in color and food value and unsuitable for making 
a first-class manufactured product. 
Leaf-spot is widely distributed east of the Eocky Mountains and 
is commonly destructive in those parts of the Middle Atlantic and 
Middle Western States that lie in a temperature belt of 73° to 78° F. 
during the growing season, but owing to the parasite's narrow range 
of sporulation temperatures, viz, 59° to 80.5° F. (i^), 2 this disease 
is relatively unimportant in States farther north and south and is 
absent in the Pacific coast region (figs. 3 and 4). It thrives best in 
a humid atmosphere and therefore is more abundant in Maryland, 
1 This is exclusive of losses in home gardens and truck patches grown for local 
markets. 
2 Serial numbers (italic) in parentheses refer to "Literature cited," at the end of this 
bulletin. 
2022 c 
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