78 Diseases of Truck Crops 



the warning from an alarm thermometer which rings 

 a bell as the danger point in temperature is reached, 

 the fires may be started. Smudging and heating are 

 extensively used by orchardists. Truckers, however, 

 have generally been slow to adopt this method. 



DROUGHT INJURY 



By drought is meant a scarcity of water in the soil, 

 affecting and preventing the normal life process of 

 plants. Drought injury is variously indicated by 

 different crops. With beans, for instance, the leaves 

 lose their chlorophyll, and the entire plant becomes 

 whitish, brittle, dead, and dry. With cabbage, on the 

 other hand, the tips of the lower leaves first bleach, 

 then wilt, eventually drying and falling off. With 

 sweet corn the plants shrivel and bend over (fig. 

 12 b). The amount of injury from drought is pro- 

 portional to the scarcity of the water in the soil. 

 The only remedy for drought is, of course, irrigation. 

 This is especially true for arid and semi-arid regions. 

 Trucking is never safe unless provisions are made 

 for proper irrigation. 



SMOKE INJURY 



As a rule, trucking centers are situated near large 

 cities, which are usually centers for industrial pro- 

 duction and manufacture. Truckers who are situ- 

 ated nearest to manufacturing plants are apt to lose 

 in crops from the effect of smoke and deleterious gases 

 that escape from the furnaces into the air. 



