Herbicides 



291 



type of injurious effects suffered by grains changes with different times 

 of application. For example, in figure 119 it can be seen that spraying 

 a stand of wheat in early April resulted principally in abnormal 

 position of spikelets in the head. Sprays in mid-April resuked in the 

 occurrence of supernumerary spikelets, and sprays in late April or 

 early May induced abnormal glume formation. In the case of corn 

 several different injurious effects have been described, inchiding the 

 production of brittle stems, seed of low viability, poor set of the 

 kernels or distorted ears (Rodgers, 1952; Staniforth, 1952). These 

 abnormalities, too, are a function of the time of spray application. 

 Reductions in yield can be closely correlated with some of these 

 injurious effects. 



Sample data on reduction of yields in peas as a function of time 

 of auxin application are shown in figure 120. It is evident that the 

 germinating seed is most sensitive to the auxin application, for treat- 

 ment at that stage reduced yields to almost zero. A second period of 

 sensitivity occurs as flowering begins. The inverse relationship of this 

 curve with figure 114 may be noted. Yield data for other crops do 

 not always follow the same trend (Derscheid, 1952; Andersen and 



Fig. 120. The effects of an heibicidal spray of 0.5 lb. /acre of MCPA (2-methyl 

 4-chlorophenoxyacetic acid) applied to peas at various stages of development upon 

 subsequent yield (Buchholtz, 1952). 



