Herbicides 



287 



Foliar Applications 



The herbicidal effects obtained are strongly dependent upon the 

 concentration or the amount of auxin applied. A comparison of con- 

 centration effects for three species is shown in figure 118. These curves 

 fit very well with the generalized scheme of Woodford shown in 

 figure 115. The effectiveness of different concentrations on mortality 

 can be appraised only in the light of the injurious effects which may 

 result to the crop itself. For example, in figure 118 it can be seen that 

 the weight of tomato plants was seriously reduced by concentrations 

 which were one hundred times more dilute than the lethal level. In 

 contrast pigweed showed no change of plant weight until the lethal 



1000 10,000 MG/L 



CONG. OF 2,4-D 



Fig. 118. The effects of various concentrations of 2,4-D on kill, plant weight, 

 and number of distorted leaves of three plant species. Plants were four weeks old 

 at time of spraying, seven and one-half weeks at end of the experiment (Warren 

 and Leopold, unpublished). 



