DONALD P. GOWING 



Pineapple Research Institute of Hawaii 



Some Comments on Growth Regulators With a 



Potential in Agriculture' 



The topic for discussion is the design of more effective plant growth 

 regulators for agricultural use. This paper will propose that a number 

 of effective growth regulators for agriculture are already designed and 

 that they simply await the recognition that will follow their wider test- 

 ing. Although a full range of variously substituted aryloxyalkyl car- 

 boxylic acids has been studied in the laboratory in biological tests of 

 relative potency, only a few have thus far found horticultural use. If 

 one names the 2-methyl-4-chloro-, the 4-chloro-, the 2,4-dichloro-, and 

 the 2,4,5-trichlorophenoxyacetic, alpha-propionic, and gamma-butyric 

 acids, he has very nearly covered the field. 



It is interesting that although the phenoxyacetic series has been 

 in use for some time, the phenoxypropionic and butyric analogues 

 are much more recent arrivals on the commercial scene, usually for 

 a higher degree of selective weeding, and the propionic derivatives also 

 for crop control in circumstances where the acetic derivatives would 

 be quite injurious. Wain (6) and co-workers have adequately pointed 

 out that the relative activities of the butyric and acetic analogues 

 derive from merely quantitative considerations in some plants, but 

 qualitative differences in others. It is the qualitative aspect that I 

 wish to stress, for in this may lie the key to greater usefulness of 

 other phenoxyalkyl carboxylic acids in crops too sensitive to those 

 mentioned. 



For instance, the pineapple plant may be forced into unseasonal 

 flowering by 2,4-dichlorophenoxyacetic acid (2,4-D) at rates from 5 

 to 10 g/acre (rates such as would be encountered in spray drift from 

 herbicidal applications of 2,4-D at 1 to 2 lb/acre). This can result 



^Published with the approval of the Director as Technical Paper No. 268 of 

 the Pineapple Research Institute of Hawaii, Honolulu, Hawaii. 



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