192 PLANT GROWTH SUBSTANCES 



New chemicals other than the chlorophenoxyacetic acids are becoming 

 available for vegetation control purposes. Possibly one of the most 

 interesting of these is sodium trichloroacetate (sodium TCA) which has 

 a herbicidal effect on many grasses (i). It also appears to be promising 

 for killing cacti and palmetto. 



Although relatively large amounts of this chemical are required for a 

 high degree of grass-kill smaller amounts have a practical growth-con- 

 trolling effect. For example, on northern species such as quack and blue 

 grass twelve to fifteen pounds per acre of sodium TCA applied when the 

 infloresence is first emerging has eliminated flowering and retarded 

 growth for several weeks. When applied as a spray with 2,4-D many 

 nongrasses can be killed and the growth of grass controlled in one 

 operation. This technique appears valuable wherever mechanical mowing 

 cannot be carried out, such as along ditches and around highway guard 

 rails. Combined with the phenolic contact sprays sodium TCA has 

 shown much promise for general weed control on railroad beds. 



The action of this chemical, which I am taking the liberty of calling 

 a growth-regulating substance, is little understood. The immediate 

 foliage-burning effect appears to be independent of the systemic effect 

 which with quack grass occurs only after root absorption takes place. 

 In my own work far more grass killing has resulted when the chemical 

 was applied to the surface of newly plowed ground than when grass 

 foHage was sprayed. Obviously soil moisture relations are important 

 with a chemical that is largely absorbed through roots. At times con- 

 siderable dormancy of grass buds occurs following treatment without a 

 lethal effect. It is hoped that more physiologists will study the action of 

 this new herbicide. It seems hkely that many of the variations in field 

 results are related to the physiologic condition of the grass as well as to 

 soil moisture and rainfall. 



No doubt we are on the threshold of many further developments in 

 chemical vegetation control. The recent report on maleic hydrazide 

 (3) indicates that growth control without lethal action has definite 

 possibilities for many kinds of plants. Such chemicals could be of great 

 value to highway departments who must maintain turf at a reasonable 

 height and also to public utilities who have a tremendous tree-trimming 

 problem. Needless to say such chemicals would be of interest to all of 

 us who have a weekly session with the lawn mower. 



Many problems in vegetation control remain unsolved. We need 



