

■*,»"$ 



■.^mMiMf^ 



Figure 5. The area in the foreground between the stakes of this quackgrass p'ot was treated 



with sodium TCA, 50 lbs. per acre, on July 26, 1951, during hot and very dry weather. 



Other annual weeds have been removed to show few remaining plants of grass. 



Selective Herbicides for Weed Control 



Controlling weeds with hormones 

 and chemicals, sprays which are se- 

 lective, is now an accomplished fact. 

 The use of 2,4-D, at once a hormone 

 and a selective herbicide, is quite 

 commonly practiced in oat and corn 

 fields. Di-Nitro compounds, too, have 

 been successfully used for weed con- 

 trol. 



Experiments with both these sub- 

 stances are under way in New Hamp- 

 shire. 2,4-D has been used very ef- 

 fectively in spraying oats, to control 

 the most common weeds in oat fields, 

 which include usually some kind of 

 mustard (kale or charlock) and white 

 pigweed (Chenopodium album). 



In spraying oats, one of the prob- 

 lems involved is to spray with such 

 a low amount of chemical that the 

 stand of clovers or alfalfa is not 



affected. In our tests, the weeds men- 

 tioned above are fairly well control- 

 led with one-half pint of 40 per cent 

 2.,4-D acid per acre. One pint of 40 

 ]ier cent 2,4-D acid, which, of course, 

 controlled weeds and allowed the oats 

 to surge ahead, was not lethal to 

 red and ladino clovers. 



Alfalfa is more easily affected by 

 2,4-D than are the clovers. For that 

 leasons, a di-nitro compound may be 

 preferable to use in spraying oats 

 which contain an alfalfa seeding. 

 Trials with this substance in 1950 

 indicated that the clovers were less 

 resistant to di-nitro than 2,4-D. The 

 type of sprayer to use for di-nitro is 

 different than for 2,4-D, the latter be- 

 ing best applied with a low gallonage- 

 low pressure outfit, while di-nitro 

 compounds should be applied with a 

 sprayer that will put on at least 100 



39 



