HERBICIDAL CONTROL 11 



growth well into the second year. Impressive top kills or brown- 

 outs produced by certain chemicals are frequently followed by vig- 

 orous regeneration from basal parts, either in the same year or the 

 next one. Rapid killing of plant tissues is often disadvantageous 

 by hindering translocation of toxic substances. 



Another factor to be considered in judging success of herbicidal 

 operations is the rate at which treated weeds return to dominance. 

 Kinds of weeds that reestablish and spread rapidly need to be 

 eliminated 95% or more, else efforts toward their control will be 

 nullified in a short time. 



CALCULATIONS 



An important aid in figuring amounts of chemicals required for 

 spray solutions and in determining how to adjust spray equipment 

 to obtain particular dosages per unit area is the Handbook of Weed 

 Control Calculations, by John T. Maletic, USDI Bureau of Reclama- 

 tion, 1949. Additional help may be available from the following 

 formulas and tables, which were prepared with the help of Clark 

 G. Webster of the Patuxent Refuge. 



CALCULATING AMOUNTS OF MATERIALS TO USE 



The starting point for ascertaining amounts of ingredients 

 needed in spray solutions is the herbicide's concentration as re- 

 corded on the container label. Commonly the concentration is ex- 

 pressed in pounds of acid equivalent or active ingredients per 

 gallon and in percentages of acid equivalent or active ingredients 

 (often referred to as "active"). Having this information, it is 

 possible to determine the amount of commercial herbicide required 

 to make a solution with 1 pound of acid equivalent or active ingredi- 

 ents per 100 gallons or a 1-pound-per-acre application of acid 

 equivalent or active ingredients (table 1), or to make other specific 

 solutions. In preparing solutions other than for 1 pound per 100 

 gallons or per acre, or for other quantities than 100 gallons, cor- 

 responding fractions or multiples of figures in the tables can be 

 computed readily. It is desirable to use acid-equivalent figures 

 when they are available. 



USEFUL CONVERSION FIGURES: 



1 gallon = 4 quarts = 8 pints = 128 fluid ounrea = 3785 milliliters. 



1 pint = 2 oxipa = 16 fluid ounces = 32 teaspoonfuis. 



1 tablespoonfui = 3 teaspoonfuls = 15 milliliters. 



1 fluid ounce = 29.6 milliliters. 



1 pound = 16 ounces = 453.6 grams. 



1 acre = 160 square rods = 43,560 square feet. 



