14 A MANUAL OF WEEDS 



costing only about a cent a pound. As an herbicide it should be 

 used as a spray, in a solution of about a hundred pounds to a barrel 

 of water (52 gallons), which should be a sufficient amount to spread 

 over about an acre of herbage. A dust spray of this chemical has 

 also been used, but is effective only when the plants are wet with 

 dew. Iron sulfate is particularly useful as a grain-field herbicide, 

 applied in dry, clear weather, when there is no likelihood that rain 

 will wash off the plants before the chemical has done its work. 

 Grains and grasses are very resistant to injury from the spray, 

 partly, no doubt, because their growth is from the center and 

 they quickly recover from such slight harm as may have been done 

 to the outer leaves ; also, they are smoother in texture than many 

 of the grain-field pests, such as Corn Cockle, Charlock, and King- 

 head, so that the spray does not cling so readily to their slender, 

 blade-like leaves. The spray must be applied before the grain 

 begins to "head" or the weeds to bloom, at a time when both are 

 making the most rapid growth, for then the grain recovers so swiftly 

 as scarcely to receive any check in its growth, and the weeds 

 succumb most readily when they are most green and succulent. 

 In the pea-field also this spray may be used to kill weeds without 

 serious injury to the crop, but not with beans. Clover and alfalfa 

 leaves are blackened, but recover rapidly if the solution has not 

 been too strong. 



When successfully carried out, this method of cleaning a field of 

 its undesirable plants pays the farmer very well ; for returns from 

 crops that have been relieved from competition with weeds for food 

 and moisture and space to grow, are often half as large again as 

 those from similar fields untreated, and are greatly improved in 

 quality as well as in quantity. 



Bluestone, or blue vitriol (Copper sulfate). This well-known 

 fungicide is also a most effective herbicide, if used when the weed 

 foliage is young and tender. The formula for the solution is eight 

 to twelve pounds of Copper sulfate to a barrel of water (52 gallons), 

 using fifty to seventy-five gallons per acre. Professor Bolley found 

 twelve pounds of Copper sulfate to be as effective as one hundred 

 pounds of Iron sulfate. Like that chemical, it should be used in 

 clear weather, when the plants are not likely to be rain-washed for 

 at least twenty-four hours, as such a bath would render the work of 



