428 ANNUAL EEPORTS OF DEPARTMENT OF AGRICULTURE. 



Reduced cost of poison supplies made it possible materially to re- 

 duce the cost of treating lands. Poisoned grain amounting to 1,323 

 tons was prepared and distributed under the direction and super- 

 vision of bureau representatives and cooperating State and county 

 officials, and 210,682 pounds of carbon bisulphide were used in fumi- 

 gating burrows to eradicate these rodents completely. Farmers and 

 stockmen numbering more than 104,000 took active part in clearing 

 their lands. Taking into consideration the low prices prevailing on 

 farm crops and range grasses during the year, it is estimated that a 

 saving of more than $8,000,000 was thus effected. The estimated sav- 

 ing in crops and forage since this work was started on a large scale 

 in 1916 totals $68,000,000. As lands are progressively and perma- 

 nently cleared of these pests the savings effected become permanent 

 additions to their productiveness. 



Field operations against these rodents progressed during the year 

 to a point where it appeared practicable to lay plans for three-year 

 campaigns to exterminate the rodents in a systematic manner from 

 great units of land. From 75 to 95 per cent of the animals are 

 usually destroyed by the first poisoning treatment and the new plan 

 of procedure contemplates follow-up applications of poisoned grain 

 and carbon bisulphide or other fumigants to complete the work by 

 the third year. In addition to several counties in western States 

 which are now reported completely cleared of prairie dogs, many 

 others have been cleared to a point where only an occasional prairie 

 dog or ground squirrel can be found. Over enormous areas of farm- 

 ing land the repressive measures employed have made it possible for 

 farmers completely to protect their crops from damage in regions 

 where the loss had been excessively heavy and where in many in- 

 stances it covered the entire crop. 



The work is so organized and conducted as to make available to 

 all farmers and stockmen supplies of poisoned bait at a moderate 

 cost. Arrangements made by the bureau for the cooperative pur- 

 chase of poisons in large quantities have greatly reduced the cost of 

 these supplies. So far as local conditions make it practicable, field 

 operations are being planned with a view to complete eradication 

 over great areas to eliminate permanently the worst rodent pests. 

 Operations will be extended from cleared areas as centers to prevent 

 reinfestation. The work is being correlated along the borders of 

 adjacent States for the purpose of protecting cleared areas in one 

 State from reinfestation from adjoining lands in another. In re- 

 gions where rodents are regularly extending their ranges they are 

 attacked along the border of such extensions and pushed back. 

 Western Arizona affords a good example of this kind, where the 

 westward movement of prairie dogs was stopped by clearing an in- 

 festation on a front 75 miles long and 10 miles deep. Without this 

 check there was serious danger of their spreading over into millions 

 of acres of new territor3^ 



In some instances county eradication campaigns reached the point 

 where only a few rodents were to be seen, and there was a tendency 

 for landowners to slacken in the work. A number of counties which 

 failed to continue effectively the follow-up work suffered consider- 

 able reinfestation and came to a realization of the danger that the 

 rodents might return to their former abundance and destructiveness. 

 The work has been taken up again in earnest with a view to perma- 



