308 YEAKBOOK OF THE DEPARTMENT OF AGRICULTURE. 



could be done with a saving of nearly 50 per cent in labor and mate- 

 rials. A single treatment of the land with poisoned alfalfa hay 

 destroj^ed 85 to 95 per cent of the mice at a cost, including labor, of 

 about 35 cents an acre. Had this method been employed earlier, it 

 is certain that the plague could have been broken and a great part 

 of the ravages averted. 



In April. 1908. mice had become so alarmingty abundant in parts of 

 Carson Valley, Xevada, that an urgent appeal for assistance was sent 

 to the Biological Survey. On visiting the valley it was found that 

 in an area of about 2,000 acres near Minden the mice numbered 500 

 to 1,000 to each acre and had already destroyed 10 to 25 per cent 

 of the alfalfa, and that by reason of rapid reproduction they gave 

 every indication of producing a plague similar to that which had 

 stricken Humboldt Valley. Preliminary tests of a number of poi- 

 soned baits were at once carried out. Poisoned green alfalfa placed 

 in the trails and in the burrows of the mice proved fatal to practi- 

 cally all the mice in the areas treated — not a remarkable result, as 

 these mice habitually cut green alfalfa, stack it along their runs, 

 and later carry it into their holes. Poisoned crushed wheat proved 

 distinctly better than the whole grain, killing a larger number of the 

 mice, particularly of the small young. 



The importance of treating quickly the infested area j^revented 

 the extensive use of green alfalfa, since this material must be dis- 

 tributed during evening hours to j)revent drying by the sun, while 

 crushed wheat may be distributed all day long. Poisoning with 

 crushed wheat resulted in the destruction of fully 85 per cent of the 

 mice, at an average cost, including labor, of about 40 cents an acre. 

 Unfortunately a large number of magpies and blackbirds fell victims 

 to the poisoned grain; while to a less extent meadowlarks, killdees, 

 and mourning doves were killed. Under conditions threatening a 

 plague the destruction of the mice is of prime importance, but care in 

 putting out the smallest amount of poison needed to destroy the mice 

 will greatly lessen the danger to birds. A teaspoonful of properly 

 poisoned grain is sufficient to treat three or four mouse holes. 



Poisoned green alfalfa should be used where it is possible in-prefer- 

 ence to crushed wheat, since it is even more effective and eliminates 

 all danger to birds. It is particularly recommended for small areas 

 or where mice are not extremely abundant. Irrigation drives the 

 mice temporarily to the elevated ditch embankments and to the bor- 

 ders of fields, thus presenting an opportunity to use this material with 

 great effect. 



