THE MONTHLY BULLETIN. 



227 



some treatment or speci^il ('iiltiii;il method employed, when in reality 

 the disappearance of the worms was due solely to some natural influence. 

 It is not only difficult to devise conti-ol measures that will prove effective 

 in every case, but it is also iiard sometimes to check up work and know 

 that results are being obtained. 



WORK AGAINST THE LARVAL STAGE. 



Poisoned Baits and Deterrents. — Work with poisoned baits proved 

 entirely unsatisfaelory. The worms either ate the poisoned bait with 

 no ill effects, or the bait proved distasteful and was not touched. 

 Prominent among the first group are strychnine, bichloride of mercury, 

 carbide, nicotine sulphate, tobacco extract, and several forms of arsenic. 

 Paris green and sodium cyanide seem to have some value as deterrents, 

 but have l)een discarded beeause they injure the germination of the bean. 

 However, in these experiments it was found that sodium cyanide has 

 other values, which will be considered next under tlie head of soil 

 fumieation. 



Fig. 75. — Adults of the su^ar beet wire- 

 worm, Limonius calif orniciis Mann. Natural 

 size. (After Essig-, Inj. and Ben. Insects of 

 Cal., p. 233, State Hort. Com.) 



Soil Fumigation. — During the spring of 1914, under the direction 

 of Mr. R. S. Vaile and Mr. J. E. Graf, carbon bisul])hide was used by 

 means of a small pressure tank rigged up on a walking plow so as to 

 throw a stream into the bottom of the furrow. In this way it was 

 immediately covered up and a crosskill was then used to pack the top of 

 the ground. The results of this experiment were entirely negative, and 

 further experiments were given up on account of the cost of the 

 material and the apparent lack of effectiveness. Cyanide was also used, 

 being put in with a fertilizer drill at the rate of i|^25.00 per acre. This 

 experiment was discontinued at the same time as the carbon bisulphide 

 experiment and for similar reasons. 



In experimenting with sodium cyanide (128-130 per cent) as a 

 poisoned bait during the spring of 1915, it was noted that in every case 

 the worms were dead, although apparently not having touched the bait. 

 This led to the conclusion that they were killed by the action of the gas. 

 A little additional work proved such to be the ease. The writer then 

 took the matter up with Donlon Bros., and they agreed to finance a 

 trial in the field. In order to find the least amount of cyanide necessary 



