THE ALFALFA CATERPILLAR. 33 



the field was irrigated thoroughly, thus starting the growth quickly. 

 The field was again irrigated as soon as the dry condition of the 

 crop required, and thus the growth was forced and not allowed to 

 be checked. 



It requires about 28 days to produce a hay crop in the Imperial 

 Valley — a little longer than this in the spring and fall, and a few 

 days less in warmer weather. It also takes practically the same 

 period of time, as has been shown on a previous page, for the butter- 

 flies to develop from egg to adult. Now, if the crop of hay be forced 

 by frequent watering, or because of good soil conditions, the worms 

 will not have gone into the resting stage at time of cutting, but, in- 

 stead, will still be feeding on the green alfalfa, and when the hay is 

 cut and removed conditions will be unfavorable for their develop- 

 ment and their food supply will be reduced. The hay in these fields 

 was cut just as it was coming into bloom, which is a few days 

 sooner than it is generally thought advisable to cut it. The advan- 

 tage of this early cutting is often very important, for if worms are 

 present in damaging numbers they will take a whole field in a short 

 time. In this case not only will the hay be saved, but a major portion 

 of the larva?, if clean cultural methods are used, will find a lack of 

 the food necessary for their complete development, and this, asso- 

 ciated with hot weather and irrigation following the removal of the 

 cured hay, will cause them ultimately to perish. 



Of the 10 fields handled according to these methods only 1 

 was damaged to any considerable extent. The other 9 were not 

 entirely free from larvae, but the numbers were so reduced as to pre- 

 clude any chance of noticeable injury to the alfalfa. In the one 

 exceptional field the damage was clue to the fact that irrigation had 

 been delayed for nearly two weeks after the cutting of the second 

 crop, owing to a new ditch which was under construction. Being 

 a thrifty field naturally, the alfalfa had made a start, assisted by 

 the moisture still present in the ground, and butterflies coming in 

 from an outside field deposited eggs on this new growth, thus en- 

 abling the worms to destroy the best of the crop after it was finally 

 irrigated. As a result almost an entire crop was lost. A field ad- 

 joining on the south, which had been irrigated immediately after 

 cutting, was not in the least damaged. This was a lesson in itself, 

 as it indicated the necessity for prompt work. 



These observations in California in 1910 have been further sup- 

 plemented by observations at Tempe, Ariz., and El Centro, Cal., in 

 1912. This year (1912) the writer made two trips into the Imperial 

 Valley. Several ranchers had kept records of their methods of hand- 

 ling alfalfa, and these records show conclusively the same results as 

 those of 1910. Two ranchers especially were found who had prac- 



