262 Appendix. 



most Important air drainage point for the great interior basin. Nearly evt^vy 

 afternoon during tlie summer tlie lieated air of tlie interior, because of it* 

 tendency to raise, produces a suction, drawing in across tliis valley the cooling- 

 air from the ocean, giving tlie long, cool growing season essential to the pro- 

 duction of this class of apples. 



These cool winds and the accompanying fogs profoundly modify the life 

 of the codling moth, for, in the most exposed localities, tliose in the lower end 

 of the immediate trough of the valley, all that region between the city of 

 Watsonville and the sea, the codling moth is practically unknown. After in- 

 troduction on fruit boxes it may do some injury the following season, but will 

 ultimately disappear. The growers in this district very wisely take pains that 

 the insect shall not be needlessly introduced in quantity, but take no remedial 

 measures. On the other hand, the larger part of the valley, particularly in 

 those orchards somewhat protected by the hills, the losses sometimes amount 

 to nearly tiie whole crop unless active measures are adopted for its contrnl. 



This variation in injury is not a gradual increase from tlie immune area 

 to that of tile greatest activit.y of the worm, but the change is abrupt from 

 no injury to much injury. Apparently the climatic conditions which cause 

 death are only sliglitly different from those in which the insect does well. 



The experience of the growers in past years in the central portions of the 

 valley has been that the difference in amount of injury from year to year was 

 very large and that spi-aying operations quite successful one season would not 

 be as effective the next. There had been numerous cases of very satisfactory 

 work against this insect, as in otlier parts of tlie United States, and it seemed 

 very mysterious that any particular plan of treatment would not effect the 

 same resulls from year to year, or in orchards somewhat differently located. 



A region with sncli a long summer season as Central ("alifornia the codling 

 moth has abundant (opportunity to multiply enormously, except where natural 

 or artificial checks produce a lieavy death rate. It will not be possible to ade- 

 quately discuss here tlie causes of death dependent upon the weather conditions 

 which were found to be operative in the I'ajara Valley, but it will be sufficient 

 to say that the critical period miglit come at any time during the summer season 

 and that in the larger part of the valley the abundance or scarcity of the insect 

 in one part of the season was no certain criterion of its condition at another. 



Our spraying operations this season have demonstrated that it is possible 

 to reduce the loss from codling motli to a very satisfactory percentage in everv 

 part of the Pajaro Valley and in the surrounding hilly country : this with a 

 single season's campaign. Doubtless persistent work year after year in the 

 same orchard would result in still more satisfactory control. In most parts 

 .of the Pajaro Valley the necessary number of sprayings will not be as great 

 as in warmer localities. We have made a large number of experiments to 

 determine the minimum number that will give satisfactory results and the 

 proper timing of the same. The results obtained were most conflicting and 

 correspond witli the spraying experiences of previous years. With the inter- 

 pretation given above, however, tliey become at once intelligible and indicate 

 that the best economic results will require for each immediate locality and per- 

 haps for each season the definite determination from time to time of tlie 

 condition of the worm as a basis for spraying operations. 



During the summer the use of bnnds on some of the trees will enable us to. 

 keep acquainted witli the relative numbers of summer moths being produced. 

 These bands should be examined at least once a week and the trnes should be 

 well poisoned as soon as the worms begin to be common and kejit poisoned as- 

 long as this continues. 



Towards fall the winter worms must be distinguished from the sumnier 

 generation. The latter may be known by the fact that they transform into 

 the brown spindle-shaped pupa very soon after spinning their cocoon, while 

 the winter worms remain as such till spring. As soon as summer worms are 

 replaced by the winter form spraying may cease, since there are no more youu.g 



