10 BULLETIN 173, U. S. DEPARTMENT OF AGRICULTURE. 



of acres in these districts were prevented from blooming — a fact not 

 attributable to unfavorable weather conditions but solely to ravages 

 of the thrips. Other orchards, under same weather conditions but 

 with little or no thrips injury, produced a full crop of blossoms. 



During the year 1911 another type of injury that was different 

 from previous years, which may be called cumulative injury, was 

 noticeable in many orchards. Barring the three heavy frosts in 

 April, the blooming and fruiting season in 1911 was exceedingly 

 favorable in so far as climatic conditions were concerned. Never- 

 theless about the 1st of May the trees in many orchards turned a 

 sickly yellow owing to the work of the thrips in 1911 and from devas- 

 tations. by this insect in previous years. Some orchards which were 

 out of the frost belt and which were not severely injured by thrips in 

 1911 showed this condition noticeably. It is possible that much of 

 this was due to neglect of the orchards by fruit growers who did not 

 obtain crops of fruit during the preceding four years because of the 

 injury of the thrips to the buds, blossoms, and young fruit. 



As mentioned before, practically all of the Santa Clara Valley 

 came into full bloom in 1911 and gave promise of a record crop, but 

 larval injury was very heavy over the entire valley. This, with the 

 result of injury in previous years, apparently greatly weakened the 

 trees and caused much of the fruit to fall at the first unfavorable 

 weather. 



Injury to pears in the Santa Clara Valley has never risen to great 

 proportions from a financial point of view, for the reason that most 

 of the acreage of this kind of fruit is set out near Santa Clara and 

 Alviso, sections of this valley where the thrips has not yet become 

 dangerously numerous. However, during the season of 1911 a num- 

 ber of orchards in these localities became badly infested. The amount 

 of damage done to cherries in this valley has not been determined 

 on account of the scattered acreage planted to cherries in the infested 

 area. 



The distinctly severe years for thrips injury in Contra Costa County 

 in pear orchards were 1908 and 1910, when the crops were practically 

 annihilated. Also there was great loss the two previous years, 

 1906 and 1907. The prune orchards suffered in these years and in 

 the year 1909, producing less than one-third of a normal crop any 

 one year. The fruit crop has been seriously menaced each year 

 since 1905, the area increasing yearly, and in 1911 it aggregated a 

 total loss to the county of between 81,000,000 and 81,250,000. 



Solano County has in some ways been more fortunate, as the thrips 

 has been known to cause serious injury only since 1907, but even 

 in that time the thrips has spread rapidly and caused great damage 

 on large areas; the damage in 1911 was very extensive and the total 



