Page 10 



given in part here in order that we 

 may become better acquainted willi 

 the progress of tlie disease from early 

 spring to the end of the growing season. 



First Flow of Blight Exudate 



On March 19th, a Spitzenberg tree 

 at Grandview showed signs of fresh 

 oozing of blight exudate. On March 

 23rd, fresh exudate was found on 

 Winter Nelis and Bartlett pear trees 

 in the Broadway district near North 

 Yakima. On March 27th more exudate 

 was observed on other pear trees in 

 the Broadway locality, and on the same 

 date the first exudate for the season 

 at Sunnyside was observed on one 

 Jonathan and one Bartlett tree, and 

 four days later was found on a Spitzen- 

 berg tree. It was expected that new 

 exudate would become noticeable in 

 the lower valley first, where the season 

 is one to three weeks in advance of the 

 upper valley, but the temperature rec- 

 ords for March for Yakima give a mean 

 maximum of 61. 8 degrees, and a mean 

 minimum of 36.4 degrees, and for Sun- 

 nyside a mean maximum of 62.4 de- 

 grees and a mean minimum of 35.1 

 degrees, which no doubt had much to 

 do with the regularity of appearance 

 of first new ooze in those localities. 

 On April Isl, first new exudate was 

 seen in the Sclah disti'ict on one pear 

 tree and new case was found April 7th 

 on the Selah Extension. On Ai)ril .'jth, 

 the first new exudate found in the 

 Clarkston district was noted, and on 

 April 6th exudate was found on Bart- 

 letts in the Euclid district, near Grand- 

 view. As early as April 10th a small 

 percentage of hold-over cankers found 

 in the vicinity of North Yakima showed 

 signs of exudations, and by the 24th of 

 April a good percentage of hold-overs 

 found showed exudate. 



New Infection 



The first new infection of the season 

 was observed on Winter Nelis blos- 

 soms in the vicinity of North Yakima 

 April 24th. and at Prosser on April 20th. 

 At that date this variety had been in 

 bloom only a few days, but where hold- 

 overs were found it was not a dilTicult 

 task as a rule to find new infection of 

 blossoms on nearby trees. Whenever 

 blight shows up in a district it seems 

 that tliere are always certain varieties 

 that show heavy percentages of blos- 

 som infection, while other trees of dif- 

 ferent varieties growing among them 

 may show no blight, or at least blight 

 in small proportion to their neighbors. 

 Although there are many factors enter- 

 ing into the probable cause, my obser- 

 vations during a number of seasons 

 lead me to think that the limitation of 

 the blossoming period and its relation 

 to the abundance of blight exudate nt 

 that time is an important factor in 

 causing infection to take place in some 

 varieties to a greater extent than in 

 nearby trees of different varieties. 

 Bartlett pears at North Yakima were 

 coming into bloom April flth, and on 

 the same date were practically in full 

 bloom throughout the Grandview dis- 

 trict. The amount of exudate exposed 

 to the visitation of insects at that date 



BETTER FRUIT 



January 



Figure 41 — A branch of a young Yellow Newtown tree. The lower (left 

 liand) fork was headed back rather heavily, the upper iright hand) fork only 

 moderately. From the upper one have developed three shoots and nine 

 fruit spurs; from the lower one four shoots and Ihiee fruit spurs. The 

 photograph shows that heading back, whether heavy or light, tends to 

 inci-case ihe amount of shoot growth in the tree. However, heavy heading 

 back is seen to afford a greater slinmlus to shoot foi-malion and less of a 

 stimulus to spur formation than a more moderate heading back. 



was very small as compared to the 

 amount exposed ten days to two weeks 

 later, when most varieties of apples 

 were in bloom. It is a well-known fact 

 that the amount of infection in the reg- 

 ular blooming season is much greater 

 in Jonathan and Spitzenbergs than in 

 Bartlett pears, and the above dates 

 would partially seem to explain this 

 point. Bartlett trees that throw out 

 later i)loom are very susceptible to 

 blight, which is probably due, first, to 

 the greater abundance of exudate, and, 

 second, to ternpeiature conditions. 



Early in May new blight became 

 easily noticeable to anyone looking 

 carefully for signs of it. On May 8th, 

 new blight was beginning to show up 

 at North Yakima on Spitzenberg, Jon- 

 athan, Bome Beauty and some Wine- 

 saps. On May 12th, new blight was 

 showing up quite generally on Spitzen- 

 bergs and Jonathans. In spite of the 

 fact that pears had bloomed heavily 

 they were less seriously affected, no 

 doubt due to the blooming season (if 



the pears being a little ahead of any 

 general activity in hold-over cankers. 

 A warm rain on May 15th, which was 

 quite general throughout the Yakima 

 Valley, apparently accelerated and pro- 

 moted the spreading of blight infection. 

 This humidity continued for several 

 days and a week later it was reported 

 that some blight had shown up in prac- 

 tically all districts in Yakima County. 

 As early as the 22nd of May the in- 

 spector assigned to the Selah district 

 reported the finding of serious infection 

 in Winesaps and Delicious. New blight 

 was showing up plentifully in the 

 vicinity of Walla Walla May 13th, and 

 some new infection was observed by 

 the middle of May in the vicinity of 

 Dayton and Clarkston. Up to May 2i)th 

 Ihe new infection of Spitzenbergs and 

 Jonathans was almost entirely fruit- 

 spur infection, but Bome Beauties were 

 beginning to show some tip infection. 

 One interesting point was reported on 

 May 20th to the effect that infection 

 that Iiad reached the base of fruit spurs 



