BETTER FRUIT 



EDITOR: W. H. WALTON 



STATE ASSOCIATE EDITORS 



OREGON— C. I. Lewis, Horticulturist. 



WASHINGTON — Dr. A. L. Melander. Entomologist; 

 O. M. Morris. Horticulturist. Pullman. 



COLORADO — C. P. Gillette. Director and Entomologist : 

 E. B. House, Irrieation Expert, State Agricultural College. 

 Port Collins. 



ARIZONA— E. P. Taylor, Horticulturist, Tucson. 



WISCONSIN— Dr. E. D. Ball, Madison. 



MONTANA— H. Tlioniber. Victor. 



CALIFORNIA— C. W. Woodwortti. Entomologist, Berke- 

 ley: W. H. Volck. Entomnlogist, WatsouTllle; Leon D, 

 Batchelor. Horticulttirist, Riverside. 



INDIANA— H. S. Jackson, Patliologist, Lafayette. 



An Illustrated Magazine Devoted to the Interests 



of Modein, Piogressive Fruit Growing 



and Marketing. 



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Entered as second-class matter April 22, 1918, 



at the PpstofUce at Portland, Oregon, under 



the Act of Congress of March 3, 1879. 



Volume XIV 



Portland, Oregon, March 1, 1920 



Number 9 



Controlling Pear Scab in the Pacific Northwest 



By D. F. Fisher, Assistant Pathologist, Fruit Disease Investigations 

 and E. J. Newcomer, Scientific Assistant, Deciduous Fruit Investigations, United States Department of Agriculture 



[This article applies particularly to that part 

 of the stale of Washington west of the Cascade 

 Mountains and to the Willamette Valley and 

 the northwestern part of Oregon.] 



THE culture of pear.s in thnt .section 

 of the Pacific Northwest located 

 west of the Cascade Mountains has 

 become an industry of rapidly increasing 

 importance. In the Willamette Valley, 

 Oregon, there is a large acreage of estab- 

 lished commercial orchards, while a con- 

 siderable planting of young orchards 

 has been made both in this section and 

 in the Pugct Sound region of Western 

 Wa.shington, where older orchards are 

 not so numerous. Pears thrive unusual- 

 ly well in these districts and have thus 

 far not suffered from the pear blight 

 scourge that has handicapped the cul- 

 ture of this fruit in other sections of the 

 Pacific Northwest. Pear growing in 

 these districts has also been greatly 

 stimulated by the development of can- 

 ning factoi'ies, which provide a ready 

 outlet for a considerable portion of the 

 crop. 



The industry has, however, sulfered 

 severe loss and its dcvelo]5ment has 

 been greatly handicapped by various in- 

 sect pests, as well as by the prevalence 

 of pear scab, a fungous disease. While 

 spring and summer spraying of pears 

 for the control of scab has been quite 

 generally practiced, the results have 

 often been disappointing, especially 

 when spraying has not included an in- 

 secticide for the control of insects 

 which cause a disfigurement that ap- 

 pears very much like scab spots when 

 the pears are mature. It is the aim of 

 this article to present to the orchardist 

 information which will enal)le him to 

 recognize and distinguish these troubles 

 and to take the necessary mea.sures for 

 their control. 



Pear Scab 



Scab is llie only fungous disease of 

 importance occurring on pears in the 

 region covered by this article. 



Next to pear blight, scab is llie most 

 serious disease to wiiich the pear is sub- 

 ,jecf. While it is readily controlled by 

 sprays it annually causes a heavy loss 

 because of inattention to spraying, inelli- 

 cient spraying iiialerials, careless meth- 

 ods of apiilicalion, or faihue lo spray 



at the right time. The crop yield is fre- 

 quently cut from 50 to 75 per cent, and 

 unsprayed fruit is usually so unsightly 

 that it is practically worthless for mar- 

 keting. If greatly deformed it can not 

 be disposed of even through the can- 

 neries. 



Influence of Climatic Conditions — 

 The economic importance of the disease 

 varies grcatlv with the climatic condi- 



FiGURE 1 — Scab on a mature Bartlett pear from 

 infection occurring early in the season. 



lions. Where the climate is strictly 

 arid and where pear growing is en- 

 tirely dependent upon irrigation, scab 

 is not found; but where humid condi- 

 lions prevail and natural rainfall is de- 

 pended upon for soil moisture, scab 

 must be contended with. Thus, in the 

 Pacific Northwest scab is entirely ab- 

 sent from the hot interior irrigated dis- 

 tricts cast of the Cascades, such as the 

 Yakima and Wenatchee Valleys, where 

 pear culture has been developed into 

 an extensive industry, while west of (he 



Cascades every pear tree is sub.ject to 

 the attack. The natural limitation of 

 the disease is due to moisture condi- 

 tions. 



Scab infection requires moisture on 

 the surface of the susceptible parts, 

 such as leaves, blossoms and fruit. 

 Moreover, it requires the surface to be 

 wet for about two days; mere dews or 

 fogs followed by drying weather will 

 not suffice, for although the spores may 

 germinate, the subsequent drying kills 

 the fungus before it has an opportunity 

 to establish itself in the plant tissues. 

 Frequent rains followed by muggy wea- 

 ther which does not permit the trees to 

 dry create the most favorable condition 

 for scab growth. This being true, it is 

 to be expected that the severity of the 

 disease will vary from year to year in 

 accordance with the precipitation and 

 that it will become more serious in 

 seasons of prolonged rainfall, but be re- 

 stricted during periods of drought. 



The climate of Western Washington 

 and Northwestern Oregon is peculiar in 

 that the winters are very mild, with 

 little snowfall but considerable rain. 

 The spring is usually rainy, with some 

 precipitation or fog during part of near- 

 ly every day. The summer, however, 

 is prevailingly without rainy periods, 

 with bright clear weather most of the 

 time. With the coming of fall, how- 

 ever, rains begin again. Under such 

 climatic conditions the greatest injury 

 from pear scab occurs early in the 

 spring, but late attacks of the fungus 

 often occur on fruit that does not ma- 

 ture before the fall rains. The early 

 infection of the fruit results in the 

 greatest disfigurement (Figure 1), as 

 well as often preventing a crop from 

 setting; consequently, it causes more 

 loss than later attacks. During the 

 summer season scab Infection is less 

 likely to occur and is entirely depend- 

 ent on chance periods of rainy weather. 



Character of the Injury— Pear scab is 

 a fungous disease that attacks the fruit, 

 foliage, and twigs. The greatest damage 

 is done to the fruit, on which it pro- 

 duces the sooty appearing spots so fa- 

 miliar to most orchardists. These spots 

 are generally somewhat irregularly cir- 

 cular in outline, with a velvefiike ap- 



