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The Canadian Horticulturi^ 



Vol. XXXV 



JANUARY, 1912 



No. I 



Peach Diseases in Ontario 



* 



EVERY peach grower is familiar with 

 the leaf curl disease, and knows 

 that it attacks the leaves early in 

 the spring and causes the mat first to 

 become thickened, curled and distorted 

 and of a pale whitish or often reddish 

 color, and later on to become brown and 

 dead and fall off. It is, next to Yellows 

 and Little Peach, the most destructive 

 disease that growers have to combat. 

 The loss takes the following forms : 

 First, In seasons of severe attack many 

 young nursery trees are killed the first 

 year they are set out and before they 

 have had a chance to get over the shock 

 of transplanting ; second, there is a great 

 drain on the vitality of older trees from 

 the loss often of a large part of their 

 foliage early in the season and the neces- 

 sity of producing a new crop of leaves. 

 Such trees are frequently not properly 

 matured for winter and are sometimes 

 killed by the cold. Trees severely at- 

 tacked two or three years in succession 

 not infrequently die, or at least lose a 

 number of their branches ; third, the fruit 

 is dwarfed and often in bad cases drops 

 off. This is to be expected from the fact 

 that the substances that make the fruit 

 are largely manufactured in the leaves ; 

 hence this source of supply is cut off for 

 a considerable period by the disease; 



•Extract from a paper read at the recent an^ 

 nual convention of the Ontario Fruit Growers' 

 Association, held in Toronto. 



Prof. L. Caesar, O. A. C, Guelph, Ont. 



fourth, the disease often attacks young 

 shoots or twigs and kills these. 



FAVORABIiE CONDITIONS 



Leaf Curl is well known not to be so 

 severe some years as others. Experi- 

 ence has shown that it is favored by 

 damp late springs, while it is almsot 

 completely kept in check by dry sunny 

 weather around the time of blooming, 

 and while the leaves are still quite 

 small. In 1910 the spring was very late, 

 cold and wet, and so the disease was 

 exceptionally severe. Last year, 191 1, 

 the spring was. early and we had beauti- 

 ful, hot, sunny J dry weather, with the 

 result that there was no Leaf Curl or 

 almost none. This fact has led some to 

 believe that Leaf Curl is not a disease, 

 but is merely the result of unfavorable 

 weather conditions. Such, however, is 

 not the case, as anyone can easily prove 

 who takes a glance through a microscope 

 at one of the dead leaves from an affect- 

 ed tree and sees the millions of spores 

 on the surface. These spores act like 

 seeds and are carried by the wind from 

 tree to tree and orchard to orchard, but 

 so far as we know do not germinate un- 

 til the next year. For their germina- 

 tion and growth plenty of moisture is 

 necessary, hence the wet seasons favor 

 their growth ; moreover, cold does not 

 interfere with their development, while 

 it retards the vigor of the leaves. 



A number of years ago we were told 

 that spraying would not control the dis- 

 ease because it was then believed that it 

 passed the winter only in diseased twigs, 

 but we now know from thousands of ex- 

 perimenters that even in the most favor- 

 able seasons for the disease we can keep 

 it under thorough control by a single ap- 

 plication. 



MEANS OF CONTROL 



Spray with lime-sulphur of the ordi- 

 nary strength as for San Jose Scale (one 

 gallon commercial wash diluted to about 

 ten with water). This application must 

 be made early in the spring and before 

 the buds have begun to swell. The dis- 

 ease begins with the growing bud, so 

 to prevent its getting a start we must 

 spray early before the spores around 

 the buds can germinate. Most of the 

 failures to control the Leaf Curl are due 

 to spraying too late and not taking suffi- 

 cient pains to see that every bud is thor- 

 oughly covered. Bordeaux \vould also 

 control the disease, but is not recom- 

 mended because in most peach districts 

 San Jose Scale is either present or likely 

 to be introduced and the lime-sulphur 

 will keep it in check, while Bordeaux 

 will not. 



MILDEW 



The Powdery Mildew (Sphaerotheca 

 pannosa, Wallr.) disease is found chiefly 

 on young, trees not yet in bearing, but 



Sem* of tht High Grade Frait Growa ia th* Proviac* of Qaebec at ibowa at reccat Aaaual Coarcatioa of tkc ProTincial Frnit Groweri' Auociatioar kcU at Macdtul^XJollcge 



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