TIMELY NOTES ON SPRAYINGS 



BY PROF. W. LOCHHEAD, O.A.C, GUELPH, ONT. 



I.— Peach Leaf-Curl. 



lEACH Leaf-Curl was very prevalent 

 in the Niagara peach orchards in 

 the spring- of 1901. Very few 

 orchards escaped, and it was not 

 uncommon to find large areas of peach trees 

 defoliated by midsummer. The writer had 

 occasion to visit the Grimsby and St. Cathar- 

 ines districts several times during the early 

 part of the season, and to observe the atti- 

 tude of the peach-growers to the question of 

 remedial treatment. The belief was current 

 that spraying had little influence in combat- 

 ing the disease, and many growers expressed 

 the opinion that the trouble was caused alto- 

 gether by unfavorable weather conditions, 

 and not by a fungus. 



It is true that Peach Curl is most injurious 

 when the spring opens with cold wet weather 

 and sudden changes of temperature, but it 

 should be borne in mind that such conditions 

 favor the development of the fungus, 

 the real cause of the Curl, and render the 

 peach more susceptible to attacks by the 



•Notes from the Biological Department, Ontario 

 Agricultural College. 



same fungus. It has been shown experi- 

 mentally that the best temperature condition 

 for the growth of a fungus like Peach Leaf- 

 Curl is much lower than that for the best 

 development of the peach. Excessive 

 moisture, while not hurtful to the fungus, is 

 hurtful to the peach, as it saturates the 

 tissues with water, and renders them soft. 

 While growth may be rapid, the new cells 

 will have thinner walls, and there will be a 

 decided decrease in the activity of the living 

 substance due to the excessive amount of 

 water and the small amount of oxygen ab- 

 sorbed. 



In the consideration of this disease, then, 

 it must be understood that the fungus is the 

 real cause of the trouble, and that the 

 weather and other conditions cannot by any 

 means produce the disease without the 

 fungus. 



There are two possible ways by which the 

 peach leaves become infected : i. By threads 

 of the fungus which winter over in the year- 

 old branchlets, and 2, by spores of the fun- 

 gus in spring. The first view is the one 

 which was generally held by botanists up to 



