i9io.] Injury to Foliage by Bordeaux Mixture. 105 



indeed, it is not confined to them — where the trees are sprayed 

 about a week or two after the fruit is set. I am inclined to think 

 that the safest time to spray those varieties the fruit of which 

 is liable to become "russeted" is immediately the bloom has 

 fallen, or even in cases where the trees are flowering pro- 

 fusely, while a little of the bloom still remains on the tree. 

 A later spraying is often necessary, especially with varieties 

 {such as Ecklinville) which produce a considerable amount 

 of fresh foliage during midsummer growth. If this fresh 

 foliage is not sprayed, the "scab" fungus increases on the 

 new (unspraved) leaves, and spreads thence to the half- or 

 three-quarter grown apples and without much affecting their 

 growth in size ruins their appearance and keeping qualities 

 by covering them with "black spots." A light spraying — - 

 just sufficient to protect the new leaves of the midsummer 

 growth — at a time when the apples are about three-quarter 

 grown, seldom, if ever, produces that serious " russeting " 

 which may occur when the whole tree has been sprayed at the 

 lime when the apples are about a quarter-grown or smaller. 



The actual causes which produce "Bordeaux injury" are 

 still very obscure ; it seems clear, however, that subsequent 

 chemical changes in the Bordeaux mixture after it has been 

 sprayed on the plant and there exposed to various weather 

 conditions (especially wet weather) are largely concerned in 

 causing the injury. The matter is complicated by the fact, 

 recently discovered by Mr. S. U. Pickering, F.R.S.,* that 

 the chemical compounds formed in Bordeaux mixture vary 

 considerably according to the exact proportions of copper 

 sulphate and lime used, and also according to the method of 

 mixing them. Without considering here the complicated 

 chemical questions involved— which are still unsettled — we 

 may note the practical conclusions on the subject of this injury, 

 and how it may best be avoided, which have been arrived at 

 by horticultural authorities in the United States, after a long 

 and careful investigation of the matter as it affects the com- 

 mercial apple-grower in that country. The following notes 

 are taken from Bulletin No. 287 of the New York Agricul- 

 tural Experiment Station, written by Prof. U. P. Hedrick : — 

 "There are many anomalies of occurrence brought about, for 



* See Wobum Exper. Fruit Farm, 8th Report, p. 7 (1908). 



I 



