DISEASES OE^ PLANTS. 775 



This 8;ime phenomenon was observed on other plants, ]>rinei])ally (|nince leaves, 

 horse chestnut, cherry, etc. 



Early in July apple growers in western New York became considerably alarmed 

 at an extensive spotting, yellowing, and premature dropping of the apple leaves. A 

 careful examination of many of the orchards showed that the trouble was primarily 

 due to weather conditions and was greatly aggravated by spraying. Injury seemed 

 to follow the use of all the insecticides used alone or in conjunction with Bordeaux 

 mixture. Whether the Bordeaux mixture used alone was capaV)le of causing the 

 injury was not determined. The trouble was at its height about the middle of July, 

 and by the end of the montli in many orchards one-fourth to one-half the leaves had 

 fallen from the trees. The affected leaves were more or less spotted, and late in 

 August it was noticed that the majority of the spots were inhabited by a species of 

 Phyllosticta, which subsec|uent investigations showed was closely related to Phyllos- 

 ticta pirina. The parasitism of this fungus has never been proved by inoculation 

 experiments, and the fact that Bordeaux mixture seems to have little effect in restrict- 

 ing the disease has led the authors to believe that it is not the real cause of the 

 so-called leaf spot, but possibly the fungus is present as a saprophyte. 



As a possible explanation of the injury, it is stated that when a shower is followed 

 by bright sunshine, drops of water on the leaves act as lenses and concentrate the 

 sun's rays to such an extent as to destroy the tissues beneath. This injury produces 

 a condition similar to that rei'ognized in leaf spots, and may possil)ly l)e preliminary 

 to the presence of the fungus. In the authors' opinion a large part of the so-called 

 apple-leaf spot is due to spray injury and weather conditions, and is not of fungus 

 origin. 



Spraying experiments in 1902 for black spot, D. McAlpine {Jour. Dept. Agr. 

 Victoria, 1 (1902), No. 4, P- 4S3). — A brief report is given of experiments conducted 

 for the prevention of apple scab by the use of Bordeaux mixture. The addition of 

 linseed oil and sal ammoniac to B)Ordeaux mixture gave promising results. 



Experiments in the treatment of apple and pear scab during 1901-2, D. 

 McAlpine {Jour. Dept. Agr. Victoria, 1 {1902), No. 6, pp. 525-538, pis. .^).— The 

 results of experiments for the prevention of black spot or scab of the ajiple and pear 

 are given in detail. The relative susceptibility of different varieties is shown, and 

 the effect of spraying with Bordeaux mixture for the prevention of this disease is 

 indicated. The effect of a single spraying is shown by the largely increased pro- 

 portion of marketable fruit, as well as the increase in the gross yield. Single appli- 

 cations of Bordeaux mixture made to i)ear trees just after the buds had opened 

 resulted in the production of almost totally clean fruit of a variety which is ordinarily 

 considered exceedingly subject to disease. 



Experiments in the treatment of black spot of the apple and pear, D. 

 McAlpine {Jour. Dept. Agr. Victarin, 1 {1902), No. 6, pp. 620-6S0, ph. -^).— An 

 account is given of experiments conducted in a number of localities in Australia for 

 the prevention of scab of ajiples and pears. The comparative value of Bordeaux 

 mixture and copper-soda solution, potassium permanganate, copper acetate, and 

 various modified formulae of Bordeaux mixture is given. All of the treatments 

 greatly reduced the amount of scab. The most successful fungicide used was that 

 known as Grant's mixture. This is composed of Bordeaux mixture, to which some 

 unknown ingredients are added. 



The fungus causing black spot of the apple and pear, D. McAlpine {Jour. 

 Dept. Agr. Victoria, 1 {1902), No. 7, pp. 70S-70S, pi. i).— The black spot or scab of 

 apple and pear is said to have been first observed in Australia in 1862. Since that 

 time it has become well established throughout the country. Lists are given of 

 varieties of apples and pears which are most subject to the attacks of the fungus, as 

 well as those least affected. The symptoms of the disease and effects are indicated, 

 and the life history of the fungus is briefly outlined. 



