34 MASSACHUSETTS HORTICULTURAL SOCIETY. 



were infected just before the blossoms opened, by the ascospores 

 from the old leaves on the ground. 



5. That late infection which often ruins the crop just about 

 picking time may be prevented by a late application (that is, when 

 the fruit is about one-half or two-thirds grown). 



6. Spray just before rain periods, not after them. The spores 

 of the scab fungus are distributed, germinate, and infect the leaves 

 and fruit only during rain periods. Watch your weather map! 



7. The development of the buds and fruit, and the character 

 of the weather must be the guide in spraying for apple scab. 

 The character of the weather during the season will determine 

 Aery largely how many applications are to be made. Some 

 seasons one application alone, will be sufficient, as was the case 

 last year (1909). Other seasons, four applications must be made 

 if a perfectly clean crop is to be obtained. 



LlME-SuLFCR AS A SUMMER SPRAY. 



1. Evidence shows that lime-sulfur is equally efficient with 

 and safer than bordeaux mixture for the control of apple seal). 



2. The fungicidal value of lime-sulfur is not due to the soluble 

 sulfide of the solution directly, but is quite certainly due to sub- 

 stances derived from the oxidation of the free sulfur which has 

 resulted from the drying of the solution on the leaves. That the 

 soluble sulfids are not the active agents has been clearly proven 

 by Mr. Wallace by the simple experiments of precipitating lime- 

 sulfur with carbon dioxid and then, by tests, showing that it was 

 exactly as efficient when sprayed on trees as was the unprecipitated 

 solution. 



3. The fungicidal value of the lime-sulfur solution is increased 

 at least oU'.', by the addition of arsenate of lead at the rate of two 

 pounds to fifty gallons. This is one of the most remarkable dis- 

 coveries which Mr. Wallace has made. You will remember that 

 we were told two years ago that the addition of arsenate of lead 

 to the lime-sulfur solution could not be made as it would destroy 

 the value of the lime-sulfur and decrease the effectiveness of the 

 arsenate of lead as an insecticide. By an ingenious laboratory 



