EXPERIMENT STATION BULLETINS. 435 



EXrERIMENT IN 1920. 



One exi3eriment of this nature was conducted in 1920 in a block of about 

 100 twelve-year-old Grimes Golden trees on the farm of Mr. H. E. Hawley 

 near South Haven. This block was divided into four plots as follows: 



1. Check — No treatment. 



2. Sprayed — Dilute lime-sulphur and lead arsenate. 



3. Dusted — Sulphur dust, 90-10 mixture. 



4. Dusted — Dehydrated copper sulphate dust. 



The dehydrated copper sulphate dust contained 10 per cent of dehydrated 

 copper sulphate.* This material is what has commonly been called the 

 "Sanders dust" and was developed by G. E. Sanders of Nova Scotia and has 

 given promising results under Nova Scotia conditions. It is made by mixing 

 the desired proportions of dehydrated copper sulphate and hydrated lime. 

 Poison is added if desired. The dehydrated copper sulphate is prepared by 

 heating ordinary copper sulphate (blue vitriol) to drive off the water of 

 crystalization. It is then usually ground to produce a uniformly fine powder 

 and mixed with the hydrated lime. When dusted on to the tree, it re-absorbs 

 water and combines with the lime, making compounds probably similar to 

 those obtained by mixing the two materials in water when making ordinary 

 bordeaux. The material used in this particular experiment was made up as 

 follows: 80 per cent hydrated lime, 10 per cent dehydrated (anhydrous) 

 copper sulphate, and 10 per cent lead arsenate. 



Applications. An equal number of applications of all materials were made 

 as follows : 



1st. When blossom buds had separated in the clusters. 



2nd. When petals had dropped. 



3rd. Two weeks after second application. 



4th. About August 1. 



All spraying was done with a power sprayer, using a spray gun. All dusting 

 materials were applied with a large power duster and from two directions at 

 each application. The dust was applied, generally, under favorable condi- 

 tions but the foliage was frequently dry at the time the work was done. 



Weather conditions. The season as a whole at South Haven was quite 

 dry but there was considerable rainfall very early, about the time the buds 

 were expanding, and again late in the summer when there was enough rain 

 and fog to make conditions favorable for scab development, 



RESULTS. 



Control of Scab. The development of scab on the fruit of the check trees 

 was not serious up to July 1, but it developed rapidly after that date. The 

 foliage of the check trees, however, was very scabby at that time and served 

 as an excellent source of infection for the fruit. At that time there was very 

 little indication of scabby fruit on any of the treated trees and only a little 

 infection on the foliage. When the fruit was picked, two average trees from 

 each plot were selected as "count" trees. The fruit from them was classified 

 into sound, scabby and wormy grades. The scabby grade included all apples 



•This is sometimes called anhydrous or monohydrated copper sulphate. 



