THE LEAF BLOTCH DISEASE OF HORSE-CHESTNUT 



417 



two additional applications in order that the foliage will be thoroughly 

 covered with the fungicide at all times. 



Lime-sulfur solution (one gallon to fifty gallons of water) or bordeaux 

 mixture may be used for controlling the disease. Considerable difficulty 

 has been experienced, however, in the use of these spraying mixtures 

 owing to the dense foliage of horse-chestnut trees. In the attempt to 

 cover thoroughly all parts of the foliage, the trees are often drenched 

 with the spray solution, and when lime-sulfur solution is used severe 

 burning of the leaves may result. 



In the summer of 1915 an experiment was made on nursery trees for the 

 control of leaf blotch by dusting. The dust mixture used contained ninety 

 parts of finely ground sulfur L and ten parts of powdered arsenate of lead. 2 

 This mixture proved as 

 effective as lime-sulfur 

 solution in controlling 

 the disease. On trees 

 that were not treated, 

 practically fifty-nine per 

 cent of the leaves were 

 diseased; while only 

 three per cent of the 

 leaves on the trees that 

 were dusted showed in- 

 fections, and the trees 

 sprayed with lime-sulfur 

 solution 1-50 had ten 

 per cent of the foliage 

 diseased 



In comparing the results on the sprayed and the dusted trees, it is 

 believed the lime-sulfur spray was the less effective mainly because of 

 the density of the foliage. The spray was applied with a hand sprayer 

 which lacked sufficient power to furnish the driving spray necessary to 

 thoroughly cover all parts of the foliage, while, on the other hand, the 

 cloud of finely ground dust mixture floated through the trees and settled on 

 the leaves, completely covering them and thus affording better protection. 



The dust mixture was applied with a hand machine, illustrated in 

 figure 88. This duster is very satisfactory for treating small shade 



DUSTING SHADE TREES 



1 The sulfur was so finely ground that at least 95 per cent would pass through a 20O-mesh sieve. The 

 method of testing sulfur is described by F. M. Btodgett in Bulletin 328 of this experiment station. 



2 The lead arsenate was added primarily for its adhesive properties. On being moistened there is a 

 tendency for it to become somewhat gelatinous and sticky, and this increases the adhesiveness of the 

 mixture. Lead arsenate is effective also in controlling insects that chew the foliage. In the case of 

 horse-chestnuts, however, which are seldom attacked by insects, finely ground gypsum, a much less ex- 

 pensive substance, may be substituted for lead arsenate. 



