18 



New Hampshire Experiment Station [Bulletin 239 



TABLE XV. 



Comparison of Costs and Results of Bordeaux Mixture and a Copper Dust in 



Blight Control. 1926. 



If costs and labor per bushel can be reduced approximately 10 

 cents and 12 minutes respectively by spraying, and spray material 

 costs add only two to five cents per bushel, the expense for spray 

 material is justified. 



Dusting compares in number of applications and effectiveness 

 to three Bordeaux sprays. It costs approximately twice as much. 



Spraying in the southern part of the state appears to be one 

 of the factors showing very favorable results. 



Moderate increases in number of applications and costs gave 

 greater returns than similar increases in fertilizer. 



Dust costs more than liquid spray for the same number of 

 applications. (Table XV.) With average methods, dusting is less 

 effective than thorough liquid spraying, but it is more effective 

 than no spraying at all, (frequently all sprays are omitted in Coos 

 County) and more effective than the three sprays usually applied 

 in the rest of the state. Hovv^ever, on two groups of farms using 

 comparable control methods, dust proved as effective as the liquid 

 spray in controlling blight in 1926 and 1927. (Table XVI.) In 

 general on areas too small to use special potato machinery effec- 

 tively, hand dusting proved very satisfactory. About 20 per cent, 

 more dust was used than with a power duster, and man labor was 

 more than doubled. The total cost was nearly 70 per cent, more than 

 that of liquid spray on larger areas. Where water was insufficient 

 in quantity, or so far from the field that hauling was an important 

 factor, dust again proved more satisfactory. Several growers 

 found less interference with other farm operations, notably hay- 

 ing, when dust was used. 



Slinging the duster over the back, filling with a prepared dust, 

 and dusting the potatoes while the dew is on the hay, was a method 

 of control frequently resorted to even though material cost is con- 

 siderably higher than Bordeaux mixture which must be applied 

 when the plants are dry and hay is ready to haul. Too frequently 

 the hay was hauled and the potato crop suffered. 



The larger areas may use traction sprayers efficiently. When 

 properly adjusted, and with mixing and filling equipment con- 

 viently arranged, spraying with Bordeaux mixture is less expen- 



