258 AGRICULTURE OF MAINE. 



In Washington, it is restricted to Snohomish county, in the 

 northwestern part, on Puget Sound. In Oregon again, the 

 two northwestern counties, Clatson and Tillamook, are the only 

 ones found affected. 



It will be noted that in each state where it is now known to 

 occur the disease is confined to those parts which have rela- 

 tively cool summers and an abundant rainfall. An extensive 

 series of experiments conducted by the federal pathologists in 

 twelve different eastern states, from jMassachusetts to Florida, 

 have shown quite conclusively that powdery scab will not de- 

 velop under the climatic conditions which exist there. More- 

 over, I believe that in Maine we have little to fear of its spread- 

 ing to such an extent as to do any material damage outside the 

 present'known area of distribution. I believe central and south- 

 ern Maine have little to fear from it, and that planting tubers 

 affected with powdery scab in this region would result in a 

 clean crop unless the growing season should be abnormally and 

 continuously cool and wet. 



Even in Aroostook county its prevalence is markedly influ- 

 enced by seasonal, climatic conditions. This year, the rainfall 

 there was not excessive and they had some periods of very hot 

 weather. As a result we had difficulty in getting enough in- 

 fected tubers in Caribou and Presque Isle to carry on our field 

 tests for the coming year, yet a few years ago you could get 

 them by the carload in a number of different towns. 



Even in northern Maine, powdery scab is restricted to the 

 wet, poorly drained soils of a definite type, and is seldom of 

 much account on the best potato land. 



None of this alters the fact that powdery scab is a very ob- 

 jectionable disease where it does occur, and may produce con- 

 siderable damage. Disinfecting the seed with formaldehyde 

 or corrosive sublimate and applying sulphur to the soil in con- 

 siderable quantity, each tend to reduce the amount of powdery 

 scab in the crop, when infected tubers are planted. To avoid 

 the introduction of the disease, our experimental work has 

 shown that the only safe method to follow is to use only healthy 

 seed tubers and then disinfect these before planting. Where 

 powdery scab occurs, land once contaminated may harbor the 

 germs of the disease for an undetermined period. 



