196 Report of the Botanical Department of the 



Each of the three spray mixtures was applied six times. The 

 first application was made on July 7 when the plants were six 

 to eight inches high and the others followed at intervals of two 

 weeks. For the control of Colorado potato beetles or " bugs " 

 arsenate of lead was used with all of the spray mixtures in the 

 first two applications at the rate of three pounds to fifty gallons. 

 On the same dates the check rows were treated with three pounds 

 of arsenate of lead in fifty gallons of water.' 



All of the spraying was done very thoroughly with a knapsack 

 sprayer which was used also for applying arsenate of lead to the 

 check rows. In the last two applications, when the plants were 

 full grown, the spray mixtures were applied at the rate of about 

 200 gallons per acre. 



EFFECT OIsT THE FOLIAGE. 



For about seven weeks following planting the weather was 

 very dry and the potatoes made a slow, spindling growth. Later, 

 rain was more abundant and the plants improved so much that 

 during August and the fore part of September the whole field 

 looked well, although the plants were somewhat smaller than 

 usual for this time of year. Late blight {Phytophthora infestans) 

 was entirely absent. Early blight (AUernaria solani) appeared 

 only to a slight extent, in October. There were very few flea 

 beetles. " Bugs " were kept under control so that they were not 

 a factor in the results. The only disease of any consequence 

 affecting the plants was a form of tip burn (a browning of the tips 

 of the leaves) which appeared about September 10 and gradually 

 increased in prevalence until all rows, excepting those sprayed 

 with bordeaux, were killed by it. For some unknown reason this 

 tip burn appeared earlier and was more destructive in the north 

 than in the south half of the field. Its exact nature is unknown 

 to the writers. But for the fact that the bordeaux rows were 

 nearly free from it until after about October 10 it would have 



1 Check Row 1 was treated with paris green ( 1 lb. to 50 gals. ) instead of 

 arsenate of lead. This was necessary because this row served also as a check 

 in another experiment in which paria green was used on the checks. 



