February, '19] britton and zappe: kerosene v. nicotine 71 



KEROSENE EMULSION VERSUS NICOTINE SOLUTION FOR 

 COMBATING THE POTATO APHID 



By W. E. Britton and M. P. Zappe, New Haven, Conn. 



The outbreak of the potato aphid (Macrosiphum solanifolii Ash- 

 mead) was so severe in Connecticut in 1917 that much damage was 

 done by it, or at least attributed to it, and the crop greatly lessened. 

 Consequently we watched for this insect in 1918, and on its appearance 

 warned the growers to be prepared to spray as soon as it promised to 

 become sufficiently abundant to cause injury. 



The first aphids were noticed at the Station farm. Mount Carmel, 

 on June 11. Three days later (June 14) they were more numerous, 

 and some were producing young. On June 15, they were observed to 

 be present in potato fields in Greenwich. On June 18, a warning was 

 sent out through the press associations. For several days thereafter, 

 there seemed to be only a slight increase in the numbers of aphids, but 

 during the last days of June they increased much faster and it was evi- 

 dent that something must be done to check them. Consequently on 

 July 2 and 3 the potato field was sprayed with Bordeaux mixture, lead 

 arsenate and nicotine solution, using "Black Leaf 40" at the rate of 

 one-half pint in a barrel (fifty gallons) of the mixture. Though this 

 spray killed some of them it was not very effective, as the waxy nature 

 of the aphids repelled the spray causing it to roll away in drops. 



We conducted several small experiments in hopes of finding some 

 inexpensive material which could safely be used as a spreader in com- 

 bination with the Bordeaux and lead arsenate. In this we were not 

 very successful, and nothing seemed to take the place of soap which is 

 commonly used when spraying to kill aphids only. Apparently there 

 is always some danger of using soap in the combination mixture, as 

 the arsenic may combine with the sodium or free alkali forming sodium 

 arsenate and injury may result. 



During the progress of applying these materials and watching re- 

 sults, the aphids continued to multiply throughout the field, and it 

 soon became apparent that something must be done to check them, 

 and done at once. Consequently all fields were sprayed from July 

 22 to 26. At this time, potatoes and tomatoes generally were threatened, 

 and the demand for nicotine solution was so great that most retail 

 dealers sold out their stock, and could not obtain more from the factory 

 until too late to save the crops. Two or three dealers still had a small 

 supply on hand but had raised the price, thus taking advantage of the 

 situation. 



We decided to spray with kerosene emulsion to kill aphids only and 



