ANNUAL REPORT, 1944-45 37 



Potato Spraying Experiments. (A. I. Bourne.) The experimental plots were 

 planted May 9. The young plants appeared within the next 10 to 14 days and 

 averaged 5 to 6 inches in height at the time of the first application on June 12. 



During the early season (June and July) the infestation by flea beetles was 

 comparatively light. In late July the number of beetles increased rapidly and 

 continued high until mid-August when the infestation dwindled rapidly and very 

 little scarring of foliage was caused thereafter. There were very few leafhoppers 

 throughout the entire season. Comparatively little damage was caused by 

 European corn borer larvae, and although the potatoes adjoined a plot of field 

 corn the number of second-brood moths hiding during the day in the potato 

 vines was not great. This was in marked contrast to 1943. No late-season 

 damage to potato vines was noted. No serious outbreak of potato aphids oc- 

 curred. An incipient attack was noted about mid-July and nicotine sulfate was 

 included in the application on July 20. No further steps in control were neces- 

 sary. 



Bordeaux mixture at standard strength of 10-10-100 was applied to the east 

 and middle plots. Calcium arsenate at the rate of 4 pounds to 100 gallons was 

 added to the bordeaux in half of the east plot. DDT (Gesarol A-20) at 2 pounds 

 to 100 was added in one half of the middle plot. Bordeaux at strength of 5-10-100 

 alone, with calcium arsenate, and with DDT was applied in the west plot. Eleven 

 applications were made at approximately weekly intervals between June 12 and 

 August 28. The new Friend field crop sprayer with a 6-row boom (3 nozzles per 

 row) was used throughout the season and rendered excellent service. 



The plants in plots which received the low-copper bordeaux began to ripen 

 and die down in late August and early September. Plants in the plots which 

 received full strength bordeaux for the most part persisted throughout Septem- 

 ber and many plants were alive and green until they were killed by the frost of 

 October 4-5. The plants suffered considerable damage by the high wind of the 

 hurricane on September 14-15 and from the heavy rain which accompanied it. 

 The injury was aggravated by the period of hot, humid weather which immedi- 

 ately followed the hurricane. 



The early ripening of plants in the plots which received the low-copper bor- 

 deaux schedule was reflected in the yield, which averaged 320 bushels per acre 

 compared with a yield of 369 bushels per acre in the plots spraj^ed with standard 

 10-10-100 bordeaux. The plots in which calcium arsenate and DDT were added 

 to bordeaux (standard strength) yielded approximately 20 bushels per acre 

 more than corresponding plots which received bordeaux alone. 



In the series of plots which received standard bordeaux, the addition of cal- 

 cium arsenate was accompanied b}' a distinct and immediate reduction of nearly 

 50 percent in the amount of flea beetle damage. This ratio held through successive 

 weeks. The addition of DDT did not give such noticeable reduction immediately, 

 but showed a cumulative benefit from successive applications which resulted in 

 marked reduction in the number of leaf punctures. Where the low-copper bor- 

 deaux alone was applied, practically the same degree of protection against flea 

 beetle was secured as was furnished by standard strength bordeaux. The addi- 

 tion of calcium arsenate or DDT in these plots did not noticeably increase the 

 degree of immediate protection although there was some evidence of beneficial 

 cumulative effects following successive applications. 



Control of Onion Thrips. (A. I. Bourne.) Application of a dinitro dust (DN-4) 

 gave 97.5 percent reduction in thrips population but caused slight burning of the 

 plants. Lethane (B-71) dust gave 78 percent reduction with no injury. DDT 

 (Gesarol A-3) dust proved only moderately effective with a reduction of 44 per- 

 cent. Very heavy applications greatly increased the effectiveness of Lethane 



