THE CARROT RUST FLY 33 



Sodium and calcium fluosilicates in a &pray or dust were either ineflFective or 

 inconsistent. In fact, with the exception of derris and cube, no insecticidal sprays 

 or dusts were sufficiently outstanding to receive commercial consideration. 



Miscellaneous Materials. — Several reports, particularly by Gibson (15) and 

 Pettit (23). have suggested the use of kerosene emulsion or Bordeaux oil emulsion 

 for combating the carrot rust fly. In 1928 and 1929, spraying with a 1 percent 

 lubricating oil emulsion and a 1 percent oil emulsion in Bordeaux mixture 4-4-50 

 was only slightly effective and did not warrant further applications. A plot 

 sprayed with a solution of nicotine sulfate containing 50 percent nicotine diluted 

 l-500showed more injury than the check, even to the point of suggesting that the 

 nicotine may have attracted the flies. 



Field Experiments with Repellents 



Naphthalene, soot, tobacco, talc, lime, and wood ashes are primarily repellent 

 to the flies. In addition to the repelling effect, naphthalene and tobacco kill the 

 eggs and newly hatched larvae by contact and fumes. Soot, talc, and similar 

 dusts maintain a dry, powdery coating which is very disagreeable to the flies. 

 The repellcncy of these materials is greatly decreased by wetting. 



Of these repellents, naphthalene flakes, Scotch soot, and ground tobacco, in 

 three or four applications on early carrots and three to five applications on late 

 carrots, gave consistently good protection in experiments from 1929 to 1936. 



Naphthalene Flakes. — Glasgow (17) in New York found naphthalene flakes 

 the most satisfactory control for carrot rust fly in late carrots when used at the 

 rate of 400 pounds per acre in four to six applications at weekly intervals. In 

 the experiments at Waltham, three or more applications gave about 80 percent 

 protection over a period of 4 years on late carrots, and in 1931 on early carrots 

 (see Table 26). Naphthalene flakes in a crude form cost 4 to 5 cents a pound in 

 barrels holding 100 pounds or more, and 6 to 8 cents a pound in smaller quantities. 

 This material was applied at the rate of 1 pound to each 100 feet of row, or approx- 

 imately 350 pounds per acre, at an approximate cost of $14 per acre. It was 

 broadcasted by hand, spread along the rows so that the flakes were scattered 

 among the crowns of the carrots. When taken from the bag or barrel the flakes 

 may be in lumps, which should be broken up by kneading and crushing by hand 

 to avoid an uneven distribution. No injury to the foliage or roots of the carrot 

 has resulted from naphthalene, and there has been a slight unexplained stimu- 

 lation from its use. 



In 1929 a mixture of equal parts of sulfur and naphthalene was used, but the 

 mixture appeared slightly inferior to the naphthalene. 



Tobacco. — Ground tobacco containing 1 to l\^ percent nicotine was used in 

 1931, 1932, and 1933 with generally good results. In 1931, three applications gave 

 perfect protection to early carrots from a very light infestation (7 percent) in 

 an adjacent untreated block. On late carrots two applications were ineffective 

 in 1932, and it appeared that three or more treatments at weekly intervals were 

 necessary. After several trial applications with this tobacco, it was determined 

 that approximately 2 pounds to each 100 feet of row .were necessary to give an 

 adequate covering on the crowns of the carrots. Ground tobacco costs $3.75 to 

 $4 per 100 pounds and on this basis the cost of making one application to an 

 acre is about $25. This expense is too great for the average commercial carrot 

 grower, but this material might have a place in the small planting or where 

 above-average yields were produced. 



Scotch Soot. — Scotch soot, which is a favorite plant stimulant among British 

 gardeners, was found to be repellent to the carrot rust fly. It was not quite so 

 effective as tobacco or naphthalene, and because of its greater bulk about 4 pounds 



