14 MASS. EXPERIMENT STATION BULLETIN 412 



at the edges two or three weeks after it had been laid, thus exposing the plants 

 to the flies and providing a sheltered location in which they could lay eggs. When 

 radish seed was sown with a double strip of mulch paper on each side of the seed 

 row, a greater infestation occurred than where no treatment was applied. 



Mulch paper caused a definite stimulation of plant growth in cabbage and 

 cauliflower as shown by the weights of a few plants in Table 8. 



Mulch paper as applied in these trials did not provide adequate and consistent 

 protection against injury by the cabbage maggot nor was the gain in plant 

 growth sufficient to offset the labor and expense of applying paper on these crops. 

 If mulch paper is used, one of the chemical treatments described later should 

 be used with it to provide protection against the cabbage maggot. 



Table 8. Stimulation of Cabbage and Cauliflower 

 BY Mulch Paper. Waltham, Massachusetts. 1930. 



INSECTICIDAL DUSTS 



Naphthalene 



Resublimed naphthalene, known to the trade as commercial naphthalene flakes, 

 repels cabbage maggot flies and kills many eggs and newly hatched maggots 

 which come in contact with it. In 1931 with a natural infestation of 75 to 90 

 percent, four applications broadcast at the rate of 3 pounds per 100 plants be- 

 tween May 7 and May 29 gave only moderate protection (Table 9). In 1934, 

 however, three applications between May 7 and 21, at the same rate but with 

 more care in applying the crystals close to the stem of the plant, gave 84 percent 

 protection and produced the largest number of large and medium heads in the 

 experiment. 



The naphthalene flakes were applied by hand at the rate of appro.ximately a 

 large handful to each three plants, but broadcasting over the entire field would 

 be effective. Some of the material should be on the soil throughout the ovi- 

 position period of the flies. On early crops this period usually extends through 

 the month of May. The number of applications needed depends on the tempera- 

 ture, since the rate of evaporation increases with the temperature and the crystals 

 must be replaced more frequently in warm weather. Observations show that 

 when the temperature at the surface of the soil is 75° F. or higher, the naphtha- 

 lene flakes from a normal application vaporize and lose their repellency in about 

 three days. 



For the home garden this treatment seems practical, but in commercial plant- 

 ings the greater number of applications required makes it less desirable than 

 corrosive sublimate or calomel. However, if mercury compounds are not avail- 

 able, or their cost becomes excessive, naphthalene might be used as a substitute. 



