THE CABBAGE MAGGOT 9 



In the text of this bulletin and in the tables, the experimental plants are 

 frequently referred to as Commercially Injured, which includes those suffering 

 Moderate or Severe Injury and Dead Plants; and as Commercially Uninjured, 

 which includes those suffering Slight Injury and those which are Free from Injury. 



Early in July, about ten weeks after transplanting, the plants in the remaining 

 row were examined and an average size of head for the planting and for the variety 

 was determined, after which each head was classified in relation to the average 

 as Very Large, Large, Medium, Small, Very Small, Dead, or Blind. Blind 

 plants, in which no head developed, were usually caused by injury to the central 

 bud by cutworms, but occasionally resulted from plant deformities or mechanical 

 injury. In this bulletin the Very Large, Large, and Medium heads are classified 

 as Salable or Marketable; and the Small, Very Small, Dead, and Blind heads are 

 classified as Unsalable or Unmarketable. Some of the Small heads might grow 

 to salable size before harvest was completed, but they were not of salable size 

 when classified. 



Although there is a general correlation between the amount of injury by 

 cabbage maggot and the number of marketable heads, there is no direct relation 

 between the percentages presented in the tables because the records were made 

 on different rows of plants, and the head records were taken about four weeks 

 later than the injurj- records. 



Natural Infestation in Experimental Field at Waltham 



Since 1930 when early cabbage was first grown in large numbers, there has 

 been a heavy infestation of cabbage maggot on the untreated plants in the ex- 

 perimental planting. In the fourteen years when records were made, the number 

 of cabbage plants commercially injured has been less than 75 percent in only 

 three years; the infestation was 95 percent or higher in 1932, 1935, and 1937; 

 and in the other eight years it ranged between 75 and 88 percent (Table 5). 

 The infestation was 10 to 15 percent greater on cauliflower than on cabbage in 

 those years when both crops were examined. Such infestations have provided 

 good conditions for experimental tests of preventive treatments. 



Table 5. Natural Infestation on Cabbage in Experimental Field 

 AT Waltham, Massachusetts. Golden Acre Variety. 



Untreated Plants Commercially Injured 



Average 78,7 



Artificial control treatments are classified as follows: Seedbed treatmen'. 

 Pre-transplanting treatment, and Field treatment. 



