6 MASS. EXPERIMENT STATION BULLETIN 412 



No repellency or attractiveness to the flies was observed and eggs were laid 

 in about equal numbers among these varieties. It, therefore, appeared that 

 the degree of injury was dependent on the ability of the plant to withstand the 

 feeding of the maggots. 



On this basis the Early Jersey Wakefield variety was consistently resistant 

 during the two years observed; Copenhagen Market, Supercurled Savoy, Marion 

 Market, and Golden Acre were very susceptible; and all others were intermediate 

 or inconsistent. In general it appears that fast-growing, more desirable market 

 varieties are the most seriously injured, with Early Jersey Wakefield an out- 

 standing exception, and that the slower growing varieties are more resistant. 



INJURY 



Injury to plants by the cabbage maggot is caused entirely by the feeding of 

 the larva or inaggot. When first hatched, the tiny maggot crawls down the 

 main root and feeds on the hairy roots. As the larva grows, it may eat all of 

 the hairy roots or it may eat channels into the main root. 



On small seedlings and transplants, the feeding of one or two maggots may 

 stunt the plant. The feeding of three or four maggots usually kills a small 

 plant or stunts it beyond normal recovery. 



Large plants in which one or two maggots have eaten channels or small cell- 

 like cavities in the main stem usually show little or no effect from the injury. 

 However, when several maggots attack a large plant, the hairy feeding roots are 

 eaten off and the main roots become perforated with tunnels. The plant tissues 

 around these tunnels decay and the lower root disintegrates (Figure 3-B). In 

 severe infestations some maggots may tunnel upward in the stem and live as 

 borers even burrowing into the petiole of the lower leaves. 



Infested plants first show the effect of maggot injury by developing a pale gray 

 color and a dull appearance. On warm, sunny days, and on windy days when 

 transpiration is rapid, infested plants wilt and droop. Badly infested plants 

 supporting five or six maggots are frequently killed, but slightly or moderately 

 infested plants may wilt for several days and recover at night until the develop- 

 ment of secondary roots enables the plant to outgrow the injury. 



On radish, turnip and kohlrabi, the fleshy edible root is usually attacked and 

 one maggot tunnel makes the vegetable unmarketable as first-class produce. 



Relation of Maggot Injury to Development of Head In Cabbage 



Most cruciferous crops, especially cabbage, have a remarkable ability to re- 

 cover from root injury by the cabbage maggot in cool, damp weather and in 

 moist soil. Even when the main root is severely damaged, secondary roots 

 usually above the point of injury frequently develop rapidly. In cool, moist 

 weather these secondary roots will support a plant one-third to one-half grown 

 and enable it to recover. The growth of these secondary roots is well illustrated 

 in Figure 3-C. 



The recovery of infested plants in favorable seasons often enables growers who 

 have applied ineffective treatments against cabbage maggot or none at all to 

 harvest a reasonably profitable crop. 



