354 



The Cabbage Root Fly. 



[SEPT., 



the swede. When full grown the larva passes into the soil 

 a little away from the attacked plant, and becomes a pupa, 

 or pupation may take place in the infested plant. The first flies 

 of the year appear for their egg-laying towards the end of April 

 and in May, and there are probably three generations in the 

 year. 



Attacked plants have their growth checked, their leaves 

 discolour, wither, and wilt, infested parts become slimy, rotting 

 takes place, and the plant falls away. 



Phorbia brassicte is an enemy to plants belonging to the 

 natural order Cruciferce, although there is an American record 

 of the maggots mining the leaves of beet. The maggot has 

 also been found at work on cauliflower, turnip and swede ; 

 cauliflowers in garden cultivation have been attacked, while 

 brussels-sprouts grown alongside and planted at the same 

 time were unharmed. Attacks have also been recorded on 

 broccoli, the radish, and the garden stock ; and Slingerland found 

 the maggots at work on such common cruciferous weeds as 

 shepherd's purse, winter cress or yellow rocket, and hedge 

 bustard. 



Preventive and Remedial Measures. 



1. Very early sown plants are noticed largely to escape ; but 

 temperature seems to be the important factor in this connection ; 

 early setting out, however, is not always practicable, and even 

 early planted cabbages may not escape attack. 



2. Protecting the cabbages and cauliflowers by means of 

 tarred paper or cards is a preventive measure which has 

 been tried in America. The protection by this method was 

 successful with 7,000 plants in one case and with 10,000 in 

 another. Slingerland satisfied himself by experiment of its 

 great usefulness, the flies not being able to get near enough 

 the protected plants for their egg-laying ; presumably maggots 

 from any eggs laid beyond the extent of the card are unable 

 to reach the plants. The cards used are six-sided, about 

 three inches across, with a slit reaching to the centre where 

 there is a star-shaped cut to fit well round any thickness of stem. 

 The caf/ds should be placed round the plants at the time of 

 transplanting or setting out. To place the card in position, 



