■92 AGRICULTURAL RESEARCH AND THE FARMER : 



University of Manchester. 



Carrot Fly. — In many parts of Lancashire and Cheshire, 

 although the soil is quite suitable for carrots, it is almost im- 

 possible to grow this crop owing to the ravages of the carrot fly. 

 The fly appears in Spring and attacks the carrots in the seedling 

 stage, causing in many cases the total loss of the crop. An 

 investigation of the disease was commenced at the University 

 in 1920, the first object being to discover the life history and 

 habits of the fly, in order to find the most vulnerable point for 

 attack. It was found that the fly does not lay her eggs on the 

 plant but in the soil, and that in about a week the larvae emerge 

 and penetrate through the soil to the root of the plant, entering 

 at the growing point. They feed on the tissues of the plant, 

 causing wilting and yellowing and ultimately killing it. The 

 larvae then leave the carrot and pupate in the soil close to the 

 root. After about a month in the chrysalis stage the flies emerge 

 in August, and start laying eggs in a week or 10 days. The 

 larvae which hatch out from these eggs remain in the soil through 

 the winter in the pupal stage and the flies from them emerge in 

 the following April. 



In the case of this pest, therefore, the object to be aimed at 

 is either to prevent the fly from laying her eggs, or, if they are 

 laid, to ensure that the maggots which hatch out do not reach 

 the plant. Many chemicals have been tried in this connection, 

 with varying degrees of success. In 1920 good results were 

 obtained on an allotment scale with green tar oil and precipitated 

 chalk in the proportion of i part oil to 99 parts chalk. The 

 experiments were repeated on a larger scale and \\ith fresh 

 chemicals in 1921, but the dry season prevented the fly from 

 appearing. It may be added that another partial method of 

 prevention arises from a knowledge of the life history of the pest. 

 If the carrots are sown late, the first generation of flies is avoided. 

 This may be a useful means of reducing risk of attack in cases 

 where the time of marketing the crop is not a vital factor. 



Onion Fly. — An investigation on somewhat similar lines to 

 the above has recently been carried out in connection with the 

 Onion Fly, which is another very serious pest in Lancashire and 

 Cheshire, practically preventing the growing of onions in that 

 area. In this case the problem of control is more difficult, for 

 it has been found, in the first place, that the fly lays her eggs on 

 the seedling plant and not on the ground, and therefore the 

 deterrent effect of chemicals spread on the soil is likely to be 

 less, and in the second place, that instead of two generations 



