672 



" Mildew " of Swedes. 



[FEB., 



very small plants, which live on the surface of, or within, the 

 leaves, and form a greyish white covering on the outside. 

 They draw their nourishment from the leaves, and so give them 

 a sickly appearance. 



Serious complaints of " mildew " were made by farmers in 

 the Midlands during September (1907), and an examination of a 

 number of affected crops was made. Mildew was found in 

 most cases, but the bulk of the damage resulted from another, 

 and quite different, cause, viz., an aggravated attack of 

 aphides (green fly or smother fly). In many cases the whole 

 swede area was badly infested, while in others only certain 

 patches suffered seriously. Even in the most healthy looking 

 crops, however, these insects were to be found in groups on the 

 underside of the leaves. Where the attack was bad the leaves, 

 the ground below, and the aphides themselves were covered 

 with a bluish white dust. This gave, to a casual observer in the 

 distance, the appearance of either true or false mildew, though 

 on closer examination no farmer could possibly have confused 

 the smother fly with mildew. As in the case of mildew, the 

 early sown crops appear most susceptible ; indeed there seems 

 little fear of devastation where late sowing is resorted to ; for 

 cool moist weather occurs before serious harm is done. 



At a farm in Derbyshire, swedes were grown alongside 

 cabbage. The cabbage suffered seriously during the summer 

 from smother fly, and on account of their sickly appearance 

 were top-dressed with nitrate of soda. After this dressing 

 the cabbage grew well and the amount of smother fly diminished, 

 but the adjoining rows of swedes showed distinct signs of being 

 affected. At the beginning of October the smother fly had 

 seriously damaged the first fourteen to twenty rows, while the 

 leaves of the rest of the crop were perfectly fresh, although sown 

 and manured in the same way. It seems clear that the affected 

 rows suffered owing to their proximity to the cabbage, and 

 a similar result has been noticed at other farms where no 

 nitrate of soda was applied. It would be well to separate 

 cabbages and swedes by sowing a few rows of mangels between 

 them. 



In the swede variety trials carried out by the Midland 

 Agricultural College, certain varieties were noticed to be more 

 susceptible than others to the smother fly. Ten varieties 



