DISEASES IN GREENHOUSE 129 



ever, especially where they are grown on a 

 large scale for seed purposes, rotation of 

 crops will have to be resorted to. 



THRIPS ' 



Heliofhrips hamorrhoidalis Bouche 



The damage done to the sweet pea by 

 Thrips is confined mostly to the foliage. 

 Thrips feed by sucking on the juices of the 

 sweet pea plants. New places and new 

 leaves are continually attacked so that the 

 affected parts are full of tiny pale spots. 

 In severe attacks the spots unite and form 

 regular white blotches. Ordinarily it is 

 on the under surface of the leaves that the 

 mites feed, but when they become very 

 numerous they also migrate to the upper 

 surface. Both sides of the affected foliage 

 thus become covered with minute drops of 



^ For a more detailed technical description, see Bull. 

 64 Bur. Ent. U. S. Dept. Agr. 



