292 VEGETABLE FORCING 



able for pollination, some growers hand pollinate each 

 flower on the first cluster or two and then jar the plants 

 to distribute the pollen for the balance of the crop. 

 Varieties differ greatly in their ability to set a good crop 

 of fruit. English varieties are especially profuse in the 

 discharge of pollen. 



Insects. The white fly is the most serious enemy of 

 greenhouse tomatoes. For description, life history and 

 methods of control see page 120. The nematode is also a 

 serious pest. (See page 116.) Red spiders (page 123) and 

 the green aphis (page 119) sometimes make it necessary 

 to use control measures. 



Diseases. General questions relating to the control of 

 diseases affecting greenhouse crops are discussed in 

 Chapters VI and VIII. The tomato has its full quota of 

 diseases. Most of them are much more serious during 

 the late fall and winter months. This is one of the chief 

 reasons for growing them most largely as a spring crop. 

 In the control of the various diseases affecting green- 

 house tomatoes, the greatest reliance should be placed on 

 preventive measures, such as soil sterilization, careful 

 watering, proper ventilation and skillful fertilization. 

 All diseased parts should be promptly removed if 

 possible and destroyed. 



Leaf mold (Cladosporium fulvum, Cooke) is considered 

 the most serious disease of greenhouse tomatoes. It is 

 likely to cause particular trouble during cool, cloudy 

 weather. It appears first on the lower leaves as irregular 

 yellow areas on the upper surface, while on the under 

 side of these areas are found the olivaceous growth of the 

 fungus. Leaves which are badly infected turn yellow 

 and then wilt and die, so that the entire plant may be 

 defoliated by the spread of the disease. If the infection 

 appears soon after the plants are set in the beds, it is 

 extremely difficult to prevent the loss of the entire crop. 

 If the plants are not attacked until the fruit is set and 



