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 
