CUCUMBER 337 



various descriptions. See page 400 for cultural directions. 



Insect enemies. Various insects feed on greenhouse 

 cucumbers. One of the most serious pests is the red 

 spider. Methods of control are discussed on page 123. 



Unless preventive means are employed, the white fly 

 often appears in such numbers as to inflict heavy losses. 

 Either potassium or sodium cyanide gas may be used to 

 check the ravages of this insect before its depredations 

 have become serious. Full instructions for their use are 

 given on page 109. 



Interesting experiments were made by Stone and 

 Thomas at the Massachusetts station, relative to the in- 

 fluence of various light intensities and soil moisture con- 

 tents on the development and character of cucumber 

 plant tissues. Plants which received the least light and 

 the most water were soft and tender and much more sus- 

 ceptible to injury from hydrocyanic gas than were plants 

 which received full light and normal amounts of water. 

 The investigators emphasize the importance of noting 

 the condition of the plants before proceeding to fumigate 

 with cyanide. If cloudy weather and perhaps high 

 temperatures have prevailed for a few days and the 

 plants have been supplied with an abundance of moisture, 

 the tissues will be soft and tender, and injuries will be 

 much more likely to occur than when the fumigation 

 follows several days of sunshine and normal conditions 

 of heat, humidity and soil moisture. Growers will do 

 well to consider these factors before fumigating their 

 houses. 



The nematode is regarded by most growers as one of 

 the worst pests of greenhouse cucumbers. Sterilization 

 with steam is the usual method of controlling this enemy. 

 See page 116. 



The aphis is also an enemy of greenhouse cucumbers. 

 For methods of control, see page 119. 



Fall and spring plants are often attacked by the com- 



