GREENHOUSE RED SPIDER. 175 



destroy them immediately, thus eliminating the chance of infesting plants 

 surrounding the greenhouse. Pruning is especially useful when judi- 

 ciously applied to the young plants in a greenhouse. Such prmnng should 

 be supplemented by spraying for a thoroughly efficient control. 



Spraying. 



If there is any possibility of infestation, spraying should commence 

 soon after the cucumber plants have been set out in the greenhouse. If 

 spraying is done at this time less material will be used, and a very thorough 

 application can be given in a minimum amount of time. In experiments 

 conducted in commercial greenhouses it was found that red spider sprays 

 applied to young cucumber plants gave very satisfactory results, while 

 on older plants these sprays did not prove as efficient. This can be ex- 

 plained by the fact that a good-sized cucumber plant has a large amount 

 of leaf surface which must be thoroughly covered by the contact spray 

 if efficiency is to be expected. This is economically impossible after the 

 plants have become nearly full-grown, because of the length of time and 

 amount of material necessary to accomplish it. Early spraying will con- 

 trol red spiders at a minimum expense of time, labor and materials. 



Linseed oil emulsion is especially adapted for use in conamercial green- 

 houses on a rather large scale. 



If only a few plants need to be treated, lemon oil, manufactured by 

 the Lemon Oil Company, Baltimore, Md., may be purchased at nearly 

 all stores carrying insecticides. This, diluted at the rate of 1 part in 20 

 parts of water, gives a very efficient spray, but for commercial spraying 

 this material is too expensive. 



Soapy solutions sprayed upon delicate plants on several successive 

 days prove to be useful. In making this solution a high-grade soap 

 (Ivory soap) should be dissolved at the rate of 4 ounces in 3 or 4 gallons 

 of water. 



Preparation of Linseed Oil Emulsion. 



{a) The necessary articles for preparation are as follows: — 



1. Bucket pump. 



2. Container or mixing tank. This should hold at least 8 or 9 gallons. 

 For this purpose a small washtub is perhaps the most available. Pails 

 may be used, provided the materials are mixed proportionally. 



3. Ivory soap. 



4. Raw linseed oil. 



5. Hot water. 



(6) The following proportions of materials for 100 gallons of spray are 

 used: — 



1. Five gallons of hot water. 



2. One and one-half pounds of Ivory soap. (Six 5-cent cakes or three 

 10-cent cakes.) 



3. One gallon of raw linseed oil. 



