GREENHOUSE RED SPIDER. 179 



house containing 1,600 cucumber plants about 4 feet high. The material 

 used wdll amount to 100 gallons. Thus the cost of one spraying when 

 the plants are nearly half grown is approximately $3. 



Spray materials, . . . . . . . . . $1 50 



Man, three hours, . . . . . 1 00 



Boy, tliree hours, .......... 50 



This is a fair estimate of the cost of the third spraying. The first and 

 second sprayings taken together should cost approximately $3. Thus, 

 for three applications of hnseed oil emulsion to 1,600 plants, the invest- 

 ment for labor and materials will be approximately $6. This should be 

 considered insurance on the crop. At the above rate the cost for three 

 applications is less than one-half cent per plant. 



The original investment for spray materials and labor will be repaid 

 many times over by prolonging the fruit-bearing period of the plants. 



CONTROL OF RED SPIDERS ATTACKING OTHER CROPS. 



Perhaps a few words relative to the control of these mites attacking 

 some of the other crops will prove useful, especially to florists. Although 

 the writer has confined most of his attention to the control of this pest on 

 cucumbers, it is reasonable to suppose the same control measures will 

 give as satisfactory results in eliminating this pest on other plants. While 

 this is true, a few factors must be thoroughly understood in order to 

 procure these results. 



On small or rather smooth-leaved plants, such as the violet, rose, 

 carnation, sweet pea and bean, the linseed oil emulsion spray as used on 

 cucumbers does not prove as satisfactory. The reason for this is that the 

 greater part of the spray applied to these plants runs off the leaf, and not 

 enough linseed oil is deposited on the mites to render them helpless. To 

 remedy this difficulty the stock linseed oil emulsion should not be diluted 

 as much as recommended for cucumber spraying. In some cases where 

 very delicate plants are to be sprayed the same dilution may be made, 

 but the solution of soap should be stronger. 



In spraying cucumbers a 1 per cent, linseed oil mixture is used. On 

 plants such as the violet it is best that the original linseed oil stock solution 

 be diluted only one-half as much, making a 2 per cent, linseed oil mixture 

 and a more concentrated soap solution. 



In the majority of cases proper experimentation by the grower will 

 furnish satisfactory evidence for the required dilution for efficiency on his 

 special crop. 



During July and August, 1917, the writer had the opportunity of thor- 

 oughly testing the efficiency of this. 2 per cent, linseed oil emulsion for the 

 control of red spiders attacking violets in the field at Mr. William Sims' 

 greenhouses, Cliftondale, Mass. This field of violets, containing about 



