GREENHOUSE RED SPIDER. 177 



up on one side of the row and back on the other. In either case a boy 

 should be employed to guide the hose, so that it will not injure the plants 

 as it is pulled from one row to the other. 



These are the most common methods of spraying, but there are many 

 modifications which the grower can make according to the conditions 

 surrounding his houses and the manner of growing his plants. 



An extension rod made from small piping with an elbowed tip or angle 

 nozzle is absolutely necessary for thoroughness in spraying. If cucumber 

 plants are grown on the vertical trellis s,ystem the extension rod should 

 be about 2§ feet in length, while if grown on the "A" treUis system the 

 rod should be 4 feet in length, as this will allow the man spraying to reach 

 the basal leaves of the plants readily. It is perhaps more satisfactory 

 to use a 45° angle nozzle, several of which may be purchased {e.g., Friend 

 and Simplex angle nozzles^ thus eliminating the necessity of a separate 

 elbow. 



Methods of Application. — From the fact that the red spider as a rule 

 passes its entire existence upon the under surface of a single leaf, early in 

 the season, when the plant is only slightly infested, it is plainly necessary 

 in spraying to cover the entire under side of every leaf. Special attention 

 should be paid leaves showing typical red spider injury, especially the 

 lower leaves of the plant, near the ground, as these are usually most 

 severely infested. To facihtate this under-surface spray an extension 

 rod with an elbow tip or angle nozzle is essential. 



The pressure necessary in power spraying varies from 50 to 125 pounds, 

 depending upon the type of nozzle. Do not allow the spray to bombard 

 the under surface of the leaf if a coarse nozzle is used. As this Unseed 

 oil emulsion is a contact spray, it is necessary that the whole under surface 

 of a leaf should be covered by a film of this material. If the spray is 

 deposited on the leaf in fine droplets which do not run together, this can 

 be remedied by the adjustment of the pressure until they unite to form 

 a film. If a coarse nozzle is used, as the Simplex, a low pressure will be 

 required for film formation, while with a fine nozzle, as the Friend, a 

 higher pressure will be necessary. A preference should be given the 

 fine nozzle and high pressure, as this is less apt to injure the leaves, while 

 it proves very satisfactory in forming the film. The success or failure of 

 the spraying depends upon this film formation and thorough application 

 of the material. 



When Applications should be made. — In general greenhouse practice 

 spraying on bright days is and should be the rule, as with sunshine there 

 is less danger that conditions favorable for disease will result. In the 

 application of the linseed oil emulsion, however, spraying conducted on 

 sunny days with a rather high temperature in the greenhouse may result 

 in a slight injury to the edges of the leaf, while if spraying is done on 

 cool, cloudy days no injury is caused by the applications. Therefore, as 

 far as possible, spraying for the red spider should be done on cloudy days 

 when the temperature in the house is not over 80°. The injury on bright 



