GREENHOUSE RED SPIDER. 171 



fii-st application. In No. 2 the plants were 2| feet tall and generally 

 infested, although not sho\\ing any noticeable injury to the plants from 

 the red spider attack. In No. 3 the plants were 4 feet high and rather 

 severely infested. In each of these houses three applications were made 

 at weekly intervals. 



The final results of these experiments are as follows: the greenhouses 

 of Group I. were not sprayed, and though the plants were very little 

 older than those in Group II. they died from the red spider injury after 

 being in the range approximately three months. In Group II. the plants 

 were sprayed and produced fruit for over a month longer than the un- 

 sprayed plants of Group I, Houses No. 1 and No. 3 contained such large 

 cucumber plants that a thorough application of a spray was found im- 

 possible, but the ravages of these mites were checked during the spraying 

 period. Although a complete control was impossible, the productive life 

 of the crop was lengthened approximately one month. In house No. 2, 

 containing the youngest cucumber plants in Group II., the control was 

 much more efficient, primarily because the plants were smaller and a 

 thorough spraying could be given them. However, even these plants 

 were too large to insure a thorough application after the first spraying. 



Experiment No. 2. 



Further tests of the efficiency of linseed oil emulsion were made in 

 commercial greenhouses at Arlington, Mass. In this establishment all 

 plants were infested in the seed-plant house while still in pots. Soon after 

 they were set in the greenhouses the first spray was applied, and one week 

 later the second application was made. These two applications were 

 made at the proper time, and controlled the mites so effectually that 

 during midsummer some of these houses were yielding good crops, while 

 only a few scattered plants were beginning to show marked red spider 

 injury. At approximately the same time in former years the plants in 

 these houses have been severely infested and dying from the ravages of 

 the red spider. This range of greenhouses consists of twelve large houses, 

 and therefore it is not surprising that the whole establishment could not 

 be thoroughly covered each week. 



An excellent demonstration of the efficiency of linseed oil emulsion was 

 made in the seed-plant house. As stated above, when the cucumber 

 plants were still in pots in this house they were noticeably infested by 

 red spiders. The grower, knowing that this house contained many mites, 

 determined that sprayings should be given with special care, in order to 

 eradicate these pests. Soon after the potted plants were set out in the 

 seed-plant house the first application was given, care being taken to 

 cover thoroughly all the leaf surface. One week after this the second 

 thorough spraying was applied. These applications were made so thor- 

 oughly that very few if any mites which originally infested the cucumber 

 plants survived, and the plants attained full growth without showing 

 any red spider injury. 



