170 MASS. EXPERIMENT STATION BULLETIN 179. 



Lemon Oil. 



The first of these commercial experiments commenced during May, 

 1916, and continued until the middle of June. Lemon oil, 1 part in 20 

 parts of water, was thoroughly tested in several greenhouse^, and in all 

 cases the spray proved very efficient, provided it was thoroughly applied 

 to the infested plants. At the time the first commercial applications 

 were made the plants were nearly full-grown, and the mites were at that 

 time rapidly spreading through the houses. All that could be expected 

 of this spray was to hold the red spiders in check, so that they would not 

 materially damage the whole house before a good crop of cucumbers had 

 been picked. Owing to the scarcity of labor it was found impossible to 

 apply sprays at weekly intervals, and therefore the results were not as 

 satisfactory as they would have been under other conditions. However, 

 these sprayings held the red spiders in check and prolonged the life of 

 the cucumber plants, which would have died early in the season had no 

 treatment been applied. 



In several instances young potted cucumber plants were dipped in a 

 1 to 20 dilution of lemon oil as they were being set in the greenhouse. 

 This proved to be injurious to the succulent leader, although the leaves 

 gave no indication of injury. 



Linseed Oil Emulsion. 



During the summer of 1916 experimental work on the determination 

 of the killing property of lemon oil led to the discovery of linseed oil 

 emulsion and its efficiency in controlling mites. This emulsion has re- 

 ceived a very thorough trial in commercial greenhouses this season (1917), 

 and proves to be satisfactory in many respects. The ingredients are 

 always at hand, the initial cost is low, being one-fourth that of lemon 

 oil, and the method of preparation is simple. 



Experiment No. 1. 



Early in the spring of 1917 this spray mixture was thoroughly tested 

 on a commercial scale in greenhouses located in Watertown, Mass. This 

 range is naturally divided into two groups. Group L contained the oldest 

 cucumber plants and Group II. the youngest. It was decided that appli- 

 cations should be made to the youngest plants, although they were really 

 too old for effective spraying. The cucumber plants became badly in- 

 fested in the seed-plant house before being set out. Therefore this in- 

 festation became serious soon after the plants were transplanted to the 

 greenhouses. Severe pruning was resorted to, but this did not hold the 

 mites in check. For efficient control, these plants should have been 

 thoroughly sprayed at the time they were transplanted. 



Group II. consisted of three greenhouses. In greenhouse No. 1 the 

 plants were very heavily infested, and were 5 feet tall at the time of the 



