180 MASS. EXPERIMENT STATION BULLETIN 179. 



100,000 plants, was sprayed, using a power sprayer, three times between 

 July 15 and September 1. The object of this spraying was not to rid the 

 plants of red spiders, although this undoubtedly could have been accom- 

 plished, but to keep their numbers so reduced during the dry summer 

 months that they could not seriously injure the new and tender foliage 

 or kill the plants as they had done in previous years. 



The results were entirel}^ satisfactory, and the violet plants were kept 

 practically free from these pests. Those plants rather seriously damaged 

 before spraying began regained their dark green foliage, and during the 

 middle of August only a few leaves could be found in the field showing 

 typical red spider injury. Thus the damage caused by red spiders was 

 reduced to a minimum by spraying, while in previous years and under 

 similar conditions they had practically stripped the plants of their foliage. 



The difficulty of thoroughly applying a spray to the lower surface of 

 the leaves of a low-growing plant is well recognized, for our modern 

 nozzles are not adapted to this type of spraying. This difficulty, however, 

 may be overcome in violet spraying by the use of a simple spray nozzle 

 consisting of a "Skinner System" plug. This plug is often used in green- 

 houses, where it is inserted at intervals in the side of a water pipe. Water 

 passes from the pipe through a small hole in the center of the plug, and 

 then strikes a curved lip which transforms the solid stream to a fine, fan- 

 like spray. This plug is placed in the end of an extension rod 5 feet in 

 length, made from one-eighth-inch piping. The rod is then bent until 

 the fan-like spray travels parallel to the surface of the ground. This 

 type of nozzle proved very satisfactory, and could be held close to the 

 plant without injuring the leaves. 



SUMMARY. 



The common greenhouse red spider (Tetranychus bimaculatus Harvey) 

 is very generally distributed throughout the United States, extending 

 from Maine to Florida, and westward to Texas and California, only a 

 few States in the western arid region being exempt from the ravages of 

 this pest. 



The red spider is very cosmopolitan in its feeding habits. In market- 

 garden greenhouses the most important vegetable attacked is the cu- 

 cumber. In floriculture greenhouses the rose, violet, sweet pea, carnation 

 and chrysanthemum are seriously injured. The most important outside 

 plants, as far as the greenhouse man is concerned, are those found around 

 most greenhouses, consisting of clover, grasses and weeds, as these are 

 undoubtedly important factors in causing inside infestation. 



It is estimated that the annual loss to cucumber men in the Boston 

 market-garden district, due to red spider injury, amounts approximately 

 to $150,000, or 10 per cent, of the whole crop. 



Experimentation on the control of this mite attacking cucumbers gave 

 no f umigant which could be used with safety to the foliage. Sulfur burned 

 to form sulfur dioxide proved to be very effective in killing all stages of 



