178 MASS. EXPERIMENT STATION BULLETIN 179. 



days has never been serious, but should be eUminated as far as possible 

 by proper management of greenhouse temperature and the selection of 

 suitable days for spraying. 



In order to effectively control red spider infestations, at least three 

 sprayings given at weekly intervals are necessary. 



The first spraying should usually be applied one week after the plants 

 have been set in the greenhouse. If the young plants show mite injury 

 before this time the application should be made as soon as possible. 

 Usually young cucumber plants do not appear to be affected early in the 

 season. However, on closer examination it will be found that the majority 

 of these plants harbor a few mites which, if allowed to develop unhin- 

 dered, will later become so numerous, and the plant so large by the time 

 injury is noticeable, that an efficient control will be found extremely 

 difficult and expensive. 



Since this spray does not destroy red spider eggs it is clear that a second 

 application is necessary to kill the individuals which were eggs at the 

 time of the first spraying. This should be applied seven to eight days 

 after the first. If the second spray is not applied at the proper time it 

 will be almost impossible to control these pests, for many mites will 

 have become adult and laid eggs unless the application is made as rec- 

 ommended. 



Some mites are sure to escape the first and second sprayings, and there- 

 fore a third application must be given in order to kill these mites, which 

 if not controlled will rapidly multiply and severely injure the plants. 



As previously mentioned in the discussion of the "Economic Im- 

 portance of the Pest," the loss to cucumber growers due to red spider 

 infestation consists in shortening the life of the plant during its pro- 

 ductive period. It is absolutely essential that these three sprayings be 

 made as directed, otherwise the producing period of the plants will be 

 reduced at least one month. 



Under normal conditions the few mites found early in the season re- 

 produce rapidly until finally the plant becomes seriously affected by 

 the injuries caused by their progeny, and usually dies before producing 

 a full crop. If the mites are held in check by weekly applications early 

 in the season the length of the period during which these regular applica- 

 tions are made will later be added to the adult life of the plant. The 

 longer the spraying period the longer the productive life of the cucumber 

 plant. 



It is therefore of great financial importance to the grower to see that 

 these sprayings are thoroughly applied at weekly intervals during the 

 early life of the crop. 



Cost of Spraying. — The comparative cost of 100 gallons of spray 

 containing lemon oil and linseed oil is as follows: lemon oil, $8.75; 

 linseed oil emulsion, $1.50. 



If sprayings are made with a power sprayer it will take a man, with the 

 help of a boy, approximately three hours to spray thoroughly a green- 



