174 MASS. EXPERIMENT STATION BULLETIN 179. 



of inside infestation. In the fall red spiders are found in large numbers 

 on these grassy borders, and being capable of wintering over out of doors, 

 it follows that a large percentage of those found in the fall will also be 

 present in the spring, and are quite certain to migrate to the more at- 

 tractive cucumber plants within the greenhouse. 



Methods of Exterminating Grassy Borders. 



1. The border for at least 10 feet away from the house should be thor- 

 oughly cultivated, preventing the gro^^i.h of weeds throughout the season. 



2. Where cultivation is not practicable, burning the border may be 

 resorted to. 



3. If neither of the above methods can be employed, kill all vegetation 

 around the greenhouse by spraying mth sodium arsenite used at the rate 

 of 1 pound to 20 gallons of water. It must be remembered, however, 

 that sodium arsenite is a poison, and care should be taken to prevent 

 animals from grazing on treated borders. Eepeat as often as necessary. 



Elimination of Artificial Dispersion. 



As described under "Feeding Habits and Dispersion," the most im- 

 portant factors in artificial dispersion are the men working in the green- 

 houses. The grower should systematize, as far as it is practicable, all 

 work which must be done in his houses according to the infestation; for 

 example, in two greenhouses, one showing red spider injury, the other 

 apparently free, pruning or "rolling up" of plants should first be done 

 in the house apparently free from infestation, and later in the infested 

 house. Also in picking cucumbers, the young houses — which usually 

 are not as badly infested as older ones- — should be picked first, and 

 older, badly infested houses last. Special care should be exercised not 

 to allow the men who have finished picking in a badly infested house to 

 start pruning or "rolling up " a very young house. Baskets used in picking 

 cucumbers should never be used in a younger house as a receptacle for 

 pruned parts of young plants. 



The wi'iter realizes that these recommendations are not all applicable 

 under commercial conditions, but every precaution which is practicable 

 should be taken if artificial dispersion and infestation are to be reduced. 



Repressive Measures. 



During the early stages of infestation it is frequently found advisable 

 to destroy plants which are found to be badly infested. These badly 

 infested plants should be pulled out before the leaves begin to die, so as 

 to prevent dispersion due to lack of food. 



If a few leaves, usually near the ground, are badly infested the pruning 

 of these will lessen the numbers of mites materially. In all cases, whether 

 a plant has been pulled or pruned, the red spiders on these leaves should 

 be destroyed by burning. Do not throw them outside of the house, but 



