GREENHOUSE RED SPIDER. 163 



been removed from the fumigating box containing benzene vapor soon 

 recovered in fresh air. The expense and danger accompanying the use 

 of benzene precludes its use on a commercial scale. 



Nitrobenzene and para-dichlorobenzene were experimentally used as 

 fumigants, but proved to be as unsatisfactory as benzene, while nitro- 

 benzene severely injured foliage. 



Spraying Experiments. 



At present the only kno\\ai method of controlling red spiders is by 

 the use of sprays. The majority of these act as adhesive sprays, while 

 only a few are truly contact poisons. 



(a) Water. 



Water alone has been found very useful in the control of this pest on 

 certain plants, such as the carnation, violet and rose. The usefulness 

 of a water spray lies in the fact that frequent syringing dislodges many 

 mites from the leaves. The majority of these fall to the moist ground 

 and become permanently pasted into the mud. Frequent use of water 

 also prevents the formation of webs, which are quite necessary as a means 

 of travel and dispersal when a leaf becomes thickly populated. Although 

 water is very useful in controlling these mites on certain plants, others 

 cannot be gro-uii in a humid atmosphere without being seriously attacked 

 by fungous diseases, and this is especially true of cucumber plants. The 

 tenderness of the forcing house cucumber also limits the usefulness of a 

 strong stream of water. 



(b) Adhesive Sprays. 



1. Flour Paste. — Perhaps the most widely known and thoroughly 

 tried adhesive spray is flour paste, recommended by W. B. Parker (1913) 

 in controlling mites attacking hops in the Sacramento Valley, Cal. He 

 found that flour paste made according to the following formula proved 

 to effectively control 99 to 100 per cent, of the mites: 8 pounds of flour 

 boiled in 8 gallons of water to form a paste, and diluted to make 100 

 gallons of spray. ^ 



In order to obtain an accurate estimate of the effectiveness of ^his 

 spray when used on cucumbers the following experiment was performed: 

 a stock solution of flour paste was made and diluted according to Parker's 

 formula. This spray was applied thoroughly to an infested plant. 



Results. — The spraj'' has excellent spreading qualities, and as an 

 adhesive is quite efficient in controlling all mites which at the time of 

 sprajdng are actively feeding. However, this spray does not affect either 

 the hatching of the eggs or the emergence of the mites from the quiescent 

 stages. 



> In a recent government bulletin McGregor and McDonough recommend the use of laundry 

 starch, thus simplifying the process of cooking in forming the stock paste solution. 



