. 22 THE RED SPIDER ON HOPS IN CALIFORNIA. 
Reason for inefficiency. — Some experiments with sulphur upon 
Tetranychus bimaculatus attacking prune, pumpkin, and sweet peas 
proved very satisfactory. Similar results were obtained when 
sulphur was applied to infested sweet peas in Los Angeles, Cal., by 
Mr. H. M. Russell, as is shown in Plate IV, figures 1 and 2. The 
efficiency of sulphur against the red spider on these plants and its 
inefficiency when applied on hops and cotton led to some careful 
observations as to conditions. It was noted that the pumpkin and 
sweet peas expose nearly all of both surfaces of their leaves to the 
direct rays of the sun at some time during the day and that the mites 
on the prune were attacking the upper and therefore the exposed 
surfaces. The hopvines and cotton plants, however, expose princi- 
pally the upper surfaces of the leaves to the sun and the mites living 
upon the undersides are thus protected. 
From these observations it is evident that sulphur is effective upon 
the red spiders only when the infested surfaces of the plant are 
exposed to direct sunshine at some time during the day or to intense 
reflected heat. 
LIME-SULPHUR SOLUTIONS. 
The results obtained in a small preliminary field experiment in 
which lime-sulphur in combination with nicotine sulphate, 40 per 
cent, was applied gave such good results that these materials were 
at once placed at the head of the list of sprays to be fully tested out 
during the course of the investigation. The lime-sulphur solutions 
are much cheaper than the nicotine solutions when used at the sum- 
mer dosage; therefore it seemed desirable to try the lime-sulphur 
solution alone hi order to reduce the cost of spraying, provided the 
omission of the more expensive nicotine solution did not alter the 
results. 
During the early work with these sprays it was evident that the 
straight lime-sulphur solutions, instead of spreading out in a film, 
formed beadlike drops on the foliage. Mites found in actual contact 
with these drops of spray were seen to draw away from them and 
escape uninjured. The results obtained with straight lime-sulphur 
solutions were most unsatisfactory. 
Soap formed a precipitate with the polysulphid, and as it was 
very evident that some " spreader" must be used if the lime- 
sulphur solutions were to prove effective, this subject was thoroughly 
investigated. 
Upon the suggestion of Prof. A. L. Quaintance, of this bureau, 
"black-strap" molasses, a cheap grade, was used with the lime-sul- 
phur spray at the rate of 2 gallons to 100 gallons of spray. This 
