February, ’24] 
frost: red spider control 
101 
question of carrying the plant over some critical period during which 
infection ordinarily takes place. 
President A. G. Ruggles : The next paper is by S. W. Frost. 
FOUR YEAR EXPERIMENTS ON THE CONTROL 
OF THE RED-SPIDER 
By S. W. Frost, State College , Pa. 
Abstract 
General notes are given as to the status of the Red spider Paratetr any elms 
pilosus C. & F., in Pennsylvania. Two methods of control, the delayed-dormant 
and summer applications are discussed. Miscible oils in the delayed dormant kill 
a large percentage of the eggs while lime sulphur has been found ineffective. 
Various types of sulphur spray during the summer have given satisfactory control 
while dusts have given little or no control. 
The red-spider (Paratetranychus pilosus C. & F.) was first noted as a 
pest on apple trees in Adams county, Pennsylvania. Later it was 
found abundant throughout Pennsylvania and is now known to be 
common throughout the eastern part of the United States. During 
the past five years it has been more or less abundant according to seasonal 
conditions. Hot dry weather is very favorable for its development. 
During such summers an alarming amount of damage has been experi¬ 
enced. Cool rainy weather on the other hand, is unfavorable for its 
development and in fact heavy rains seem to wash them from the trees. 
Dr. H. E. Ewing believes that the species which inhabit low growing 
plants, as the raspberry, suffer considerable injury from driving rains. 
He says that they are pasted in the mud and never gain access to the 
plants again. The writer has frequently noticed the beneficial effects of 
driving rains in reducing the infestation on apple trees. In conducting 
spraying experiments it seems that high pressure is a valuable factor 
in the control of the red-spider. 
Nature of the Injury 
The injury by Red-spiders is confined entirely to the foliage. They 
have never been known to attack the fruit of apple. The fruit suffers 
only indirectly through the injury of the foliage. The vitality of the 
tree is lessened and a premature dropping of the foliage and in some 
cases a premature dropping of the fruit has been noticed. This pest 
often works in conjunction with the leaf-hopper (Empoa rosae L.) 
when it is difficult to determine which is causing the more serious injury. 
