SHADE TREE INSECTS 



77 



Red Spiders, or Mites 



Red spiders, or mites, are not true insects but belong to the same group as 

 spiders. They do not chew foliage as do many species of insects but suck the plant 

 juices with their sharp-pointed, piercing mouth parts and sometimes cause very 

 serious injury to the foliage of plants. 



There are numerous species of mites which attack many kinds of broad-leaved 

 trees and cause various types of injury, such as the growth of leaf galls, the ap- 

 pearance of velvety patches on the leaves, and the discoloration of the foliage. 

 This discoloration is the result of the removal of the green coloring matter of the 

 leaf in the vicinity of the puncture made by the insertion of the piercing mouth 

 parts into the tissues of the leaves. Severel}- affected foliage becomes mottled in 

 appearance and later brownish or rusty as though scorched. Badly infested leaves 

 may fall prematurely, thereby reducing the vitality of the tree. Many needle- 

 bearing evergreens are also injured by mites. 



Mite attack may be identified by the following: numerous tin\- discolored spots 

 on the leaves; very fine strands of silk stretched over the leaf surfaces, which 

 at times may become very noticeable; and tiny spherical eggs and broken egg 

 shells. Mites are very minute in size, and var>- in color. I'he body is oval with 

 long spine-like hairs. There are four pairs of legs. 



The common red spider, Tetranychus telarius 

 I,., attacks many broad-leaved trees and hhrubs. 

 In the Northern States it is reported to pass the 

 winter successfully as an adult or a second stage 

 nymph beneath debris and in loose, dry soil. 



The European red mite, Paratctranychiis 

 pilosus Can. and Fanz., is common on apple 

 and other fruit trees. It is reported to attack 

 elm and a few other shade trees occasionally. 

 It passes the winter in the egg stage upon the 

 smaller twigs and branches. The eggs of this 

 species are dark red, and masses of them appear 

 like red brick dust on the twigs. 



The spruce mite, Paratetranychus imunguis 

 Jacoby, is common on some of the needle- 

 bearing evergreens such as spruce, arborvitae, 

 and red cedar. It spends the winter in the egg 

 stage around the bud scales and at the base of 

 the needles. The eggs are brown. 



When warm weather approaches, these and other mites attack the leaves, 

 producing the characteristic injury described above. Mite injury is usually most 

 abundant during hot, dry weather. Several generations are produced a >ear. 



Control. \\ here sufficient water pressure is available and the size of the trees 

 permits, drenching infested trees and shrubs frequentK- with a hose helps to 

 reduce mite infestation by washing off the mites. 



During the spring and summer after the new foliage appears, an application 

 of one of the wettable sulfurs at the strength recommended by the manufacturer 

 should give satisfactory control of mites if it is applied when the temperature is 

 high. 



For those mites which overwinter in the egg stage on fruit trees or evergreens, 

 in addition to the above summer spray a dormant spray of a miscible oil or oil 

 emulsion, diluted according to the directions of the manufacturer and applied 



Common Red Spider, 



Tetranychus telarius. 



Greatly enlarged. 



Courtesy, Oreg. Agr. Expt. Station. 



