PEAR GROWING IN CALIFORNIA. 387 



H. S. Smith, in his work of poisoning Argentine ants in the citrus 

 groves of Los Angeles Covuity, recommends the use of either one or 

 one-half pound paper bags as containers for the poison. These are 

 treated with paraffine and tacked to the trunks of the trees after putting 

 in the liquid and folding the top downward. The ants enter by means 

 of holes punched in the bags above the height that it is desired the 

 poison should reach. 



RED SPIDERS (Bryobia pratensis and Tetranychus sps.). 



The red spiders, or mites, at times become serious in the pear orchard. 

 The former species, more commonly known in California as the almond 

 mite, spends the winter on the trees in the form of small, red, glassy 

 eggs, plainly visible to the naked eye, and usually deposited about the 

 buds or in the smaller crotches. These hatch with the opening of the 

 buds and the tiny mites immediately begin their destructive work, which 

 is confined very largely to the spring months. Later in the season or 

 coincident with the hot weather in June or July, appear other species of 

 the web-spinning mites belonging to the genus Tetranychus. The most 

 common and destructive species in California is one that is closely allied 

 to Tetranychus mytilaspicUs, the citrus species, but apparently not the 

 same. It becomes so bad that frequently more or less defoliation of the 

 trees results if nothing is done to control it. This species also winters 

 in the egg stage. The eggs may be distinguished from those of the 

 brown mite by their redder color, flattened surface with central stem, 

 and usually sparse occurrence on the twigs as compared to those of the 

 brown mite. The common red spider, Tetranychus bimaculatus, is 

 frequently found on pear trees, the principal difference in its life history 

 lying in the fact that it hibernates in the soil during the winter months. 



Injury. 



The damage consists in a discoloration and drying of the leaves from 

 which the sap is extracted. Affected foliage presents a yellow, mottled, 

 sickly appearance, the presence of black spots or the droppings always 

 being in evidence. When species of Tetranychus are present there is 

 always a fine web spun over the leaves. This collects the dust during 

 the summer time, giving voice to the popular opinion that dust breeds 

 mites. 



Control. 



If eggs of the two species which winter in that stage occur on trees 

 they may be killed by an oil emulsion spray at a dormant strength in 

 the early spring when the buds are beginning to swell. Lime-sulphur 

 applied at dormant strength is also effective, but in this case the spray 

 has no eff'ect on the eggs, killing the young mites as they hatch. 

 Consequently the nearer hatching time of the eggs lime-sulphur can 

 be applied, the better. Lime-sulphur retains its effectiveness for weeks 

 after the application providing excessive rains do not wash it from the 

 trees. 



In the summer time all species can be controlled ])y applications of 

 "atomic" sulphur, "milled" sul])hur, lime-sulphur, in fact, sulphur, 

 which is the standard remedy for mites, is effective, in practically every 



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