which normally begins blooming betweer January 10 and 14. Under these condi tions, supplemental feeding should bc done between December 20 and 25 tc prepare colonies for almond pollinatior in February. The date of the first natura. bloom will vary with plant species grow YUMA ing in winter locations of colonies. Feeding colonies with Beevert twc weeks before they entered alfalfa seed SPIDER MITE fields for pollination in 1968 resulted in a 15 per cent increase in the amount oj pollen collected during alfalfa bloom. The consistency of results obtained in ON CITRUS these four Fresno County bee feeding ex. periments suggests it is advisable for bee. keepers in this area to feed weak colonies in the fall and to feed all colonies two and H. S. ELMER a half to three weeks before the first nat. ural bloom after winter to increase the strength of bee colonies for almond pol- lination. When natural pollen supplies are HE YUMA SPIDER MITE, Eotetrany- plant may be the native host of this mite not adequate, supplemental feeding of Tchns yumensis (McGregor) , was species. natural pollen or natural pollen mixed first observed near Yuma, Arizona, in The body of the Yuma spider mite is with drivert sugar has stimulated an in- about 1928 by J. L. E. Lauderdale, and usually pinkish but may become quite crease in egg laying. Weak colonie: was described in 1934 by E. A. McGregor dark, particularly in older adults. It re- should also be fed two and a half to three from specimens collected on lemon foli- sembles the six-spotted mite, E. sexma- weeks before they move to alfalfa seed age by R. S. Woglum and H. C. Lewis. cdatus (Riley), and the Lewis spider fields for pollination purposes. This mite occasionally becomes a serious mite, E. lewisi (McGregor). Eggs vary Pollen or pollen and sugar supple- pest on citrus in certain desert regions of in color from white to almost colorless mental foods have been readily accepted the southwestern United States, but little but become light pink just prior to hatch- in the liquid syrup form; however, bees information has been published on its life ing. The mite feeds on the leaves, fruit, in these experiments have rejected the history, distribution, host range, and the and green twigs of the citrus tree and pro- dry form of these same foods during means of reducing injurious populations. duces a heavy webbing to which dust par- warm dry weather. ticIes adhere. This dust-covered webbing Limited areas facilitates detection of heavy infestations. Bob Sheesley is Farm Advisor, Fresno The Yuma spider mite is evidently con- The mites may produce a silvering of County; and Bernard Poduska is Senior mature hitssimilar to that caused by the Apiary Inspector, Fresno County. Finan- fined to very limited areas: the citrus areas around Yuma, Arizona, the Coa- Lewis spider mite, and they are believed cial assistance was received from fly- to accentuate a tree condition known as Queen Research Inc., Fresno County chella and Imperial Valleys in California, and adjacent desert regions in northern “fall dieback,” which may also be en- Pure Seed League, and California Al- hanced to a lesser degree by the citrus red mond Growers Exchange. Mexico. In the Coachella Valley it is fur- ther limited to citrus plantings within a mite, Panonychus citri (McGregor) . Branches up to 1% inches in diameter By feeding pollen 2% to 3 weeks prior to the 20-mile radius of the northern end of the may lose their leaves and die due to the occurrence of natural bloom in the area, re- Salton Sea-although citrus plantings ex- peated supplemental feedings were not needed combination of mite injury, low humid- tend much farther than this. The reason to maintain the rapidly growing colonies. this mite has not become established in ity, wind, and lack of sufficient soil mois- ture. other desert citrus growing areas Qf Cali- fornia and Arizona with similar climatic Population increase conditions is not known, especially since Yuma spider mite populations gener- there are few restrictions on the transpor- ally brgin to increase in October and tation of citrus fruit and nursery stock November and may remain high through- between mite-infested and noninfested out the winter, then decreasing in the areas. In addition to citrus, this mite has spring and early summer. The mites live been found on grapes, castor beans, grain through the summer as adults under the sorghum, puncture vine (Tribulus ter- bark of the trunk or limbs and in cracks restris L.) , brown-eyed primrose (Oeno- in shaded areas. Large populations re- thera ctavaejormis Torr. & Frem.), and main alive later in the spring near the on quail brush [Atriplex lentiformis Salton Sea. At Yuma, Arizona, moderate (Torr.) Wats.]. The mites have been infestations may be found throughout the found on quail brush far removed from summer. Mite population numbers may citrus trees, therefore suggesting that this be quite variable during the winter

CALIFORNIA AGRICULTURE, OCTOBER, 1969 15 months even in areas where dense popu- duction, egg mortality, length of the egg lations sometimes develop. Such varia- stage, and life cycle. No eggs were pro. tions are apparently the result of preda- duced at a temperature of 50° F, regard- Chemical tors and parasites, climatic differences, less of the humidity. Eggs produced at all varying tree conditions such as tree vigor three humidities and at 60' F failed to and the plant growth cycle, all o€ which hatch within 60 days. However, after 60 JAMES J NU SSBAU M affect the feeding mites. days at 60' F those eggs exposed to SO The effects of temperature and humid- per cent and 78 per cent humidity did A more branched, fibrous root system is ity were the only considerations in the hatch when removed to a room tempera- possible by chemically pinching the roots study reported here. Climatological con- ture of 80' F. of young container-grown nursery plants. ditions were found to vary from grove to Temperatures in the areas where Yuma Copper naphthenate painted on the bot- grove and from locality to 1.ocality. The spider mite does not exist often remain tom of the seedbed was effective and easy microclimate affecting individual mites bclow 60' F for 60 days or more and to use. Treated seedlings formed more might, even if the parasite-predator com- when these temperatures rise they are not lateral roots than untreated plants. Root plex were not a factor, explain mite popu- accompanied hy a rise in humidity. In pruning to prevent roots from being kinked lation differences that occur from place to areas where this mite thrives, daytime and twisted when transplanted was mini- place. Numcrous attempts at gathering temperatures nevcr stay below GOo F for mized. This technique should be particu- information on the relationship of tem- any period of time even though the hu- larly adapted to taprooted plants. perature and humidity to populations midity is generally low. Mite, exposed to a temperature of produced a few under field conditions were abandoned llOo F ECENT STUDIES ha\e indicated that after two seaPons because of the difficulty eggs which failed to hatch after 60 days R kinked, circled, or twisted root pat- in studying this small mite in various and did not hatch when moved to a tem- terns frequently formed when nursery citrus groves where different irrigation, perature of 80' F. Adult? exposed to a plant scedlings were not root pruned and pest control and other cultiiral practices temperature of 110' F survived only four carefully transplanted. Plants of low \igor were used. days. This extreme temperature prohably and short life often resulted. Better Yuma spider mites have not been docs not exist for any period of time in branching patterns on tap rooted species found near Phoenix, Arizona, nor in some the micro area where these mites exist. but were obtained by pinching the root tip. the to temperatures that do areas in California where their presencr 100 120O F Lateral roots formed above the pinched could be expected since environmental occur for short daytime periods prohably root tip. The resulting well-branched root explain the near absence of adult popu- conditions there are similar to thoTe of system should provide improx ed anchor- lations during the summer months. areas where this mite is prevalent. Lab- age and support as the plant matures. oratory tests showed that certain preda- Control Manual root pruning is time consum- cious mites and thrips, often found on Yuma spider mite on citrus can be con- ing and easily skipped. An easier method, citrus, prey on the Yuma spider mite, and trolled with a fall application of sulfur which would allow for differential root in some areas may prevent their popnla- used as a dust at 50 to 100 pounds per growth rates from plant to plant, would tions from increasing. Populations of the acre or with a thorough outside coverage be to pinch the roots as they reach the Yuma spider mite near Yuma, Arizona, spray application of wettable sulfur at 4 and in portions of the Coachella and 11)s per 100 gallons of water. A second Imperial Valleys may exist because of INFLUENCE OF TREFLAN, OSMOCOTE, AND application of sulfur some time hefore COPPER NAPHTHENATE ON TOP AND ROOT the ahsenre of predators and parasites, LENGTH OF CORK OAK SEEDLINGS THREE bloom in early spring may he applicd to hut the principal reason for the mites' WEEKS AFTER PLANTING GERMINATED redncr populations of both the Yuma ACORNS. DAVIS 1968. choice of habitat area is probably temper- spider mite and thc citrus flat mite, Brcvi- ature and humidity conditions. pnlpu~lrwisi Mt Gregor. Citrus flat mite Laboratory tests is also of primary concern on all citruq CONTROL TREFLAH OSMOCOTE COPPER except grapefruit at petal fall time in the Yuma spider mites were colonized on spring. Sulfur should not be applied dur- green lemon fruits and were held in lab- thc warmer months when temperatures oratory isolation boxes where tempera- are likely to cxctwl 100' F within two ture and humidity were controlled. Thc weeks following application. Numerous normal range of relative humidities found new acaricides have bcen used wcessfully in m0.t citrus growing areas was covered. to control Yuma spider mite hit none The mites were allowed to live under vari- have pro1 en to be superior to sulfur. How- ous combinations of temperatures he- mer, if it is nece-ary to reduce Yiima tween 50' and and at humidities TOP GROWTH ' llO°F spider mite populations during thc time of 10, 50 and 78 per cent. A comparison when the tcmperatrire is too high to use TREATED LAYER of the mites exposed to these different sulfur. either clicofol (Kelthanc) or chlor- rnvironmental conditions established that TAPROOT ohenzilate may be used as recommended 0 at humidities of SO per cent or below, the hy local agriculturc authorities. optimum ternperaturc for this mite is be- tween 80' and 90OF. H. S. Elnicr is Specinlist, Dcpartmcizt The effcct of varying- environmental o/ Entonzology, Uniccrsity of Cafifornin, * Osmocote is a controlled release fertilizer pro- conditions was also observed on egg pro- Rizerside. duced by Sierra Chemical; Treflan is a preemergence herbicide produced by Eli Lilly and Compony; and copper naphthenate is a wood preservative prepared 16 by Gilbreoth Chemical Company as Coppernate "55".