• October–December 2003 13(4) 668 RESEARCH REPORTS role in sustainable agriculture systems in the future. The IP40 Black material shows great promise as a soil mulch and would go a long way towards solving the disposal problem created when non-degradable black plastic mulch is used in annual and perennial fruit and vegetable production. Variations in the carbon black additive or in colors may modify the degradation properties of the material to make it more useful for various production practices in the future. Literature cited Albregts, E.E. and C.M. Howard. 1972. Comparison of polyethylene and polyethyl- ene-coated bio-degradable paper mulches on strawberries. HortScience 7:568–569. Anderson, D.F., M.A. Garisto, J.C. Bourrut, M.W. Schonbeck, R. Jaye, A. Wurzberger, and R. DeGregorio. 1995. Evaluation of a paper mulch made from recycled materials as an al- ternative to plastic film mulch for vegetables. J. Sustainable Agr. 7:39–61. Edmond, J.B. 1929. Mulch paper for vegetable crops is tested. Mich. Agr. Expt. Sta. Bul. 11: 115–117. Flint, L.H. 1928. Crop-plant stimulation with paper mulch. USDA Tech. Bul. 75:1–20. Gomez, K.A. and A.A. Gomez. 1984. Statisti- cal procedures for agricultural research. Wiley, New York. Greer, L. and J.M. Dole. 2003. Aluminum foil, aluminum-painted, plastic, and degradable mulches increase yields and decrease insect-vec- tored diseases of vegetables. HortTechnology. 13:276–284. Hutchins, A.E. 1933. Mulch papers in veg- etable production. Minn. Agr. Expt. Sta. Bul. 298. Peavy, W.S. 1973. Paper mulch for muskmel- ons in low rainfall areas. Proc. Nat. Agr. Plast. Conf. 11:192. Pritts, M. and D. Handley (eds.). 1988. Strawberry production guide. N.E. Region. Agr. Eng. Ser. Bul. NRAES-88. Cornell Univ., Ithaca, N.Y. Pritts, M.P. and M. Kelly. 2001. Early season weed competition reduces yield of newly planted matted row strawberries. HortScience. 36:729–731. Sanford, J.C., D.K. Ourecky, and J.E. Reich. 1985. ‘Jewel’ strawberry. New York’s Food Life Sci. Bul. 114. New York State Agr. Expt. Sta., Geneva, N.Y. Shogren, R.L. 2000. Biodegradable mulches from renewable resources. J. Sustainable Agr. 16:33–47. Smith, A. 1931. Effect of paper mulches on soil temperature, soil moisture, and yields of crops. Hilgardia 6:159–201. Yang, S. 1999. Degradable plastic films for agricultural applications in Taiwan. Natl. Agr. Plastics Congr. Proc. 28:4–9. Managing Orchard Floor Vegetation in Flood-irrigated Citrus Groves Glenn C. Wright, 1 William B. McCloskey, 2 and Kathryn C. Taylor 3 ADDITIONAL INDEX WORDS. chemical weed control, citrus limon, citrus sinensis, cover crops, herbicides, lemon, me- chanical weed control, orange SUMMARY . Several orchard floor man- agement strategies were evaluated beginning in Fall 1993 in a ‘Limonei- ra 8A Lisbon’ lemon (Citrus limon) grove on the Yuma Mesa in Yuma, Ariz. and in a ‘Valencia’ orange (Cit- rus sinensis) grove at the University of Arizona Citrus Agricultural Center, Waddell, Ariz. At Yuma, disking pro- vided acceptable weed control except underneath the tree canopies where bermudagrass (Cynodon dactylon), purple nutsedge (Cyperus rotundus), and other weed species survived. Mowing the orchard floor suppressed broadleaf weed species allowing the spread of grasses, primarily bermu- dagrass. Preemergence (norflurazon and oryzalin) and postemergence (glyphosate and sethoxydim) herbi- cides were used to control weeds in the clean culture treatment in Yuma. After three harvest seasons (1994–95 through 1996–97), the cumulative yield of the clean culture treatment was 385 kg (848.8 lb) per tree, which was significantly greater than the 332 kg (731.9 lb) and 320 kg (705.5 lb) per tree harvested in the disking and mowing treatments, respectively. In addition, the clean culture treatment had a significantly greater percent- age of fruit in the 115 and larger size category at the first harvest of the 1995–96 season than either the disk The authors would like to thank the Arizona Citrus Research Council and the Yuma County Pest Abate- ment District for their financial assistance in completing this project. We would also like to thank Glen Curtis Incorporated for their cooperation, and technicians Philip Tilt, Gary Dixon, and Heather Geitzenauer for their invaluable assistance. 1 Associate specialist, Department of Plant Sciences, Yuma Mesa Agriculture Center, University of Arizona, 2186 W. County 15th St., Somerton, AZ 85350. 2 Associate specialist, Department of Plant Sciences, Forbes 303, University of Arizona, Tucson, AZ 85721. 3 Assistant professor. Current address: University of Georgia, Horticulture Department, Southeastern Fruit and Tree Nut Laboratory, 21 Dunbar Rd, Byron, GA 31008. or mow treatments. At Waddell, the management strategies compared were clean culture (at this location only postemergence herbicides were used), mowing of resident weeds with a veg- etation-free strip in the tree row, and a ‘Salina’ strawberry clover (Trifolium fragiferum) cover crop with a vegeta- tion-free strip. The cumulative 3-year yield (1994–95 through 1996–97) of the clean culture treatment was 131 kg (288.8 lb) per tree, which was significantly greater then the 110 kg (242.5 lb) per tree yield of the mowed resident weed treatment. The yield of the strawberry clover treatment, 115 kg (253.5 lb) of oranges per tree, was not significantly different from the other two treatments. The presence of cover crops or weeds on the orchard floor was found to have beneficial effects on soil nitrogen and soil organic matter content, but no effect on orange leaf nutrient content. The decrease in yield in the disked or mowed resident weed treatments compared to the clean culture treat- ment in both locations was attributed to competition for water. M anaging weeds on orchard floors in flood-irrigated Arizona citrus groves can be accomplished by disking, mowing, applying pre- and postemergence her- bicides, or by growing a cover crop. Weeds in flood-irrigated Arizona lemon groves have traditionally been managed by disking of the orchard floor (two to eight times per year) (Hilgeman and Rodney, 1961; Jordan and Day, 1973; personal observation by the authors in 2002). Disking is done in two directions (i.e., crossdisked), so that there is no herbicide-treated strip down the tree middle. Disking adequately controls weeds on the orchard floor except for nondisked areas underneath the tree canopies where bermudagrass, purple nutsedge, and other weeds survive. However, disking prunes tree roots near the soil surface reducing shal- low root density compared to clean culture with herbicides (Hogue and Nielsen, 1987; Parker et al., 1993). Additionally, tree shallow root den- sity under cover crops is often even less than in disked areas (Hogue and Nielsen, 1987; Parker et al., 1993). These shallow roots are the primary sites of water and nutrient uptake for the tree (Davies and Albrigo, 1994). Careless operation of equipment also results in broken branches and injured