• Reduced Tillage and Crop Residue Effects on Cotton Weed Control, Growth and Yield

      Adu-Tutu, K. O.; McCloskey, W. B.; Husman, S. H.; Clay, P. A.; Ottman, M. J.; Martin, E. C.; Teegerstrom, T.; Tronstad, Russell; Husman, Steve; Norton, Randy (College of Agriculture, University of Arizona (Tucson, AZ), 2004-05)
      The tillage operations conducted in a barley and cotton double-crop rotation were reduced by eliminating tillage prior to planting cotton, eliminating cultivations for weed control in cotton, and especially by eliminating tillage following cotton prior to planting barley. Data collected in 2002 and 2003 in Coolidge and Marana showed that a weed sensing, automatic spot-spray system reduced the amount of spray volume and herbicide used by 50 to 60%. Data from Maricopa in 2003 indicated that the savings can be much greater (e.g., in a treatment with thick Solum barley cover crop residues) or much less if volunteer grain germinates after grain harvest. Similar weed control was obtained with the weed sensing, automated spot-spray system compared to conventional continuous spray systems for most weed species. At Coolidge in 2002, the minimum tillage treatment with a barley cover crop produced 24% more lint than the conventional tillage system (1089 versus 880 lb/A) because more water was applied in that treatment. In 2003, the minimum tillage treatment yielded 24% less than the conventional tillage treatment (1178 versus 1539 lb/A) due to herbicide injury. There were no differences in cotton yields among the tillage systems at Goodyear in 2002 and 2003. In Marana (2002 and 2003) and Maricopa (2003), there were yield differences between treatments related to planting date, with late-planted cotton yielding less than early-planted cotton. At Marana, the cotton yields of the minimum-till and conventionally tilled treatments were not statistically different. At Maricopa, the early-planted minimum-till cotton yielded less than the early-planted conventionally tilled cotton (956 versus 1141 lb/A). The yield comparisons between conservation tillage and conventional tillage cotton production systems are not yet definitive and more research needs to be conducted. Economic comparisons between productions systems indicated an advantage for conservation/minimum tillage treatments if cotton yields were comparable.
    • Round Ready Flex Cotton: Glyphosate Tolerance and Weed Management 2002-2003

      McCloskey, William B.; Adu-Tutu, Kwame O.; Hicks, T. Vint; Tronstad, Russell; Husman, Steve; Norton, Randy; Department of Plant Sciences, University of Arizona, Tucson, AZ; Monsanto Company, Fountain Hills, AZ (College of Agriculture, University of Arizona (Tucson, AZ), 2004-05)
      The tolerance of Roundup Ready (RR) Flex cotton to topical Roundup Weathermax (glyphosate) applications and weed management programs in RR Flex cotton were studied in 2002 and 2003 at the University of Arizona Maricopa Agricultural Center. RR Flex cotton demonstrated excellent tolerance to glyphosate as measured by flower pollen shed and lint yield when sprayed topically with glyphosate at 2.25 lb ae/A four times (at the 3 leaf, 6 node, 10 node and 14 node growth stages). Line 1445 containing the current commercial RR genetic construct had a flower sterility/pollen shed rating of 4.6 (1 equals full pollen shed and 5 equals no pollen shed) on 28 June 2003 compared to ratings of 1.1 to 1.9 in lines containing the RR Flex genetic construct. Cotton yields followed a similar pattern with 1145 yielding 386 lb seed cotton/A compared to 1477 to 1894 lb seed cotton/A for the best lines containing the RR Flex genetic construct (yields were generally low because all lines had a Cocker genetic background that is not adapted to hot desert production conditions.) The presence of the RR gene did not affect the yield of genotype pairs that were identical except for the presence or absence of the RR Flex genetic construct. In the weed management study, delaying the first topical glyphosate application resulted in larger, more difficult to control weeds and reduced cotton yield by allowing greater early season competition between weeds and cotton. The best weed control programs included early (1 to 2 leaf growth stage) topical applications at rates greater than 0.75 lb ae/A and a second Roundup application after the first post-planting irrigation (10 node growth stage). The data also suggested that there may be significant value in making a layby, directed-broadcast application that includes a residual herbicide such as prometryn at layby.