• Postemergence Weed Control in Onions

      Umeda, K.; Fredman, C.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1995-08)
      Oxyfluorfen (Goal®) herbicide at 0.125 to 0.25 lb. a.i./A applied postemergence (POST) to onions at the 3-leaf stage of growth effectively controlled London rocket, yellow sweetclover, and prostrate pigweed with marginal injury to onions. Earlier POST applications on 1- and 2-leaf onions caused injury and some stand reduction. Bromoxynil (Buctril®) herbicide at 0.25 lb. a.i./A applied early POST gave generally good weed control but did not adequately control sweetclover. Buctril® applied in clear weather did not injure 1-leaf onions but caused severe injury on 2- and 3-leaf onions when applied during cloudy weather conditions. Buctril® plus pendimethalin (Prowl®) tank-mix combination applied POST provided good control of London rocket, sweetclover, and prostrate pigweed; however, onion injury was severe due to applying Buctril® in cloudy weather. Buctril® and Goal® effectively controlled weeds present in the onions but timing of POST applications was critical with respect to onion size and weather conditions to minimize injury.
    • Preemergence Herbicide Weed Control in Spinach

      Umeda, K.; Fredman, C.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1995-08)
      Two field studies were conducted to evaluate metolachlor (Dual®) for preemergence weed control in spinach to provide support to gain registration through the IR-4 program. Dual® at 1.0 to 1.5 lb a.i./A gave acceptable control of London rocket, black mustard, lambsquarters, and knotweed. Nettleleaf goosefoot, cheeseweed, and yellow sweetclover control was not acceptable. In one test, dimethenamid (Frontier® or SAN -582H, Sandoz) controlled London rocket, lambsquarters, knotweed, and goosefoot at 0.25 lb ai. /A and did not control cheeseweed or sweetclover. Spinach was not injured by Dual® or Frontier®.
    • Relative Susceptibility of Red and Gree Color Morphs of the Green Peach Aphid to Foliar and Systemic Insecticides

      Kerns, David L.; Palumbo, John C.; Byrne, David N.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1995-08)
      Foliar and systemic insecticide bioassay techniques were developed for testing insecticide susceptibility to two color morphs of the green peach aphid. Six foliar and one systemic insecticide were used in our evaluations. These insecticides included three organophosphates, two pyrethroids, one organochlorine, and one chloronicotinyl. One of the green colored populations tested was collected from spinach, and red and green color populations were collected from the within the same cabbage field. The red morph was found to be less susceptiblethan the green morphs to Dimethoate, Karate, and Endosulfan. Their were only slight differences in susceptibility to the foliar insecticide between the green morphs. The greenmorph from spinach was found to be the most susceptible to Admire, while the two morphs collected from cabbage did not differ. Leveling off of aphid mortality at about 85% with high doses of Admire may indicate highly tolerant types in the populations, or an artifact of the methodology.
    • Soil-Applied Herbicides for Weed Control in Broccoli

      Umeda, K.; Gill, A.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1995-08)
      Three commonly used herbicides for use in broccoli were effective when applied alone or in combinations as a preplant incorporated (PPI) or a preemergence (PE) application. DCPA (Dacthal®) at 10.0 lb product/A PE gave acceptable control of most weeds. Trifluralin (Treflan® SEC) at 1.0 pt/A and bensulide (Prefar® 4EC) PPI were also effective but mustard weeds were not adequately controlled. Combinations of the herbicides at lower rates did not provide any advantage in improving weed control efficacy.
    • Subsurface Drip Irrigation of Leaf Lettuce and Broccoli I: Spatiel Distribution of Roots and Soil Water Tension

      Thompson, Thomas L.; Maki, Kerri L.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1995-08)
      The objectives of this research were i) to observe the movement of the wetting front in subsurface drip irrigated lettuce and broccoli, 2) to analyze variability in soil water tension (SWT) within the profile, and 3) to determine root distributions of subsurface drip irrigated lettuce and broccoli. Lettuce and broccoli plots at the Maricopa Agricultural Center during the 1992-93 and 1993-94 winter growing seasons were intensively instrumented with automated tensiometers. During both seasons, there was good agreement between mean daily SWT, and SWT measured before irrigation. During 1992-93, the maximum variation in mean SWT among tensiometers was 2.5 kPa. Among tensiometers within the zone of greatest root density, the maximum variation was only 1.5 kPa. Therefore, the range of SWT within the lettuce root zone was small, and tensiometer placement anywhere within the root zone would have been adequate. During 1993-94, the maximum variation in mean SWT among tensiometers was 7 kPa. The maximum variation among tensiometers within the zone of greatest root density was 5.3 kPa. The larger variation in mean SWT among tensiometers, compared to lettuce, is due to the greater water use of broccoli. Tensiometer placement will be more critical for higher water use crops. During both seasons roots proliferated around the drip tubing. These results substantiate the assumption that tensiometer placement anywhere within the zone of greatest root density will be adequate for irrigation scheduling of subsurface drip irrigated crops.
    • Subsurface Drip Irrigation of Leaf Lettuce and Broccoli II: Water Balance

      Thompson, Thomas L.; Maki, Kerri L.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1995-08)
      The objective of this research was to estimate a season -long water balance under one subsurface trickle- irrigated plot each of lettuce (Lactuca sativa L. var. Waldmann's Green) and broccoli (Brassica olearacea L. var. Claudia). One lettuce plot during 1992-93 and one broccoli plot during 1993-94 were intensively instrumented with automated tensiometers. Tensiometer readings and estimates of evapotranspiration were used to estimate seasonal water contents in the crop root zone, and water losses due to leaching. For the monitored portion of the 1992-3 growing season, 19.1 an of irrigation water was applied, 12.5 cm of rainfall fell, and ET, was 11.5 cm. Estimated deep percolation was 60% of total water applied (irrigation plus rainfall). Leaching was periodic, and was mostly associated with rainfall events. During the monitored portion of the 19934 season, 21.2 cm of irrigation water were applied, 8.0 an of rainfall fell, and ET, was 21.9 cm. Estimated deep percolation was 28% of total water applied. Almost all of this leaching was associated with one major rainfall event. Water stored in the root zone (top 50 cm) was relatively constant at 12-14 cm water/50 cm soil except after rainfall.
    • Use of Non Toxic Materials for Whitefly Control and Growth Enhancement in Crisphead Lettuce

      Molin, W. T.; Oebker, N. F.; Brown, J. K.; Palumbo, J. C.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1995-08)
      Field studies were conducted in Yuma and Tucson in 1993 to determine the effect of several non toxic substances purported to enhance growth and yield of lettuce, and to determine whether these treatments have an effect on whitefly populations. Five applications of the treatments were made beginning four weeks after planting and continuing at weekly intervals. Results indicated that there may be some positive effects of foliar applied methanol and nutrient (nitrogen/iron) treatments, as well as, from the use of Capture insecticide.
    • Vine-Decline of Melons Caused by Monosporascus cannonballus in Arizona: Epidemiology and Cultivar Susceptibility

      Stanghellini, M. E.; Rasmussen, S. L.; Kim, D. H.; Oebker, N.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1995-08)