• Herbicide Weed Control in Sweet Corn

      Umeda, K.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1995-08)
      Preplant incorporated and/or preemergence herbicide treatments including metolachlor (Dual®), EPTC with safener (Eradicane®), cyanazine (Bladex®), pendimethalin (Prowl®), and tank-mix combinations provided good (88 %) to excellent ( >98 %) weed control of prostrate and tumble pigweeds and purslane in sweet corn.
    • Field Evaluation of Potential New Fungicides for Control of Downy Mildew of Broccoli in 1994 and 1995

      Matheron, Michael E.; Porchas, Martin; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1995-08)
      Downy mildew of broccoli is caused by the plant pathogenic fungus Peronospora parasitica. Cool damp weather with high humidity is highly favorable for sporulation, dissemination of spores, and infection by this pathogen. The severity of disease is affected by the duration of weather conditions favorable for disease development. Potential new fungicides were evaluated for disease control in field trials conducted during 1994 and 1995. Downy mildew did not occur in the 1994 trial. In 1995, disease was moderate and all tested fungicides provided significant disease control compared to no treatment at all. Three new fungicides, Fluazinam, Dimethomorph, and ICIA-5504, show promise as potential new materials for control of downy mildew on broccoli.
    • 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)
    • 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®.
    • Impact of Sweet Potato Whitefly Infestation on Yield and Quality of Cantaloupe

      Palumbo, J. C.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1995-08)
      A range of population levels of sweet potato whitefly, Bemisia tabaci Gennadius was evaluated in three field experiments allowing measurement of the effect of whitefly numbers on melon quality and yield. An increase in total numbers of immature whitefly was associated with significant declines in harvested melon weight, a decline in number of boxes harvested, a decrease in fruit size, a decrease in percent sugars, and an increase in sooty mold. Regression analysis of individual whitefly life stages with yield parameters indicated that adult number was a more precise parameter and higher R2 values were obtained with increased range of whitefly population densities. Adults were sampled at the third leaf node in both locations. Nymph samples were taken at varying nodes from the base of the plant. Estimates of the mean adult whitefly density resulting in 5% and 15 % dollar yield loss were 3 and 10 adults per leaf Estimates of the mean total nymph density resulting in 5% and 15% dollar yield loss 0.5 and 2 (AZ) nymphs per cm² of leaf area, respectively.
    • An Action Threshold for Management of Sweet Potato Whitefly in Cantaloupe

      Palumbo, J. C.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1995-08)
      A range of action thresholds for the control of sweet potato whitefly, Bemisia tabaci Gennadius were evaluated in field experiments with high population density of B. tabaci. Action thresholds for whitefly adults, based on seasonal whitefly averages that could result in 5% and 15 % dollar losses, of 3 and 10 adults per leaf, respectively, were tested. All thresholds were compared to weekly insecticide treatments and an untreated check The resulting best threshold treatment was 3 adults per leaf area which provided a 170% increase in net return over the untreated check. The 3 adult per leaf threshold resulted in 6 applications of insecticide, compared with 10 applications used in the weekly regime.
    • Dry Bulb Onion Variety Trial

      Umeda, K.; Fredman, C.; McGrath, B.; Pettigrew, T.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1995-08)
      Forty-five different dry bulb onion varieties were grown and evaluated to provide a comparison of varietal characteristics including firmness, size, shape, and maturity.
    • Comparative Efficacy of B.t. Insecticides Against Lepidopterous Pests in Cabbage

      Umeda, K.; Fredman, C.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1995-08)
      Several commercial formulations of Bacillus thuringiensis (Al) insecticides were applied on cabbage and lepidopterous pests including Tricoplusia it (cabbage looper, CL), Spodoptera exigua (beet armyworm, BAW), and Plutella xvlostella (diamondback moth, DBM) were effectively reduced in population. The ten commercial products did not appear to vary significantly in controlling CL, the dominant species present in the cabbage.
    • Insectide Combinations for Whitefly Control in Broccoli

      Umeda, K.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1995-08)
      Two pyrethroid insecticides, fenpropathrin (Danitol®) and bifenthrin (Capture®), were evaluated in several combinations with other insecticides for whitefly control in broccoli and demonstrated good efficacy to reduce eggs and immature stage insects. At one week after the second of three applications, Danitol® or Capture® plus methamidaphos (Monitor®), acephate (Orthene®), or endosulfan (Thiodan®) significantly reduced egg counts relative to the untreated check.
    • Imidacloprid Does Not Enhance Growth and Yield of Cantaloupe in the Absence of Whitefly

      Palumbo, J. C.; Sanchez, C. A.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1995-08)
      Imidacloprid is a new, chloronicotinyl insecticide currently being used to control sweetpotato whitefly (Bemisia tabaci Genn, also known as silverleaf whitefly, Bemisia argentifolii Bellows and Perring). Large growth and yield increases of cantaloupes (Cucumis melo L.) following the use of imidacloprid have caused some to speculate that this compound may enhance growth and yield above that expected from insect control alone. Greenhouse and field studies were conducted to evaluate the growth and yield response of melons to imidacloprid in the presence and absence of whitefly pressure. In greenhouse cage studies, sweetpotato whiteflies developed very high densities of nymphs and eclosed pupal cases on plants not treated with imidacloprid, and significant increases in vegetative plant growth were inversely proportional to whitefly densities. Positive plant growth responses were absent when plants were treated with imidacloprid and insects were excluded. Results from a field study showed similar whitefly control and yield responses to imidacloprid and bifenthrin+ endosulfan applications. Hence, we conclude that growth and yield response to imidacloprid is associated with control of whiteflies and the subsequent prevention of damage, rather than a compensatory physiological promotion of plant growth processes.
    • 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.
    • Early Postemergence Herbicide 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 0.25 lb. ai./A and bromoxynil (Buctril®) at 0.38 lb.a.i. /A applied early postemergence (POST) to onions at the 1- to 2-leaf stage of growth gave near complete control ( >98 %) of lambsquarters, knotweed, cheeseweed, London rocket, and good control ( -90 %) of shepherd's purse. Buctril® did not control annual bluegrass and Goal® only slightly reduced some of the heavy population. Both herbicides caused marginally unacceptable onion injury at 17-20 %. Buctril® plus pendimethalin (Prowl®) tank-mix combination applied POST also gave very good broadleaaved weed control but annual bluegrass was reduced only 50 %. Similar onion injury was observed for the combination treatment as Buctril® alone. Buctril® caused onion injury when it was applied during cloudy weather. Buctril® and Goal® were effective for broadspectrum broadleaved weed control but onions were sensitive when treated before reaching the full 2-leaf stage of growth. Cloudy weather during applications also intensified the onion injury by Buctril® treatments.
    • 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.
    • 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.
    • Broccoli Variety Trials 1994/1995

      Wilson, Mark; Oebker, Norman F.; The Barkley Company (College of Agriculture, University of Arizona (Tucson, AZ), 1995-08)
    • Basal Crop Coefficients for Vegetables in Central Arizona

      Martin, E. C.; Slack, D. C.; Pegelow, E. J.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1995-08)
      The world supply of quality water for irrigation of crops is being depleted. Growers in the arid and semi-arid regions of the world, where irrigation is a requirement for crop production, are looking for ways to conserve their water use and increase their irrigation efficiency. One tool that has been useful in helping growers reduce their irrigation water inputs is computerized irrigation scheduling programs. This study is part of a joint project between the government of Egypt (National Agricultural Research Project), USA1D and The University of Arizona. Working together, researchers from Egypt and Arizona are developing water management tools that will help both countries better use their scarce water resources in arid environments. The main thrust of this segment of the project is to develop water use data on vegetables grown in both regions. These data will then be used to develop crop coefficient data to be used in AZSCHED, a computerized irrigation scheduling program developed at the University of Arizona. Using a subsurface drip irrigation (SDI) system, carrots, cauliflower, head lettuce, and tomatoes were grown to determine water use patterns and develop basal crop coefficients. Water use data were collected using a neutron moisture gauge and a time domain reflectometer (TDR). Soil water data were collected 1 day following an irrigation and just prior to the next irrigation. Additionally, three different watering regimens were employed using available water content in the rootzone as a trigger to initiate irrigation (20 %, 30% and 40% depletion). The carrots, cauliflower and lettuce were planted in early October, 1993, using a randomized block design. Yield data showed no significant differences between treatments for any of the vegetables. Also, the soil moisture data did not indicate water stress in the treatments. In March of 1994, tomato transplants were planted and the irrigation treatments were altered to 30 %, 40% and 50% depletion, in an attempt to get significant differences between treatments. The results for all four vegetables showed high variability in soil water data between replications, although an initial determination of basal crop coefficients was possible. Additional data will be required to better refine the crop coefficients.
    • Efficacy of Insecticides to Green Peach Aphid on Iceberg Lettuce

      Kerns, David L.; Palumbo, John C.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1995-08)
      Three tests were conducted evaluating foliar and soil applied aphicides for efficacy to green peach aphid infesting iceberg lettuce. Aphid population densites were low in all three studies and differences among treatments were difficult to discern. At low aphid populations we could not detect whether or not soil applications of Admire enhanced or inhibited the activity of subsequent foliar applications of other aphicides. Although when used alone, some products did offer statistically significant aphid control. However, in a commercial setting these differences would probably not be significant. At low aphid populations none of the pyrethroid tank mixes evaluated gave significantly better aphid control than the products used alone. All of the experimental aphicides evaluated appeared to have some degree of efficacy to green peach aphid.
    • 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.
    • Dacthal® Herbicide Rate Comparison for Preemergence Weed Control in Onions

      Umeda, K.; Fredman, C.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1995-08)
      DCPA (Dacthal®) herbicide was applied preemergence (PE) to the soil surface after onion planting and no crop injury was observed for rates of 5.3, 7.5, and 10.5 lb. a.i. /A at one of two locations. Dacthal® gave good control of London rocket and cheeseweed (90 -94 %) at one location and marginal control at the second location (79 -85 %). Dacthal® did not exhibit a rate response to control the two weeds common to both locations. The lower rate of Dacthal® did not differ in efficacy compared to higher rates to completely control lambsquarters and nettleleaf goosefoot. All rates of Dacthal® marginally controlled yellow sweetclover and other mustard weeds present. Dacthal® provided adequate weed control to allow onion stand establishment.
    • Field Evaluation of Potential New Fungicides for Control of Sclerotinia Leaf Drop of Lettuce in 1994 and 1995

      Matheron, Michael E.; Misaghi, Iraj J.; Porchas, Martin; DeCianne, Dominic; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1995-08)
      Leaf drop of lettuce is caused by the plant pathogenic fungi Sclerotinia minor and S. sclerotiorum. Cool and moist environmental conditions favor disease development. Potential new fungicides were evaluated in field trials for control of this disease in 1994 and 1995. In the 1994 trial, Fluazinam and Topsin M provided significant decrease of disease and significant increase inmarketable yield compared to no treatment in plots infested with Sclerotinia minor or S. sclerotiorum. In 1995, Fluazinam, Topsin M, and two compounds from Ciba significantly reduced disease caused by Sclerotinia minor and increased marketable yield of treated lettuce when compared to nontreated plots.