• 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)
    • Crisphead Lettuce Variety Trials 1994/1995

      Wilcox, Mark; Oebker, Norman F.; Yuma Valley Agricultural Center (College of Agriculture, University of Arizona (Tucson, AZ), 1995-08)
    • Efficacy and Temporal Mortality of Selective Insecticides on Beet Armyworm Larvae in Lettuce

      Palumbo, J. C.; Oebker, Norman F. (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.
    • Field Evaluation of Potential New Fungicides for Control of Lettuce Downey and Powdery Mildew in 1994 and 1995

      Matheron, Michael E.; Porchas, Martin; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1995-08)
      Downy and powdery mildew are caused by the plant pathogenic fungi Bremia lactucae and Erysiphe cichoracearum, respectively. Cool and moist environmental conditions favor development of downy mildew, while warmer and dry weather is conducive for development of powdery mildew. Potential new fungicides were evaluated for control of these diseases during 1994 and 1995. In 1994, downy mildew did not occur in the test plots; however, powdery mildew was severe and was controlled most effectively by Microthiol. In the 1995 study, both downy and powdery mildew developed in the test plots. The highest level of downy mildew control was achieved with three experimental compounds, Fluazinam, Dimethomorph, and BAS-490. The most effective fungicides for control of powdery mildew in 1995 were BAS-490 and Microthiol.
    • 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.
    • Identifying Short-Range Migration by the Sweet Potato Whitefly

      Byrne, David N.; Palumbo, John C.; Orum, T. V.; Rathman, Robin J.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1995-08)
      Populations of the sweet potato whitefly, Bemisia tabaci, have been shown to consist of both migratory and trivial flying morphs. The behavior of these forms as part of the process of short-range migration needed to be examined under field conditions. Insects were marked in a field of cantaloupes using fluorescent dust. During the first growing season traps, used to collect living whiteflies, were placed along 16 equally spaced transects (22.5° apart) radiating out from the field to a distance of up to 0.6 miles. Wind out of the northeast consistently carried migrating whiteflies to traps placed along transects in the southwestern quadrant because cold air drainages dictate wind direction during early morning hours. For this reason, during the second season traps were laid out in a rectangular grid extending 3 miles to the southwest of the marked field. If dispersal was entirely passive or wind directed patterns could be described using a diffusion model. Statistical examination of the data, however, demonstrate that the distribution on all days was patchy. Traps in the immediate vicinity of the marked field caught more whiteflies than the daily median. Large numbers were also collected from around the periphery of the grid. Whiteflies were far less prevalent in the grid's center. As a result, the distribution of captured whiteflies can be described as bimodal. These patterns confirm behavior observed in the laboratory, i.e., a portion of the population are trivial fliers that do not engage in migration and are consequently captured in traps near the field and a portion initially ignore vegetative cues and fly for a period of time before landing in distant traps. This second population comprises the second peak in the model that appeared 1.6 miles from the marked field. On a localized level, 1.6 miles seems to be how far whiteflies move in a day. Earlier studies indicate that whiteflies only fly one day.
    • New Insecticides for Potential Use for Whitefly Control in Cantaloupes

      Umeda, K.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1995-08)
      Most experimental treatments effectively reduced Bemisia tabaci [sweetpotato whitefly (WF) also known as silverleaf WF, B. argentifolii] adults and eggs in cantaloupes relative to the untreated check at 6 days after treatment of each of five applications. Acephate (Orthene®), buprofezin (Applaud®), bifenthrin (Capture®), endosulfan, fenpropathrin (Danitol®), naled (Dibrom®), and pymetrozine(CGA -215944, Ciba) treatments had the fewest adults and eggs. Insect growth regulator (IGR) materials in combinations, pyriproxyfen (S-71639, Valent) and fenoxycarb (Ciba),were more effective in reducing WF relative to the untreated check than when applied alone. Registered products, Dibrom®, endosulfan, and methamidaphos (Monitor®) were effective in combinations or in alternating applications.
    • 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.
    • Efficacy of Biorational Insecticides to Beet Armyworm and Cabbage Looper on Iceberg Lettuce

      Kerns, David L.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1995-08)
      Four tests were conducted evaluating biorational insecticides for control of beet armyworm (BAW) and cabbage looper (CL) on iceberg lettuce. Treatment means for BAW were difficult to separate due to low population densities. The new formulation of Javelin appeared to be the most efficacious Bt overall. However, when Bts were compared on a equal cost/A basis, there were no significant derences among products for CL control. All Bts were comparable to Lannate for CL control. The neem oil extract Align, provided adequate BAW and CL control, and its efficacy at low rates seemed to be slightly enhanced by the addition of Sunspray Ultrafine Oil. Larvin at lower than label recommended rates gave good BAW and CL control as did Javelin. The tank-mix of these two products did not enhance worm control over that of the products used alone. Mustang gave good control of CL but appeared to be slightly weak against BAW.
    • 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.
    • Evaluation of Admire Soil Treatments on Colonization of Green Peach Aphid and Marketability of Lettuce

      Palumbo, John; Kerns, David; Hannan, Todd; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1995-08)
      Admire (imidacloprid), applied as a soil treatment, protected lettuce plants from developing infestations of green peach aphid, Myzus persicae (Sulzer), for 60-100 d after planting based on two small plot and two commercial field trials. Admire applied 7.6 cm sub-seed furrow provided longer and more consistent protection from green peach aphid than treatments applied to the soil surface, as a side-dress, or 15.2 cm sub-seed furrow. Surface band applications of Admire provided inconsistent control probably because of inadequate hydrological incorporation into the soil. In small plot trials, effective control of aphids by Admire applied 7.6 cm sub seed furrow resulted in greater than 90.0% marketable heads while the untreated plots contained 20.0% marketable heads. When used in a commercial setting, Admire applied 7.6 cm sub-seed furrow on leaf lettuce prevented aphid colonization (<3 aphids per plant) for approximately 100 d after planting, while the untreated and commercial standard treated areas contained 30.7 and 26.8 aphids per plant respectively at 100 d after planting. In addition, marketability of lettuce was greater in Admire treated plots. As a sub-seed furrow treatment, Admire provides a more suitable approach to aphid control than is currently available with foliar insecticides.
    • Admire® Insecticide Use and Influence on Cantaloupe Growth

      Umeda, K.; Fredman, C.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1995-08)
      Cantaloupe growth was influenced by using imidacloprid (Admire®) insecticide to control, suppress, or reduce whiteflies. The growth rate of cantaloupe was evaluated at regular intervals after crop emergence and a rate response was observed with greater growth with respect to increase in Admire® rate. Following at planting time applications, at 3 and 4 weeks after treatment (WAT) cantaloupe plants had more foliar growth and a greater number of leaves with increasing Admire® rate. At 5 to 8 WAT, cantaloupe vines exhibited greater growth with increasing rates of Admire®.
    • Field Evaluation of Potential New Fungicides for Control of Powdery Mildew of Cantaloupe in 1994

      Matheron, Michael E.; Porchas, Martin; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1995-08)
      Powdery mildew of cantaloupe in Arizona is caused by the plant pathogenic fungus Sphaerotheca fuliginea. The disease is found in melon fields each year; however, the incidence and severity of the disease is quite variable. Disease development is favored by low relative humidity, moderate temperatures, and succulent plant growth. Potential new fungicides were evaluated for disease control in a field trial conducted in the spring of 1994. In this study, Rally and Reach provided the highest level of disease control and highest percentages of marketable fruit when compared to untreated cantaloupe plants.
    • 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.
    • 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.
    • 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.
    • 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.
    • 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.
    • 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.