• A Critical Examination of Flight by the Sweet Potato Whitefly

      Blackmer, Jacquelyn L.; Byrne, David N.; Rathman, Robin J.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1992-12)
      In the past we have assumed that sweet potato whiteflies, Bemisia tabaci (Gennadius), were poor fliers with a limited ability to disperse. This assumption was based on the fact that sweet potato whiteflies are extremely small insects (24 -44 μg) and consequently would be subject to desiccation. We also thought small size would limit their capacity to store sufficient energy reserves to sustain flight for long periods of time. Recent experiments have indicated we were wrong on several counts. Data collected in the laboratory using a vertical flight chamber have revealed a number of interesting facts. Of importance is the fact that a portion of the population is capable of sustaining flight for more than 2.5 hours. In a wind-aided situation, this means they can be moved more than 25 miles in a 10 mph wind. Other details of flight behavior are being made clear to us. For example, we found that flight activity is influenced by host plant quality and age of the whitefly. We hope to eventually be able to predict when whiteflies are going to migrate between crops. This will allow growers to make informed decisions concerning planting dates. We are also working in the field to confirm laboratory results.
    • Rate by Timing Interactions of Propel on Head Lettuce

      Butler, Marvin; Hall, Don; Brooks, Dave; Oebker, Norman F.; University of Arizona; Brea Agricultural Service, Inc.; Pasquinelli Produce Company (College of Agriculture, University of Arizona (Tucson, AZ), 1992-12)
    • Effect of Insecticides on Sweetpotato Whitefly Numbers and Growth of Broccoli

      Rethwisch, Michael D.; McDaniel, Charles W.; Shaw, Mary; Theissen, James; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1992-12)
      Eleven treatments were applied for sweetpotato whitefly B- biotype control. Best control (62.4%) was evidenced by the Ambush + Thiodan treatment, which had fewest nymph numbers 8 days post treatment and had larger plant sizes (46.3%) 14 days post treatment than the untreated check. Plants in plots receiving treatments including Thiodan and/or Lorsban were also at least 20% larger than the untreated check. Fewest number of adult whiteflies two days post treatments were noted in the Thiodan + M-Pede treatment. Certain treatments increased whitefly numbers.
    • 1991 Virus Survey of Cantaloupe in Yuma

      Butler, Marvin; Brooks, Dave; Watson, Mike; Oebker, Norman F.; University of Arizona; Pasquinelli Produce (College of Agriculture, University of Arizona (Tucson, AZ), 1992-12)
    • Evaluation of Agri-Mek with Various Oils and Adjuvents for Control of Leafminers in Spring Head Lettuce

      Rethwisch, Michael D.; Meadows, Michael; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1992-12)
    • UA Seedless Watermelton Cultivar Trial - 1991

      Oebker, M. F.; McCreary, T. W.; Roth, R. L.; Doerge, T. A.; Pier, J. W.; Gibson, R. D.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1992-12)
      Seedless watermelons have become an important commodity in Arizona. In 1991 16 cultivars were compared and evaluated at the Maricopa Agricultural Center. Tri-X 313 had overall good performance and remains the standard. Several other cultivars show promise.
    • Watermelon Response to Soluable and Slow Release Nitrogen Fertilizers

      Doerge, Thomas A.; Pier, Jerome; McCreary, Ted; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1992-12)
      A field experiment with subsurface drip irrigated watermelon was conducted on a Casa Grande s.l. soil at the Maricopa Agricultural Center in 1992 to evaluate the field performance of two slow release nitrogen (SRN) fertilizers in comparison to a conventional soluble N source, urea, ammonium- nitrate (UAN-32). Single, preplant applications of 0, 100 and 200 lbs N/acre supplied from methylene urea (Nutralenes) or 100, 150 and 3(X) lbs N/acre from a methylene urea-ammonium sulfate mixture (MUAS) were evaluated in comparison to treatments of UAN-32 containing from 52 to 445 lbs N/acre made in five split applications. Yield response to N rates above 100 lbs/acre were similar for all three N sources, indicating that a single, preplant application of a suitable SRN material at an adequate rate could provide N efficiently over the entire growing season. The highest numerical yield (49.3 tons/acre) was obtained with a N rate of 150 lbs N/acre from the MUAS material. Monitoring of petiole nitrate levels throughout the season indicated that N release from the MUAS was more rapid and more complete than from the methylene-urea product. At suboptimal N rates, i.e. < 150 lbs N/acre, split applications of UAN-32 appeared to be somewhat more efficient than the slow-release products.
    • Effectiveness of Oils in Water for Leafminer Control in Fall Head Lettuce

      Rethwisch, Michael D.; Hood, Larry; Meadows, Mike; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1992-12)
    • Effect of Oil Treatments on Head Lettuce Photosynthesis and Growth

      Rethwisch, Michael D.; McGrady, John; Main, Greg; Coates, Wayne; Meadows, Mike; McDaniel, Charles; Shaw, Mary; Thiessen, James; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1992-12)
    • Cantaloupe Variety Trial, 1991

      Butler, Marvin; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1992-12)
    • Cauliflower Variety Trials 1990/1991

      Butler, Marvin; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1992-12)
    • Effects of Lettuce Insecticides Applied at Planting

      Rethwisch, Michael D.; Meadows, Michael; Hagerman, Shari; Thiessen, James; McGrady, John; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1992-12)
    • Fungicides Evaluated for Control of Sclerotinia Leaf Drop of Lettuce in 1991 Field Test

      Pier, J. W.; Doerge, T. A.; McCreary, T.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1992-12)
    • Effect of Oils and an Insecticide Applies to Snap Beans on Leafminer and Associated Parasitoid Numbers

      Rethwisch, Michael D.; Meadows, Michael; Hood, Larry; Winans, Sherwood; Coates, Wayne; Main, Greg; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1992-12)
    • Effects of Insecticides on Leafminers, Liriomyza spp., and Associated Parasitoids on Spring Cantaloupes

      Palumbo, J. C.; Mullis, C. H. Jr.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1992-12)
      A study was conducted to determine the effects of repeated insecticide applications on leaf niner and parasitoid populations on spring melons. After four applications, none of the insecticides induced large build-ups of leafminer larvae. A new material, AC 303630, was very effective in maintaining low numbers of pupae. However, the results of this preliminary test indicate that all insecticides tested had a negative impact on the parasitoid population. In general, in the absence of insectcides, parasitoids were capable of maintaining L. sativae populations at low levels in the experimental plots.
    • Comparative Effectiveness of Bacillus thuringiensis Formulations Against Lepidopterous Pests of Fall Lettuce

      Palumbo, J. C.; Mullis, C. H. Jr.; Reyes, F. J.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1992-12)
      A field study was conducted at Yuma in 1991 to examine the relative effectiveness of several formulations of Bacillus thuringiensis on beet armyworm and cabbage looper on seedling and pre-cupping lettuce. Several applications were made before and after thinning. Results of the study suggest that most formulations are capable of controlling small larvae. However, because of the inherent variation in beet armyworm dispersion, it was difficult to statistically attribute differences in pest levels due to insecticide efficacy.
    • Optimizing Nitrogen and Water Inputs for Trickle Irrigated Watermelons

      Pier, J. W.; Doerge, T. A.; McCreary, T.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1992-12)
      Rising water costs and concern for groundwater contamination are driving growers to improve irrigation and fertilization efficiency. A tentative Best Management Practice (BMP) for nitrogen fertilization of watermelon, a high water and nitrogen fertilizer use crop, has been developed, but needs further field verification. Information from tensiometers is used to schedule irrigations and watermelon petiole nitrate levels at critical growth stages are used to recommend rates of nitrogen fertilizer to apply with the objective of producing economic yields while limiting conditions which favor nitrate leaching to groundwater. In 1991, a field experiment consisting of a complete 3x4 factorial arrangement of soil moisture tensions, -12, -7 and -4 kPa, and 60, 214 315 and 500 kg N/ha, respectively, applied through a subsurface trickle irrigation system to watermelon was conducted on a Casa Grande sandy loam at the Maricopa Agricultural Center. Petioles were sampled from the youngest mature leaf beginning at the 3-4 leaf stage and then at major growth stages until first harvest. Harvested melons were weighed and soluble solids, dry matter and N uptake were determined on two representative melons from each experimental unit. An estimate of vine dry matter and N uptake was also determined. Soil samples were taken at 30 cm depth intervals to 1.2 m and analyzed for extractable N. A trench profile method was used to determine root distribution patterns for the three soil moisture treatments receiving optimum N. Petiole nitrate levels were highly responsive to N fertilizer treatments and accurately quantified visual observations of crop N status. Petiole nitrate results also indicated that the preliminary tissue nitrate test was adequate in assisting with a nitrogen management program though minor modifications were necessary. Marketable yield showed a tension x N interaction with a ridge of maximum yield occurring from high soil water tension and low N to low soil water tension and high N with yield reductions on either side of the ridge. Yield estimates along the ridge ranged from 101 Mg/ha (45.4 ton /ac) at -8 kPa tension and 280 kg N/ha to 105 Mg/ha (47.3 ton /ac) at -4.4 kPa tension and 376 kg N/ha. A cost return analysis determined that maximum economic returns were $12,059/ha when 311 kg N/ha were applied in conjunction with -6 kPa soil tension (145 cm water). Unaccounted for N, as determined by an N balance method indicated large amounts of N were unaccounted for when high rates of N were applied under wet soil conditions. N loss was concluded to be due to either leaching and/or denitrification under these conditions.
    • Nitrogen Management in Drip Irrigated Leaf Lettuce, Spinach and Green Crops

      Doerge, Thomas A.; Pritchard, Kevin H.; McCreary, Ted W.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1992-12)
      Preliminary nitrogen (N) management experiments with spinach, leaf lettuce, romaine collard and mustard were conducted on a Casa Grande s.l. soil at the Maricopa Agricultural Center in the winter and spring of 1990-91. The purpose of this N rate experiment was to develop initial Best Management strategies for N fertilizer use for emerging high value crops grown in Arizona using subsurface drip irrigation. Three rates of urea, ammonium nitrate were applied to each cultivar to provide deficient (N1), adequate (N2) and supraoptimal real (N3) levels of N. All cultivars responded dramatically to the application of N. Fresh weight yields in the N1 and N2 treatments averaged 45 and 53% of the N3 treatment The average N3 yields recorded in these trials were 23.1, 12.8 and 21.8 tons of marketable produce per acre for greens, spinach and leaf lettuce/romaine crops, respectively. Preliminary plant tissue test results indicated that for all five crops, whole plant total N (TN) levels and midrib + petiole NO₃-N and leaf blade TN concentrations in the youngest mature leaf were responsive to differences in soil N supply and show promise as diagnostic N tissue test procedures. The midrib + petiole NO₃-N test appeared to be the best indicator of plant N status throughout the growing season for all five crops studied.
    • Control of Thrips in Seed Onions and Resultant Seed Yields

      Rethwisch, Michael D.; Daily, Bill; Sanderson, David; McDaniel, Charles; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1992-12)
      Four insecticides were evaluated for their effect on onion seed production in Yuma County where two species on thrips (western flower and onion) were present in seed fields. Visual differences between treatments resultant from onion thrips damage was evident within 10 days after treatments were applied at flower opening. Lorsban, Ammo and Capture treatments provided control of onion thrips based on condition of seed heads. Only Ammo and Capture treatments increased seed yield as the Lorsban treatment was thought to repel bees which are needed for pollination. Pyrethroid treatments yielded 40% more than the untreated check. Damage from onion thrips to onion seed in Yuma County is conservatively calculated to currently be at least $1.1 million annually.
    • Evaluation of Oils and Insecticides for Leafminer Control in La Paz County Snap Beans

      Rethwisch, Michael D.; Meadows, Michael; Hood, Larry; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1992-12)