• Field and Laboratory Evaluation of Migration and Dispersal by the Sweet Potato Whitefly, Bemisia tabaci (Gennadius)

      Byrne, David N.; Blackmer, Jackie; Rathman, Robin; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1994-09)
      Although problems associated with the sweet potato whitefly, Bemisia tabaci (Gennadius), are not as dramatic as they were in 1992. they were still significant in 1993. Laboratory research in 1993 focused on defining the cues that result in migratory behavior, specifically host quality. In addition, field studies were conducted to learn more about timing, direction, and distance flown. Our goal is to develop a predictive model that can be used for forecasting whitefly movement. During our behavioral studies, B. tabaci was presented with two cues that lead to disparate behaviors. More than 70% of the whiteflies we tested ended their flights (within three presentations of the cue) when given a choice between settling on a 'host' (550 nm interference filter) and continued flight. Only 6% of the individuals we tested, demonstrated what would be considered to be true migration Both endogenoous and exogenous factors can play an important role in determining when insects will fly. Finally, although the oogenesis-flight syndrome is thought to be a strong component of insect migratory activity, whiteflies do not appear to postpone egg production until after they have engaged in flight. In the field marked whiteflies were also collected in the most distant of these traps. These field results support our hypothesis that most whitefly movement in the fall in the Yuma Valley is in a SW direction (prevailing winds are from the NE). Within a 3 hr time frame whiteflies can travel as far as 2.2 miles from the source field. We examined the effects of female flight distance and eggload. We found significant differences in the eggload of field collected whiteflies versus whiteflies collected in traps at all distances from the source field. There was no relationship between distance flown and eggload. These results may indicate that dispersing individuals are capable of delaying egg laying until a suitable host plant is located
    • Field Testing of Potential New Fungicides for Control of Downy Mildew of Broccoli, Cabbage, and Cauliflower, 1993

      Matheron, M. E.; Matejka, J. C.; Porchas, M.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1994-09)
      Downy mildew of broccoli, cabbage, and cauliflower 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 these weather conditions favorable for disease development. Potential new fungicides were evaluated for disease control in a field trial conducted in the winter of 1992-93. For broccoli, no significant differences in disease severity were detected among treatments. On the other hand, Microthiol and Microthiol + Maneb significantly reduced the number of downy mildew lesions on cabbage and cauliflower compared to nontreated plants. Maneb alone provided significant disease control on cabbage, but not on cauliflower.
    • Field Testing of Potential New Fungicides for Control of Lettuce Diseases, 1993

      Matheron, M. E.; Matejka, J. C.; Porchas, M.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1994-09)
      Several diseases caused by plant pathogenic fungi can cause economic losses to lettuce growers in Arizona. Leaf drop of lettuce is caused by Sclerotinia minor and S. sclerotiorum, while downy and powdery mildew are caused by Bremia lactucae and Erysiphe cichoracearum, respectively. Cool and moist environmental conditions favor development of leaf drop and 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 the winter of 1992-93. For leaf drop, two nonregistered materials, Fluazinam and Topsin M, controlled disease at least well as the standard registered fungicides. Fluazinam and Aliette provided equivalent control of downy mildew, while Fluazinam but not Aliene significantly reduced the severity of powdery mildew on lettuce.
    • Field Testing of Potential New Fungicides for Control of Phytophthora Root and Crown Rot of Chile Pepper

      Matheron, M. E.; Call, R. E.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1994-09)
      Root and crown rot and blight of chile peppers is caused by the soil -borne plant pathogenic fungus Phytophthora capsici. The root and crown rot phases of the disease are favored by saturated soil conditions, while rainfall accompanied by wind helps initiate the blight phase. The purpose of this study was to evaluate potential new fungicides for disease control. Some treatments of Aliette and Fluazinam as well as Ridomil tended to reduce the incidence of disease in this trial. However, the high variability in disease incidence among the replicates of each treatment prevented the demonstration of statistically significant differences in this study. We hope to repeat this trial next year and achieve more definite results.
    • Field Testing of Potential New Fungicides for Control of Powdery Mildew of Cantaloupe, 1993

      Matheron, M. E.; Matejka, J. C.; Porchas, M.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1994-09)
      Powdery mildew of cantaloupe in Arizona is caused by the plant pathogenic fungus Sphaerotheca fuliginea. The disease is usually found in some 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 1993. All tested materials provided significant control when compared to untreated cantaloupe plants. In this study, none of the compounds provided disease protection significantly superior to that demonstrated by Bayleton, the fungicide currently registered for use on cantaloupes.
    • Nitrogen and Water Inputs for Trickle-Irrigated Winter Vegetables

      Thompson, T. L.; Doerge, T. A.; McCreary, T. A.; Rodriguez-Casas, J.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1994-09)
      An experiment was conducted during 1992-93 at the University of Ariwna Maricopa Agricultural Center to investigate the effects of nitrogen (N) and water management on yield, midrib nitrate-N, and N and water use efficiency of subsurface trickle-irrigated leaf lettuce, collard, and spinach. The experiment was a randomized complete block factorial with three water levels (deficient, optimum, excessive), four N fertilizer levels (deficient, suboptimal, supraoptimal, excessive) and four replications. Trickle tubing was placed in the center of the beds at 15 cm depth. Irrigation was applied daily as needed to maintain the appropriate target soil water tension and N fertilizer (urea ammonium nitrate solution) was applied in 4 to 5 split applications. Midrib samples were collected for nitrate -N analysis at 4 growth stages, and portions of the plots were harvested when plants were marketable size. The 1992-93 growing season was excessively wet, therefore optimum yields were achieved in the deficient irrigation treatment. The wet conditions apparently led to excessive N losses, therefore high rates of N fertilizer were needed for optimum yields. Nitrogen and water use efficiencies were maximized at low rates of water and fertilizer input. Midrib nitrate-N concentrations were responsive to N fertilizer treatments.
    • Pepper Variety Trial in Cochise County, 1993

      Clark, L. J.; Call, R. E.; Oebker, N. F.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1994-09)
      A variety trial including 12 long green chile varieties, 6 jalapeño varieties and 3 paprika varieties was implemented in Cochise county in 1993. Alpha was the top yielding green chile with a yield of 23.8 tons per acre and Fresno lead the jalapeño varieties with a yield over 30 ton per acre. Conquistador variety of paprika appeared to have a slight advantage over the other varieties in its class. A characterization of the fruit from the varieties tested are given in this paper.
    • The Response of Leaf Lettuce to Phosphorous Fertilizer Placement and Rate

      Pritchard, Kevin H.; Doerge, Thomas A.; McCreary, Ted W.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1994-09)
      A one-year field study was conducted at the Maricopa Agricultural Center in the winter and spring of 1991-92 with the purpose of comparing the response of leaf lettuce grown with subsurface drip irrigation to various broadcast and banded phosphorus (P) fertilizer applications and rates. Two rates of banded treble superphosphate, 250 lbs. (1X) and 125 lbs. (1/2X) of P2Osper acre, were applied immediately before planting in a concentrated strip 1 inch directly below the row to be seeded. One broadcast rate, 250 lbs. (1X) of P205 per acre of the same material, was applied and folded into the planting beds during listing. Control plots, in which zero P fertilizer was applied, were also maintained. Whole plant total P concentrations were higher in the first one-third of the growing season for the band treatments, though the differences in responses between band and broadcast applications were not statistically significant in the final third of the season. The 1X band treatment exhibited both greater plant heights and diameters than all other treatments during the first one-half of the growing season, and maintained greater height dimensions in the second half. The 1X broadcast and 1/2X band treatments exhibited similar growth throughout the season. By harvest there were not significant differences in head or plant size or in marketable yield among the three P treatments.
    • Sampling Schemes and Action Thresholds for Sweet Potato Whitefly Management in Spring Melons

      Palumbo, John C.; Tonhasca, Athayde, Jr.; Byrne, David N.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1994-09)
      Early season infestations of sweet potato whiteflies, Bemisia tabaci ( Gennadius) were monitored in fields of cantaloupe, Cucumis melo L., near Yuma, Arizona. We used these data to describe the relationship between the proportion of infested leaves and mean adult population density for the entire field. This model was used to develop a binomial sampling plan based on a presence- absence approach. We evaluated the model with three independent data sets, and the level of agreement between the model and data was reasonable for pest management purposes. A minimum sample size of 200 leaves is suggested for maximum accuracy. By turning over 50 leaves in the four quadrants of a field and determining what proportion have whiteflies (i.e., are there whitefly adults on the leaf or not), growers can estimate field populations. We recommend that if 60% of the sampled leaves have whiteflies then it is time to make a pesticide application because that tells you that population levels are approaching 3 adults per leaf.