• Interactions Between Herbicides and Cotton Seedling Damping-off in the field

      Heydari, A.; Misaghi, I. J.; Silvertooth, Jeff; Department of Plant pathology, University of Arizona (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      We studied the impact of three pre plant herbicides, trifluralin, pendimethalin and prometryn on the incidence and the development of Rhizoctonia solani- induced cotton seedling damping-off in the field. In a field experiment conducted in Safford, Arizona, pre plant application of pendimethalin or prometryn but not trifluralin caused significant (P < 0.05) increases in disease incidence. In another field experiment in Tucson, Arizona, significant (P < 0.05) increase in disease incidence was observed in plots treated with prometryn and not in those treated with pendimethalin and trijuralin. In Tucson field experiment, application of herbicides also affected disease development as judged by the slope of disease progress curves.
    • Agronomic Evaluations of New Transgenic and Non Transgenic Cotton Varieties in La Paz and Mohave Counties

      Knowles, Tim C.; Wakimoto, Del, 1947-; Sprawls, Greg; Hurtado, Greg; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      In 1996 transgenic Bt cotton was first grown on a commercial level in Arizona. In 1997 transgenic Roundup and Buctril herbicide resistant cotton varieties were introduced and grown on commercially in Arizona. Furthermore, in 1997, four new heat tolerant non- transgenic cotton varieties for commercial release in 1998 were available for University field tests. Prior to 1997, the agronomic characteristics of these new cotton varieties had not been evaluated inside by side replicated field comparisons beyond the level of the developing companies. Field tests were conducted in La Paz and Mohave Counties in 1997 examining agronomic characteristics of new transgenic Bt ( Deltapine 5415 vs. Deltapine 32 B and 33B) and herbicide resistant (Paymaster 1220 BGRR vs. 1244 BGRR and Stoneville 474 vs. BXN 47) and non transgenic heat tolerant (SureGrow 125 vs. 180 and 821, Stoneville 474 vs. 468, and Germain's GC 9230) cotton varieties.
    • Review of the 1997 Arizona Cotton Season

      Silvertooth, Jeffrey C.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
    • Defoliation of Pima and Upland Cotton at the Safford Agricultural Center, 1997

      Clark, L. J.; Carpenter, E. W.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      Nine defoliation treatments were applied to Pima and upland cotton to compare the treatment effects on percent leaf drop and percent green leaves left and any effects they might have on yield or fiber qualities. All of the treatments were beneficial compared to the untreated check, the treatments including Ginstar performed better than those without.
    • Diversity and Global Distribution of Whitefly-Transmitted Geminiviruses of Cotton

      Brown, J. K.; Silvertooth, Jeff; Department of Plant Sciences (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      Geminivirus diseases of cotton are on the rise, worldwide, yet few have been studied in adequate detail to permit the implementation of rational approaches to disease control. The rising costs of managing the whitefly vector, coupled with substantial losses caused by geminivirus-incited diseases now hinder cotton production by requiring inputs that are beyond economic feasibility. The need for geminivirus disease resistant cultivars in diverse cotton producting areas and against different viral genotypes presents a new challenge. To meet this need, information about the identity, distribution, and relevant biotic characteristics of cotton -infecting geminiviruses is needed This project addresses this problem through the molecular analysis of the genomes of cotton-infecting geminivirus from cotton throughout the world Here, sequence similarities of the coat protein gene and of the non-coding IR/CR involved in regulating virus replication and transcription were examined by comparative sequence analysis to achieve virus identification. This is the first effort to determine virus identity and to map the distribution of geminiviruses on a global basis. The outcome of this effort will be a data base containing biotic and molecular information that will permit rapid and accurate geminivirus identification, and the selection of relevant viral species for development of cotton cultivars with disease resistance to the geminiviruses specific to individual production areas.
    • Silverleaf Whitefly Cotton Cultivator Preference

      Chu, C. C.; Natwick, E. T.; Henneberry, T. J.; Cohen, A. C.; Castle, S. J.; Silvertooth, Jeff; USDA-ARS, Western Cotton Research Laboratory (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      All of nine cotton cultivars tested were susceptible to silverleaf whitey, Bemisia argentifolii Bellows and Perring in Imperial valley, CA in 1995 and 1996. Using 4.1 adults per leaf turn as an insecticide- treatment action threshold, Deltapine (DPL) 5409 and 5415 required 5.5 applications of insecticide, DPL 50, 5461, and 5517 required 6 applications, DPL 5432 and 5690 required 65 applications, Louisiana (LA) 887 required 7 application, and Stoneville (ST) 474 required 7.5 applications. Results indicate the potential to reduce insecticide application by selecting appropriate cultivars that are commercially available.
    • Seasonal Distribution of Bemesia Honeydew Sugars on Pima and Upland Cotton Lint

      Henneberry, T. J.; Forlow Jech, L.; Hendrix, D. L.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      Bemisia argentifolii Bellows and Perring populations were higher on Pima S-7 cotton compared with DPL 50 cotton. Higher numbers of mature open cotton bolls occurred earlier for DPL 50 compared with Pima S-7. Also, numbers of open bolls for DPL 50 peaked 8 to 14 days before Pima S-7 and decreased dramatically by 15 September reflecting termination of the first fruiting cycle in August In contrast the indeterminate fruiting pattern of Pima S-7 showed that numbers of open bolls per week declined gradually after the peak without a clear cut termination occurrence. About 95 and 80% of the open cotton bolls, of the Deltapine and Pima S-7 cottons, respectively, occurred by mid- September. This suggests that defoliation timing and early harvest can be important management tools to avoid sticky cotton. For upland cotton, extending the cotton season after 95% of the crop matured (≅ 15 September) resulted in development from non - sticky cotton to lightly- sticky cotton within 21 days following the occurrence of increasing whitefly populations after 15 September. Later fruiting and lack of a distinct end of the first cotton fruiting cycle probably precludes using early defoliation for long -staple Pima cotton. At harvest, thermodetector counts for all weekly harvests were greater than amounts found in lint for randomly selected 20 boll samples; and samples from all cotton picked from 4 m of row. This probably occurred because weekly picked cotton escaped rainfall and exposure and other weathering, in 1995 but not 1996, and machine - picked cotton contains more honeydew- contaminated leaf trash. Except in one instance, thermodetector counts and trehalulose and melezitose content in lint for all sampling methods were significantly correlated.
    • Lygus Chemical Control: Are Combinations Sprays Worth It?

      Ellsworth, Peter C.; Gibson, R.; Howell, D.; Husman, S.; Stedman, S.; Tickes, B.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      We need efficient sampling methods, appropriate thresholds based on a well -defined Lygus density yield relationship, and knowledge of the most effective chemical controls available. Insecticides were evaluated for control of Lygus at 5 'at risk' grower locations, as well as at 4 other experimental sites. Application methods were different at each site according to grower practice or experimental protocol (5-20 GPA; by ground, air, or electrostatically-assisted ground sprayers). Evaluations were made based on the number of Lygus per 100 sweeps. Orthene®, Vydate® or to a lesser degree, Monitor® used alone and at high rates appeared to perform adequately at all sites. Both rates of Regent™, a new chemistry under development by Rhône- Poulenc, provided excellent levels of control comparable to Orthene in a high density test. In this same test, none of the experimental and registered pyrethmids provided adequate control when used alone. Thiodan®, when mixed with Mustang®, provided some level of control. Over all tests measured for yield, a positive net return was possible with no more than 2 sprays of solo materials which yielded between 0.3 and 0.5 bales/A more than untreated comparisons or between $51-130/A net return. Also, at one site where yields were in excess of 4.2 bales/A, optimum planting and fruit-set prior to heavy Lygus pressures and monsoon-associated heat stress was an important cultural tactic for avoiding losses to Lygus - the check yielded over 3.7 bales /A! As seen at grower sites and confirmed in experimental studies, solo compounds, at appropriate rates, performed as well or better than any combination tested. And, mixtures at this time do not appear to provide any additive, synergistic or economic benefits in the control of Lygus. Combinations, unless indicated by another pest problem (e.g., whiteflies), are not "worth it," and needlessly expose the grower to larger input costs, "empty" applications, and higher risks of resistance, pest resurgence, secondary pest outbreaks, and phytotoxic effects by insecticides.
    • Evaluation of a Nitrogen-15 Microplot Design in a Furrow Irrigated Row Crop System

      Silvertooth, J. C.; Navarro, J. C.; Norton, E. R.; Sanchez, C. A.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      Two field experiments were conducted in Arizona in at two locations, Maricopa in 1991 (Casa Grande sandy loam) and Marana (Pima clay loam) in 1995. The purposes of the experiments were to evaluate the dimensions of an ¹⁵N microplot design used in a furrow irrigated row crop system. The experiments each utilized ammonium sulfate fertilizer with 5 atom % ¹⁵N enrichment applied at a rate of 56 kg N/ha in simulated side-dress band application during the early bloom stage of development of Upland cotton (Gossvpium barbadense L). At each location, microplots were 4, 1.02 m rows wide and 1.00 m in length. Whole plant samples were collected at specific locations within and near the microplots. Uptake of ¹⁵N by plants was uniform within microplots but declined symmetrically in relation to microplot borders. Collection of plant materials within 25 cm of microplot borders provided uniform ¹⁵N enrichment levels for determining fertilizer N uptake and recovery. Use of microplots with the dimensions of those used in this study are sufficient for collecting plant materials from a 1 m² area; consisting of two, 50 cm segments from the interior two rows of the four row microplot. This also allows for sufficient distance from the perimeter of the microplot to account for border effects.
    • Effects of Cotton Ginning and Lint Cleaning on Sticky Cotton

      Henneberry, T. J.; Hendrix, D. L.; Perkins, H. H.; Silvertooth, Jeff; USDA, ARS Western Cotton Research Laboratory, Phoenix AZ; USDA, ARS, Cotton Quality Research, Clemson, SC (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      Ginning and lint cleaning effects on cotton stickiness were minimal but reduced amounts of trehalulose and reduced thermodetector counts occurred following each lint process Leaf trash from ginned seed cotton contained trehalulose and melezitose. Removal of leaf trash in ginning and lint cleaning probably accounts for some reduced lint stickiness.
    • Effects of Entomopathogentic Nematodes on Pink Bollworm Mortality

      Henneberry, T. J.; Forlow Jech, L.; Burke, R. A.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      Steinernema riobravis Cabanillas, Poinar & Raulston infected pink bollworm Pectinophora gossypiella (Saunders), larvae over a temperature range of 15.6 - 38.0° C. Temperatures of 32.2° C and higher and exposure for 48 h or more often resulted in decreased numbers of nematode killed larvae with living nematodes and increased numbers of dead larvae with dead or no nematodes.
    • Late Season Pink Bollworm Pressure in the Top Crop of Bt and Non-Bt Cotton

      Knowles, Tim C.; Dennehy, Tim J.; Rovey, Albert; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      Green bolls (100/field) were sampled from the uppermost internodes within adjacent fields of Bt (Deltapine 33B) and non-Bt (Hyperformer HS 44) cotton experiencing severe pink bollworm pressure late in the growing season. Average top crop lint yield reductions ranging from 30 to 70% were observed in the uppermost bolls of the non-Bt cotton variety. Average top crop lint yield reductions ranging from 0 to 40% were observed in the uppermost bolls of the transgenic Bt cotton variety.
    • Voluntary Area-Wide Whitefly Monitoring Project Implementation 1995-1997, Gila Bend, AZ

      Husman, S. H.; Jech, L. E.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      Growers, Pest Control Advisors (PCA), and University of Arizona Cooperative Extension personnel formulated and coordinated area-wide pest management strategies in the production area near Gila Bend, Az. from 1995-97. The primary pest target was whitefly with secondary control strategy implementation for pink bollworm in 1995. In 1995-1996, the coordinated effort encompassed approximately 10,000 and 6000 acres which included 10 and 8 cotton producers respectively and 6 pest control advisors. Due to producer interest and initiative in an adjoining production area, project acreage increased to over 18,000 acres and included 14 producers and 9 pest control advisors in 1997. The project cost of $3.00/acre was supported by participating producers with the monies used to hire University of Arizona trained students for field scouting of whiteflies. An economic development grant from the Electrical District #8 supported the project coordinator's salary who is a University of Arizona employee. Each field was sampled weekly for whitefly populations using recommended University of Arizona sampling procedure. The population data was then faxed to the responsible producer and pest control advisor on the date of sample. Treatment thresholds and chemistry class suggestions were made by Cooperative Extension with final control decisions and material choice at the producer and pest control advisor discretion. Weekly community wide meetings were conducted and used to discuss general area-wide and field specific population dynamics, treatment suggestions, crop condition, and agronomic and entomological area -wide production strategy recommendations.
    • Short Staple Cotton Advanced Strains Trial, Safford Agricultural Center, 1997

      Clark, L. J.; Carpenter, E. W.; Hart, G. L.; Nelson, J. M.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      Twenty five short staple advanced strains /varieties were grown in a replicated field on the Safford Agricultural Center in 1997. These included thirteen lines from Australia (including transgenic Bt lines), four lines from Georgia, five lines from NMSU, and two lines from Terra. The transgenic Australian lines dominated the trial with three of them yielding over 3 bales. The next nine varieties yielded over 2.5 bales per acre, they included six Australian variety, DP 90 (the standard variety) and an experimental from New Mexico. IF 1003 was the highest yielding non-transgenic variety in the trial. Much agronomic information is included in the paper as well as HVI values for each variety.
    • Whitefly Management in Arizona: Contribution of Natural Enemies to Whitefly Mortality

      Naranjo, Steven E.; Ellsworth, Peter C.; Diehl, Jonathon W.; Silvertooth, Jeff; USDA-ARS, Western Cotton Research Laboratory, Phoenix, AZ; University of Arizona, Maricopa, AZ (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      Direct-observation studies were conducted to identify causes and estimate rates of mortality of whiteflies over the course of four generations between late June to early September in replicated experimental plots. In plots receiving no whitefly insecticides. predation and dislodgment were major sources of egg and nymphal mortality and overall survival from egg to adult ranged from 1-8.5%. Similar patterns were observed in plots treated with insect growth regulators. except that Knack caused high levels of egg inviability and Applaud was a major source of mortality in small nymphs during the second generation immediately following single applications of these materials. Mortality due to predation was generally lowest for eggs and nymphs in plots treated with a rotation of conventional insecticides reflecting disruption of the predator fauna. Parasitism was a very minor source of mortality throughout. The selective action of the IGRs enhances the abundance and activity of natural enemies resulting in high levels of whitefly control with minimal use of disruptive insecticides. Natural enemies likely contribute to the "extended" residual effects of IGRs so commonly reported by growers.
    • Efficacy of Experimental Insecticides for Whitefly Control in Cotton, 1996

      Kerns, David L.; Tellez, Tony; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      Experimental insecticides were evaluated for control of sweet potato whiteflies relative to a commercial standard in cotton. Ni-25 provided excellent whitefly control and was equivalent to the commercial standard (Knack followed by Danitol + Orthene). Fenoxycarb + pymetrozine provided goodwhitefly control but seemed to require 2 sequential applications before control was equivalent to Ni-25. Diofenolan + pymetrozine appeared to be a slightly weaker treatment, but still provided acceptable whitefly control.
    • New Insights Regarding Estimating Lygus Susceptibility to Insecticides

      Dennehy, T. J.; Russell, J. E.; Antilla, L.; Whitlow, M.; Silvertooth, Jeff; Extension Arthropod Resistance Management Laboratory; Department of Entomology, University of Arizona, Tucson, AZ; Arizona Cotton Research & Protection Council, Tempe, AZ (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      Lygus susceptibility was found to vary widely from year to year, from region to region and, for some insecticides, even within the season. It is for this reason that producers need current, region-specific recommendations in order to determine which insecticides are most effective at their locale. Our studies were intended to improve understanding of the reliability of glass vial bioassays for estimating efficacy of insecticides used against lygus bugs. Results show that the standard glass vial method offers considerable promise for detecting differences in susceptibility of lygus to some, but not all, insecticides. However, mortality in vial bioassays did not serve as a reliable predictor of the relative toxicity of residues of five insecticides in field treatments. Therefore, field evaluations of insecticide efficacy continue to be essential for selecting the insecticides that provide the best control of lygus. Once the most effective materials are selected from field trial results, bioassays can be used to efficiently monitor changes in population susceptibility to these insecticides. Additional new insights provided by our studies are that efficacy of residues of insecticides declined rapidly, such that after three days all insecticides caused very little mortality to adult lygus bugs. Lastly, we found a marked difference between residual and direct contact toxicity of the five insecticides evaluated. Even the insecticide treatments that resulted in relatively low toxicity in residual exposure tests killed 95-100% of lygus bugs that they contacted directly under field conditions. This finding indicates that producers experiencing severe problems with lygus control would be well advised to improve insecticide coverage.
    • 1997 Season Update on Resistance of Arizona Whiteflies to Synergized Pyrethroid and Select Non-Pyrethroid Insecticides

      Dennehy, Timothy J.; Williams, Livey III; Li, Xiaohua; Wigert, Monika; Silvertooth, Jeff; Department of Entomology, The University of Arizona; Extension Arthropod Resistance Management Laboratory, Tucson, AZ (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      A whitefly resistance crisis in Arizona in 1995 prompted the development of a resistance management strategy in 1996 that recommended maximal once per season use of two insect growth regulators, pyriproxyfen (Knack®) and buprofezin (Applaud®), and limited and delayed use of synergized pyrethroid insecticides in cotton. Statewide monitoring of whitefly resistance has shown that implementation of this strategy has substantially reduced whitefly resistance to the synergized pyrethroids and has also resulted in increased susceptibility to key non pyrethroid insecticides. Having benefited from two years of success with this strategy, the Arizona cotton industry now faces the question of whether it can be sustained as pyriproxyfen and buprofezin gain additional registrations for use against whiteflies in vegetables, melons and glasshouse crops.
    • Evaluation of a Feedback Approach to Nitrogen and Pix Applications, 1997

      Silvertooth, J. C.; Norton, E. R.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      A single field experiment was conducted in 1997 at Marana, AZ to compare a scheduled approach (based on stage of growth) versus a feedback approach (based on growth parameters) to both nitrogen (N) and mepiquat chloride (P1X) applications on Upland cotton (Gossypium hirsutum L.). PIX feedback treatments were based upon fruit retention (FR) levels and height to node ratios (HNRs) with respect to established baselines for Arizona growing conditions. Scheduled and feedback FIX applications were made for a total of 0.75 and 1.50 pt./acre, respectively, with the scheduled treatments being initiated earlier in the fruiting cycle (early and peak bloom). Feedback PIX treatments consisted of a single 0.75 pt./acre application near peak bloom (approx. 2000 heat units after planting, HUAP, 86/55 °F threshold). Scheduled applications of fertilizer N totaled 150 lbs. N/acre from two applications and feedback N treatments received a total of 100 lbs. N/acre from two applications. Treatments consisted of all combinations of scheduled or feedback applications of both N and PIX. The highest lint yields were from treatments receiving PIX applications, with significant differences (P ≥ 0.05) between a check treatment (with no FIX applications) and several other treatments that did receive PIX applications. If FIX was applied, there were no significant differences between the scheduled or feedback approach. Applications of PIX in relation to increasing HNRs (feedback approach) are demonstrated and reinforced in this study.
    • Date of Planting by Long Staple and Short Staple Variety Trial, Safford Agricultural Center, 1997

      Clark, L. J.; Carpenter, E. W.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1998-04)
      Four varieties each of Long Staple and Short Staple cotton were tested over five and four dates of planting, respectively, in this study. The first date of planting for the Long Staple cotton was pushed up to the 18th of March because planting is now legal in Graham county as early as March 15th. The latest planting was May 13th. Cultivars of differing maturities were tested for both long and short staple cotton to determine their optimal planting time. Many agronomic and hvi values were evaluated to determine the effect of different planting dates