• Impact of Temperature and Relative Humidity on Defoliation of Pima S-7 and Deltapine 5415 Cotton Treated with Dropp (Thidiazuron)

      Bartels, Paul G.; Easley, Jack; Nelson, John; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1993-03)
      Chemical defoliation of cotton is a cultural practice that induces abscission of cotton foliage earlier than normal leaf shedding. Early cotton defoliation is an integral part of short- season cotton production because it facilitates the mechanical harvesting of cotton and helps reduce insect population in late summer. Effectiveness of the chemical defoliants depends upon the environmental conditions at the time of application. Research was conducted to access the impact of temperature, relative humidity (RH), and water stress at time of defoliation on effectiveness of thidiazuron (Dropp) a chemical defoliant to defoliate cotton grown under field and growth chamber conditions. Humidity was increased by spraying a fine mist over the cotton canopy. Plant moisture stress was achieved by terminating irrigation of cotton at selected times before defoliation. In growth chambers, the greatest defoliation of Pima S -7 and Deltapines 5415 cotton treated with Dropp occurred at day /night temperatures of 32C/18C with 80% RH whereas, lowest defoliation occurred at day /night temperatures of 40C /19C and 22C/9C with 80% RH. In the field, irrigation termination dates of Sept 4, Sept 18, and Oct 2, 1992 were evaluated for their effect on defoliation of Pima S -7 cotton defoliation on Oct 16, 1992 with Dropp. The Sept 4 irrigation termination date resulted in higher percent defoliation than Oct 2 irrigation termination date 14 days after Dropp was applied.
    • Weather Conditions Associated with Outbreaks of Severe Whitefly Infestations in Arizona

      Brown, P. W.; Watson, T. F.; Silvertooth, J. C.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1993-03)
      An analysis of weather conditions prior to and during the severe sweet potato whitefly (SPWF) outbreaks of 1981 and 1992 in Arizona revealed some striking similarities. Both bad outbreaks were preceded by 1) weak monsoons during the summer preceding the outbreak (1980 and 1991); 2) winters with very warm minimum temperatures and no incidence of extreme cold; and 3) springs with above normal temperatures and precipitation. The analysis also revealed the presence of above normal minimum temperatures during most winters since SPWF became an important pest in the Desert Southwest.
    • Pima Regional Cotton Variety Test, Maricopa Agricultural Center, 1992

      Nelson, J. M.; Clark, L. J.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1993-03)
      Twelve pima varieties were grown in a replicated trial at the Maricopa Agricultural Center as part of the National Cotton Variety Testing Program.
    • Evaluation of the Pressure Chamber for Timing Early Season Irrigations

      Brown, P.; Silvertooth, J.; Malcuit, J.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1993-03)
      Use of the pressure chamber to time the initial post- planting irrigation of short season upland cotton was evaluated in a pilot study at Marana during 1992. Top yields and better overall plant performance were obtained when the initial post - planting irrigation was applied before leaf xylem potential (ψx) dropped significantly below -15 bars. Our findings were similar to those previously observed with Acala cotton in California. The authors believe more work is required before use of the pressure chamber is recommended for irrigation management in Arizona. Specifically, an effective means of separating changes in ψx resulting from day-to-day climate fluctuations from those caused by soil-water depletion must be developed. This study also clearly showed the importance of avoiding early season water stress when growing short season cotton.
    • Sweetpotato Whitely Control on Cotton by Treating Only the Field Edges

      El-Lissy, Osama; Antilla, Larry; Butler, George D. Jr.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1993-03)
      The edges of one of each of five pairs of long staple cotton fields were treated for sweetpotato whiteflies. Treated fields had 61% fewer eggs and 53% fewer nymphs than untreated fields. Adult populations were reduced 64% in the treated fields at the edges. In the center of treated fields adult populations remained low and unchanged but in untreated fields there was a 70% increase. According to minicard tests, cotton from treated fields was not sticky but cotton from untreated fields was sticky. Thus, populations of whiteflies and their damage can be significantly reduced by treating only the periphery of cotton fields at the onset of infestation. The treating of only 12 to 15% of the acreage greatly reduces costs and preserves the untreated center for beneficial insects.
    • The Effects of PIX Application Timing on Upland Cotton Lint Yield and Growth and Development Parameters

      Husman, S. H.; Silvertooth, J. C.; Ramsey, C.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1993-03)
      Four commercial scale field studies were conducted in 1991 and 1992 to further evaluate Upland cotton yield and development responses to PIX application timing as a function of cotton growth stage. Treatments imposed in both years intended to further clarify some response trends observed in previous years of field studies. Treatments were all at the maximum label rate of one and one half pints with application timing the main variable. Timing was based on heat unit accumulation and resultant growth stage since date of planting. Two of the four studies resulted in significant lint yield increase of roughly one hundred pounds across all PIX treatments in contrast to the untreated check. The two studies which resulted in lint yield increases both had height:node ratio measurements in excess (vegetative) of previously defined guidelines.
    • Sweetpotato Whitefly Preference and Performance on Medium Maturity Cotton Varieties in Arizona

      Ellsworth, P. C.; Meade, D. L.; Husman, S. H.; Ramsey, C. S.; Silvertooth, J. C.; Malcuit, J. E.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1993-03)
      In conjunction with the 1992 cotton variety testing program (see Silvertooth 1993), 12 medium maturity varieties were evaluated for the presence of sweetpotato whitefli.es (SPWF). Three sites (Queen Creek, Maricopa, Coolidge) were selected for expression of a full range of infestation intensity. Total immatures per square inch ranged from less than 8 up to more than 8(X), depending on site, sample date and variety. The results indicated that there were significant effects of variety on SPWF numbers; however, the ranking of varieties was not always the same nor significant. Most varieties performed comparably, but one consistently had more SPWFs than the remaining varieties (chi 1 35). Comparative results from the three sites indicate that there may be separate preference and performance components which lead to the development of an infestation. Lea f hairiness was quantified front samples at one site, and the relationship of this factor to whitefly susceptibility is discussed. Two varieties, cb1135 and stv453, were found to be significantly more hairy than the remaining varieties. The results provided here represent a preliminary evaluation of the data. Further analyses will attempt to relate various crop production and agronomic factors to SPWF susceptibility (e.g., plant height, fruit retention, height:node ratio, canopy closure, growth habit, maturity, yield, crop protection regimen). One fact was clear, however. None of the varieties evaluated here demonstrated resistance to SPWFs and certainly not to the extent that a producer could eliminate substantial risk of infestation through variety selection.
    • Expression of Insectical Protease Inhibitors in Arizona Cotton

      Thomas, John C.; Bohnert, Hans J.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1993-03)
      Insect damage impacts tremendously on the value of the Arizona cotton crop. As traditional pesticides become increasingly less useful, due to insect resistance and regulatory problems, new methods for insect control are needed. For these reasons, we engineered genes encoding protease inhibitors (PIs) from Manduca sexta (tobacco hornworm), for expression in cotton, with the hope that these inhibitors would have insecticidal activity. Transgenic plants containing PIs have been generated: 22 fertile lines of the duplicated 35S promoter anti-elastase, 4 fertile lines of the anti -chymotrypsin and 5 fertile lines of the anti -trypsin. Over 3,000 T-1 seeds have been collected and T-2 generation seeds are in production. Many crosses have been made into Delta Pine 16, 90 and 5415 respectively. No significant effect of the PIs on boll number or seed yield was observed. Insect tests have been conducted and the results indicate that plants expressing the protease inhibitors (PI's) have decreased emergence of whiteflies compared to control plants. We believe this research is a significant step towards a bio- pesticide producing Arizona cotton variety.
    • Early Season Irrigation Effects on Low Desert Upland Cotton Yields Using Leaf Water Potential Measurements

      Husman, S. H.; Garrot, Donald J. Jr.; O'Leary, J. W.; Ramsey, C. S.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1993-03)
      Leaf water potential (LWP) measurements using a pressure chamber were used to determine optimum timing of the first irrigation following planting on Upland cotton. Previous studies have indicated that leaf water potentials are dependent on the vapor pressure deficit (VPD) of the surrounding air. As a result, the VPD was accounted for in the development of a Leaf Water Potential Index (LWPI). The field study consisted of three irrigation treatments with four replicates arranged in a randomized complete block design (RCBD). Targeted treatment thresholds were 0.15 LWPI (wet), 0.30 LWPI (medium), and 0.45 LWPI (dry). Timing of the first irrigation occurred at 36, 53, and 63 days after planting for the wet, medium, and dry treatments respectively. There were no significant lint yield differences between irrigation treatments.
    • Effect of Foliar Applications of PGRIV on Yield of Pima and Upland Cotton

      Nelson, J. M.; Hart, G.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1993-03)
      The commercial product PGRIV was tested in small plots on cotton at the Maricopa Agricultural Center. Multiple foliar applications of this product had no significant effect on lint yield of Pima S-7 and DPL 90 cotton.
    • Sweetpotato Whitefly Control: Enhancement of the Repellency of Oils

      Butler, George D. Jr.; Henneberry, T. J.; Silvertooth, Jeff; USDA, ARS, Western Cotton Research Laboratory, Phoenix, AZ (College of Agriculture, University of Arizona (Tucson, AZ), 1993-03)
      The repellency to adult SPW of 1% Saf -T -Side and 1% Natur'1 Oil was enhanced by the addition of Butracide + Pounce, Butracide + Pyrellin, or a pyrethrum + diatomaceous earth. Several materials containing pyrethrum appeared to improve the repellency of 2% Saf -T -Side. The number of eggs laid was correlated with the number of adults observed on the plants, thus emphasizing the importance of the repellency of SPW adults. Three oils at 1% concentration gave a high mortality of SPW nymphs. Several materials killed nymphs when applied with a fine spray, simulating the deposit of a mist blower.
    • Chemical Control of the Sweetpotato Whitefly in Cotton

      Watson, Theo F.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1993-03)
      Both registered and experimental insecticides were evaluated for effectiveness against the sweetpotato whitefly in several field experiments at Yuma, Arizona. Best results were obtained with combinations of two insecticides, particularly a pyrethriod and an organophosphate, rather than with individual materials. Results of these experiments indicate that unusually heavy infestations can be currently controlled even though sustained use of these insecticides would probably lead quickly to the development of resistance.
    • Sweetpotato Whitefly Natural Enemies: Parasite Surveys in Urban Areas and Cotton Fields and Identification of a New Predator

      Butler, George D. Jr.; Henneberry, T. J.; Silvertooth, Jeff; Western Cotton Research Laboratory, USDA -ARS, Phoenix, AZ (College of Agriculture, University of Arizona (Tucson, AZ), 1993-03)
      Surveys for adult sweetpotato whitefly parasites on ornamentals in urban areas and in cultivated cotton fields show high parasite activity in urban areas vs. activity in cultivated cotton fields. A previously unreported Drapetis spp. fly was identified and found to occur in cotton fields in several areas in the state.
    • Germination and Respiration of Cotton Seed Produced in Arizona

      Dobrenz, Albert K.; Silvertooth, Jeffrey C.; Martin, Jill; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1993-03)
      The germination percentage and seedling respiration were evaluated on 11 cultivars of Cotton produced in Arizona. Respiration rates of 5-day old seedlings ranged from 6.0 to 16.9 mg /g⁻¹ hr⁻¹ for DP -5690 and KC-311, respectively. Germination percentage ranged from 31 to 87% for KC-311 and DP-51, respectively. A significant negative correlation (r = -.90) between respiration rates and the germination percentage indicates that seed quality is closely associated with early seedling metabolic rates.
    • Drought Tolerance in the Progeny of Interspecific Cotton Hybrids

      McDaniel, R. G.; Dobrenz, A. K.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1993-03)
      The F2 and F3 progeny of interspecific cotton crosses were evaluated under field conditions. The plants were maintained under drip irrigation with stress applied by withholding water during plant development and early flowering periods. Physiological and biochemical plant responses were measured throughout the growing season on an array of representative plants from the field population. Considerable variability was found to exist among these progeny for all traits measured in both years of the present study. Responses of parental controls were quite consistent for both seasons.
    • HVI Lint Quality as Affected by Defoliation Treatments, Marana 1991

      Thacker, Gary; Odom, Phil; Silvertooth, Jeff; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1993-03)
      This study was conducted to determine the effect of various defoliation treatments on the HVI quality of short staple cotton. We compared two applications of sodium chlorate and Accelerate to single applications of Dropp plus crop oil with and without Accelerate. We measured significant differences in percent defoliation and desiccation. We also measured significant differences in the HVI parameters of staple, micronaire, and length.
    • Progress on the Use of Trap Crops for Whitefly Suppression

      Ellsworth, P. C.; Meade, D. L.; Byrne, D. N.; Draeger, E. A.; Chernicky, J. P.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1993-03)
      In 1992, a repeat of a trap -cropping experiment was conducted for the suppression of sweetpotato whiteflies in Pima (S-6) cotton (see Ellsworth et al. 1992). The 1991 experiment showed some promise, but was characterized by low to moderate and later infestations of whiteflies than was desired. The 1992 experimental design (land area = 9.5 acres) was modified to accomplish three improvements: 1) the cotton crop area was doubled in size to 8 rows by 50 ft to improve the ratio of crop to trap area, 2) a fourth treatment was added to form a Latin square design which consisted of cotton plots surrounded only by bareground (i.e., no trap crop): the other three were surrounded by Wright groundcherry that was untreated or treated with 1X or 2X rates of soil-applied aldicarb, and 3) melons (1 row X667') were late planted between blocks to ensure locally abundant whiteflies during the time of the test. The melons were watered regularly in order to retain whiteflies until the start of the test. Early groundcherry establishment was variable and later compromised by insufficient water. This prompted later than usual flushes of groundcherry growth and delayed canopy development. This fact coupled by the intense level of whitefly movement following melon dry -down effectively overwhelmed the insufficiently developed trap crop. Aldicarb was applied on two dates (7/29 & 8/15), and whiteflies were sampled from all plots five times through August. The sampling data are preliminary at this point, but several observations were apparent: 1) the groundcherry trap crop was insufficiently developed to protect the Pima crop, 2) the addition of melons to the system dramatically increased the ,cumbers of locally abundant whiteflies, 3) maintaining the melons in good condition (i.e., well- watered) effectively retained whiteflies in the melons until dry-down, 4) upon dry-down, the melons released overwhelming numbers of adult whiteflies which could not be suppressed on the groundcherry trap crop before reaching the adjacent cotton, 5) the groundcherry was still selectively attractive to the whiteflies (relative to cotton), but was insufficiently developed w trap and retain the huge numbers of dispersing whiteflies, 6) soil - applied aldicarb did accomplish some degree of control of whiteflies on the groundcherry plants, but was inadequate in the face of the tremendous immigration of whitefly adults, 7) the intense whitefly pressure ultimately killed the majority of immature groundcheny plants with the aldicarb-treated plants lasting somewhat longer than the untreated plants, and 8) the yield and quality of the adjacent, late -planted Pima crop was commercially unacceptable and judged to be virtually a total loss. The failure of this implementation of the trap -cropping concept does not preclude the possibility that a better implementation would have succeeded; however, the observation that melons in close proximity to the test area dramatically changed the number of locally dispersing adult whiteflies cannot be denied. It would seem unlikely that a suitable trap crop system could be developed where such an intense proximate source and near instantaneous release of thousands of whiteflies (i.e., at dry-down of melons) is occurring.
    • Irrigation Efficiencies, Nitrogen and Phosphorous Applications, and Lint Yields of Upland Cotton Grown at the Maricopa Agricultural Center, 1992

      Sheedy, Mike; Watson, Jack; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1993-03)
      The computer program AZSCHED, with weather data obtained from AZMET, was used to schedule irrigations for a yield trial of Upland Cotton (DPL 90) at the Maricopa Agricultural Center. Cotton lint yields were compared between plots from eight treatments involving the combination of two irrigation efficiencies (70% and 90%), two nitrogen fertilizer placements (sidedressed and broadcast), and two phosphate fertilizer applications (0#/a and 50#/a). A potassium bromide (KBr) tracer was applied to select areas in each plot prior to the first irrigation. The total amount of fertilizer as nitrogen applied in split applications to both the sidedressed and broadcast plots was 120 #/a. The average amount of water applied to the plots were 33.5" for 70 % efficiency and 26.9" for 90% efficiency. Soil samples from each KBr applied plot were taken to a depth of 10' for analysis of bromide and nitrate to determine the depth of water movement through the soil profile. The plots were harvested on October 7, 1992. This year there was no significant difference in lint yield between any of the treatments: irrigation efficiencies, nitrogen placement, or phosphorous application.
    • The Use of AZSCHED to Schedule Irrigation on Cotton, Safford Agricultural Center - 1992

      Clark, Lee J.; Carpenter, Eddie W.; Slack, Donald C.; Martin, Edward C.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1993-03)
      AZSCHED Irrigation scheduling software was used on Pima and upland cotton with irrigations being scheduled at 40, 50 and 60% water depletion. Around 8 inches of rain fell during the growing season so no statistical differences were seen between treatment yields.
    • Arizona Upland Cotton Variety Testing Program

      Silvertooth, J.; Hood, L.; Husman, S.; Cluff, R.; Stedman, S.; Thacker, G.; Silvertooth, Jeff; University of Arizona Cooperative Extension (College of Agriculture, University of Arizona (Tucson, AZ), 1993-03)
      Eight field experiments were conducted across the cotton growing areas of Arizona in 1992 for the purpose of evaluating Upland cotton varieties in terms of adaptability and performance. Five commercial cottonseed companies participated in the program. Two varieties were submitted from each company at each location. Experiments were conducted on grower-cooperator fields in each case except one, which was conducted on a University of Arizona Agricultural Center. Locations used in the program spanned the range of conditions common to cotton producing areas of the state from about 500ft. to 3,000ft. elevation. Results indicated a broad range of adaptability and competitiveness on the part of each of the participating companies and their representative varieties. Each of the companies offers a compliment of varieties that can serve to match various production strategies commonly employed in the state as well as showing a strong capacity to be regionally adaptive.