Search Results

You are looking at 1 - 8 of 8 items for

  • Author or Editor: Charles W. Coggins Jr. x
  • Refine by Access: All x
Clear All Modify Search
Free access

Michael F. Anthony and Charles W. Coggins Jr.

The synthetic auxins NAA and 3,5,6-TPA were investigated for reducing abscission of mature citrus fruit in California (CA). NAA was investigated on navel orange trees in San Joaquin Valley and southern CA locations. Of the seven NAA experiments presented, five had substantial fruit drop. In these five experiments, a treatment of NAA reduced drop by 31% to 88% compared to the untreated control. Although NAA treatments as low as 25 mg·L-1 (acid equivalent) reduced drop, the greatest reductions in drop were obtained by spray concentrations in the 100 to 400 mg·L-1 range. 3,5,6-TPA was investigated for fruit drop control properties on navel orange and grapefruit grown in various CA locations. The untreated control in seven of the ten 3,5,6-TPA experiments had substantial fruit drop. In each of these cases, a treatment of 10, 15 or 20 mg·L-1 (acid equivalent) of 3,5,6-TPA reduced drop 69% to 96% compared to the untreated control. A strong linear response from 3,5,6-TPA in these seven experiments indicates maximum fruit drop reduction from the highest rate investigated. On an acid equivalent basis 3,5,6-TPA seems to be comparable to 2,4-D. Both NAA and 3,5,6-TPA were effective in controlling preharvest fruit drop in citrus under CA conditions. Both materials provided fruit holding late into the harvest season. NAA, and in particular 3,5,6-TPA, offer the potential to provide a substitute for 2,4-D which is commonly used for controlling fruit drop in many countries. Chemical names used: naphthaleneacetic acid (NAA); 3,5,6-trichloro-2-pyridinyloxyacetic acid (3,5,6-TPA, triclopyr); 2,4-dichlorophenoxyacetic acid (2,4-D).

Open access

Yair Erner and Charles W. Coggins Jr.

Abstract

Good preharvest fruit drop control toward the end of navel orange [Citrus sinensis (L.) Osbeck] and grapefruit (Citrus paradisi Macf.) harvest seasons in California may require higher than maximum label rates of 2,4-D. Therefore, residues from preharvest aqueous applications of 2,4-D made at 1.5 to 2 times higher than current label rates for preharvest fruit drop control were determined. In navel orange, the residue range found for free plus bound 2,4-D was 0.03 to 0.52 ppm in the flavedo and 0.05 to 0.14 ppm in the albedo. The free plus bound 2,4-D residue range found in grapefruit rind tissue was 0.11 to 0.22 ppm. Only trace amounts were found in pulp tissue of either cultivar. When pH was carefully controlled during each step of the fractionation procedure, recoveries of 2,4-D in excess of 83% were obtained. Residues found were considerably lower than established tolerances of 5 ppm in the United States and 2 ppm in some other countries. Thus, residues would permit higher application rates if needed and if label rates were increased. Chemical name used: 2,4-dichlorophenoxy acetic acid (2,4-D).

Free access

Kurt D. Nolte, Eugene A. Nothnagel, and Charles W. Coggins Jr.

Studies were conducted to determine whether certain physiological effects of gibberellic acid (GA3) on the peel of citrus fruits may be attributed to GA3 interaction with cellular membranes. Excised mesocarp tissue from pummelo [Citrus maxima (Burm.) Merrill] fruits was analyzed for electrolyte and K+ release over time in varying concentrations of GA3. Electrolyte leakage and K+ efflux was significantly reduced (up to 30%) when tissue was incubated in the presence of GA3. GA3 improved the viability of mechanically isolated protoplasts during 72 hr of storage at 7C, as shown by the use of fluorescein diacetate. These results suggest that some of the GA3-elicited responses in citrus fruits may be membrane related.

Free access

Mohamed El-Otmani, Charles W. Coggins Jr., and Andrew Duymovic

Open access

Mohamed El-Otmani and Charles W. Coggins Jr.

Abstract

Changes in ‘Washington’ navel orange [Citrus sinensis (L.). Osbeck] fruit epicuticular wax quantity and structure were followed during fruit development, maturation, and senescence. Whole-tree sprays of 10 ppm GA3, 16 ppm 2,4-D, and a combination of GA3 (10 ppm) plus 2,4-D (16 ppm) were made at fruit color-break, and effects on wax were examined at 4-week intervals. The total epicuticular wax produced per fruit and per unit of fruit surface area increased with time on control and on treated fruit. GA3-treated fruit produced significantly lower amounts of wax per unit of surface area than did control or fruit treated with 2,4-D alone. Total epicuticular wax per unit of fruit surface area of the control was similar to that of the 2,4-D-treated fruit until late in the season, when that of the control significantly exceeded that of the 2,4-D treatment. Wax per unit of fruit area of the GA3-treated fruit was not significantly different from that of the GA3 plus 2,4-D-treated fruit until late in the season, when GA3 plus 2,4-D treatment resulted in significantly higher values. Scanning electron microscopy revealed significant changes in surface morphology and ultrastructure of the epicuticular wax during fruit development, maturation, and senescence. Control fruit and 2,4-D-treated fruit were similar, but GA3 delayed ultrastructural changes that were seen in the control fruit. The incidence of ‘sticky’ rinds was reduced significantly by GA3 treatment, and ‘sticky’ rind surface wax had a structure similar to that of senescing surfaces. Chemical names used: (2,4-dichlorophenoxy)acetic acid (2,4-D); gibberellic acid (GA3).

Open access

Charles W. Coggins Jr., Anthony E. Hall, and Winston W. Jones

Abstract

‘Frost Valencia’ [Citrus sinensis (L.) Osbeck] budded to trifoliate orange rootstock [Poncirus trifoliata (L.) Raf. 1, with orange-colored fruit, were subjected to 4 temperature regimes consisting of 2 day-night shoot environments and 2 constant soil temperatures in 2 glasshouses. In the cool shoot environment (20×15°C, day×night air temperature), carotenoid content of fruit increased substantially, whereas, in the warm glasshouses (30×15°), carotenoid content either changed little (apical and equatorial regions) or decreased slightly (basal region). Chlorophyll content of fruit increased to detectable levels only in the warm glasshouse. Soil temperatures of 15 and 25° had little or no influence on carotenoid or chlorophyll content of fruit in either glasshouse. Thus, regreening occurred only in the warm shoot environment and at both root temperatures. These temperature effects did not appear to operate through a redistribution of nitrogen to the rind.

Open access

Mohamed El-Otmani, Charles W. Coggins Jr., and Irving L. Eaks

Abstract

Relationships among fruit age, epicuticular wax, weight loss, internal atmosphere composition, and respiration were investigated in mature ‘Washington’ navel orange fruit [Citrus sinensis (L.) Osbeck]. Fruit epicuticular wax, internal CO2, and internal C2H4 increased, whereas as the season advanced, weight loss during storage and respiration decreased. Concomitantly, fruit conductance to CO2 was reduced. GA3 (10 ppm) application prior to fruit color break reduced the increase in epicuticular wax and thereby delayed the decrease of CO2 conductance, resulting in less of an increase in internal CO2. GA3-treated fruit were not consistently different for other parameters evaluated. Chemical name used: lα,2β,4aα,4bβ,10β)-2,4a,7-trihydroxy-l-methyl-8-methylenegibb-3-ene-l,10-dicarboxylic acid l,4a-lactone (gibberellic acid).

Free access

Etaferahu Takele, John A. Menge, John E. Pehrson Jr., Jewell L. Meyer, Charles W. Coggins Jr., Mary Lu Arpaia, J. Daniel Hare, Darwin R. Atkin, and Carol Adams

The effect of various integrated crop management practices on productivity (fruit yield, grade, and sire) and returns of `Washington Navel' oranges [Citrus sinensis (L.) Osbeck] was determined in the San Joaquin Valley of California. Seventy-two combinations of treatments comprised of three irrigation levels [80%, 100%, and 120% evapotranspiration demand (ETc)], three N fertilizer levels (low, medium, and high based on 2.3%, 2.5%, and 2.7% leaf N, respectively), gibberellic acid (±), miticide (±), and fungicide-nematicide (±) were included in the analysis. Using a partial budgeting procedure, returns after costs were calculated for each treatment combiition. Costs of treatments, harvesting, packing, and processing were subtracted from the value of the crop. The value of the crop was calculated as the sum of returns of crop in each size and grade category. The overall result indicated that returns after costs were higher for the +fungicide-nematicide treatment and also were generally more with increased irrigation. The combination of 120% ETc, +fungicide-nematicide, medium or high N, -miticide, and -gibberellin showed the highest return of all treatment combinations. Second highest returns were obtained with high N or with miticide and gibberellin used together.