Citrus Research Report 2002
ABOUT THE COLLECTION
The Citrus Report, first published in 1978, is one of several commodity-based agricultural research reports published by the University of Arizona. The purpose of the report is to provide an annual research update to farmers, researchers, and those in the agricultural industry. The research is conducted by University of Arizona and USDA-ARS scientists.
Both historical and current Citrus Reports have been made available via the UA Campus Repository, as part of a collaboration between the College of Agriculture and Life Sciences and the University Libraries.
Contents for Citrus Research Report 2002Citrus
- Analysis and Evaluation of the Performance of Surface N-Fertigation on the Yuma Mesa
- Development of Best Management Practices for Fertigation of Young Citrus Trees, 2002 Report
- Foliar applications of Lo-Biuret Urea and Potassium Phosphite to Navel Orange trees
- Citrus Orchard Floor Management 2001: Comparison of a Disk, "Perfecta" Cultivator, and Weed Sensing Sprayer
- Woodrat Control in Citrus Groves with Zinc Phosphide and Diphacinone
- Insecticidal Control of Woolly Whiteflies
- Pest Management and Yield Enhancement Qualities of Particle Film Technologies in Citrus
- Relative Susceptibility of Citrus Thrips Nymphs and Adults to Insecticides
- Results of 'Fallglo' Trials for Citrus in Arizona - 2001
- Results of New Cultivar Selection Trials for Orange in Arizona - 2001
- Biology and Control of Lemon Tree Wood Rot Diseases
- Effect of Organic Amendments on Lemon Leaf Tissue, Soil Analysis and Yield
- Established 'Lisbon' Lemon Trials in Arizona - 2001-02
- Lemon Rootstock Trials in Arizona - 2001-02
- Results of New Cultivar Selection Trials for Lemon in Arizona - 2001
Managing Septoria Leaf Spot of Pistachio in Arizona With FungicidesSeptoria leaf spot was detected in the United States for the first time in 1964 within an experimental pistachio planting at Brownwood, Texas. The first observation of the same disease in Arizona pistachio trees did not occur until 1986. In 1988, a survey of the 2,000 acres of pistachio orchards in southeastern Arizona revealed a widespread incidence of the disease. Since the initial discovery of the disease, Septoria leaf spot has appeared annually in some Arizona pistachio orchards. The onset and severity of the disease is influenced by summer rainfall that occurs in this region. Pistachio trees infected with Septoria leaf spot and not treated with an effective fungicide can defoliate in the autumn up to 2 months prematurely. The objective of this field study was to evaluate the efficacy of several different fungicides against this disease. All fungicides were applied to tree foliage on June 26 and July 31, 2001. Disease severity was lowest on trees treated with Flint (trifloxystrobin) and Abound (azoxystrobin). Other materials that significantly reduced the final level of disease compared to nontreated trees included Break (propiconazole), Procop R (copper hydroxide) and Elite (tebuconazole).
Pecan Leaf Tissue Nutrient Concentrations: Temporal Relationships and Preliminary StandardsLeaf samples were collected from five trees each of Bradley, Cheyenne, Sioux, Western Schley, and Wichita at Picacho, Arizona and five trees each of Bradley, Western Schley, and Wichita at Las Cruces, New Mexico, and analyzed nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, iron, copper, manganese, boron, and copper at two-week intervals from mid-May to Mid-October, 2000. Yield, average nut weight, and percent kernel data were collected for each individual tree. Leaf tissue analysis indicated that concentrations of nitrogen, phosphorus, potassium and sulfur decreased. The overall trends were for zinc levels to declined, although they increased at the end of the season. Boron, calcium, magnesium and manganese, and iron concentrations increased during the growing season. Copper concentrations were variable. Preliminary nutrient standards are presented and compared to existing standards. Most nutrients were within recommended ranges, but magnesium levels were much higher than the top of the Arizona and New Mexico sufficiency ranges. Manganese was higher than the Arizona sufficiency range, but within that of New Mexico, whereas zinc was higher than the New Mexico range, but within that of Arizona.
Results of New Cultivar Selection Trials for Lemon in Arizona - 2001Three lemon cultivar selection trials are being conducted at the Yuma Mesa Agriculture Center in Somerton, AZ. Data from these trials suggest that 'Cavers Lisbon' and 'Limonero Fino 49' selections may be suitable alternatives for the varieties most commonly planted in Southwest Arizona today.
Lemon Rootstock Trials in Arizona - 2001-02In a rootstock evaluation trial planted in 1993, five rootstocks, 'Carrizo' citrange, Citrus macrophylla, 'Rough Lemon', Swingle citrumelo and Citrus volkameriana were selected for evaluation using 'Limoneira 8A Lisbon' as the scion. 1994-2002 yield and packout results indicate that trees on C. macrophylla, C. volkameriana and 'Rough Lemon' are superior to those on other rootstocks in both growth and yield. C. macrophylla is outperforming C. volkameriana. For the second year in a row, 'Rough Lemon' trees performed similarly to C. macrophylla and better than C. volkameriana. 'Swingle' and 'Carrizo' are performing poorly. In two other rootstock evaluation trials, both planted in 1995, C. macrophylla and/or C. volkameriana are outperforming other trifoliate and trifoliate-hybrid rootstocks under test.
Established 'Lisbon' Lemon Trials in Arizona - 2001-02Four 'Lisbon' lemon selections, 'Frost Nucellar', 'Corona Foothills', 'Limoneira 8A' and 'Prior' were selected for evaluation on Citrus volkameriana rootstock. 1994-2002 results indicate that the 'Limoneira 8A Lisbon' and 'Corona Foothills Lisbon' are superior in yield and fruit earliness.
Effect of Organic Amendments on Lemon Leaf Tissue, Soil Analysis and YieldAn experiment was initiated in 2000 to study the feasibility of growing organic lemon in the southwest desert of Arizona. An eight-acre field was selected on Superstition sandy soil at the Mesa Agricultural Research Center to conduct this investigation. Lemon trees were planted at 25 feet spacing in 1998. The initial soil test in top 6 inches was 5 ppm nitrate-nitrogen and 4.9 ppm NaHCO3-P. Soil pH was 8.7 in the top 6 inches. Four treatments were applied in randomized complete block design repeated four times. The treatments were beef cattle feedlot manure and perfecta, clover and guano, guano and perfecta, and standard practice treatment. Soil samples were collected from 0-6 and 6-12 inches the first week of March 2001 and analyzed for NO₃-N NH₄-N, total nitrogen, organic matter and available P. Preliminary results showed no difference in NO₃-N, NH₄-N in 0 to 6 and 6 to 12 inches between treatments. Total nitrogen increased significantly from 0.0262% in standard treatment to 0.0375% in the manure treatment. Similarly, soil organic matter increased from 0.297% in standard treatment to 0.4337% in the manure perfecta treatment. Phosphorus level increased significantly from 6.962 ppm in guano perfecta to 11.187 PPM in manure perfecta treatment. Leaf tissue analysis indicated that nitrate level was influenced by treatment. Yields of Guano treatments were significantly greater than yields of the other treatments. Both commercial standard and organic treatments were equally effective in controlling citrus thrips, but repeated applications were required. Mite population has been detected at low level with no significant differences observed among treatments.
Biology and Control of Lemon Tree Wood Rot DiseasesBrown heartwood rot is commonly found in mature lemon groves in southwestern Arizona. Two basidiomycete fungi, Antrodia sinuosa and Coniophora eremophila, have been isolated from symptomatic trees. A major difference between the two pathogens is that Antrodia forms spore-producing fruiting bodies on infected wood within lemon groves, whereas fruiting on lemon wood infected by Coniophora has not been observed. A third fungus, a species of Nodulisporium, recently was recovered from small dead lemon tree branches with an internal white wood rot. Experiments were conducted to compare the severity of wood rot caused by each of these pathogens. The highest rates of wood decay for each pathogen occurred from May through October, when the mean length of wood decay columns for Antrodia, Coniophora and Nodulisporium was 183, 94 and 146 mm, respectively, and the mean air temperature was 29°C. In comparison, the mean length of wood decay columns from November through April for the same pathogens was 35, 18 and 38 mm, respectively, with a mean air temperature of 17°C. When inoculated with Antrodia, Coniophora or Nodulisporium, the length of wood decay columns on 40- mm-diameter branches was 26, 38 and 24% larger, respectively, compared to wood decay on 10-mm-diameter branches. The length of wood decay columns on inoculated Lisbon lemon was always numerically greater than that on tested orange, grapefruit and tangelo trees. Compared to lemon, wood decay columns ranged from 45 (on grapefruit) to 62 %( on orange) shorter when inoculated with Antrodia, 52 (on orange) to 59% (on tangelo) for Coniophora and 20 (on tangelo) to 51% (on grapefruit) for Nodulisporium. Compared to non-treated branches, suppression of wood decay in the presence of a test fungicide ranged from 28 to 79% for Antrodia, 77 to 91% for Coniophora and 71 to 92% for Nodulisporium. For each pathogen, the lowest numerical degree of wood rot suppression occurred in the presence of trifloxystrobin (Flint), whereas the highest level of suppression was observed with propiconazole (Break). On greasewood, mesquite, Palo Verde and salt cedar, the length of wood decay columns ranged from 20 to 60 mm when inoculated with Antrodia, 1 to 63 mm for Coniophora and 24 to 90 mm for Nodulisporium. For all three wood-rotting fungi, resultant wood decay columns were always much greater on lemon compared to tested desert-dwelling plants. Current disease management strategies include minimizing branch fractures and other non-pruning wounds as well as periodic inspection of trees and removal of infected branches, including physical removal of all wood infected with Antrodia from the grove site.
Results of New Cultivar Selection Trials for Orange in Arizona - 2001Three orange cultivar trials have been established in Arizona, one at the Yuma Mesa Agricultural Center, Yuma, AZ and one at the Citrus Agriculture Center, Waddell, AZ. For the navel orange trial in Yuma, 'Fisher' navel continues to have the greatest yield, but is unacceptably granulated. For the 'Valencia' trial in Yuma, none of the cultivar/rootstock combinations have been particularly successful. For the Waddell trial, only the first year data has been collected.
Results of 'Fallglo' Trials for Citrus in Arizona - 2001A 'Fallglo' mandarin trial was established at the Yuma Mesa Agriculture Center in 1995. Results suggest that trees on C. volkameriana rootstock, rough lemon rootstock, and, in 2001-02, Gou Tou orange rootstock had the greatest yields. There was little effect of rootstock upon fruit size or juice quality.
Relative Susceptibility of Citrus Thrips Nymphs and Adults to InsecticidesAgri-Mek, Assail, Baythroid, Carzol, and Success were all evaluated for their activity towards citrus thrips nymphs relative to adults. Based on leaf dip bioassays, Dimethoate was approximately 3 times more toxic to the adults than to the nymphs. However with leaf dip bioassays, a 3-fold difference, although statistically significant, is usually inconsequential. Success was the only insecticide that demonstrated a noteworthy difference in toxicity to nymphs compared to adults in the bioassay; it was 45 times more toxic to the nymphs than to the adults. Based on X2 contingency tables, lemon trees treated with Carzol, Success, or Baythroid all had significantly lower percentages of nymphs relative to the untreated control. Based on these data, when the citrus thrips population is composed primarily of nymphs, citrus growers and pest control advisors might consider using Carzol, Success, or Baythroid since they appear to impact the nymph population more than the adult population.
Pest Management and Yield Enhancement Qualities of Particle Film Technologies in CitrusSurround WP and Snow were evaluated for their ability to manage citrus thrips populations in lemons on the Yuma Mesa, and their impact on lemon yield, fruit quality, and packout. Both Surround and Snow effectively controlled citrus thrips and prevented fruit scarring, but their ability to manage Yuma spider mite was inconclusive. Preference tests indicated that both Surround and Snow act primarily by repelling the thrips, but also induce some mortality. Surround produced higher yields than Snow at the first harvest (#8 ring), but did not differ from the commercial standard. There were no differences in yield among treatments for the strip harvest, nor were their any differences in total yield. These data suggest that Surround may have some yield or increased fruit earliness enhancement qualities and that Snow may be slightly detrimental. There were no statistical differences among any of the treatments in fruit size frequency or quality for any of the harvests, and there was no apparent benefit from applying an additional application of Surround or Snow post thrips season solely for quality, fruit size, or yield enhancement.
Insecticidal Control of Woolly WhitefliesFour foliar insecticides (Esteem, Provado, Applaud and Assail) and one soil systemic insecticide (Admire) were evaluated for their control of woolly whitefly in lemons. These insecticides were chosen for evaluation because they have demonstrated efficacy to other whitefly species and have little or no impact on whitefly parasitoids. Admire was injected with a single shank about 5-in deep around each tree approximately at the tree’s drip line. All of the foliar insecticides were effective in controlling woolly whitefly. Admire also appeared to have efficacy, but due to inconsistent data on one sample date more testing should be conducted. Six weeks after the beginning of this test, whitefly parasitoids, Eretmocerus comperei or E. dozieri (exact species not certain) reduced the whitefly population across all treatments. Within two more months, no live whiteflies could be found in the test grove, and as of July 15, 2002, there was still no detectable woolly whitefly activity.
Woodrat Control in Citrus Groves with Zinc Phosphide and DiphacinoneTwo studies were conducted investigating the efficacy of Prozap (zinc phosphide), Ramik Green, and Ramik Brown (diphacinone) rodenticides on woodrats infesting citrus. Based primarily on using feeding activity as an indication of population density, Zinc phosphide (ZP) provided a rapid knockdown of the rat population, and offered 60 to 75% control. However, this product is known to cause "bait-shyness" following the initial application so additional control with subsequent applications of ZP targeting the same rat population would not likely result in a significant increase in control. Ramik Green and Ramik Brown are slow acting anticoagulant rodenticides, and performed similarly to each other. Anticoagulant rodenticides are not known to cause bait-shyness. In this study, these products only offered 20 to 38% control, but it is possible that these values may be artificially low since the rats may have been preferentially feeding on stored oat groats used to gauge feeding activity rather than consuming the anticoagulant baits.
Citrus Orchard Floor Management 2001: Comparison of a Disk, "Perfecta" Cultivator, and Weed Sensing SprayerMechanical (disk and Perfecta cultivator) and chemical weed control strategies were compared in a Yuma, AZ lemon orchard. In addition, an optical weed sensing sprayer (WeedSeeker) was evaluated for making post-emergence Roundup Ultramax herbicide applications. The use of pre-emergence herbicides in conjunction with the WeedSeeker spray units has the potential to significantly reduce the amount of post-emergence herbicide and water needed to spray flood irrigated citrus orchards. There was a relationship between weed ground cover and the area sprayed by the WeedSeeker units that indicated the maximum herbicide saving will occur a low weed densities. The use of the Kawasaki Mule with its superior suspension system allowed for faster spraying speeds than were possible with the tractor mounted sprayer and this also reduced spray volume per plot. Weed control was similar for the conventional and the WeedSeeker sprayers. Future investigations will include efforts to improve the estimation of percent weed groundcover, the use of higher rates of pre-emergence herbicides and the development of crop budgets based on experimental operations.
Foliar applications of Lo-Biuret Urea and Potassium Phosphite to Navel Orange treesThis experiment was established in January 2000 in a block of 'Washington' navel orange trees at Verde Growers, Stanfield, AZ. Treatments included: normal grower practice, winter low biuret (LB) urea application, summer LB urea application, winter LB urea application plus winter and spring potassium phosphite, winter LB urea application plus summer potassium phosphite, and normal grower practice plus spring potassium phosphite. Each treatment was applied to approximately four acres of trees. For 2000-01, yields ranged from 40 to 45 lbs. per tree, and there was no effect of treatments upon total yield, and only slight effect upon fruit size, grade and quality. For 2001-02, there was a slight effect of treatment upon yield as LB urea led to improved yield, while potassium phosphite led to reduced yield. Normal grower practice was intermediate between these two extremes.
Development of Best Management Practices for Fertigation of Young Citrus Trees, 2002 Report'Newhall' navel oranges on 'Carrizo' rootstock were planted in Mar. 1997 at the Citrus Agricultural Center. The objectives of this experiment were to i) determine the effects of N rate and fertigation frequency for microsprinkler-irrigated navel oranges on tree N status, and crop yield and quality; and ii) develop Best Management Practices which promote optimum tree growth and production while minimizing nitrate leaching. The trees are equipped with a microsprinkler irrigation system. The experiment is a randomized complete block factorial with N rates of 0, 0.15, 0.30, and 0.45 lb N/tree/year, and fertigation frequencies of weekly, monthly, and three times per year. Unfertilized control trees are also included in the experimental design. Each of the ten treatments is replicated five times. The trees were harvested in Jan. 2002. Fruit were processed through an automatic fruit sizer, and fruit from each plot were further evaluated for fruit quality. Leaf N concentration was responsive to N rate, but not to fertigation frequency. Leaf N in all fertilized plots was above tissue critical levels. Fruit yield in fertilized plots was higher than in unfertilized plots, but, in fertilized treatments, there was no significant effect of N rate or fertigation frequency on fruit yield or quality.
Analysis and Evaluation of the Performance of Surface N-Fertigation on the Yuma MesaThe application of N-fertilizers mixed with a surface irrigation stream (surface N-fertigation) is widely practiced in the Yume Mesa. Guidelines for the efficient management of surface N-fertigation systems are needed. The purpose of the work reported herein is to evaluate the relative effectiveness of existing surface N-fertigation management practices in the Yuma Mesa. This has been accomplished through the following steps: (1) a complete set of performance indices that can be used to assess the relative merit of alternative management scenarios are identified and defined and Equations as well as solutions for quantifying the performance indices are proposed; (2) surface fertigation field experiments (using Br- as a tracer) were performed in two irrigation basins at the Yuma Mesa research farm of the University of Arizona during the fall season of 2000; (3) the spatial distribution as well as the application efficiency and adequacy of Br- applied with irrigation water was determined using the performance functions proposed herein; and (4) the results were analyzed to assess the merits and limitations of existing practices.