Citrus Research Report 2001
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 2001Citrus
- Evaluation of Insecticide Applications for Citrus Thrips Control Under Hot Conditions
- Evaluation of Pre-Petal Fall Citrus Thrips Control
- Insecticidal and Yield Enhancement Qualities of Surround Particle Film Technology in Citrus
- Potential Use of Esteem for Control of Woolly Whitefly in Citrus
- Evaluation of Fungicidal Management of Alternaria Rot on Citrus Fruit in 2000-2001 Season
- Studies of the Biology and Control of Brown Heartwood Rot on Lemon Trees in 2000
- Foliar applications of Lo-Biuret Urea and Potassium Phosphite to Navel Orange Trees
- Development of Best Management Practices for Fertigation of Young Citrus Tree
- Organic Lemon Production
- Results of Scion and Rootstock Trials for Citrus in Arizona - 2000
Rejuvenation of Neglected, Mature "Wichita" Pecan Trees By Corrective PruningAn attempt was made in 1997 to rejuvenate neglected, mature 'Wichita' pecan trees in a commercial Pinal County grove by applying two types of heading back pruning cuts. The treatments were applied during the dormant season prior to the growing season. The trees were pruned using proven horticultural techniques which included dehorning (cutting main scaffolds to within 2 feet of the trunk) and cutting main scaffolds by 50%. After four years of data, the trees receiving no pruning treatments are producing as well or better than trees to which the pruning treatments were applied. The data suggests that a return to normal irrigation and fertilization practices alone will return neglected, water-stressed trees to normal productivity as early as trees that have been headed-back.
Effect of fungicide treatments on incidence of powdery mildew of pecan and on pecan nut qualityPowdery mildew of pecan, caused by Microsphaera ulni, was observed on pecan shucks by the latter part of June 2000 in a commercial pecan orchard near Sahuarita, Arizona. Results of 1999 studies indicated that infection does not reduce nut quality. In order to determine effects of fungicide treatments and to substantiate results from 1999, preventive applications of micronized sulfur and azoxystrobin were initiated on June 8, 2000 in selected clusters in both Wichita and Western varieties. Trials were established in plots that had a high incidence of powdery mildew in 1999. Whole nut weights, kernel weights, or color ratings were not significantly different among clusters of nuts that were treated with fungicides and untreated nuts that were infected with powdery mildew. Percent disease incidence was 100% in untreated clusters, 0% in clusters treated with azoxystrobin every two weeks, and 5.3% (Wichita) and 8.8% (Western) in clusters treated with sulfur three times early in the season. Results indicate that disease did not affect nut weight or quality and that early preventive fungicide treatments are effective in controlling infections.
Results of Scion and Rootstock Trials for Citrus in Arizona - 2000Five rootstocks, 'Carrizo' citrange, Citrus macrophylla, Rough lemon, Swingle citrumelo and Citrus volkameriana were selected for evaluation using 'Limoneira 8A Lisbon' as the scion. 1994-2000 results indicate that trees on C. macrophylla and C. volkameriana are superior to those on other rootstocks in both growth and yield. C. macrophylla is outperforming C. volkameriana. Rough lemon is intermediate, and 'Swingle' and Carrizo’ are performing poorly. For 2000-01, rough lemon trees performed similarly to C. macrophylla and C. volkameriana. In a similar trial, Four 'Lisbon' lemon selections, 'Frost Nucellar', 'Corona Foothills', 'Limoneira 8A' and 'Prior' were selected for evaluation on Citrus volkameriana rootstock. 1994-2001 results indicate that the 'Limoneira 8A Lisbon' and 'Corona Foothills Lisbon' are superior in yield and fruit earliness. Results from another lemon cultivar trial suggest that 'Cavers Lisbon', 'Limonero Fino 49' and 'Villafranca' lemons may be good candidates for plantings as well. Results from three other lemon scion trials, a navel orange cultivar trial and a 'Valencia' orange trial, and a 'Fallglo' mandarin trial are presented as well.
Organic Lemon ProductionThis experiment was initiated in March 2000 to study the feasibility of growing organic lemon in the desert southwest of Arizona. A ten-acre field planted to lemons in 1998 was selected on Superstition sand at the Yuma Mesa Agricultural Research Center. The initial soil test in top 6 inches was 5 parts per million (ppm) NO₃⁻ and 4.9-PPM NaHCO₃⁻-extractable P. Soil pH was 8.7 in the top 6 inches. Seven treatments were applied in randomized complete block design repeated three times. The treatments were control, compost and clover, compost and perfecta, compost and steam, manure and clover, manure and perfecta and manure and steam Leaf tissue analysis indicated that nitrate level was significantly influenced by treatment. Organic insect control treatments for citrus thrips were as equally effective as the non-organic commercial standards.
Development of Best Management Practices for Fertigation of Young Citrus Tree'Newhall' navel oranges on 'Carrizo' rootstock were planted in Mar. 1997 at the Citrus Agricultural Center. The objectives of this experiment were: i) to 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) to 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 for the first time in Feb. 2001. Fruit were processed through an automatic fruit sizer, and fruit from each plot were further evaluated for fruit quality. Although unfertilized control trees had lower leaf N content than fertilized trees, fruit yield and quality of controls was no lower than fertilized trees. Similarly, there were few statistically significant differences in fruit yield and quality between trees receiving different N rates and fertigation frequencies.
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. There was a slight effect upon fruit size and grade. Trees subject to summer LB urea application had significantly more fruit of size 56, compared to trees subject to winter LB urea, and untreated, and untreated trees had significantly more fruit of size 88 than did treated trees. Also, treated trees had slightly more fruit in the fancy grade than did untreated trees.
Studies of the Biology and Control of Brown Heartwood Rot on Lemon Trees in 2000Brown 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. Similarities between the two pathogens include the following: each fungus grows optimally at 30 to 35°C, neither organism produces a fleshy fruiting body, they colonize lemon trees primarily through branch fractures and other non-pruning wounds, and both cause a brown wood rot in infected 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. The rate of wood decay in lemon branches inoculated with Antrodia is at least three times greater than that caused by Coniophora. Wood decay columns produced by either fungus from late spring to early autumn were at least three times larger than those that developed from late autumn to early spring. When inoculated with either pathogen, the length of wood decay columns on branches 10 mm in diameter was numerically smaller than those on branches 20 and 40 mm in diameter. Wood decay on Lisbon lemon branches inoculated with either Antrodia or Coniophora was significantly greater than that on Marsh grapefruit, Orlando tangelo, and Valencia orange. Treatment of lemon branch inoculation sites with azoxystrobin or propiconazole at 20 g of active ingredient per liter of solution reduced the resultant length of wood decay columns by 61 and 77%, respectively, for Antrodia, and 92 and 85%, respectively, for Coniophora. When selected desert plants were inoculated, Antrodia produced wood decay columns on Palo Verde, salt cedar, greasewood, and mesquite branches that were much shorter than those recorded on Lisbon lemon branches. On the other hand, Coniophora produced longer wood decay columns on salt cedar and mesquite than on Lisbon lemon, whereas wood rot on lemon was greater than that on Palo Verde and greasewood. Current disease management strategies include minimizing branch fractures and other non-pruning wounds, and periodic inspection of trees and removal of infected branches, including physical removal of all wood infected with Antrodia from the grove site.
Evaluation of Fungicidal Management of Alternaria Rot on Citrus Fruit in 2000-2001 SeasonAlternaria fruit rot on Minneola tangelos and navel oranges can reach economically important levels in central Arizona. The objective of this study was to test the efficacy of a new fungicide in development, BAS 500, for disease management. A trial was conducted in a commercial Minneola tangelo grove with a history of Alternaria fruit rot. Within this grove, nine trees were sprayed monthly from August to December 2000 with BAS 500 at a rate of 0.25 lb active ingredient per acre. Another nine trees were not sprayed and served as controls. Disease severity was evaluated monthly from September 2000 to March 2001 by counting the number of infected fruit that had dropped from trees. No disease was evident on fruit from August through November, when fruit were green. By December the fruit had matured and turned color; additionally, the first fruit were detected with Alternaria fruit rot. In December and January there was little difference in the number of infected fruit on treated compared to nontreated trees. On the other hand, by February and March the cumulative number of infected fruit from trees treated with BAS 500 was 3.0 and 3.7 %, respectively, whereas the cumulative number of diseased fruit from nontreated trees during the same months was greater at 4.9 and 6.4 %, respectively. This study will be repeated next year with an adjusted spray schedule with the goal of increasing the level of disease control.
Potential Use of Esteem for Control of Woolly Whitefly in CitrusEsteem was evaluated for its efficacy towards woolly whitefly in grapefruit and Minneola tangelos. Esteem was efficacious, but because of spray coverage problems on large trees, failed to offer complete control. Higher rates should be used where infestations are severe, or the trees are large and coverage difficult. Follow-up applications may be necessary to maintain control.
Insecticidal and Yield Enhancement Qualities of Surround Particle Film Technology in CitrusSurround WP was evaluated at various spray volumes to determine if volumes lower than the label recommended volume of 250 gallon per acre would provide equivalent citrus thrips control and yield enhancement potential. All the spray volumes evaluated (50, 100, 150, and 250 gpa) appeared to be equally effective. It appears that as long as the spray coverage appears to be visually adequate, then coverage is sufficient. Application of Surround WP led to some increase in fruit size, particularly for the first harvest.
Evaluation of Pre-Petal Fall Citrus Thrips ControlA small plot trial was conducted to evaluate the benefit of applying insecticides for citrus thrips management pre-petal fall. Because of low thrips densities during the pre-petal period, we were not able to discern tangible benefits from making prepetal applications. However, in situations where fruit is present and petal fall has not fully occurred, these applications may be useful to protect these fruit. Of the acute toxicants evaluated pre-petal fall (Assail and Success), Assail appeared to be the best choice. However, if temperatures are approaching 95°F, Assail should be avoided. Pre-petal fall applications of Surround and Snow are beneficial in respect that several applications of these products may be required to obtain adequate coverage, and by making these applications during the pre-petal fall period, thrips can be managed before many susceptible fruit are present.
Evaluation of Insecticide Applications for Citrus Thrips Control Under Hot ConditionsA small plot efficacy trial was conducted evaluating citrus thrips control under hot conditions. Average daily maximum temperatures ranged from the mid-90’s to low 100°F’s. Success and Carzol were the most efficacious products evaluated, followed by Lorsban and Dimethoate. Both Lorsban and Dimethoate provided good initial thrips control but were short lived. Lorsban appeared to have a slightly longer residual than Dimethoate. Both of the pyrethroids, Baythroid and Danitol, performed poorly. Neither provided good thrips knockdown or residual control. Pyrethroids should be avoided for thrips control when temperatures equal or exceed 95°F. We were not able to demonstrate any adverse effect on efficacy towards thrips by acidifying Success. However, Success is not prone to hydrolysis at high pHs, and acidification is not necessary or advised.