Citrus Research Report 2000
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 2000Citrus
- Insecticide Rotation and Pre-Petal Fall Applications for Citrus Thrips Management
- Residual Activity of Insecticides to Citrus Thrips on Lemon Foliage
- Protective and Yield Enhancement Qualities of Kaolin on Lemons
- Tank Mixing Success for Citrus Thrips Control is Not Necessary
- Effect of Temperature and Moisture on Survival of Phytophthora in Citrus Grove Soil
- Effect of Foliar Boron Sprays on Yield and Fruit Quality of Navel Oranges in 1998 and 1999
- Development of Best Management Practices for Fertigation of Young Citrus Trees
- Girdling "Fairchild" Mandarins and "Lisbon" Lemons to Improve Fruit Size
- Results of Scion and Rootstock Trials for Citrus in Arizona -- 1999
- Use of a Slow Release Triazone-Based Nitrogen Fertilizer on Lemon Trees
- Evaluation of Temik (aldicarb) for the Control of the Pecan Aphid Complex for Pecans Grown in Arizona
- Effect of Powdery Mildew on Pecan Nut Weight and Quality
- Pecan Variety Study on the Safford Agricultural Center
- Fungicidal Performance in Managing Septoria Leaf Spot of Pistachio in Arizona
- Performance of Mature Pecan Varieties in the Low Desert of Pinal County 1997-1999
- Population Dynamics of Pecan Aphids and Their Green Lacewing Predators in Insecticide-Free Pecans
- Improvement of "Flame Seedless" Grape Coloration at Harvest as Influenced by Trunk Girdling
Population Dynamics of Pecan Aphids and Their Green Lacewing Predators in Insecticide-Free PecansField surveys of aphids and their natural enemies were conducted in a 30 acre unsprayed block of 'Wichita' pecans in Southeastern Arizona (FICO, Sahuarita) during the growing seasons of 1997, 1998, and 1999. Each season showed a different pattern of aphid population development. In general, numbers of the more damaging black pecan aphid, Melanocallis caryaefoliae were always lower than those of the blackmargined pecan aphid Monellia caryella and no serious aphid damage by either species was observed. Two species of green lacewings were the dominant natural enemies in the orchard, and eggs could be found throughout the season.
Performance of Mature Pecan Varieties in the Low Desert of Pinal County 1997-1999Twelve varieties of pecans were evaluated for yield, viviparity, and nut quality. The commercially recommended varieties 'Western Schley' and 'Wichita' produced the greatest yields but also had the highest percentage of pregermination. The varieties 'Cheyenne' and 'Sioux' exhibit great potential for commercial production in the low desert of Arizona.
Fungicidal Performance in Managing Septoria Leaf Spot of Pistachio in ArizonaSeptoria 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 acreage. 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 July 13 and August 10, 1999. Disease severity was lowest on trees treated with Flint (trifloxystrobin). Other materials that significantly reduced the final level of disease compared to nontreated trees included Abound (azoxystrobin), Break (propiconazole), and Procop R (copper hydroxide).
Pecan Variety Study on the Safford Agricultural CenterIn 1986 a replicated study of eight varieties of pecans was planted on the Safford Agricultural Center at an elevation of 2954 feet above sea level. The objective of the study was to determine which varieties would produce best under the saline conditions found in the Safford valley. WO-3, the highest overall producer of the study, produced the best yield in 1999, with a yield over 2600 pounds per acre. This paper also contains kernel percentages and other nut characteristics found in the study during the 1999 harvest seasons and a summary of the yields since 1997.
Effect of Powdery Mildew on Pecan Nut Weight and QualityPowdery mildew of pecan, caused by Microsphaera ulni, results in discoloration of pecan shucks, but its effects on yield and quality of kernels are not known. In 1999, powdery mildew was observed on pecan shucks by the latter part of June in a commercial pecan orchard near Sahuarita, Arizona. The fungus continued to be active throughout the summer. However, results of a field test comparing diseased and healthy nuts from two varieties of pecans indicate that powdery mildew did not affect nut weight or quality. Whole nut weights, kernel weights, color ratings or percentage of discarded nuts were not significant between paired clusters of nuts that were treated with fungicides and remained disease free and untreated nuts that were infected with powdery mildew. Although shucks may have a high percentage of area covered by powdery mildew, results from this trial indicate that fungicide treatments are not warranted.
Evaluation of Temik (aldicarb) for the Control of the Pecan Aphid Complex for Pecans Grown in ArizonaThis experiment was conducted to extend the label for Temik use in Arizona pecan orchards for aphid control. Spring application of Temik controlled both yellow and black aphids throughout the season and significantly increased yield.
Use of a Slow Release Triazone-Based Nitrogen Fertilizer on Lemon TreesTrisert CB replaced conventional foliar applied low-biuret urea and liquid urea ammonium nitrate in a typical N fertilization regime, a urea triazone based N source. There was no yield decrease, change in fruit size or grade with the use of the Trisert CB. There were no differences in leaf P, K, Ca, Mg, Cu, Fe, Mn or Zn concentration. Occasionally, leaf N concentration of trees supplied with foliar applied Trisert CB was higher than that of the control treatment.
Results of Scion and Rootstock Trials for Citrus in Arizona -- 1999Five rootstocks, 'Carrizo' citrange, Citrus macrophylla, Rough lemon, Swingle citrumelo and Citrus volkameriana were selected for evaluation using 'Limoneira 8A Lisbon' as the scion. 1999-2000 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. In a similar trial, Four 'Lisbon' lemon selections, 'Frost Nucellar', 'Corona Foothills', 'Limoneira 8A' and 'Prior' were selected for evaluation on Citrus volkameriana rootstock. 1998-99 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 two other lemon scion trials, a navel orange cultivar trial and a 'Valencia' orange trial, and a mandarin trial are presented as well.
Girdling "Fairchild" Mandarins and "Lisbon" Lemons to Improve Fruit Size'Fairchild' mandarins in the Phoenix area and 'Lisbon' lemons in Yuma were girdled beginning in November 1996. November, March and May girdling of the mandarins led to the greatest yield the first year, while March and May girdling led to the greatest yield in years 2 and 3. March girdling yield increases were generally due to greater fruit numbers, while in May, yield increases were due to greater fruit numbers and fruit size. Returns per acre suggest that March and or May girdling of mandarins will lead to greater profits for the grower. Like mandarins, lemon yields were greater following November, or November and March girdling after one year of the experiment. However, yields of these trees dropped considerably the second year, and the trees appear to be in an alternate bearing cycle. No lemon girdling treatment appears to be better than the untreated trees after three years.
Development of Best Management Practices for Fertigation of Young Citrus TreesMicrosprinkler irrigation offers excellent flexibility for site-specific management of water and nitrogen inputs for citrus orchards in the southwestern United States. Escalating water costs, declining water availability, and increasing regulation of nitrogen (N) fertilizer use are causing growers to adopt practices to improve water and N use efficiency. 'Newhall' navels on 'Carrizo' rootstock were planted in Jan. 1997 and an experiment was initiated. This experiment was continued during 1999. The objective of the experiment was to develop appropriate management guidelines for N fertigation of 3-4 year old microsprinkler-irrigated navel orange trees. Treatments were factorial combinations of three N rates (0.15, 0.30, 0.45 lb N tree⁻¹ yr⁻¹) and three fertigation frequencies (3x/year, monthly, weekly). An untreated control was included. Trunk diameter was not responsive to N rate or fertigation frequency. Leaf N in all treatments, even controls, remained above the critical level (2.5%). However, at each N rate leaf N was highest with the weekly fertigation frequency. Nitrate analyses of soil samples indicate that nitrate leaching was highest with the highest N rate and 3x/year fertigation. Frequent fertigation is recommended because it results in higher leaf N and less nitrate leaching.
Effect of Foliar Boron Sprays on Yield and Fruit Quality of Navel Oranges in 1998 and 1999A field study was designed to determine if foliar boron (B) sprays could increase fruit set and yield of 'Parent Washington' navel oranges (Citrus sinensis). Treatments consisted of two application timings (prebloom and postbloom) and five application rates 0, 250, 500, 750 and 1000 ppm B as Solubor. Leaf B levels had a significant response to both application timing and rate in 1998, but there were no significant differences in 1999. There were no significant difference in fruit quality or yield in either year.
Effect of Temperature and Moisture on Survival of Phytophthora in Citrus Grove SoilBefore replanting a citrus grove in Arizona, different preplant cultural activities may be performed, such as immediate replanting of the new citrus grove, allowing soil to lay fallow for various lengths of time, or planting the site to alfalfa for one or more years before the new citrus grove is established. A study was conducted to compare the effect of these different cultural preplant practices on the survival of Phytophthora in citrus grove soils. In June, 1998, and July, 1999, a total of 18 soil samples were collected within mature lemon groves. Each initial bulk sample was pretested, found to contain Phytophthora parasitica, then thoroughly mixed and partitioned into 1-liter plastic containers, which were subjected to different environmental and cultural conditions. The soil in each 1-liter container was tested for the presence of P. parasitica 1 and 3.5 to 4 months later. All soil samples then were placed in the greenhouse and a 6-month-old Citrus volkameriana seedling was planted in soil samples not containing plants. Three 1-liter sub-samples from each of ten 7-liter volumes of soil incubated outside for three months were also planted to citrus in the greenhouse. The soil containing plants in the greenhouse was watered as needed for 3 months, then again tested for the presence of Phytophthora. Irrigating soil infested with Phytophthora parasitica, whether it was planted to a host (citrus) of the pathogen, planted to a non-host (alfalfa) of the pathogen, or not planted at all, did not lower the pathogen to nondetectable levels. Phytophthora became and remained nondetectable only in the soil samples that were not irrigated and subjected to mean temperatures of 35 to 37° C (94 to 98° F). On the other hand, the pathogen was detectable in some soil samples subjected to dryness at lower mean temperatures of 26 to 30° C (79 to 86° F) after a citrus seedling subsequently was grown in the soil for 3 months. A dry summer fallow period following removal of a citrus grove (including as much root material as possible) was the only cultural practice among those tested that reduced the level of Phytophthora to nondetectable levels in all soil samples tested.
Tank Mixing Success for Citrus Thrips Control is Not NecessaryA small plot efficacy trial was conducted evaluating thrips control with Dimethoate, Baythroid, and Success at rates of 4, 6, and 9 oz/ac, and tank mixes of the low and medium rates of Success with Dimethoate or Baythroid. Based on a 10% fruit infestation threshold, Dimethoate required three applications while the other treatments required two applications to achieve season long thrips control. However, when evaluating the treatments based on a cost effectiveness index, none of the tank mixes or Success at 9 oz./ac were economically advisable. The most cost effective treatment was Success at 4 oz/ac, followed by Success at 6 oz/ac, Dimethoate, and Baythroid.
Protective and Yield Enhancement Qualities of Kaolin on LemonsKaolin (Surround) was highly effective at preventing citrus thrips populations from reaching damaging levels in Arizona lemons. Applications should be initiated before thrips become numerous. Applying the material before petal fall may offer protection of early set fruit, but may not be necessary if thrips densities are low. However, since kaolin should be applied in advance of thrips populations increase, determining the benefits of pre-petal fall applications of kaolin is difficult. Kaolin applied on a maintenance schedule offers continual suppression of thrips populations, whereas traditional standard insecticides offer temporary population knockdown. Kaolin did not interfere with photosynthesis or stomatal conductance, and may possess yield enhancement qualities.
Residual Activity of Insecticides to Citrus Thrips on Lemon FoliageThe residual activity of insecticides to second instar citrus thrips was measured on lemon foliage in 1998 and 1999. Dimethoate, Agri-Mek and acetamiprid provided only knockdown control of thrips, dropping to <70% mortality by 3 days after treatment (DAT). Baythroid performed slightly better, providing about 95% mortality 3 DAT during three of the evaluation periods, but by 7 DAT was giving about 75% mortality. Alert, Carzol, and Success provided the longest residual activity, lasting 7 to 14 DAT. Residual activity in general appeared to be greater in the May and June evaluation, relative to the April evaluation. The apparent shorter residual activity under cooler condition in April 1998 is not understood but maybe due to a difference in the physiological nature of the leaves earlier in the season.
Insecticide Rotation and Pre-Petal Fall Applications for Citrus Thrips ManagementUnder low citrus thrips pressure and cool temperatures, Alert, Baythroid, Carzol, Success and Acetamiprid applied at petal fall were all effective control agents. Mid-season applications of Baythroid and Danitol were also effective but appeared to be slightly inferior to Success and Alert in residual control. Despite the prolonged blooming and petal drop period experienced during this trial, plots receiving pre-petal fall applications of Acetamiprid did not produce higher quality fruit than treatments where applications began following petal fall. The fact that thrips densities were low during this period may be the reason. Before pre-petal fall insecticide applications can be deemed useful and economically justifiable, evaluations must be made at higher thrips infestation levels.