Citrus Research Report 1999
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 1999
- Efficacy of Insecticides to Citrus Thrips on Lemons in Yuma Arizona 1998
- Growth of Citrus volkameriana inoculated with AM fungi in moist or periodically dry soils
- Residual activity of insecticides to citrus thrips on lemon foliage
- Impact of preplant soil treatments on survival of Phythophthora in citrus soils
- Effect of foliar boron sprays on yield and fruit quality of navel oranges
- Evaluation of thinning agents for "kinnow" mandarins
- Evaluation and management of a "salina" strawberry clover cover crop in citrus: first year preliminary results
- Applying roundup to the base of lemon tree canopies: effects on leaves, flowers, fruitlets, and yield
- Results of scion and rootstock trials for citrus in Arizona - 1998
- Performance of mature pecan varieties in the low desert 1997 and 1998
- Effects of fluid nitrogen fertigation and rate on microsprinkler irrigated grapefruit
- Pecan variety study on the Safford Agricultural Center 1997-1998
- Rejuvenation of mature pecan trees by pruning
- Pecan yields and nut quality as influenced by soil trenching and tree pruning
Pecan yields and nut quality as influenced by soil trenching and tree pruningTrenching and pruning applications were placed on mature Wichita pecan trees in Maricopa, Arizona in 1998. Yield and nut quality data from the test are presented. Unfortunately, the cool, favorable growing weather minimized quality degradation during the growing season and confounded the test. Data presented probably do not reflect the true benefits of the treatments.
Rejuvenation of mature pecan trees by pruningNeglected mature 'Wichita' pecan trees were rejuvenated using various pruning techniques in 1997. Trees were pruned using proven horticultural techniques which included dehorning (cutting main scaffolds to within 2 feet of trunk) and cutting main scaffolds by 50%. To date the treatments have resulted in an increase in yield when compared to trees that received no pruning. In 1999 the grower has developed an orchard management program conducive to maximum production.
Pecan variety study on the Safford Agricultural Center 1997-1998In 1986 a replicated study of eight varieties of pecans were 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. This paper contains yield, kernel percentages and other nut characteristics found in the study during the 1997 and 1998 harvest seasons. Cheyenne and WO-3 were the highest yielding varieties in 1997 and 1998, respectively. The respective yields were 1894 and 2286 pounds per acre.
Effects of fluid nitrogen fertigation and rate on microsprinkler irrigated grapefruitMicrosprinkler 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. A three-year field experiment was initiated in the spring of 1996 on six-year-old pink grapefruit trees at the University of Arizona Citrus Agricultural Center. The objectives of this experiment are to i) evaluate the effects of fertigation frequency and fluid N application rate on the yield and fruit quality of microsprinkler irrigated grapefruit, and ii) develop best management guidelines for fluid N application frequency and rate for microsprinkler irrigated citrus. Treatments include a factorial combination of two N rates (recommended and 2 the recommended rate) and three fertigation frequencies (weekly, monthly, and tri-monthly). Minimal treatment effects were observed during the first season due to the influence of previous management practices. During the second season, fertilized trees yielded greater than the control trees. There was no significant difference between N rates, but fruit yield was generally higher with monthly or weekly fertigation. Leaf tissue samples collected during the second and third growing seasons showed increasing leaf N with increasing fertigation frequency at the high N rate.
Performance of mature pecan varieties in the low desert 1997 and 1998Mature pecan trees at Picacho, Arizona were evaluated for variety performance during 1997-98. Total average yield per tree, percent kernel and percent viviparity were observed. During 1997, a severe viviparity year, only Bradley, Cheyenne, Souix and Tejas showed viviparity values of 20% or lower. Tejas did not return an acceptable percent kernel leaving Bradley, Cheyenne and Souix as potential varieties able to withstand low desert growing conditions on a regular basis. In 1998, the cool growing season confounded the test and no conclusions were drawn from the data.
Results of scion and rootstock trials for citrus in Arizona - 1998Five rootstocks, 'Carrizo' citrange, Citrus macrophylla, Rough lemon, Swingle citrumelo and Citrus volkameriana were selected for evaluation using 'Limoneira 8A Lisbon' as the scion. 1998-99 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 beginning to outperform C. volkameriana. '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' selection is superior, and that ‘Corona Foothills Lisbon’ may also be superior to the other selections in both growth and yield. 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 are presented as well.
Applying roundup to the base of lemon tree canopies: effects on leaves, flowers, fruitlets, and yieldThe effect of Roundup on lemon trees (Citrus limon) was evaluated by repeatedly spraying 0.5, 0.75, 1, 1.25, and 1.5 lb. a.i./acre (corresponding to 0.5, 0.75, 1, 1.25, 1.5 quarts of Roundup Ultra/acre) on the bottom 20 to 24 inches of the tree canopies, over a three year period. The Roundup applications caused significant leaf injury in the sprayed area of the canopies and there was also significant defoliation of branches at the higher Roundup rates in all three years of the study. In 1996 after three Roundup applications, increasing rates of Roundup had no effect on flower or fruitlet production in either the sprayed or unsprayed portions of the tree canopies as judged by the counts collected from branches in each canopy zone. Similarly, in 1997 after five Roundup applications, and in 1998 after nine Roundup applications, increasing rates of Roundup had no effect on flower or fruitlet production in the sprayed or unsprayed portions of the tree canopies. Spraying Roundup on the bottom of the tree canopies did not reduce total lemon yield per tree in 1996, 1997 or 1998 at any of the application rates. In all three years of the study, increasing Roundup rates had no effect on the yield of the first or second ring picks or the percentage of the total crop picked on the first harvest date. Increasing Roundup rates also did not affect fruit size at any harvest date in 1996, 1997 or 1998. Similarly, increasing Roundup application rates did not affect fruit quality at any harvest in 1996, 1997 or 1998. Thus, there was no relationship between the rate of Roundup sprayed on the trees and yield, fruit size or quality in all three years of this study. The three years of data collected in this study indicate that accidental drift or inadvertent application of Roundup onto lemon trees when spraying weeds on the orchard floor has no significant effect on lemon tree productivity.
Evaluation and management of a "salina" strawberry clover cover crop in citrus: first year preliminary resultsTwo orchard floor management strategies were evaluated beginning in the fall of 1997 in a 'Valencia' orange (Citrus sinensis) grove at the University of Arizona Citrus Agricultural Center (CAC) in Waddell, Arizona. The clean culture or bare ground treatment produced more yield than the ‘Salina’ strawberry clover treatment when harvested on March 10, 1999 and the tree canopy volume of the clean culture treatment was also greater than that of the clover treatment. Yield efficiency (lbs of fruit per cubic meter of canopy) was similar in the two treatments. The clean culture treatment produced more large size fruit (size 88 and larger) and less small size fruit (size 113 and smaller) than the strawberry clover treatment. Although the yield efficiency parameter suggests that it may be possible to produce as much fruit in the clover treatment as the clean culture treatment, the total yield and fruit size distribution of the clover treatment compared to the clean culture treatment were characteristic of the negative effects of competition from vegetation on the orchard floor found in other studies. Based on previous studies, competition for water was the most likely cause of the negative competitive effect. Installation of additional tensiometers to measure soil moisture at greater depths and leaf water potential measurements to assess the degree of water stress in both treatments prior to irrigation will hopefully allow further improvement in irrigation scheduling to eliminate the negative affect of having vegetation on the orchard floor in the clover plots.
Evaluation of thinning agents for "kinnow" mandarinsAn experiment was designed to determine the effectiveness of foliar prebloom boron (B) sprays for thinning 'Kinnow' mandarins (Citrus reticulata). Treatments consisted of a control and foliar B applied at 1000, 1500, 2000, 2500 and 3000 ppm. Leaf tissue B levels were not significant between treatments. Likewise, fruit quality was similar for all treatments. Fruit weight and number were significantly greater for the control compared to the 1500, 2000, 2500 and 3000 ppm B treatments for the undersize fruit. There was a clear reduction in yield as the rate of B applied increased, however, the reduction was not statistically significant.
Effect of foliar boron sprays on yield and fruit quality of navel orangesA 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. There were no significant difference in fruit quality or yield.
Impact of preplant soil treatments on survival of Phythophthora in citrus soilsSeveral different approaches are used with respect to land preparation prior to replanting citrus in Arizona. A study was initiated to examine the effect of cultural preplant practices on the survival of Phytophthora in citrus orchard soils. In June, 1998, a 2-gallon volume of soil was collected from eight different sites within a mature lemon planting on a sandy soil in Yuma or a lemon planting on a heavier soil in Mesa, AZ. Each initial sample was pre-tested, found to contain Phytophthora parasitica, then thoroughly mixed and distributed into six 1-qt plastic containers, which were subjected to different environmental and cultural conditions. The soil in each container was tested for the presence of P. parasitica 1, 4 and 9 months after initiation of the study. The preliminary results of this ongoing study are as follows. Detection of P. parasitica was lower in non-irrigated as compared to irrigated soil. P. parasitica was not detected in non-irrigated soil subjected to a mean temperature of 38°C (100° F) for 3 months. During the 9-month period of time, detection of P. parasitica in soil planted to alfalfa was not reduced compared to soil planted to citrus. Of the treatments examined, dry summer fallow may be the most effective method of reducing the population of P. parasitica to below detectable levels; however, these preliminary findings must be validated by additional planned tests.
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. In April, Dimethoate and Agri-Mek provided only knockdown control of thrips, dropping to <70% mortality by 3 days after treatment (DAT). Baythroid performed slightly better, providing 95% mortality 3 DAT, but by 7 DAT was giving about 74% mortality. Alert, Carzol, Success and AZEXP-2 provided the longest residual activity, lasting 7 days, but began to slip at 14 DAT. AZEXP-1 induced only 74% 0 DAT. Although, residual activity in general was greater in June than April, however this increase in residual activity did not necessarily increase the length of commercially acceptable residual. Agri-Mek and Dimethoate still only provided knockdown activity, and Baythroid was still giving 3 days of good activity. AZEXP-1 performed much better following the June application relative to the April application, providing 3 days of adequate activity. Although we are not certain the reason for this result, it maybe due to the adsorption properties of this chemical relative to leaf physiology. Alert performed similarly in June and April, and Carzol, Success and AZEXP-2 each lasted about 1 week longer.
Growth of Citrus volkameriana inoculated with AM fungi in moist or periodically dry soils‘Volkamer’ lemon (Citrus volkameriana Tan. and Pasq.) seedlings were inoculated with either of five communities of arbuscular mycorrhizal (AM) fungi collected from either citrus orchards in Mesa and Yuma, Arizona or from undisturbed Sonoran or Chihuahuan desert soils. Plants were then grown for four months under low or high irrigation frequency treatments such that soil water tension reached about -0.01 MPa (moist) or -0.06 MPa (periodically dry), respectively. Plants grown in moist substrate had greater shoot mass than plants grown in periodically dry substrate. Plants inoculated with AM fungi from the Yuma orchard soil had significantly less shoot and root mass, higher specific soil respiration rates, and lower photosynthesis rates than plants treated with inoculum from other soils. Plant phosphorus nutrition did not limit growth. These data show that growth of ‘Volkamer’ lemon seedlings can be substantially affected by arbuscular mycorrhizal fungal communities in moist or periodically dry soils.
Efficacy of Insecticides to Citrus Thrips on Lemons in Yuma Arizona 1998Two small plot efficacy trials were conducted evaluating different insecticide rotation regimes using commercially available insecticides and the effectiveness of new insecticide chemistries to control citrus thrips. Under the consistently cool conditions experienced during the first four weeks of the trial, Dimethoate, Success, Baythroid, Agri-Mek, Vydate and Carzol all of the offered adequate control and would fit well in the petal fall window. This is in contrast with previous years experiences when high temperatures within a week of petal fall would result in all treatments except Carzol requiring a re-treatment within ten days. All of the rotation schemes evaluated required three insecticide applications to get through the season, and did not appear to be greatly different in controlling thrips and producing high quality fruit under the environmental conditions experienced. However, the Dimethoate - Success - Baythroid rotation scheme was most cost effective. When temperatures were in the 70's to low 80's, Dimethoate and Vydate offered about three weeks control, Success, Carzol, Baythroid and Agri-Mek all offered about four weeks control. When temperatures were in the mid to upper 80's and low to mid 90's, Success provided about three weeks control while Carzol didn t require re-treatment for 4 weeks. Under these same temperature conditions, Dimethoate and Vydate gave about 7 to 12 days control, and Agri-Mek provided 12 to 14 days of control. Other than the one control failure with Baythroid, under warmer conditions, it provided about seven days control. In the experimentals test, AZEXP1 appeared to offer knockdown activity at temperatures less than 90 F, and only suppression at higher temperatures. AZEXP2, appeared to be a viable citrus thrips material, with activity similar to Success and Carzol. The knockdown activity of M96 appeared to be enhanced by including Dimethoate or Carzol, but will require multiple applications to achieve the level of repellency experienced in 1997.