6 pp. / Low Desert Citrus Varieties; Irrigating Citrus Trees / Diagnosing Home Citrus Problems includes information on all the commonly encountered dooryard citrus problems encountered in Arizona. Problems/disorders are grouped into three catagories: problems with fruit, problems with leaves, and problems with stems, branches and entire tree. Symptoms, causes and control measures are given for each disorder.

The 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.

'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.

'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.

Dissertation submitted to the Faculty of Science in fulfilment of the requirements for the degree Master of Science. Johannesburg, April 2013 / Phenology refers to “the study of the timing of recurrent biological events, the causes of their timing with regard to biotic and abiotic forces, and the interrelationship among phases of the same or different species” (Badeck et al., 2004: 295). This discipline has recently gained popularity in bio-geographical climate change studies, as it is recognized as an accurate and easily measured signature of the impact that changing temperature and precipitation over recent decades have had on plants. A five-decadal dataset (1960-2010) comprising daily temperature and rainfall records, and of the annual timing of peak flowering of five citrus types (orange, tangerine, sweet lemon, sour lemon and sour orange) was acquired for the Iranian cities of Gorgan, Kerman and Shiraz. The cities are geographically and climatically distinct, with arid Kerman located on the central Iranian plateau, humid Gorgan on the Caspian lowlands and Shiraz situated at the foot of the Zagros Mountains with a semi-arid climate. These climate data for Kerman and Shiraz reveal strong, statistically significant increases in Tmax of 0.03°C/yr, and even stronger increases in Tmin of 0.05°C/yr-0.07°C/yr, whilst Gorgan presents a statistically significant decrease in precipitation of 4.69mm/yr over the study period. Significant increases in daily sunshine hours of 7.09h/yr and 19.01h/yr are demonstrated for Gorgan and Kerman respectively. Negligible delays in the timing of peak flowering for the five citrus types in Gorgan by 0.05-0.01d/yr, and more considerable advances in the timing of flowering for Kerman (0.12-0.17d/yr) and Shiraz (0.56-0.62d/yr), occur concurrently with these climate trends. These differences in the direction of shift in flowering dates, combined with differences in climate trends, highlight the extent to which the location of the crops, and the associated abiotic forces, influence flowering dates. Significant relationships between the flowering dates of the citrus types and Tmax are demonstrated for Kerman and Shiraz, equating to advances of 1.85-3.08d/°C and 6.14-7.86d/°C respectively, with similar advances in flowering dates associated with increases in Tmin. Significant relationships between the timing of peak flowering and precipitation are demonstrated for Kerman. Across the majority of the climate variables studied, the strongest monthly relationships with flowering dates were for the month in which peak flowering occurs, suggesting a direct effect on control over this phenophase. The development of multiple regression models facilitated the simultaneous analysis of the effects of all of the climate variables, and increased the associated explanatory potential. The rate of change in peak flowering dates observed for the period 1960-2010, and the relative influence of some climate variables over others, highlight the importance of monitoring fruit tree phenology in a water scarce region such as Iran. With decreases in precipitation, increases in Tmin and Tmax and the potential for heightened frost risk by the end of the century due to the increased likelihood of late-winter flowering, citrus cultivation in Kerman is under threat. Shiraz is likely to survive continued climate variability and change throughout the 21st century, provided that sufficient water is available either naturally or through irrigation. Gorgan demonstrates the greatest capacity to continue successful citrus farming, and the greater Caspian Lowlands hold potential as a suitable location for the expansion of citrus farming required to compensate for any yields lost in the more arid areas of Iran and the Middle East.

Includes bibliographical references

Lemon oil quality is affected by numerous factors including lemon variety, climate, soil type, extraction method, etc.. Therefore, quality largely depends upon the lemons' origin, and aroma profiles of oils obtained throughout the world have potential to vary considerably. This research was conducted to identify differences in the aroma profiles of lemon oil samples from a variety of sources (Argentina, Brazil, California coast, California desert, Spain, South Africa). Two sensory methods commonly used to identify such differences are descriptive analysis and gas chromatography/olfactometry (GCO). A trained sensory panel identified significant differences (p<0.05) in the aroma profiles of the nine tested lemon oils in terms of overall intensity, peel, lime, orange, and sweet aromas. While descriptive analysis is useful in identifying perceived product differences, it does not provide information regarding the chemical components responsible for product differences. GCO is an effective method for identifying a flavor system's important odorants and their odor quality, but there are numerous methods by which it may be performed. Two different GCO methods, Osme and aroma extract dilution analysis with flavor dilution (FD) factors, were used to analyze cold-pressed lemon oil, and results obtained from each method were compared. Conclusions drawn from each method regarding the most critical odorants were slightly different, and better agreement among subjects was found to be present with Osme. Upon concluding that Osme provides a less variable method of identifying critical odorants, the relationship between Osme and descriptive analysis data was examined to determine if samples were characterized similarly by both sensory methods. Considerable agreement between methods was evident. In addition, neral, geranial, limonene, linalool, and gamma-terpinene were identified as important base contributors to lemon oil aroma. / Graduation date: 1998

Several 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.

Four 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.

Agri-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.