A physiological characterization has established that vascular changes in Macrophylla decline affected trees are not similar in character to xyloporosis affected trees. In addition, a survey of Macrophylla decline affected citrus did not establish any genetic similarity between Macrophylla decline and xyloporosis. We report diagnosis of either CCV or CEV by reverse transcription-polymerase chain reaction (RT-PCR), as well as diagnosis of Macrophylla decline or xyloporosis by Zn-distribution, water conductivity, accumulation of decline- specific proteins and examination of phloem morphology in lemon trees on the Macrophylla rootstock.

Deficiency of boron (B) in citrus has serious consequences for tree health and crop production. There is evidence that B deficiency may be a problem in Arizona citrus. Certainly, many symptoms of B deficiency are apparent, especially on the Yuma Mesa. A field trial was conducted at Yuma, Arizona to examine the effect of foliar boron application on fruit yield and quality of Citrus sinensis and C. limon. Boron was applied to 5 year old Citrus sinensis cv. Hamlin and C. limon cv. Rosenberger Lisbon trees at 5 different concentrations (0 ppm, 500 ppm, 1000 ppm, 2000 ppm, 3000 ppm) either before flowering or after flowering. At harvest, fruit yield and quality, and boron concentrations were determined. Foliar application appeared to increase leaf boron concentration (r= 0.50, p= 0.004). Fruit set was increased in Hamlin trees receiving bloom and post bloom applications of boron at the 1000 ppm level. Boron applications had no significant effect on lemon yield in these studies. This fruit set increase in Hamlin accounted for a 35% increase in overall yield relative to control trees. However, there was no significant difference in fruit weight, fruit pH, titratable acidity, peel thickness, juice volume, or soluble solid content of the fruits among treatments. Previous studies indicate that boron influenced in vivo and in vitro pollen germination in many crops. A plausible explanation for increased fruit yield may be that the applied boron was transported to the flowers where it exerted its influence of increased fruit set through an effect on pollen viability and/or pollen tube growth. However, clearly boron supplementation must be performed judiciously to avoid fruit drop from over -application of the element.

The potato leafhopper, Empoasca fabae L., is a significant pest in the United States, and elsewhere, of alfalfa and potatoes In Arizona and in Coastal and Central California it can also be a pest of citrus. In 1994 and 1995 we collected information concerning their seasonal abundance in a large citrus orchard near Newman Peak Arizona. To do so we employed yellow sticky traps around the orchard periphery, at the same time using a D-Vac® vacuum sampler in the weeds growing in the interior of the orchard During both years peak populations occurred near mid April. This was correlated with a drop in relative humidity and a rise in ambient air temperature.

Experiments were initiated to evaluate chemical disease management tools for Alternaria fruit rot on navel orange and Coniophora brown wood rot on lemon trees, examine the possible effect of branch diameter on development of Coniophora wood rot on lemon trees and continue evaluations of relative resistance of rootstocks to root rot and stem canker development when inoculated with P. citrophthora and P. parasitica. Rovral or Kocide did not significantly reduce the amount of Alternaria fruit rot on navel orange trees occurring in late summer and early autumn when applied during the preceding winter or spring months. Of several chemical treatments tested, only Nectec paste inhibited the development of Coniophora brown wood rot on inoculated lemon branches. The size of wood decay columns on branches 10 mm (0.5 inch) in diameter were significantly smaller than those developing on branches 50-70 mm (2.0-2.75 inches) in diameter. In extensive trials evaluating root rot caused by Phytophthora citrophthora and P. parasitica, some relatively tolerant rootstocks were found among the group of new potential rootstocks as well as currently used rootstocks such as rough lemon, C. macrophylla and Troyer citrange. C. volkameriana was relatively tolerant to the development of root rot by P. citrophthora but demonstrated variable tolerance to P. parasitica. Comprehensive evaluation of stem canker development on citrus rootstocks inoculated with P. citrophthora or P. parasitica revealed that rough lemon is usually highly susceptible to both pathogens, while C. volkameriana was at times less susceptible (more tolerant) than rough lemon to both pathogens. Some of the new potential rootstocks were highly tolerant or resistant to infection of stem tissue by P. citrophthora or P. parasitica.

Seasonal flight of beet leafhopper vectors of stubborn disease was monitored at wholesale nurseries in Yuma County, and at young citrus groves in Maricopa County using yellow sticky traps exposed at successive two-week intervals. Trapped leafhoppers were removed and assayed for presence of the citrus stubborn agent by PCR. Leafhoppers were collected live from weed plants in groves and nurseries using an insect vacuum and both leafhoppers and tissue from weed plants were assayed by PCR for the stubborn agent. Selected trees in groves in Yuma and Maricopa Counties were visually inspected for stubborn symptoms.

Four arbuscular mycorrhizal (AM) fungal isolates (Glomus sp.) from disparate edaphic conditions were screened for effects on whole -plant transpiration of juvenile 'Volkamer' lemon (Citrus volkameriana Ten. and Pasq.) plants of similar shoot mass and canopy leaf area. Mycorrhizal and non -mycorrhizal plants were grown in 8 -liter containers for 2.5 months under well- watered conditions before subjection to three consecutive soil drying episodes of increased severity (soil moisture tensions of -0.02 [still moist], -0.06 [moderately dry], and -0.08[dry] MPa respectively). Whole plant transpiration measurements were made on the last day of each soil drying episode and measurements were repeated on the first and second days after re- watering, when soil profiles were moist. The percent root length colonized by AM fungi differed among isolates. Three AM fungal isolates, Glomus sp. 25A, Glomus mosseae (Nicol. & Gerde.) Gerde. & Trappe 114C, and Glomus intraradices Schenck & Smith FL 208-3 increased root length and subsequently increased lemon plant water use. Conversely, plants inoculated with Glomus mosseae 51C did not enhance lemon plant root length nor improve plant water use compared with nonmycorrhizal control plants. Inoculating citrus with AM fungi that promote root extension may reduce plant water deficit stress under field conditions.

Citrus thrips populations (adults and nymphs) were monitored through the spring of 1991-1992 in several locations throughout most of the commercial citrus production areas in Yuma County to determine if citrus thrips seasonality was similar to that previously reported in California. Study findings indicate that seasonality is similar throughout the winter and very early spring. Adult thrips numbers increase rapidly in groves due to attractive foliage, whether it is weeds or citrus. High nymph numbers did not always follow adult peaks, and were not statistically correlated. Predatory mites and rains may have affected 1992 results.

Citrus peel miner populations were monitored to evaluate various methods of trapping citrus peel miners. Observing 25 fruit per tree and 10 trees per block on the lower three feet of the tree canopy provided the best technique for determining the level of citrus peel miner infestations. The use of oleander plants, clear plates and green 3 inch diameter balls sprayed with Tangle-Trap were not effective in trapping citrus peel miner. In 1996, the first of September citrus leaf miner populations rose above the 10% infestation level. Success, Lorsban, Alert and Agri-Mek provided the highest mortality levels of citrus peel miner larvae. In citrus fruit, Success, Lorsban and Alert had the greatest efficacy of citrus peel miner larvae.

Bibliography: leaves 204-211. / v, 211 leaves : ill. (chiefly col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This study investigates the effects of a number of petroleum and vegetable oils against citrus pests. / Thesis (Ph.D.)--University of Adelaide, Dept. of Applied and Molecular Ecology, 2000

Two 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.