Carzol and Success with and without the addition of the feeding stimulants molasses and bee-collected pollen were evaluated for their control of citrus thrips on lemons on the Yuma Mesa. Although normal use rate of Carzol and Success were efficacious toward citrus thrips, the addition of either molasses or pollen to these insecticides as a means of increasing efficacy at low rates was not encouraging. At no point did the feeding stimulants appear to increase the efficacy of the same rate of Carzol when used alone, and it appeared that the additives may have actually decreased the efficacy of Success.

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.

Several differentially expressed markers of compatibility or incompatibility were isolated and are being molecularly characterized One marker is present in young Eureka on Macrophylla trees and on Macrophylla decline affected, Eureka on Macrophylla trees, while absent on healthy, Eureka on Macrophylla trees of the same combination. A second marker appears similar to a gene that encodes a Zn-binding homeodomain of a DNA binding protein in plant cells. This particular marker was found in the leaves of healthy trees, but absent in Macrophylla decline trees, which are known to be Zn deficient. Thirty-five markers are being characterized in all.

Lemons were left untreated or treated for mites with Danitol (fenpropathrin). Mite populations were estimated and yield and fruit damage was accessed. Yuma spider mite, Eotetranychus yumensis, was the predominate mite species present during the high fruit susceptibility period. Although there was no apparent impact of mites on yield in this study, there was significant fruit damage that could be attributed to Yuma spider mite. The damage appeared as bronzed colored pitting of the fruit peel. Based on damage ratings, the treated plots produced 56% fancy, 34% choice, and 10% fruit grade based on mite damage, whereas the untreated plots produced 47%, 31% and 22% fancy, choice and juice grade fruit respectively. Statistically, the treated plots produce more fancy and less juice fruit, but did not differ in choice fruit. Although the treated areas produced better quality fruit, the amount of damage suffered in those plots was higher than desired. Fruit in the treated plots likely suffered some mite damage before treatments were initiated. In addition to the fruit damage test, a miticide efficacy test targeting Yuma spider mite on lemon was conducted comparing Agri-Mek, Danitol, Kelthane, Microthiol, and Nexter to an untreated check. Agri-Mek, Nexter, and Microthiol offered 14 days of control; although at 6 DAT Agri-Mek and Nexter did not differ from the untreated. Danitol and Kelthane contained fewer mite that the untreated for at least 35 DAT.

Second year yield and packout data from a trial containing ‘Fina’, ‘Fina Sodea’, ‘Sidi Aissa’, ‘Oroval’, ‘W. Murcott Afourer’, ‘Fremont’, and ‘Gold Nugget; selections were collected in 2004-05. For the year, ‘Fina Sodea’ had the greatest yield, and average fruit size, while ‘Fremont’ had the smallest yield, and the smallest fruit size.

In a rootstock evaluation trial planted in 1993, five rootstocks, ‘Carrizo’ citrange, Citrus macrophylla, ‘Rough Lemon’, Swingle citrumelo and Citrus volkameriana were selected for evaluation using 'Limoneira 8A Lisbon' as the scion. 1994-2002 yield and packout results indicate that trees on C. macrophylla, C. volkameriana and ‘Rough Lemon’ are superior to those on other rootstocks in both growth and yield. C. macrophylla is outperforming C. volkameriana. For the second year in a row, ‘Rough Lemon’ trees performed similarly to C. macrophylla and better than C. volkameriana. ‘Swingle’ and Carrizo’ are performing poorly. In two other rootstock evaluation trials, both planted in 1995, C. macrophylla and/or C. volkameriana are outperforming other trifoliate and trifoliate-hybrid rootstocks under test.

Studies are being conducted which aim to improve the efficiency of irrigation and N fertilization for lemons produced on sandy soils in the low desert The first experiment evaluates the response of 'Lisbon' lemons to various flood irrigation intervals. Irrigation intervals are based on soil moisture depletion (SMD) as calculated from frequent neutron probe soil moisture measurements. Individual treatments were irrigated when total SMI) was 25 %, 40 %, 55 %, and 70 %, respectively. The second experiment compares the performance of young lemons produced under flood, trickle, and micro-spray irrigation systems. The third experiment evaluates the response of young lemons to water and N combinations (3 by 3 factorial) under micro - spray irrigation. The three irrigation rates were targeted for 30 cnbar, 20 cnbar, and 10 cnbar tension. The three N rates were 0.1, 0.2, and 0.4 kg N/tree. One flood irrigation treatment was added for comparative purposes. Overall, results obtained in experiment 1 during 1994, 1995, and 1996 indicate optimal fruit growth and yield is obtained at approximately 40% SMD. The results of experiment 2 show that after 3 years, only micro-jet irrigation produced less tree growth than flood irrigation. In 1995, first year fruit yields were significantly greater for pressurized irrigation compared to flood irrigation. However, by 1996 there were no differences in yield to irrigation treatment. Results from experiment 3 show a linear response in tree growth to irrigation. In 1994 and 1995, tree growth at the high micro - spray soil moisture regime was significantly greater than trees irrigated by flood. However, in 1996 where we failed to increase the micro-spay irrigation time to meet the increased water demand by the trees, the flood irrigation regime was superior. Yields were also increased to irrigation. There were no significant differences in tree growth to N fertilization rates in 1994 and 1995. However, there was increased tree growth in 1996 and a yield increase to N fertilizer rate at the highest soil moisture regime.

Three lemon cultivar selection trials are being conducted at the Yuma Mesa Agriculture Center in Somerton, AZ. Data from these trials suggest that ‘Limonero Fino 49’ selections may be a suitable alternative for the varieties most commonly planted in Southwest Arizona today. ‘Femminello’ and ‘Villafranca’ might also be planted on an experimental basis.

Four 'Lisbon' lemon selections, 'Frost Nucellar', 'Corona Foothills', 'Limoneira 8A' and 'Prior' were selected for evaluation on Citrus volkameriana rootstock. 2004-05 results indicate that the 'Limoneira 8A Lisbon' and ‘Corona Foothills Lisbon’

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.