Several orchard floor management strategies were evaluated beginning in the fall of 1993 in experiments on the Yuma Mesa in a Limoneira 8A Lisbon lemon grove and in a Valencia orange grove at the University of Arizona Citrus Agricultural Center (CAC) in Waddell, Arizona. On the Yuma Mesa, disking provided satisfactory weed control except underneath the tree canopies where bermudagrass, purple nutsedge, and other weed species survived. Mowing the orchard floor suppressed broadleaf weed species allowing the spread of grasses, primarily bermudagrass. Preemergence (Solicam and Surflan) and postemergence (Roundup and Torpedo) herbicides were used to control weeds in the clean culture treatment in Yuma. After two harvest seasons (1994-95 and 1995-96), the clean culture treatment resulted in greater yield than the other treatments. At the CAC, clean culture (in this location no preemergence herbicides were used), mowed resident weeds, and Salina strawberry clover orchard floor management schemes were compared. Again the clean culture treatment yielded more than the mowed resident weeds. The yield of the strawberry clover treatment was somewhat less than the clean culture yield but not significantly less. The presence of cover crops or weeds on the orchard floor were found to modulate tree canopy temperatures, and to have beneficial effects on soil nitrogen and soil organic matter content, but no effect on citrus leaf nutrient content. The decrease in yield in the mowed resident weed treatments compared to the clean culture treatment in both locations was attributed to competition for water.

Several orchard floor management strategies were evaluated beginning in the fall of 1993 in experiments on the Yuma Mesa in a 'Limoneira 8A Lisbon' lemon grove and in a 'Valencia' orange grove at the University of Arizona Citrus Agricultural Center (CAC) in Waddell, Arizona. On the Yuma Mesa, disking provided satisfactory weed control except underneath the tree canopies where bermudagrass, purple nutsedge, and other weed species survived. Mowing the orchard floor suppressed broadleaf weed species allowing the spread of grasses, primarily bermudagrass. Pre-emergence (Solicam and Surffan) and post-emergence (Roundup and Torpedo) herbicides were used to control weeds in the clean culture treatment in Yuma. After three harvest seasons (1994-95 through 1996-97), the clean culture treatment resulted in greater yield than the other treatments. At the CAC, clean culture (in this location no pre -emergence herbicides were used,) mowed resident weeds, and Salina strawberry clover orchard floor management schemes were compared. Again the clean culture treatment yielded more than the mowed resident weeds. The yield of the strawberry clover treatment was somewhat less than the clean culture yield but not significantly less. The presence of cover crops or weeds on the orchard floor were found to have beneficial effects on soil nitrogen and soil organic matter content, but no effect on citrus leaf nutrient content. The decrease in yield in the mowed resident weed treatments compared to the clean culture treatment in both locations was attributed to competition for water.

No description available.

A lemon rootstock trial and a lemon scion trial were established in 1993. After two years growth, C. volkameriana and C. macrophylla rootstocks have begun to show significant growth and yield increases, compared with 'Swingle' citrumelo and 'Carrizo' citrange. These two rootstocks also have led to larger fruit size, especially early in the season. Trees on Rough lemon rootstock had equivalent growth, but less yield. 'Limoneira 8A Lisbon' scion cultivar had the greatest yield and largest early season fruit size, compared to 'Frost Nucellar', 'Corona Foothills' and `Prior Lisbon' lemons.

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.

Five rootstocks, 'Carrizo' citrange, Citrus macrophylla, Rough lemon, Swingle citrumelo and Citrus volkameriana were selected for evaluation using 'Limoneira 8A Lisbon' as the scion. Early results indicate that trees on C. volkameriana and C. macrophylla are superior to those on other rootstocks in both growth and yield. 'Swingle' and Carrizo' are performing poorly. In a similar trial, Four 'Lisbon' lemon selections, 'Frost Nucellar', 'Corona Foothills', 'Limoneira 8A' and 'Prior' from the University of Arizona Citrus Budwood Certification plot were selected for evaluation on Citrus volkameriana rootstock. Early results indicate that the 'Limoneira 8A Lisbon' selection is outperforming the other selections in both growth and yield. Preliminary results from another lemon cultivar trial and a navel orange cultivar trial are presented as well.

This report summarizes some of the information that I gained during a trip to the Mediterranean region during Spring 1997. The first two days of the trip were spent in Murcia, Spain, as a guest of Dr. Angel Garda Lidón. We discussed the Spanish lemon industry. After Murcia, I traveled to Valencia, Spain to take part in an International Society of Citrus Nurserymen pre-conference tour. The conference itself took place in Montpellier, France. Following the conference, I participated in a post-conference tour to Sicily.

Five 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.

An 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.

Five 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.