‘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.

Quality, leaf gas exchange and mineral content of fruit from internal be canopies were compared with those from extemal canopy positions in 4 citrus varieties: 'Kinnow' mandarin; 'Redblush' grapefruit; 'Valencia' orange; and 'Lisbon' lemon. Fruit weight, total juice per fruit, peel fresh and dry weight, and rind thickness of fruit from internal canopies of all 4 varieties were significantly higher compared with external fruit Mandarin, grapefruit, and orange fruit from external canopies had higher soluble solids and specific gravity. Leaves from internal canopy had higher photosynthesis than those of external canopy in all varieties. Fruit from internal canopies of all varieties had generally higher peel concentrations (%dry weight) of N, P and K due to a dilution effect, while the opposite condition existed in mandarin when these elements were expressed on a percent fresh weight basis. Peel Mg and S from external fruit were higher in all varieties, expressed as percentages of either dry weight or fresh weight. Nitrogen content of mandarin and orange juice and calcium content of grapefruit and lemon juice from external fruit were significantly higher, compared to those from internal canopy fruit. Eliminating fruit quality and mineral variations resulting from canopy positions is recommended by the means of cultural practices.

Research has shown that the presence of ice-nucleation-active (INA) bacteria, such as Pseudomonas syringae and Erwinia herbicola, will result in ice formation several degrees centigrade higher than would otherwise occur. Seven possible chemical frost protectants were applied to Lisbon lemons of the Yuma Mesa Ag Center. Four replications of effectiveness of the materials were evaluated by determining tip bum and fruit damage following two subfreezing episodes in December 1987. There were no statistically significant differences between treatments under the conditions of this study.

The effects of the navel orange prorate suspension on packinghouse to retail price spreads are analyzed When compared with price spreads for the 1986 season, F.o.b.-retail price spreads declined for Atlanta and San Francisco, but increased for Dallas.

New methods of determining the content of virus and virus-like disorders in citrus trees are heralding a new era of the Arizona Cooperative Citrus Registration-Certification Program (ACCRCP). It has been 25 years since the first budwood was released to participating nurseries. During that time, the program has relied on indexing using various indicator plants. Last year, indexing was begun in the laboratory using the ELISA unit for tristeza tests. Efforts are now being made to obtain antiserum for stubborn disease which currently has no reliable indexing method using indicator plants.

Five chemical frost protectants and a water treatment were applied to Lisbon lemons by dipping branches to insure complete coverage. A constant temperature bath was used to determine the effect of chemical frost protectants on the freezing temperature for leaf samples placed in test tubes with 10 ml of distilled water. Although the relative temperature at which the different treatments froze remained fairly constant, the differences were not significant.

Three chemical frost protectants were applied to Lisbon lemons using a hand gun operated from a John Bean sprayer. Leaf samples were placed in test tubes with 10 ml of distilled water to determine the temperature at which they froze using a constant temperature bath. Although the sample size was increased by 50 percent over the previous year, the treatments were not significantly different from the untreated.

No description available.

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.