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Glenn C. Wright

The date palm (Phoenix dactylifera L.) originated in the Arabian Peninsula, spread throughout North Africa, then was carried to Mexico and the United States. Planting began in earnest in Arizona and California in the late 1800s and continues today. As of 2014, date production in Mexico and the United States is valued at almost $13,000,000, and comprises about 7400 ha. ‘Deglet Noor’ and ‘Medjool’ are the major cultivars. Modern practices for date palm cultivation include planting, irrigation, fertilization, pollination, thinning the fruit, ringing the bunches, bagging the bunches, and harvest. After harvest, the fruit must be sorted, dried or rehydrated, and graded. Date palms are sometimes sold for landscaping purposes. Current research at the University of Arizona and University of California at Riverside is focused on pollination and thinning practices, improving fruit quality and controlling insects. There are four date palm germplasm collections located in Arizona and California.

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Glenn C. Wright

Five rootstocks, `Carrizo' citrange, Citrus macrophylla, Rough lemon, `Swingle' citrumelo, and Citrus volkameriana, were selected for evaluation using `Limoneira 8A Lisbon' as the scion. Four years of yield and fruit packout data indicate that trees on C. volkameriana and C. macrophylla are superior to those on other rootstocks in growth and yield. `Swingle' and `Carrizo' are performing poorly, and Rough lemon is intermediate. In a similar trial, four `Lisbon' lemon selections, `Frost Nucellar', `Corona Foothills', `Limoneira 8A', and `Prior' selections of Lisbon lemon were selected for evaluation on Citrus volkameriana rootstock. Four years of yield and packout data indicate that the `Limoneira 8A Lisbon' selection has generally outperformed the other selections in both growth and yield, although `Corona Foothills' has been superior in the 1998-99 harvest season.

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Glenn C. Wright

Two lemon [Citrus limon (L.) Burm.] cultivar selection trials are being conducted at the Yuma Mesa Agriculture Center in Somerton, Ariz. Some selections in these trials include: `Allen Eureka', `Berna', `Cook Eureka', `Cascade Eureka', `Cavers Lisbon', `Strong Lisbon', `Femminello Comune', `Lapithkiotiki', `Limoneira 8A Lisbon', `Limonero Fino 49', `Monroe Lisbon', `Primofiori', `Santa Teresa', `Walker Lisbon', and `Villafranca'. Selections that have had superior yields include `Cascade Eureka', `Cook Eureka', `Strong Lisbon', `Limoneira 8A Lisbon', `Limonero Fino 49', `Primofiori', `Femminello Comune', and `Villafranca'. Fruit size data suggest that `Limonero Fino 49' has consistently good fruit size, and consistently larger fruit than `Limoneira 8A', the industry standard. `Cavers Lisbon' and `Femminello Comune' also have good fruit size. `Lapithkiotiki' also had large fruit size, but its shape was unacceptably elongated. We also found significant differences in peel thickness and juice pH among the selections. `Santa Teresa' had significantly lower juice pH and a thinner peel than some of the other selections under evaluation.

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Glenn C. Wright and Stephen E. Poe

Arizona Farm Safety Day has been held annually since 2000 as an attempt to educate students and farm workers (pesticide applicators, tractor and equipment operators, irrigators, and field workers) in farm safety. Our programs have emphasized tractor safety, pesticide safety, ATV safety, electrical safety, and firearms safety. The all-day events have been held in Yuma and in Safford, Ariz., and most of the attendees are high school students. Agriculture students from six to eight high schools typically participate. The agenda is determined by consulting with local agriculture leaders. Attendees have the opportunity to attend a 4-hour training session in the morning. Subjects taught at these sessions might include reading a pesticide label, sprayer calibration, wearing proper protection, avoiding spray drift, tractor safety, and farm safety. At least one of these sessions is an outdoors “hands-on” session. Individual participants receive up-to-date information and literature, a certificate of completion, CEUs, CCA credits, a hat, and a lunch. Spanish translation is available at each session. In the afternoon, a tractor driver safety course and equipment demonstration is typically held. In the course, selected representatives from local farms or local youth get a chance to demonstrate their tractor and ATV driving and safety skills for recognition and awards. Plaques and trophies are awarded to the winners. Additionally, there is an equipment demonstration. Attendees are tested before and after the event.

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Glenn C. Wright, William B. McCloskey and Kathryn C. Taylor

Several orchard floor management strategies were evaluated beginning in Fall 1993 in a `Limoneira 8A Lisbon' lemon (Citrus limon) grove on the Yuma Mesa in Yuma, Ariz. and in a `Valencia' orange (Citrus sinensis) grove at the University of Arizona Citrus Agricultural Center, Waddell, Ariz. At Yuma, disking provided acceptable weed control except underneath the tree canopies where bermudagrass (Cynodon dactylon), purple nutsedge (Cyperus rotundus), and other weed species survived. Mowing the orchard floor suppressed broadleaf weed species allowing the spread of grasses, primarily bermudagrass. Preemergence (norflurazon and oryzalin) and postemergence (glyphosate and sethoxydim) herbicides were used to control weeds in the clean culture treatment in Yuma. After three harvest seasons (1994-95 through 1996-97), the cumulative yield of the clean culture treatment was 385 kg (848.8 lb) per tree, which was significantly greater than the 332 kg (731.9 lb) and 320 kg (705.5 lb) per tree harvested in the disking and mowing treatments, respectively. In addition, the clean culture treatment had a significantly greater percentage of fruit in the 115 and larger size category at the first harvest of the 1995-96 season than either the disk or mow treatments. At Waddell, the management strategies compared were clean culture (at this location only postemergence herbicides were used), mowing of resident weeds with a vegetation-free strip in the tree row, and a `Salina' strawberry clover (Trifolium fragiferum) cover crop with a vegetation-free strip. The cumulative 3-year yield (1994-95 through 1996-97) of the clean culture treatment was 131 kg (288.8 lb) per tree, which was significantly greater then the 110 kg (242.5 lb) per tree yield of the mowed resident weed treatment. The yield of the strawberry clover treatment, 115 kg (253.5 lb) of oranges per tree, was not significantly different from the other two treatments. The presence of cover crops or weeds on the orchard floor was found to have beneficial effects on soil nitrogen and soil organic matter content, but no effect on orange leaf nutrient content. The decrease in yield in the disked or mowed resident weed treatments compared to the clean culture treatment in both locations was attributed to competition for water.

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Mohammad R. Karim, Glenn C. Wright and Kathryn C. Taylor

A field trial conducted at Yuma, Ariz., examined the effect of foliar boron application on fruit yield and quality of Citrus sinensis cv. Hamlin. Boron was applied to 5-year-old trees at five treatment levels (0, 500, 1000, 2000, and 3000 ppm) before or after flowering in a split plot design. At harvest, fruit number, size and quality were determined. Yield (P = 0.01) and average fruit number per tree (P = 0.02) were different among treatments. The highest yield was obtained with the 500 ppm treatment. In this first year of the trial there was no difference in average fruit weight, fruit pH, titratable acidity, peel thickness, juice volume, or soluble solid content of fruit between the treatments. Previous studies indicate that boron influenced in vivo and in vitro pollen germination in many crops. Increased fruit yield may have occurred because boron was transported to the flowers where it exerted its influence on increased fruit set through an effect on pollen viability or pollen tube growth. Further investigation of this hypothesis is underway.

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Glenn C. Wright, Kim D. Patten and Malcolm C. Drew

`Tifblue' and `Brightwell' rabbiteye blueberry (Vaccinium ashei Reade) and `Sharpblue' southern highbush blueberry (primarily V. corymbosum) were treated with 0, 25, and 100 mm Na+ as Na2SO4 or NaCl, and 0, 1, 3, and 10 mm supplemental Ca2+ in sand culture in the greenhouse. For rabbiteye plants salinized with Na2SO4, leaf Na+ concentrations increased 54-fold and the percentage of total plant Na+ found in the leaves increased from 9% to 63% with increasing external Na+. Calcium supplementation reduced the Na+ concentrations in leaves by up to 20%. Leaf Ca2+ concentrations increased with Ca2+ supplementation, but accounted for a decreasing percentage of the total Ca2+ found in the plant, since root Ca2+ concentrations were much higher. Root Na+ concentrations increased with increasing Na+ treatments to a smaller extent than in the leaves and were also reduced by Ca2+ supplements. Potassium concentrations in leaves and roots decreased with increasing Na+ treatment levels, particularly in roots, where K+ concentration was about half at 100 mm Na+ (as Na2SO4.) Leaf Na+ concentrations were up to two times greater when Na was supplied as NaCl compared to Na2SO4. For plants salinized with NaCl, leaf Na+ levels increased to 1.1% and did not decrease when supplemental Ca2+ was applied. Leaf Cl- concentrations also increased greatly with NaCl, reaching >1.0% (dry weight basis.). Root Cl- concentrations also increased with increasing salinity and were not affected by Ca2+ supplements. Ca2+ supplementation led only to a greater Ca2+ concentration in leaves and roots, but this did not alter Na+ concentrations. Nutrient concentrations in `Sharpblue' leaves, stems, and roots were greater than those of the rabbiteye cultivars, but were influenced by salinity and Ca2+ in essentially the same way. Excess Na+, Cl-, or both, together with lowered K+, were likely the cause of extensive leaf necrosis and may be indicative of a lack of a mechanism to control Na+ influx into blueberry leaves.

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Glenn C. Wright, Kim D. Patter and Malcolm C. Drew

`Tifblue' rabbiteye blueberry (Vaccinium ashei Reade) plants grown in complete nutrient solution were supplied with 25 mm NaCl and with either 0, 3, or 10 mm supplemental Ca2+ added as a mixture of the sulfate, nitrate, and chloride salts. Uptake and partitioning of 22Na+ into leaves, stems, and roots from labeled nutrient solutions and subsequent translocation in the absence of additional labeled Na+ (pulse-chase experiment) was determined. Plants were harvested at intervals following the uptake period. At 28 days, plants supplied with 10 mM Ca2+ accumulated 35% to 68% more 22Na+ in the 3rd-18th leaves from the apex and in herbaceous stems than plants not supplied with Ca2+. Leaf Na+ concentrations followed a similar trend. There was a preferential translocation of Na+ to the shoots compared to the other plant parts, which accounted for 30% of the total plant Na+ immediately following the uptake period and 15% at 28 days. Blueberry plants supplied with 3 mm Ca2+ did not have greater leaf or stem 2Na+ concentrations or total Na+ content than plants not supplied with Ca2+. The 2Na+ content did not decrease with 3 mM Ca2+ treatments. It is proposed that the failure of a high level (10 mm) of Ca2+ to protect against Na+ uptake and translocation to the herbaceous shoots is due to metabolic dysfunction. Abnormally high levels of Ca2+ in the cytoplasm may lead to an inability to sequester or exclude Na+.

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Glenn C. Wright, Kim D. Patten and Malcolm C. Drew

`Tifblue' rabbiteye blueberry (Vaccinium ashei Reade) and `Sharpblue' southern highbush blueberry (primarily V. corymbosum) were treated with 0, 25, or 100 Mm Na+ as Na2SO4 or NaC1, and 0, 1, 3, or 10 Mm supplemental Ca2+ in sand culture in the greenhouse. Greatest stomatal conductance (gs) and net assimilation (A) occurred in unsalinized `Tifblue' plants not given additional Ca2+. Stomatal conductance, A, transpiration (E), and xylem water potential(Ψ)of `Tifblue' and `Sharpblue' plants were all lowered as salinity increased, and these effects were more pronounced with NaCl than with Na2SO4. After 63 days, for plants given 100 Mm Na+ as NaCl, gs and net assimilation rate were reduced to only 10% of the unsalinized controls, while for plants salinized with 100 mm Na+ as Na2SO4, gs and A were 35% and 43%, respectively, of unsalinized controls. Leaf necrosis was more extensive on `Sharpblue' plants given NaCl than on `Tifblue' plants. Neither Ca2+ nor Na+ treatments led to severe chlorosis; reductions in leaf chlorophyll content were mainly due to necrosis. The Na+- induced reduction in gas exchange was associated with negative Ψw Ca2+ deficiency, or a combination of these factors. Additional factors leading to inhibition of gas exchange in NaCl- stressed plants include Cl- toxicity and leaf necrosis. Calcium supplements were unable to ameliorate NaCl damage in `Tifblue' or `Sharpblue' plants, possibly because of the inability of Ca2+ to counter Cl- entry and toxicity. In contrast, additional Ca2+ improved gs, A, Ψw, and leaf chlorophyll content of `Tifblue' plants that received Na2SO4. For plants treated with 25 mm Na+ as Na2SO4 and 1 mm Ca2+, gs was 1.5 to 2.5 times higher than in plants without added Ca2+. Low (1 mm) concentrations of Ca2+ were more effective in ameliorating the effects of 100 mm Na+ as Na2SO4. than were 3 or 10 mm Ca2+ supplements, possibly because higher Ca2+ concentrations damaged the metabolism of the calcifuge blueberry.