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Craig E. Kallsen

The relationship between the number of commercially valuable sized fruit produced per unit land area vs. total number of fruit produced per unit land area for mature navel orange (Citrus sinensis) has not been documented. Knowing this relationship, referred to as the commercial fruit production function (CFPF) within this paper, may aid growers in making fruit thinning and tree pruning decisions and researchers in evaluating the interaction of fruit yield and size in response to fruit thinning, tree pruning, variety selection and tree spacing experimentation. For midseason navel oranges in the southern San Joaquin Valley of California, a reliable CFPF for total annual fruit production ranging from 14,000 to 130,000 fruit/acre was found to exist over multiple seasons in three orchards. The CFPF for two early maturing navel orange varieties was not significantly different with respect to slope or intercept from the CFPF for midseason varieties over the range of 12,000 to 63,000 fruit/acre, but became unreliable when fruit number exceeded 63,000 fruit/acre.

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Craig E. Kallsen

The objective of this experiment was to determine how yield, size, and quality of fruit would respond to mechanical topping and manual pruning of mature `Frost nucellar' navel orange (Citrus sinensis) trees. Mechanically topping trees at 4.3 m (14 ft) or 4.9 m (16 ft) produced annual fruit yields and quality similar to that of untopped trees. Over the 4 years of this experiment, trees that were not manually pruned produced as much or more of the most valuable fruit sizes than either the severe or moderate manual pruning treatments without the associated pruning costs. Manual pruning did not improve fruit grade compared to unpruned trees. A highly significant positive and linear relationship was found between numbers of commercially valuable fruit and the total number of fruit produced annually within the range of 50,000 to 325,000 fruit/ha (20,235 to 131,528 fruit/acre). Manual pruning, which reduced total fruit numbers, reduced the number of commercially valuable fruit predictively according to this relationship.

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Craig E. Kallsen

The potential of petroleum sprays to thin navel orange (Citrus sinensis) crops in the San Joaquin Valley of California was examined in 1996, 1997 and 1998. Petroleum oils had not been used within the experimental site as adjuvants in other sprays or as pesticides in the previous year or during the experiment. `Bonanza' navel oranges trees were treated annually or in alternate years with a light narrow-range petroleum oil [distillation midpoint of 415 °F (213 °C)], a medium narrow-range oil [distillation midpoint of 440 °F (227 °C)] and/or heavier oil [distillation midpoint 470 °F (247 °C)] in a range of applications from 5 to 15% by volume in a total spray volume of 200 gal/acre (1870 L·ha-1). Trees treated with oil in 1996, 1997 and 1998 had 38% and 27% fewer fruit per tree in 1997 and 1998, respectively compared to trees not treated with oil indicating that crop thinning had occurred. In 1998, yield was lower in the trees that had been treated with oil annually for three consecutive years. Consecutive, annual applications of petroleum oil applied 1 to 3 weeks after petal fall produced a shift from smaller fruit sizes to larger fruit sizes beginning the second year.

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Craig E. Kallsen

Information on how annual pistachio yield is affected by air temperature (Ta) during the winter and growing season is lacking. Timely advance knowledge of the magnitude of the yield of the California pistachio harvest would be beneficial for the pistachio industry for efficient allocation of harvest and postharvest resources, such as personnel, harvesting machinery, trucks, processing facility capacity, crop storage facilities, and for making marketing decisions. The objective of this study was to identify parameters, especially Ta variables and time periods, calculated from Ta data during the previous fall, winter, spring, and summer, that were associated most closely with fall nut-crop yield. The premise of this study was that sequential, historical yield records could be regressed against a number of Ta-derived variables to identify Ta thresholds and accumulations that have value in explaining past and predicting subsequent nut yield. Of the 27 regression variables examined in this study, the following, which were all negatively correlated with subsequent yield, explained the greatest proportion of the variability present in predicting yield of ‘Kerman’ pistachio: yield of the previous-year harvest, hourly Ta accumulations above 26.7 or 29.4 °C from the time period between 20 Mar. and 25 Apr., hourly Ta accumulations below 7.2 °C from 15 Nov. to 15 Feb., and hourly Ta accumulations above 18.3 °C from 15 Nov. to 15 Feb.

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Craig E. Kallsen*

Yield, fruit quality parameters and pruning costs were compared among differentially-pruned, mature navel orange trees planted at a density of 222 trees per hectare (90 trees per acre) in 2000, 2001 and 2002. The experiment was designed as a replicated, split block with topping height as the main plot split by three levels of interior pruning as subplots. A tree was reduced in height by mechanical topping to 4.3 m, 4.9 m or left untopped and hand pruned according to one of the three following options: 1. scaffold removal in March of 2000 followed by dead-brushing in 2001, and 2002; 2. dead-brushing only in 2000, 2001, and 2002; or 3. no topping or dead-brushing. Scaffold removal resulted in removal of approximately 50% of the tree canopy. Data were collected from experimental trees surrounded by similarly topped and interiorly pruned border trees. A highly significant positive-linear correlation (r 2 = 0.95) was found between the total numbers of fruit produced annually per hectare versus the total number of fruit sized 72 to 88 mm in diameter (i.e. fruit sized such that 88 to 48 may be packed in a standard 17-kg packing carton). This functional relationship existed whether reductions in fruit numbers were the result of severe pruning in March or from, apparently, weather-related year to year variability in fruit set. These results suggest that anything in this orchard that reduces fruit numbers below approximately 250,000 fruit per hectare at harvest (100,000 per acre) will result in a mathematically predictable decrease in the total number of harvested fruit sized 72 to 88 mm in diameter. Trees that were not topped and which had no interior pruning produced the largest number of valuable fruit without additional pruning costs.

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Craig E. Kallsen and Dan E. Parfitt

‘Gumdrop’ is a new female pistachio (Pistacia vera L.) cultivar for California. It matures earlier than all commercial cultivars with equivalent yield and nut quality to ‘Kerman’. ‘Gumdrop’ can be harvested about 10–12 days before ‘Golden Hills’ pistachio (Parfitt et al., 2007) and 24 days before ‘Kerman’, the standard pistachio cultivar grown in California (Parfitt et al., 2012). ‘Gumdrop’ has very good yield, nut quality, and processed nut appearance similar to ‘Golden Hills’ and ‘Kerman’. ‘Gumdrop’ blooms about 5 days before ‘Golden Hills’ and 10–11 days before ‘Kerman’. ‘Gumdrop’, ‘Golden Hills’, and ‘Kerman’ comprise a harvest series, maturing over a 24–30 day period. The early nut maturity of ‘Gumdrop’ will permit pistachio growers to extend their harvest period. The earlier maturing date of ‘Gumdrop’ also makes it less susceptible to insect damage from navel orangeworm, a major pest of pistachio implicated in the occurrence of aflatoxin contamination. An application for a U.S. Plant Patent was submitted on 4 Apr. 2016.

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Craig E. Kallsen and Dan E. Parfitt

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Craig E. Kallsen and Dan E. Parfitt

Scion and rootstock circumferences of seven male and 26 female cultivars or potential cultivars of pistachio trees (Pistacia vera L.) were measured at 16 locations in the San Joaquin Valley of California. The trees were of variable age and on Pistacia integerrima-type or UCB1 (a P. atlantica Desf. × P. integerrima Stewart hybrid) rootstock. Differences were found in the ratio of scion to rootstock circumference (SRR) between the standard industry female cultivar Kerman and the other cultivars collectively. ‘Kerman’ produced a smoother trunk with a SRR closer to one than other cultivars. The SRR was also affected by rootstock with values closer to one for UCB1 as compared with higher values for P. integerrima rootstocks. The relationship between SRR and tree age demonstrated here can be a tool for comparing, evaluating, and selecting new rootstocks with growth rates to match those of newly developed or introduced scion cultivars.

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Dan E. Parfitt, Craig E. Kallsen, Brent Holtz and Joseph Maranto