The three things which seem to be unavoidable during life in the southern end of the San Joaquin Valley are death, taxes, and a considerable price premium in the marketplace for having the earliest of the early citrus for sale. The most robust early market in the San Joaquin Valley of California is for navel orange, however, early lemons and mandarins also reap price benefits. The early citrus market for a given variety may only last for a few weeks or even days.
For navels, the early market usually begins with the first navels picked in mid-October. The chance of a grower being able to profit from this early market requires that the correct planting and cultural decisions be made. To be a player in the early market, the grower has to produce an orange that meets a minimum sugar/acid ratio and the minimum level of color change at the earliest possible date. Pick too early and the fruit receives a red-tag from the Agricultural Commissioner’s Office and may have to be discarded; pick too late and you miss the 100% premium that often goes with the earliest fruit.
To be acceptable to the consumer, this early fruit must be treated with ethylene gas at the packing shed to change the color from yellow-green to orange. Ethylene gas treatment is commonly knows as “sweating” or “gassing” the orange. Generally speaking, the greener the orange, the longer it must be sweated. Sweating the fruit generally reduces fruit size and shelf life and increases problems with the rind and disease susceptibility. There is concern in the citrus industry that the rush to produce the first fruit of the season may compromise fruit quality characteristics such as sweetness and juiciness. A disappointed early-season fruit consumer may not return later in the season to buy more citrus fruit.
Choosing the Right Location
The production of the earliest of the early navel oranges, or the earliest of any of various kinds of citrus in the San Joaquin Valley requires that your trees are located in warm areas. However, very hot mid-summer temperatures are not the key. Temperatures greater than 98°F are probably more harmful than beneficial to citrus production. The earliest citrusmaturing areas in the San Joaquin Valley are south-facing slopes and terraces located along the higher elevations of the citrus belt on the east side of the southern San Joaquin Valley. The Edison area and foothills west of Arvin south and southeast of Bakersfield are examples. These areas tend to retain the insulating layer of fog common in the lower areas of the valley in the coldest months, but break out of the fog in the spring. Less spring fog means more sun and warm temperatures in the early spring, which creates an earlier start in setting and sizing fruit. All else being equal, sandy soils appear to mature fruit earlier than heavier soils.
Choosing the Right Variety
Having the earliest microclimate in the valley does no good if the grower plants late-maturing varieties. As yet, there is no price premium for having the earliest of the late navels, although some growers are cashing in by having the earliest ‘Valencia’ oranges in the spring. Even varieties like ‘Atwood’ or ‘Parent Washington’ will probably be too late for the very early market most years. ‘Fisher’ navels, like the various selections of ‘Thompson Improved’, do have the ability to attain a legal sugar/acid ratio as early as anything else in the Southern San Joaquin, but color is usually delayed. If ‘Fisher’ navels are picked too early the long sweating required to bring up the color usually is associated with substantial green?spotting, especially if the fruit is wet and turgid at picking.
Two navel orange varieties, that have almost disappeared from the San Joaquin Valley, but which still occasionally make an early profit for the owners of the few remaining healthy groves, are ‘Bonanza’ and ‘Tule Gold’. For early fruit producers the ‘Bonanza’ and ‘Tule Gold’ are somewhat frustrating in that unlike the ‘Fisher', they tend to show color very early, but getting the sugar/acid ratio above that required for legal harvest proceeds more slowly. The time lag between the show of acceptable color and the achievement of an acceptable sugar/acid ratio often produces unacceptable levels of anticipation in the grower. All of the early navel trees tend to grow slowly but ‘Bonanza’ and ‘Tule Gold’ trees may be the slowest growing of all. ‘Bonanza’ trees have a problem with what appears to be self girdling, which causes an early decline, although testing conducted a few years ago demonstrated that many trees in these blocks were infected with Stubborn disease. As the groves become older, ‘Bonanza’ and ‘Tule Gold’ trees tend toward the production of heavy loads of small, split, and sunburned fruit.
Two proven producers and similar looking navel oranges for the early market are the ‘Earli-Beck’ and the ‘Newhall’. These two varieties produce a characteristically football-shaped navel. Generally, color and the sugar/acid ratio appear roughly together and usually in the same time-frame as the ‘Bonanza’. The ‘Earli-Beck’ and ‘Newhall’ can achieve a deep, orange-red color and these varieties are prime candidates for the grower who wants to participate in the early market. For a brief period of time years ago, the ‘Earli-Beck’ navel was available in two budlines. One budline contained a viroid and another was free of the viroid. The budline containing the viroid generally appears to produce fruit a few days earlier, however, the growth of the trees is non-uniform and may be associated with an earlier decline of the tree. Although some orchards remain, the budline containing the viroid has not been available for many years.
A relatively new entry (1990s) into the early market is the ‘Fukumoto’. ‘Fukumoto’ navel is early, as early as the ‘Earli- Beck’ and ‘Newhall’ in many years and colors early. This navel is capable of producing a large, well-shaped fruit that responds as well to application of ethylene as any of the other earlymaturing navels. Successfully administered, ethylene produces a very, deep, attractive orange color in these oranges. The ‘Fukumoto’ as with most early navels grows slowly, suckers heavily, suffers from a currently unknown malady called foamy bark rot during hot weather, and the fruit appears more prone to ridging or chimeras. Some evidence suggests that this tree may be exhibiting some growth incompatibility with current rootstocks commonly used in the San Joaquin Valley. Trees that were planted in colder areas and were one or two years of age when struck by a significant frost event may be more susceptible to tree decline as they age.
Choosing the Right Rootstock
The commonly reported sugar/acid ratio consists of a separate measurement of the total soluble solids (i.e. sugar) divided by a separate measurement of the acidity. When a given scion variety is budded onto a wide selection of different rootstocks, significant differences are normally found among the different rootstocks for both, total soluble solids (i.e. sugars) and for acidity. However, significant differences are seldom found for the sugar/acid ratio. The reason for this is that some rootstocks, such as the trifoliates and citranges, will produce a scion fruit with juice high in soluble sugars and high in acidity. Other rootstocks, such as those with lemon heritage, produce fruit low in sugar and low in acids. A high value for soluble solids divided by a high value for acids will produce a sugar/ acid ratio similar to that of a fruit low in sugars and low in acids. Thus, there does not appear to be a rootstock that consistently produces early, high sugar/acid ratios.
Observational evidence suggests that rootstock may affect the development of color in the orange as well. Rootstocks with lemon heritage, for example, such as ‘rough lemon’ or ‘Volkameriana’, when compared in side by side plantings to trees on rootstocks with trifoliate heritage, such as ‘Carrizo’, ‘C-35’ or pure trifoliate types, appear to color more slowly. As an example, in the Edison/Arvin area of Kern County, some of the citranges, like ‘Carrizo, are probably the most common rootstock choice. Rootstocks with lemon heritage, although often producing a more vigorous tree with higher yields, tend to have greater problems with fungal diseases such as those caused by Phytophthora organisms and overall fruit quality. Trifoliates, and some citranges such as ‘C?35’, are more tolerant of Phytophthora, but often become very chlorotic due to a difficulty in absorbing or transmitting micronutrients like iron, zinc and manganese to the scion when grown in the alkaline, boric, and calcareous soils of this area.
Nutrition
Some evidence suggests that earliness is improved by keeping leaf-tissue samples at the low end of the recommended leaf nitrogen range. If nitrogen levels are too low, overall yield and size might be adversely affected, but for maximum earliness without hurting other fruit quality and yield characteristics, leaf nitrogen levels should probably be in the range of 2.2 - 2.4% nitrogen by dry weight in September and early October. Additionally, the bulk of the nitrogen fertilizer for the season should be applied before June 1. Late season nitrogen fertilizations, as well as overall high leaf?tissue nitrogen levels, will likely postpone the date at which a legal sugar/acid ratio is attained. High potassium levels in leaf tissue samples and late season applications of potassium fertilizers will have a similar effect. By maintaining leaf potassium percentages below 0.7 percent and by avoiding foliar applications of potassium, navels should be ready to harvest earlier. Some evidence suggests that high leaf-tissue phosphorous levels decrease fruit acidity, thereby increasing the sugar/acid ratio.
The presence of arsenic in some of the soils and in the well water has been discussed as the reason for the early, early navels in the Edison area, and there is some experimental evidence that arsenic does decrease acidity in the juice of treated trees. Most growers no longer use their high-arsenic well water, which tends to be very high in boron and salts, and use high quality district water from surface sources. Other growers who have never had access to water with high arsenic concentrations have some of the very earliest oranges. Warm locations and the right variety are far more important. Arsenic fertilizer compounds, including sodium arsenate, are prohibited from commercial use.
Leaf-tissue samples on early navels should always include a test for copper. Early navels may require nutritional sprays for copper. Normally, early navels are not treated with brown rotand Septoria?inhibiting copper sprays in the field because they are usually picked before the fall rains. As a result, some groves become deficient in copper, something later navels almost never show due to disease-preventing copper sprays applied in the fall. Treating even the early navels with copper sprays for disease prevention is not a bad idea anyway, since these sprays can reduce the incidence of some post-harvest rots.
Irrigation
Not much is known on the effect of irrigation on earliness. There seem to be as many early navel growers that insist on irrigating close to the day of picking as those who shut the water off or reduce irrigation several weeks before picking. Water stress of short duration can temporarily decrease the amount of water in the orange, and thus increase the concentration of solids (i.e. sugar) in the juice. Less turgid fruit reduces the incidence of green-spotting of the fruit, which may occur when oil glands of the rind are crushed in handling during picking and transportation.
In an experiment conducted from 2006 through 2008 in the extreme southern foothills of the San Joaquin Valley, water stress initiated in August a continuing through harvest in October, resulted in earlier color development of ‘Earli-Beck’ navels, but increased the risk of loss of yield, fruit size, and quality. Care must be taken in removing irrigation from the orchard early because temperatures in October can remain high, and waterstressed trees can result in fruit losing turgor and premature fruit and leaf drop. Often the first rains of the season come in October, so water-stressing the trees prior to harvest, even if desired by the grower in the hopes of rapidly increasing the sugar/acid ratio, is not always an option.
Other Planting and Cultural Tips For Growing Early Navels
Even though early-maturing varieties grow slower than later maturing varieties, the trees should not be allowed to crowd each other. Besides difficulty associated with picking trees that have grown together, and increased pruning costs associated with trying to keep the trees apart, experimental work done in Kern and Riverside County in the late 1960s and early 1970s, demonstrated that trees that are too close together produce smaller fruit with delayed color and lower sugar/acid ratios. Crowding trees together appears to be a better strategy for producing late-maturing citrus fruit.
Insecticidal narrow-range petroleum oils should not be sprayed in the grove within 60 days of the harvest of early navels. Oil sprays tend to interfere with the rate of coloring either on the tree or in the sweating room because early-harvested navels must be sweated for relatively long periods of time to induce the color change from yellow-green to orange. The presence of the oil on the rind in combination with the ethylene gas, can result in some fairly severe rind staining and spotting.
Control of California red and yellow scales using an augmented Aphytis melinus parasitoid wasp release program is, often, less effective when used on early navels in comparison to its use on later-maturing navels. The reason for the reduced efficacy is that Aphytis are not as active during the hot summer months as they are later in the season. At just about the time the Aphytis begin controlling the scale populations in heavily infested groves, it is time to harvest the early navels in October. Long-season navels have at least two additional, and effective, months for the Aphytis to control the California red scale populations.
