The wildfires in San Diego and Ventura Counties during the fall of 2003 were certainly devastating to many avocado groves adjacent to burning native chaparral. Many of the avocado trees were singed in the canopy without extensive damage to the large scaffold branches; these trees will re-grow new foliage with some relatively minor pruning to clear out smaller dead branches. However, other groves have had extensive damage, complete with charring of the bark in the trunk and boiling of the sap through the bark of the trunk. In these cases, the sap became hot enough to steam the cambium layer (the layer of living cells just beneath the bark), killing the tree above the soil line.

In the latter case, the tree above the soil line is dead, but the roots are still alive. Beginning about the first of March 2004, we have noticed that many of these trees are sending up rootstock suckers near the trunk. If left to grow un-grafted, these suckers will become an avocado tree, but not a known cultivar. The question is: should these burned trees be removed and replanted with a new tree? Or should a sucker be tip-grafted back to a known cultivar?

Sucker grafting in avocado is a well-known practice and has been used extensively in the industry when a grower desired to change cultivars. Generally, the tree is cut down leaving a threefoot stump, which is used as a stake for the new tree. A strong sucker growing from the base of the tree is selected (the sucker should be about 3/4 to 1" in diameter and stiff, not rubbery), and the other smaller suckers should be removed. The sucker is cut with a horizontal cut about 6-8" above the soil line, a 2”vertical slit is made down through the center of the sucker, and 3" to 4" long piece of budwood, cut like an arrowhead at the bottom end, is slipped into the slit, matching the cambium layers together on at least one side, and preferably on both sides. The graft is wrapped tightly with grafting tape, and the entire budstick is wrapped with Parafilm to prevent moisture loss, and grafting tape is used to tie the new grafted sucker to the stump (used as a stake).

Advantages from sucker grafting (as opposed to planting a new tree).

• Sucker grafting is cheaper. As recently quoted by a grafter in Fallbrook, sucker grafting usually costs about $2 per tree after the tree has been cut down to a 3 foot stump. If the grafter supplies the budwood and grafting tape, the price will probably be $2.50 per tree. If the grafter has to travel away from Fallbrook, the price will be higher according to the distance traveled. A new replacement tree will cost about $14 on a seedling rootstock, or $19-22 on a clonal rootstock. The labor cost for planting the new tree would be about $2.00 per tree. These costs do not include cutting down the older burned tree, or follow-up care for the young tree.
• The older, burned avocado tree has an extensive root system with a lot of stored energy. When the sucker graft begins to grow it usually grows very rapidly, much faster than a young replant tree. The sucker grafted tree should start to set fruit two years after grafting.

Disadvantages from sucker grafting.

• We are assuming that the sucker-grafted tree is healthy and does not have root rot or some other disease. If the older tree has root rot, it would be better to remove the old tree and replant with a new tree grown on one of the newer root-rot tolerant clonal rootstocks.
• In the system described above, the trunk is used as a stake. When the new tree grows enough to be selfsupporting, the old stump should be cut down close to the ground. The stump should be slightly sloped to drain water away from the new tree. This takes some careful chainsaw work.
• Suckers. Until the new tree gains strength and starts to shade the old stump, there will be other suckers emerging. These must be removed or they will take over and shade the grafted sucker.
  

  Replant or Sucker-Graft?

The best key to unlock efficient irrigation practice is to know exactly how much water your crop uses and replace it in a timely fashion that matches your irrigation system capacity and avoids crop stress and water logging. We have good “normal year” estimates of citrus water use (evapotranspiration, ET) for the San Joaquin Valley, but as any grower knows very few blocks are “normal”. The Frost Nucellar on the Cajon loamy sand and fanjets in Edison doesn't behave the same as Fukumoto navel planted to double-line drip on an Exeter clay loam.

So what's the trick for hitting optimum water management for a particular block? You have to keep account of your soil moisture reservoir in the crop root zone. Tracking soil moisture tells you whether you're putting on too much or too little water to meet crop needs. It's also the key to increasing fruit set and quality in many crops such as canning tomatoes, improving flavor in most wine grape varieties and possibly help control puff and crease in citrus.

But any farmer and most ag consultants will tell you that checking soil moisture is not for the faint of heart because it requires auguring holes, pushing a steel probe tube, and/or installing soil moisture monitoring instruments to depths of 2 to 6 feet depending on the crop. Checking instruments or hand probing needs to be done on at least a weekly basis to be useful.

After pushing, twisting, pounding and digging thousands of holes in hundreds of fields around the San Joaquin Valley I can testify to the fact that this is only slightly more fun than shoveling manure, and it's a whole lot harder on your shoulders and wrists. The result is that it's not done very often, if at all, and farmers tend to stick to a traditional irrigation schedule. Given all the other decisions and details growers have to see to on a daily basis it's not surprising this activity gets pushed to the side. At the same time, the years of experience a farmer has with a crop and with a particular field often give him an intuitive sense of how to run the water and end up being 75 to 90% efficient anyway! So if you're already this efficient then why auger holes and check moisture anyway?

There are two reasons: 1) You're not really sure that you're at the optimum point of the crop water use curve until you check, and 2) The simple math of cost versus benefit. Water monitoring consulting services run around $15/acre/season depending on total acreage and what degree of technology and reporting you want done. If this is the only cost you incur to get the extra 5% out of a 3-bale cotton crop then you've made an extra $22/acre even if cotton is only 50 cents/lb. Even at just $2 net/box, the total from an extra 15 boxes of grapes or extra fancy oranges is a 100% return on your $15 investment.

Many growers have tried tensiometers in the past and usually get fed up with the maintenance. A new generation of medium and high technology sensors is now available to growers and consultants. The huge diversity of sensors can be intimidating at first glance but these systems can make this job easier, more accurate and even more affordable. The biggest advantage to the new technology is the use of a continuously recording data logger coupled to responsive soil moisture sensors.

A series of irrigation management/monitoring demonstrations by UC Cooperative Extension over the last 3 years in Kern County has looked at using a combination of 6 granular matrix electrical resistance blocks (Watermark®) coupled to a logger with a graphic display (Hansen AM400®) to allow growers a “push button” look at 5 weeks of soil moisture history at any time during the season. The cost of this system is about $600 and should be good for 3 to 5 years. This gives growers a look at the dynamic changes in soil moisture due to actual crop water use and subsequent recharge of the profile during irrigation. The pattern of the peaks and rate of change of these readings is more useful than the actual numbers themselves. Many different sensors and loggers provide this type of information but the AM400/Watermark system is the only combination providing a graphic display in the field without having to download to a computer. Computer downloads can also be done anytime during the season to develop charts such as those shown below.

Charts (a), (b) and (c) show the changes in soil moisture for 2 different blocks of early navels in the Edison area of Kern County for summer 2003. Comments are placed in boxes connected to explain what these patterns mean.

Even though all three of these monitoring locations are within 800 feet of each other we see very different changes in soil moisture. The hedgerow block (a) has many skips as the grower has begun pulling trees and he wants to avoid over watering the whole block.NEW PARA Charts (b) and (c) are for trees in the same row but different sets. Slightly higher hose pressures and loamier ground keep (b) moister than (c), which shows almost a perfectly efficient pattern of crop water use and recharge. To keep the trees in (c) from looking “hot” required an irrigation frequency for this block that resulted in the wetter condition at location (b). But the bottom line for the grower is these trees have never looked better, he used less water in 2003 and had a better packout than in 2002.

Checkout my website,for some calibration curves and other field examples, both good and bad, under “Using Watermarks in Different Soils”. Irrometer, Onset and Spectrum companies also make inexpensive loggers (can be found here. (Note: use of any product names is not intended as a commercial endorsement.)

Tracking soil moisture tells you whether you’re putting on too much or too little water to meet crop needs.

Vertebrate pests that have caused damage to citrus trees include rodents and small mammals, large mammals, and birds. Citrus orchards provide food and shelter for a number of these pests, and damage may be severe if the pest resides in the orchard. Damage can occur to the fruit such as rat chewing or bird droppings. Bark damage and tree death can occur from rodents and larger mammals. Damage to irrigation systems such as chewing on hoses can easily be the most expensive damage.

The goals of a successful management program include reducing the number of pest problems and using control methods that are affordable. There are four key points to establishing and maintaining a vertebrate pest management program. First, one must identify the specific damaging species. Second, review all the management control options. Third, one must take action quickly and early, and use the best option that is appropriate for the time of year and the orchard. Fourth, use a monitoring system to detect when re-infestation occurs and thus more controls are needed.

The first key point is identification and observation. Many of the agricultural commissioners’ offices in the counties can help with this problem. In addition, University of California Production Manuals such as almond and walnut have reference material on different pests. It is critical to identify the specific species or type of pest causing damage. You can use direct observations with some pests such as birds or squirrels that are active during the day. With pests that are active at night or tend to hide, one looks for tracks, burrows, or the type of feeding; or one can use traps. With rodents, one can use the size of the incisor marks on plants to help identify the pest. This is also useful on irrigation systems, where one can remove the damaged part and take it to an expert. Traps are also used where trails are established to capture and identify the pest. Pictures, especially close-ups are very useful and can be emailed or sent to experts on the Internet. If you also describe the adjacent habitat such as foothills, streams or rivers, etc., that information will help.

For some pests, there are many possible control options. It is very important to check with the agricultural commissioner’s office as animals vary by protected status and how the animal can be legally controlled. The pest’s life cycle will determine when and if a certain control method can be used. For example, ground squirrels can be controlled effectively with poisoned baits but not in early spring when the animal is feeding on green material. Gophers can be controlled all year with poisoned baits that are applied into the burrows, but are more active when the soil is moist. Habitat modification may be an economical option, as brush piles near an orchard will provide shelter for pests. Biological control such as attracting owls and hawks to an orchard can assist with control, but seldom keeps rodent levels below economic levels.

It is important to act quickly when a control measure is selected. Some vertebrate pests can increase in population quickly, and control is less expensive with lower numbers of pests. Some pests will reside in the orchard, and create a home there. It is much easier to control them when the pests live outside the orchard.

Finally, it is important to have a monitoring system in place after controlling a vertebrate pest so as to detect if the pest is re-entering the orchard. A good record system is important.

Many of the citrus orchards in the San Joaquin Valley (SJV) are located near the foothills on the eastern side. Some of the more common vertebrate pests include gophers, ground and tree squirrels, mice, rats, rabbit, coyote, feral (wild) hogs, and starlings. Rare tree damage has occurred from bear and beaver. There is more new acreage in the SJV planted in the middle of the valley. Those trees will be susceptible to the vertebrate pests already found nearby.

Rodents such as gophers and meadow mice (or voles) feed on plant roots, and can girdle and kill young citrus trees. Occasionally, gophers can kill mature trees, especially if the tree is weakened by other factors such as root rot. Many members of the rat family and deer mice will feed on citrus fruit. The effectiveness of control measures depends on identifying the specific rodent. The Eastern Fox Squirrel (EFS) is a tree squirrel found near big cities in the SJV and throughout the metropolitan areas of Southern California. It has moved to adjacent commercial citrus orchards and will feed on ripe fruit.

Coyotes, rabbits, and squirrels will damage irrigation hoses. By examining the damage, experts can identify the pest. The EFS has caused considerable damage to irrigation systems in some nut crop orchards in the Fresno area.

Larger mammals can be economic pests. Wild hogs will feed on fruit, damage bark, and create large holes or “wallows” on the orchard floor where it is moist. Occasionally, hogs will destroy irrigation hoses. Beavers have destroyed young citrus trees located near streams.

Bird problems have occurred mainly due to large flocks of starlings that nested in orchards at night. The damage resulted from the bird droppings on the fruit.

More information about vertebrate pests can be found here.

Identification and observation is key to vertebrate pest control.

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.

Growers can enjoy a considerable price premium in the marketplace for having the earliest of the early citrus for sale. Photo by Jack Kelly Clark.