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					                                  University of California Cooperative Extension

                  Kern Citrus and Subtropical Fruit
                 Kern County • 1031 S. Mt. Vernon Avenue • Bakersfield, CA 93307 • Telephone 661-868-6221

                                                                                                        January 18, 2007

Frost Special
          This newsletter is being written on January 18 and will arrive more timely for those on the E-mail list. From a
limited survey made of growers in Kern County, it would appear that almost all groves in Kern County experienced
temperatures cold enough to freeze fruit, with many orchards experiencing temperatures that would freeze most of the
fruit regardless of what was done in the way of protection. Very rough estimates suggest that 80% of Kern County
fruit still on the tree at the beginning of the actual freeze event is lost. Actual losses could vary considerably from
these initial estimates.

Ag Commissioner Says Evaluate Fruit for Freeze Damage
        The Kern County Agricultural Commissioner, Mr. David Moore, and the Ag Commissioners in Fresno and
Tulare County, have issued a notice to citrus handlers containing the following points
     All fruit sent to packinghouses will be placed under a Disposal Order.
     It is requested that packers voluntarily hold fruit harvested on or after January 12, 2007 for five days from the
        date of harvest. This interval will provide an opportunity to fully assess the level of freeze damage.
     If fruit is packed or shipped prior to the expiration date of the five-day period, an official sample will be taken
        at the time of packing and held until such time that a full determination of quality can be made. This
        determination will be made within eight days of taking the sample. If the sample fails to meet the minimum
        quality standards, a Notice of Violation will be issued and the case forwarded to the District Attorney‟s Office
        for appropriate action.
     For example, if fruit is harvested January 15, 2007, an official sample will be taken if it is packed and shipped
        prior to January 19, 2007.

         Please contact the Ag Commissioner‟s Office (661-868-6300) if you have questions regarding what constitutes
the size of an official sample or other questions.

Blogs from the Past
         I am reprinting two sections (in italics) of a February 1999 newsletter in the hopes that we as an industry won‟t
repeat mistakes made shortly after other major freezes. Selling frozen fruit on the market not only destroys the market
for those with unfrozen fruit this season, but can seriously undermine the confidence of domestic and foreign buyers
the following season as well. My remarks in 1999 were as follows:

Tell Me It Isn’t True
        I saw my first frost-damaged oranges for sale the other day in a grocery store in Bakersfield. This particular
store was part of a well-known national chain and I suspect similar oranges were being sold throughout the state. The
oranges were being sold as fancy under a national trademark. Each orange was stamped and stickered advertising the
source of the fruit. Ice marking was minimal, but the rind was separating badly from the pulp, many were moldy, they
contained minimal juice and they smelled like only a rotten orange can. The oranges were 99 cents a pound and since
they only weighed one-half to one-third as much as they normally would, the consumer ended up with a lot of oranges
for 99 cents. Obviously, the oranges should not have been placed on the shelf (or been sold to the grocery) and not
surprisingly, it did not look as if any had sold. The consumer might buy fruit like this one time but they will not do it a
second time.
                          University of California and U.S. Department of Agriculture Cooperating.
          Based on what I have seen and read the following appears to have occurred to the citrus fruit as a result of the
freeze. Freezing temperatures caused cellular damage to the rind, limonene or similar compounds leaked into the
vesicles from the albedo which turned the juice bitter. Water from the juice vesicles in turn slowly evaporated through
the damaged rind causing the orange to dry. The natural “debittering” which occurs with time appears to be
associated with considerable and, probably, unacceptable levels of juice loss. So, even if the fruit passes a transverse-
cut test, it does not necessarily mean the orange is a quality product. By the time this newsletter reaches the groves,
the supposition that fruit can “wait out” damage done by this freeze should pretty well be put to rest.

Valencia Oranges Freeze at Higher Temperature
Than Do Navels
        As of this writing in early February 1999, Valencia oranges are dropping from the trees all over Kern County.
Considerable evidence exists demonstrating that because Valencia oranges are less mature than navels in December
and January, they freeze at a higher temperature than do navels (as much as 2 degrees F). Valencia oranges at this
time do not have the soluble solids that ripe navels have. The soluble solids act as natural antifreeze. Where
temperatures were low enough to freeze navels, I suspect waiting for Valencia oranges to “heal” themselves is a
process similar to waiting for the navels to “debitter.” Valencia oranges will heal, but they generally heal over
damaged and dry juice sacs. Unlike the navels, the time lag between the freeze and the normal harvest of the
Valencias will help ensure that the marketing of large numbers of frozen Valencia oranges is not likely to occur.

Frost Damage to Citrus Wood, and Fruit-Production
Potential in 2007
         Even the more frost hardy citrus varieties, like navels and mandarins, are already demonstrating frozen leaf
canopies and small-diameter twigs. Damaged fruit wood in Kern County varies from some in every grove to quite a bit
in others. Most trees have or will soon suffer major defoliation. The good news is that most growers kept temperatures
warm enough in their Kern County citrus groves so that damage to fruiting wood should be minimal across Kern
County. With the damage to wood being relatively light, many cultural practices that growers typically do in normal
years will be conducted in 2007, as well. The major exception might be with lemon trees which are less tolerant of
frost (and other citrus trees in the coldest swale pockets or trees too far out on the Valley floor). Prices of lemons have
been higher in the past few years, plantings have increased. Young lemons are especially susceptible to frost.
         This spring, regardless of citrus variety, vegetative and fruit buds on leafless branches will probably push at the
same time on the same branch. With the older leaves gone, there might not be enough carbohydrate to go around, and
yields might be limited.
         Leaves are the transpiring organ of trees. Irrigation schedules will have to be adjusted downward in late
winter, spring and summer based on the degree of defoliation. Too much water will retard growth by depriving roots
of oxygen and will increase problems with root rots.
         As far as pruning and normal cultural practices are concerned, growers should take a “wait and see” attitude
with lemon trees, groves with citrus trees in the process of being budded over to other varieties, and other citrus in the
coldest areas. If vigorous new growth occurs in the spring in lightly or moderately damaged lemon trees, pruning
decisions often arise. The advice in 1990 was to avoid pruning lemons the year after the freeze and this advice is
sound for badly damaged trees. Growers with lemons or other trees that froze back to scaffold branches face a
dilemma. Every adventitious bud on undamaged scaffolds or on the main trunk will sprout in the spring, producing a
tree covered with light feathery green shoots. If the growers heavily prunes and thins these shoots to begin the process
of reforming a tree canopy, he or she risks considerable limb damage in following years, when the new relatively weak
branches produce a huge, unsupportable crop of fruit. If no pruning is done and all the feathery sprouts are left to grow,
future year‟s fruit load will be spread over many branches reducing the risk of limb damage. However, this porcupine-
like growth will produce a tree that is difficult to access for picking and will postpone the day of reckoning when an
organized tree canopy must be formed. The best solution might be to do very little pruning the first and second year,
and then begin the process of selecting branches that will reform the top of the tree. Select more scaffolds than you
need, and thin some of these out in future years as the permanent scaffolds gain girth and strength. Lemons produce
more evenly, with less limb breakage, when they are given frequent light pruning as opposed to infrequent, heavy
         With any frozen citrus trees, wait until the degree of damage is known. Frozen wood may take months to die.
When pruning finally begins, remove wood that shows weak bud push. It is best to cut into living, green wood. Frozen
or partially frozen wood can harbor disease organisms that will slowly grow into healthy wood eventually killing limbs
or the whole tree.
                          University of California and U.S. Department of Agriculture Cooperating.
Removing Frozen Fruit from the Tree
          Badly frozen fruit may start dropping from the tree shortly after the freeze, but other damaged fruit may hang
on the tree longer than unfrozen fruit. Many growers resist removing frozen fruit in that is another expense, at a time
of little income.
          Reasons for dropping the fruit, even if it cannot be sold for juice, include:
               Ensuring that the frozen fruit does not interfere with spring fruit set. Navel oranges, for example, will
                  not set as much fruit if last season‟s fruit remains on the tree.
               Old frost-damaged fruit may harbor fungal pathogens that may infect the new crop, such as clear rot
                  (Penicillium sp.), tear staining (Colletotrichum sp), brown rot (Phytophthora sp) or Septoria
               Avoiding having to separate last year‟s partially frozen fruit from the new crop at harvest next year.
               Preventing partially frozen fruit from providing habitat for insect pests.

Evaluating Damage to Baby Trees Requires Patience
         Based on temperature lows reported to me by growers, there is hope that most young plantings of citrus (that
were actually planted in the citrus belt and are not lemons) in Kern County escaped fatal damage. Time will tell. Badly
frozen wood can look surprisingly healthy when temperatures remain cool and semi-dormant wood in the winter looks
dry even when it is healthy, so any final decisions based on a damage evaluation should be conducted in the warmth of
spring. With warmer temperatures, frozen bark will peel easily from the young trunk and the degree of damage more
easily estimated. A tree, even those frozen down to the top of the wrap, can make an amazing recovery. Growers, in
the summer after the 1990 freeze had some success budding onto the rootstocks that remained after the scions were
killed by frost.
         If the trees are still alive under the wraps bud badly damaged, it may be better to replace the tree. Badly frozen
trees regrow fairly slowly, and often are not able to resist pathogens that grow into the wood such as fungal Fusarium
species causing dry root rot. Slow-growing Fusarium (and a host of other wound-related fungi) in the wood can take
up to 10 or 15 years to kill a tree.

New Method for Detecting Freeze Damage in Citrus Fruit
         Separating freeze damaged from undamaged fruit has always been a challenge. Dr. Mary Lu Arpaia, UCCE
citrus postharvest specialist stationed at the Kearney Research and Extension Center will be cooperating with Drs.
James Thompson and David Slaughter, of the Biological and Agricultural Engineering Department, at UC Davis and
D. Oberland, USDA, in testing the efficacy of the ethanol sensor to measure whether a sample of oranges contains a
threshold level of freeze-damaged fruit. Levels of freeze damage in individual fruit will be estimated using black lights
and peel fluorescence. Development of these technologies has been greatly assisted by grants from citrus growers
through the Citrus Research Board. Testing will be conducted in late January and early February at the UC Lindcove
Research and Extension Center.

Pest Control for 2007 – Can It Be Ignored?
         Even with some type of insurance, the loss of a crop will mean less money available for producing next year‟s
crop. Budget preparation usually occurs now and careful consideration should be given to pest control for 2007.
         Monitoring and control of some pests will still be necessary, even if fruit is not present. For example,
California red scale infestations were more severe following the freeze in 1990, probably because of the proliferation
of young leaf and wood tissue produced on the trees in response to the loss of old leaves on many trees. Scale (and
many other citrus pests) thrive on young tissue. Leaving fruit on the tree, especially fruit that may not be totally
frozen, may provide additional habitat.
         Additionally, weed control was much reduced for the same budgetary reasons. Many of these weeds, such as
the mustards, are hosts of the beet leafhopper which spreads the disease and the spiroplasma which causes the disease.
Past research suggests that weeds are a primary source of stubborn infestation. Frost-stressed trees are less tolerant of
some of the preemergent herbicides, so more reliance should be placed on postemergent materials in localized areas
where tree damage was moderate to severe. Once weeds are left to grow uncontrolled, seed numbers can build in the
soil, and getting them back under control can be an expensive process, usually requiring some hand hoeing. Care
should be taken in applying preemergent herbicide for another reason. Recently, simazine was found above tolerance
in California fruit in Japan. Simazine can be absorbed by the tree through the roots or can possibly cross the rind if

                          University of California and U.S. Department of Agriculture Cooperating.
sprayed on the fruit. By following application rates on the label, calibrating application machinery, and by not directly
spraying fruit on the tree skirts, growers should be able to avoid the risk of closing markets as a result of simazine
        Quality fruit will still be demanded by the markets in the winter of 2007 and spring of 2008, freeze or no

Did the Freeze Create a Citrus Leafminer Paradise?
         The summer of 2006 saw the arrival of the leafminer to Kern County. Yes, we already have a moth called the
citrus peelminer. I found an old 1997 copy of my newsletter, which announced the peelminer‟s arrival in Kern County.
At that time I, and most growers, PCAs, or packinghouse managers, were unfamiliar with the pest and had not even
heard of it being in Kern County. PCA Robert Walther originally brought it to my attention by bringing samples to my
office. In 1998, this pest was reported in Tulare County in a big way.
         The citrus peelminer differs from the citrus leafminer in several ways. Unlike the peelminer the leafminer does
not mine fruit or sucker wood. In contrast, the citrus leafminer lives and feeds heavily on citrus leaves, which the
peelminer does not. According to David Haviland, entomology farm advisor in Kern County, his pheromone traps
have shown that the citrus leafminer is now present in most citrus growing areas of Kern County. I have seen one
grove in which the leaves of watersprouts that grew in response to heavy interior pruning were infested across most of
a large block.
         So the question is this. Did the freeze knock back the new population of citrus leafminer or is the young, lush
and tender vegetative growth that will arise from defoliated trees this spring destined to be decimated by this new pest
in the summer and fall of 2007?

Something Unusual Eating Lemon Bark
         For some reason, probably the lack of anything else to eat, lemon tree bark was seriously damaged by rabbits
in at least three frozen lemon groves in Kern County in February of 1999, following the freeze in late 1998. The groves
were located in the General Beale Road area and along Highway 65. Orange trees immediately adjacent to the lemons
were not harmed. As is commonly seen in lemons, there was older damage higher in the tree that was probably caused
by roof rats. However, the most serious damage extended from the bud union and up to the base of the scaffold
branches. In one grove, 50% of the trees or more in a 40 acre block were damaged and some trees girdled and probably
would not have survived (the block was removed so we will never know). The damage near ground level exhibited
tooth marks similar in width to those of rabbits. The bark has been peeled from the trunk and scaffolds down to hard
wood in strips about 1/2 to 1 1/2 inch long and less than 1/2 inch wide at the middle and tapering slightly toward the
ends. It appeared the animal was eating the cambium or soft-inner bark. An examination of the stomach contents of
two rabbits in the block clearly demonstrated that the rabbits were eating lemon-fruit rinds but no obvious bark or
xylem tissue was found. Extremely large numbers of jackrabbits were present in the block that was most thoroughly
surveyed. No rat nests, ground squirrel or other burrows were found in this block after a careful search. This unusual
bark feeding by the jackrabbits was probably brought about by the loss of other food sources. Once the spring grasses
appeared, new rabbit damage disappeared as well.
         If rabbits or other vertebrate pests begin causing damage in your groves, check with the local County Ag
Commissioner‟s office before undertaking control measures that might not be legal. One way to determine what pest is
causing damage is to check tracks. Talc powder, or some other powder in which the animal will leave clear tracks, can
be layered on a piece of linoleum under a fresh feeding site. Knowing which pest is causing the damage can help you
determine which method of control might be most effective.

For Most Potential Mandarin Growers ‘Bullet-Proof’ Seedless
is Best
          The freeze may encourage some growers to change the variety of the citrus in their grove. Some may consider
planting a variety of Clementine mandarin. The main attractions of the Clementine mandarin is that it matures
relatively early in the season and if it is grown so that it is seedless, can be sold into a market that has been ready made
for it in the United States and other parts of the world by growers in Spain, north and south Africa. The fruit does ship
well for a mandarin and has an attractive deep orange color. These advantages appear, at least for the present, to
outweigh some significant disadvantages. For example, Clementine mandarins do not encourage good relations with
ones neighbors. For Clementine mandarins to be seedless, and thus marketable to many packers and consumers, they
must be grown in isolation, possibly miles from other sources of citrus pollen, or in areas free of possible insect
pollinators. To be a successful Clementine grower probably necessitates groves that are isolated from other citrus
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varieties that produce viable pollen and areas free of insect pollinators. Neighbors with citrus trees such as Valencia,
many grapefruits, many mandarins, pummelos, tangelo and lemon trees, or the lady down the road who has been
keeping bees for 20 years all become potential targets of resentment for the Clementine grower. In many areas of the
San Joaquin Valley, it is unlikely that even the most attentive grower will be able to keep this fruit seedless enough,
even if commercial bee hives are absent because of well-established neighboring citrus, feral bee colonies, solitary
bees and other insect pollinators present in suburban and riparian areas.
         Growing the Clementine market for the world market will be a big challenge for the growers with limited
acreage. In the hot, southern San Joaquin Valley the harvest window for most mandarins is short, Clementine
mandarins included. When grown under hot days and warm nights, Clementine mandarins granulate readily and are
often not particularly juicy or sweet. Clementines do not peel as well as some mandarins, and it is not unusual to find a
seed or two. To produce mostly seedless fruit when grown in isolation, most Clementine varieties require spray
treatments at bloom and petal fall with a plant growth regulator to ensure adequate fruit set.
         In the citrus belt of the San Joaquin Valley there are other options for the grower wanting to plant an early-
maturing truly seedless mandarin. The Satsuma is an early-maturing, easy-peeling mandarin that is popular all over the
world. Older satsuma varieties, like the „Owari‟ are hard to beat, but for those that like novelty, new varieties are or
soon will be available. The Satsuma, like the navel is „bulletproof seedless‟ in that it has nonviable pollen and
degenerating mother cells, so remains mostly seedless even if insect pollinators and other variety of citrus surround the
grove. The seedless Kishu is another interesting early-maturing mandarin variety, and like the satsuma mandarin has
fruit with very few in any seeds. While getting the Kishu to produce large fruit is a challenge, the possibilities of this
fruit remain largely unexplored. The fruit is even cuter than the Clementine and the Satsuma, peels easily into distinct
sweet sections, and can be eaten in the family car without need of a paper towel even by those with limited manual
dexterity. Growing any mandarin can be difficult, and the Satsuma, the Kishu, and any of the new seedless UC
releases, will provide many challenges to the new mandarin grower, but seediness won‟t be one of them.
         Research and evaluation continues at UC Riverside to release seedless versions of sweet mandarins that can be
excessively seedy in their original state. The recently released „Tango‟ is a seedless or very low-seeded version of the
popular and late-maturing „W. Murcott‟. Additional superior, neighbor-friendly, early-maturing mandarins will
undoubtedly be released in the not-so-distant future as well.

                                       Craig Kallsen, Citrus, Subtropical Horticulture, Pistachios Advisor
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