- Author: Anne Schellman
- Author: Ed Perry
- Why are the leaves on my orange tree turning yellow?
It's common for citrus tree leaves to turn yellow in winter*. Fertilize to provide the tree with nutrients now, then watch as leaves green up in spring. Avoid fertilizing in fall, which encourages new growth favored by pest and can leave the tree susceptible to frost injury.
- How do I know if my oranges are ripe/when should I pick my oranges?
You don't have to pick all your oranges once they ripen. In fact, the best place to store oranges is on the tree, where they stay fresh! Pick as needed, unless temperatures below 28 F are predicted, then you'll want to harvest.
- What is this pest?
Scales and whiteflies suck plant juices and weaken the plant. Ants do two things:
- Protect pests from predators like ladybugs, parasitic wasps (very tiny wasps) and lacewings.
- “Harvest” honeydew (a sticky sugary substance excreted by these pests) for food, in a symbiotic relationship that does not include the gardener.
- Why are my oranges splitting?
The reason this happens is not well understood, although it's often related to changes in weather conditions. However, allowing the soil to dry out too much between irrigations is believed to result in increased splitting. Make sure your tree has a constant supply of moisture by watering monthly during the dry season.
- When should I prune my orange tree?
When pruning deciduous trees like peach, plum or cherry, after leaf drop, don't be tempted to prune citrus! Citrus trees are evergreen and require little if any pruning except to control size. If you'd like to keep a new citrus tree under 5 feet tall, you can carefully prune it in spring to manage the height. This way, you won't need a ladder to pick fruit again!
Avoid pruning in fall or winter, which encourages new growth favored by pests and can leave the tree susceptible to frost injury.
*if your tree leaves turn yellow and it's not winter, this may be a different problem.
- Author: Ed Perry
For many in California, the backyard orange or grapefruit tree is almost a member of the family, and any negative change in its appearance elicits concern. One such change in appearance is leaf yellowing and drop that often occurs during the winter in citrus. Citrus leaves can remain on the tree for as long as three years depending on tree vigor, but disease, inadequate or excessive nitrogen fertility, excessive salt or born in the soil, poor irrigation practices, freezing temperatures, pest pressures and low light levels significantly reduce leaf longevity. Excessive leaf drop during the growing season is more likely to indicate a serious problem than leaf drop during the winter. Winter leaf drop normally reflects nothing more than a momentary swing in the natural balance between the natural elimination of old senescing leaves and their replacement.
Reduce winter water applications to citrus trees that have defoliated or that have a significantly thinning canopy. Trees like this require little, if any, supplemental irrigation. Even a mature tree with a full leaf canopy will require less than 10% of the water that it would require during the summer.
The best indicator of tree health for a defoliating citrus tree during the winter will be how well it produces the first flush of new growth in the spring. A decision to keep or remove a citrus tree based on tree health should not be made during the winter. Even trees that lose most of their leaves during winter are capable of replacing leaf canopies with the spring flush of growth, usually with little loss in fruit production. Trees that do not produce a vigorous flush in early spring may have a more serious problem. March is an excellent month to begin applying fertilizer to encourage new leaf growth and fruit production and to help keep an old friend of the farm or family backyard around for years to come.
Ed Perry is the emeritus Environmental Horticultural Advisor for University of California Cooperative Extension (UCCE) in Stanislaus County where he worked for over 30 years.
- Author: Jules Bernstein, UC Riverside
Sweet Mother Orange Tree released from quarantine
The 1000th tree okayed for growing by California's Citrus Clonal Protection Program happens to be the oldest living orange variety in the state.
The program, housed at UC Riverside, is the first of its kind in the world. It began in the 1950s, and its scientists spend up to three years testing and clearing citrus trees of disease so they can be released to commercial and private growers.
By law, every citrus tree newly propagated in California can be traced back to one mother tree created at UCR through the protection program. Program Director Georgios Vidalakis and his group begin their process by testing incoming trees for more than 30 citrus diseases, whether the diseases are known to have emerged in the state or not.
The treatment for any disease identified in that first round of testing is to make a new mini tree from a few cells of the original budwood — short, leafless twigs with buds meant for propagation. “We use special plant cells for this process that diseases cannot penetrate,” Vidalakis said.
After the mini tree grows large enough, program scientists go back and do a second round of testing for disease, making sure they picked the right cells for propagation and eliminating any prior trace of illness.
If it passes the arduous second set of tests, the new tree gets a variety index or VI number that accompanies it for the rest of its life, and it is released to the public.
Dubbed the Mother Orange Tree, Bidwell's Bar is a sweet Mediterranean orange brought to California from Mazatlán, Mexico, and planted in 1856. It was first planted near the Bidwell Bar Bridge near Oroville, then dug up and replanted twice.
Its survival skills are some of the reasons Tom Delfino, former California Citrus Nursery Society director, recommended the old orange tree for the protection program.
“Apparently this variety is very rugged,” Delfino said. “Not only has it survived a lot of cold Northern California winters, but the tree has been dug up and replanted twice — once to protect it from impending flood, and again to make way for the Oroville Dam.”
Much of the state's orange industry is based in areas with warm weather. Delfino, who lives in the San Francisco Bay Area, finds citrus an exciting challenge to grow. By suggesting Bidwell's Bar for approval, he was hoping the protection program would clear it so he could buy its budwood.
On the occasions he has visited the original tree, Delfino said the fruit in reaching distance was always gone. “I think it must be tasty because locals grab it for themselves,” he said. “Makes me even more eager to grow and eat my own. I'm extremely pleased the VI testing is completed so I can acquire it.”
Delfino also hopes that this variety will catch on with commercial growers.
“My thought is our citrus industry is concentrated in the southeastern San Joaquin Valley and is subject to a number of pests that like the warm climate there,” Delfino said. “Though this has seeds, which may be a deterrent, it can be grown in colder areas that discourage some of those insects.”
The tree arrived in California nearly two decades before the better-known Washington Navel orange grown by Eliza Tibbets in Riverside. The navel is named for a structure at the bottom end of the fruit, which resembles a belly button. This structure is actually a separate fruit inside the larger fruit. The Washington Navel is also seedless, contributing to its popularity.
“Bidwell's Bar is an example of what was grown in California before the Washington Navel came to dominate, and now that it has a VI number, others can grow it too,” said Tracy Kahn, curator of the Givaudan Citrus Variety Collection at UCR.
Kahn says it's important to preserve the genetic material from a tree with such significance to California. “Some people were worried it was going to die, but now we have an officially cleared source of this historic tree, and it is protected for future generations,” Kahn said.
/h3>- Author: Pamela Kan-Rice
A new study outlining the costs and returns of establishing and producing navel oranges with low-volume irrigation in the southern San Joaquin Valley has been released by UC Agriculture and Natural Resources, UC Cooperative Extension and the UC Davis Department of Agricultural and Resource Economics.
“A cost study gives a ‘new' grower a better idea of all the costs that are involved with producing the crop,” said co-author Greg Douhan, UC Cooperative Extension citrus advisor for Tulare and Fresno counties.
Real estate agents, land leasers, bankers evaluating loan applications and others can use the cost study to estimate current costs to plant and produce oranges and expected profits.
This study updates an earlier version, using as an example the Cara Cara navel, which is known for its distinctive pink-colored flesh rather than the conventional orange flesh of the Washington navel.
“The Cara Cara has been returning very good prices to growers for the past decade or so and is a relatively new navel,” said co-author Craig Kallsen, UC Cooperative Extension farm advisor in Kern County. “Of course, grower returns are driven by consumer demand. Why consumers like it so much I do not know, but I suspect it is because it tastes good and is different. You cut it and get a pink surprise. Its harvest maturity is similar to that of the Washington navel.”
The updated version takes into consideration “things like inflation, chemical availability, changes in markets both domestic and foreign, governmental regulations and other things,” Kallsen said.
The study is based on a hypothetical farm that consists of 65 contiguous acres onlandin the San Joaquin Valley previously planted to another tree crop. Establishment and production costs are based on 10 acres being planted to oranges. Mature orange trees are grown on 50 acres and the remaining five acres are roads, equipment, shop area and homestead. The grower owns and farms the orchards.
The two major orange varieties grown in the San Joaquin Valley are navels and valencias. Navels are grouped into three types by harvest timing – early, mid and late season. Due to current planting practices, only navels are included in this budget. Cara Cara is the variety of navel oranges currently most commonly planted.
The Cara Cara orange trees are planted double density, 10-by-20-foot spacing, at 218 trees per acre. At this density, it is possible to start harvesting in year 3 or 4. At year 8 or 9, full maturity is achieved and growers begin pruning back every other tree. This allows the grower to maintain yields while at the same time converting the field to 20-by-20 spacing – maximizing yield for a fully mature orchard.
For pest management, the study includes detailed information and links to UC Integrated Pest Management guidelines for citrus. The narrative contains tables of insecticide treatment cycles for establishment and production years.
The section “Exotic Pests of Economic Concern to Citrus Growers” contains information to meet quarantine regulations on exporting oranges from California to countries such as South Korea.
The authors describe the assumptions used to identify current costs for oranges establishment and production, material inputs, cash and non-cash overhead. A ranging analysis table shows profits over a range of prices and yields.
“2021 - Sample Costs to Establish an Orchard and Produce Oranges in the Southern San Joaquin Valley” can be downloaded for free from the UC Davis Department of Agricultural and Resource Economics website at coststudies.ucdavis.edu. Sample cost of production studies for many other commodities are also available for free on the website.
For additional information or an explanation of the calculations used in the studies, refer to the Assumptions section or contact Donald Stewart at (530) 752-4651, destewart@ucdavis.edu or Karen Jetter at (530) 792-8255 or jetter@ucanr.edu. To discuss this study with a UC Cooperative Extension farm advisor, contact your local UC Cooperative Extension office: http://ucanr.edu/County_Offices.
This study was funded in part by the National Institute of Food and Agriculture, U.S. Department of Agriculture, under award numbers 2017-70016-26755 and 2019-70016-29068.
- Author: Ed Perry
Splitting of navel oranges is a disorder that shows up every few years in the Northern San Joaquin Valley. It's difficult to predict the problem, and once you see oranges beginning to split, it's too late to do anything about it. However, it may be useful to talk about why splitting may occur, and what you can do to help lessen the problem.
While you may not notice it until the fruit begins to ripen, splitting in navel oranges begins in green fruit. The split usually starts at the stylar or navel end of the fruit, the weakest point in the rind. The split may be short and shallow, or it may be deep and wide, exposing the segments. Splitting is most serious in navel oranges, but it may occur in Valencia oranges too.
It is not well understood just what causes splitting, but it's thought to be caused mainly by a combination of environmental conditions. Some studies show that changes in climate such as temperature and relative humidity may have more effect on splitting than anything else. A couple of my citrus reference books indicate that splitting is caused by hot, dry weather, alternating with humid, cloudy weather. Allowing the soil to dry out too much between irrigations is believed to result in increased splitting. However, other research and observations in orange groves have shown that irrigation, fertilizers and other cultural practices make no difference in the amount of splitting that occurs in any given year.
It is obvious that you cannot control all of the factors that cause splitting, since weather conditions are involved. However, you may be able to minimize the problem by making sure that your orange tree is well watered. Remember that orange trees (as well as other citrus) are not drought tolerant and need a constant supply of moisture in the root zone. If your soil is sandy you may need to water a fully-grown orange tree every ten to fourteen days during the summertime. In clay soils, the watering schedule may be every fourteen to twenty-one days. You should continue to water your trees periodically in fall, at least until rain begins.
Ed Perry is the emeritus Environmental Horticultural Advisor for University of California Cooperative Extension (UCCE) in Stanislaus County where he worked for over 30 years.