- 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: Ben Faber
Although you never know about the weather, we do know that if heavy rain occurs after color break in mandarins there can be significant rind breakdown. This problem can destroy much of the crop and the problem is largely preventable.
Pre-harvest rind decay of mandarins in California generally occurs shortly after rain falls and is most severe on Satsuma mandarins. Although some researchers have associated the problem with fungi such as Alternaria species, isolations from affected fret have been inconsistent. Inoculations with isolated fungi only sometimes reproduce disease symptoms and only on water-soaked fruit. Furthermore, in preliminary field trials there were conducted in Butte Co in the fall of 2002 and 2003, fungicide treatments that included Topsin-M, Pristine and Abound only reduced the incidence of disease from 99% in the control to approximately 90% . These data suggested that mandarin rind breakdown is a physiological, abiotic disorder of fruit rather than a pathological problem and the fungi isolated are rather secondary causes of rind decay than primary pathogens.
Rind breakdown of citrus was previously reported by Fawcett and others in the 1930s. Wet weather combined with a sudden decrease in temperature was shown to result in generation of rind oil and collapse of cells just under the cuticle. In laboratory and field trials in 2003, fruit treatments with water repellants reduced the incidence of rind breakdown to very low levels. Field trials were again conducted in the fall of 2004. Fungicide treatments were ineffective in these trials. In all trials, application so Vapor-Gard or Omni oil significantly reduced the disorder. In all programs with Vapor-
Vapor-Gard and Omni oil, a first application was made at the end of October and there was no significant difference in efficacy when additions applications were done. When tree were protected from rainfall using a tent, the disorder could not be detected, indicating the rind breakdown is correlated to rainfall.
In summary, results from the trials support previous findings by Fawcett that mandarin rind disorder is an abiotic, weather-related problem of mature fruit that has undergone a green to orange color change. Using a water repellant helps protect the fruit.
https://apsjournals.apsnet.org/doi/pdf/10.1094/PDIS-07-10-0484
Etiology and Management of a Mandarin Rind Disorder in California
- Author: Ben Faber
The UC IPM Citrus Pest Management Guidelines has been updated to include new research out of the Rosenheim lab at UC Davis. Early-season pests like citrus thrips, earwigs, and katydids damage some types of mandarins differently. Learn how to adjust your management program accordingly. Many new photos have been added to these sections to improve pest identification and show more damage symptoms.
Scarring on the stylar end of citrus fruit caused by citrus thrips, Scirtothrips citri, feeding. Photo credit: Tobias G. Mueller
Adult male European earwig, Forficula auricularia. Photo credit: Beth Grafton-Cardwell.
Scar on citrus fruit caused by European earwig, Forficula auricularia, feeding. Photo credit:Hanna Kahl.
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By Susanne von Rosenberg, UC Master Gardener of Napa County
Citrus trees are a familiar sight in Napa County, and many of us grow them. In general, citrus is pretty easy to care for: it just needs consistent water and fertilizer and perhaps frost protection in the winter.
Citrus is also easy to prune. You only need to prune it for shape. However, if you remove the trailing skirts that some varieties develop, you will reduce snail and slug damage.
Citrus is believed to have originated in the foothills of the Himalayas. Citrus was brought to California by Spanish missionary Junipero Serra and first planted at Mission San Diego in 1769, but the first commercial grove of orange trees wasn't planted until 1841, in Los Angeles.
The first citrus trees in Northern California were planted in in 1856. One of the two original orange trees, called the “Mother Tree,” is still alive in Oroville and is the oldest citrus tree in California. It's at 400 Glen Drive, and it is a historical landmark. I'm definitely going to take a drive sometime soon to visit it.
California also has a Citrus State Historic Park. It is an open-air museum describing the citrus industry's role in the history and development of Southern California through the experiences of the migrant and immigrant groups who made it possible.
If you want to know even more about citrus, check out the UC Riverside citrus variety collection website. The Citrus Research Center and Agricultural Experiment Station that is part of UC Riverside maintains a collection of over 1,000 varieties of citrus.
Citrus botany is complicated because plants in this genus readily interbreed and produce fertile offspring. The ancestral varieties of today's common citrus are the pummelo (also spelled pomelo), mandarin and citron. All other varieties are hybrids of these three.
For example, botanists believe that a grapefruit may be a cross of a pummelo and a sweet orange, and that a sweet orange originated as a cross between a mandarin and a pummelo. More recently, plant breeders crossed grapefruits with mandarins to create tangelos.
Although we consider them citrus, kumquats are part of a related genus, Fortunella. They are in the same family as citrus, and they, too, can interbreed with citrus.
Citrus trees are also unusual in that they can produce two types of embryos in the same seed: one from sexual reproduction and one from asexual reproduction. Citrus fruits can develop seeds as long as the flowers are pollinated; the flowers do not actually have to be fertilized by the pollen. Embryos resulting from asexual reproduction are duplicates of the parent. Embryos resulting from sexual reproduction have different traits.
If you sprout a citrus seed and more than one seedling develops, one is from a sexual embryo and the others from asexual embryos. Usually the weakest one is from the sexual embryo.
If you're tempted to grow citrus from seed, remember that the fruiting part of the citrus tree (the scion) is almost always grafted onto rootstock. The rootstock provides desirable traits such as improved disease resistance, better fruit quality and cold hardiness. Also, commercially grown trees are grafted from mature wood and yield fruit in a few years. It can take 10 to 15 years before a citrus tree grown from seed is mature enough to produce fruit.
Citrus needs heat to ripen, and the lower the temperatures where it is growing, the longer it takes to ripen the fruit. It usually takes 8 to 16 months from flowering for citrus to reach eating quality. Some citrus varieties flower more than once a year.
That's why, in our relatively cool climate, our trees tend to bear lemons and limes year-round. The trees produce several rounds of flowers, and then it takes a long time for the fruit to ripen. Most other citrus trees flower only in the spring and then produce their crop sometime between the fall and the following summer.
We tend to think that citrus fruits are ripe when they color up. The color change happens because the rind is losing chlorophyll and gaining carotenoids (yellow, orange and red pigments). This transformation happens as the fruit matures, but the same process also occurs in the fall when temperatures decrease. The only way to really know if your citrus is sweet enough is to taste one.
The UC Master Gardeners of Napa County are volunteers who provide University of California research-based information on home gardening. To find out more about home gardening or upcoming programs, visit the Master Gardener website (napamg.ucanr.edu). Our office is temporarily closed but we are answering questions remotely and by email. Send your gardening questions to mastergardeners@countyofnapa.org or leave a phone message at 707-253-4143 and a Master Gardener will respond shortly.
Enjoy the nearly infinite variety of citrus from UC Riverside's comprehensive website:
- Author: Ben Faber
The USDA has released their Fruit and Nuts Outlook Report which shows the forecast the 2019/2020 seasons and provides an overview of the markets.
The 2019/20 citrus crop is forecast to be 7.63 million tons, down 4 percent from the previous season. Declines in overall production can mostly be attributed to smaller lemon, tangerine, and mandarin crops in California. Orange production in California has remained stable since last season. Citrus production in Florida has also remained stable with a 1 percent decline in orange production, and significant increases in grapefruit, tangerine, mandarin, and tangelo production over last year. Overall decreases in production of lemons, tangerines, mandarins, and tangelos are expected to result in increased imports, and higher prices compared with last year.
Fruit and tree nut grower prices began 2020 at low levels. At 117.8 (2011=100), the January 2020 index was down 10 percent from the January 2019 index and below the January average for 2016-18 (fig.1). The January 2020 index was the lowest since January 2013. Significantly lower grower prices for citrus fruit and apples drove down the index (table 1).
As of mid-March 2020, U.S. citrus exports were down except for orange juice and tangerines. Reduced exports have increased the domestic supply of citrus, putting downward pressure on prices. The January 2020 price of all- grapefruit is down 36 percent from the year before, and all-oranges and oranges for the fresh market are down by 6.9 and 9.4 percent respectively. All- lemon prices are down 28.5 percent, and fresh lemons prices are down by 8.6 percent.
Apple prices were down 21 percent in January 2020 from the year before. USDA, National Agricultural Statistics Service (NASS) estimates the 2019 total apple crop to be up 3.6 percent from 2018. The strong dollar and increased tariffs in several countries have reduced exports, putting downward pressure on prices.