Commercial orange production in the United States can be divided into two categories: juice and fresh-market consumption. Florida leads the country in production volume for orange juice, but citrus greening, also known as HLB (Huanglongbing) disease threatens to cripple the crop’s viability there. The U.S. Department of Agriculture’s (USDA) “Citrus: World Markets and Trade” report released in July 2017 forecasts that U.S. production was down 20 percent as a result of citrus greening.
Although the future of oranges in Florida is bleak, fresh-market growers in other states are experiencing an uptick in production. California ranks second in the country for total orange production, but is the leading producer for fresh market oranges. The state has more than 3,000 growers farming 270,000 acres of citrus. Texas ranks third in the nation for total citrus production. Texas is predominantly a grapefruit-growing state, but there are nearly 8,000 acres of early and late oranges currently in production.
“In terms of value in Texas, we are a $180 million total economic impact crop,” said Dale Murden, president of Texas Citrus Mutual.
Producers in the Lone Star State are increasing acreage now and should have more than 30,000 acres of combined grapefruit and orange production in the near future.
“Fresh market is healthy and we continue to work on export opportunities, although typically only about 1 percent of our crop is exported,” he said.
Growers in Georgia are investing in the crop. Groves were first established there in 2013, after the Lowndes County Extension Service in Georgia collaborated with the Madison County Extension Service in Florida and a private nursery called Loch Laurel Nursery, explained Jake Price, an extension agent with the University of Georgia.
In this article, you’ll find an overview of best practices for establishing and maintaining a grove of fresh-market oranges. Raising a bountiful citrus crop is a complex topic with guidelines that vary from one geographic region to the next. For details regarding best practices in your area, contact the local extension agent of Citrus Mutual.
Establishing a grove
As with any crop, soil preparation is the foundation for a bountiful crop. First, a soil test will determine the soil’s fertility and pH level. The results of a soil test will provide guidance for soil amendments if they are needed. “The pH should be around 6 to 6.5,” Price said.
Fertilizer is not recommended until growth begins in the spring. Then an 8-8-8 or 10-10-10 bag is best in the first three years after Feb. 15 and before Aug. 1. This avoids promoting new growth during winter months. The University of Georgia Extension suggests spreading fertilizer in a 30-inch circle the first year and gradually increasing the area treated in the following years.
Then the soil needs to be deeply plowed to break up any hardpan and leveled. If the soil is well drained, a raised bed is not needed. However, if there is a chance that drainage could be an issue, a raised bed is recommended. Removing weeds and applying a pre-emergent herbicide is an important part of the preparation process. The next step is to determine tree spacing. In Georgia, this is largely dependent on the available land, the grower’s preference and the rootstock used. In Georgia, a rootstock called Poncirus trifoliata is recommended because it is considered the most cold hardy. Two types of P. trifoliata are called “Rubidoux” and “Flying Dragon.”
In addition, planting evergreen windbreaks on the north and west sides of the grove is very important for cold protection. Normally cold winds come from the north and west in the winter and windbreaks can make the difference in whether your trees are damaged or not in the winter.
“I figure an average of 145 trees per acre,” Price said.
For 145 trees to the acre that spacing is equal to 20 feet between rows and 15 feet between trees for when a standard “Rubidoux” rootstock is used. Growers who prefer high-density planting could opt for a rootstock like “Flying Dragon.” That variety would be planted with 15 feet in between the rows and 8 feet between the trees, which equates to 363 trees per acre, Price explained. Typically, grass is allowed to grow and is mowed in between each row.
Choosing a variety
Variety selection is as important as proper soil preparation. “In Georgia and North Florida, cold tolerance is key,” Price said.
Satsuma mandarins are a popular cold-tolerant variety of citrus in Georgia. Price estimates that nearly 95 percent of all citrus planted in the state of Georgia are satsumas. These are a type of mandarin that are cold tolerant, seedless and easy to peel. Although less cold tolerant than satsumas, some growers are planting two orange varieties called Hamlin and Navel. Wayne Hanna, Ph.D., with the University of Georgia’s College of Agriculture, has recently released three new cold-tolerant citrus varieties, including the seedless Changsha mandarin, which is like a tangerine, a red grapefruit and a large lemon.
The Asian citrus psyllid is the most dreaded pest in every geographic region that grows oranges. The pest spreads the citrus greening disease and there is no cure. Florida citrus crops have been the hardest hit, but growers in Texas, Arizona and California have to contend with the pest as well. Because oranges are such a new crop in the state of Georgia, the pest has not yet migrated there in droves.
“HLB has already been detected in some homeowner trees along the Georgia coast, but not in any commercial citrus trees,” Price said. “Keeping a sharp eye out for psyllids is a must. If they start showing up everything will change.”
Cold winter temperatures can kill the Asian citrus psyllids and thus keep the disease out of Georgia. “Cold winters could be our ally,” Price said.
Georgia does not have abandoned groves like they do in Florida.
“Abandoned groves are a breeding ground for psyllids, which transmit the greening bacteria,” Price said. “We do have a lot of homeowner citrus and that is most likely where we will have a problem if greening becomes an issue up here.”
In Georgia, growers and extension agents know that citrus greening is something to watch out for and prepare for.
“In Florida it was already too late and with their tropical temperatures, they have not been able to stop the insects that spread the disease,” Price said.
Although the Asian citrus psyllid has gained the most attention, other pests are also problematic for citrus growers. Pest pressures vary geographically. In Georgia, the most troublesome pests are currently citrus leaf miners, leaf-footed bugs, citrus rust mites, spider mites, orange dog caterpillars and citrus scab.
In Texas, the Mexican fruit fly, also known as the Mexfly, threatens citrus production. The Texas Citrus Mutual website noted that the female flies lay eggs in the ripening fruit. As the eggs hatch, the larvae eat the flesh of the fruit, which leads to rot.
“This is one of the state’s top pests,” Murden said.
The most effective method of control is to remove all oranges from the tree at the end of the season. Eating or throwing away any leftover fruit reduces the Mexican fruit fly population.
Murden also includes rust mites as one of the top three pests in Texas citrus crops. Rust mites, also called silver mites, feed on the outside exposed surface of fruit, such as lemons. According to the University of California Integrated Pest Management, “feeding destroys rind cells and the surface becomes silvery on lemons [and] rust brown on mature oranges, or black on green oranges. Rust mite damage is similar to broad mite damage, except that somewhat larger fruit are affected. Most rust mite damage occurs from late spring to late summer. If the mite numbers increase quickly or if scarring appears, a pesticide application is generally required. In some cases, the infestation is localized and a spot treatment may be sufficient for control.”
Worms, called nematodes, can also be troublesome for orange growers across the United States. “HLB destroys half of a tree’s feeder roots before symptoms appear above ground,” said Larry Duncan with the University of Florida Institute of Food and Agriculture Sciences’ Citrus Research and Education Center. “So, other root problems such as nematodes are much more serious today than before HLB infected our trees.”
The citrus nematode (Tylenchulus semipenetrans) is present in all citrus industries worldwide, said Duncan. This pest is specialized to citrus plants and has only a few other hosts. It causes moderate damage and is not considered as damaging as other species and can be controlled.
“Often growers don’t even know citrus nematodes are on their trees. The trees can have good yield but with control, a grower can increase yield by about 15 percent,” Duncan said. “It does not cause major damage to trees, but as the population grows slowly, there is a thinning of the tree canopy and fruit become smaller.”
The citrus nematode is most damaging in dry land groves such as those found in Texas, California and Israel. It is not as damaging in tropical and subtropical regions. Dense populations rob carbon from the tree, thus creating smaller fruit size.
The burrowing nematode (Radopholus similis) is a more serious pest. Worldwide it impacts bananas, but it only attacks citrus in Florida. As its name implies, this nematode burrows deep below the soil’s surface and feeds on the roots there. Cultural practices such as irrigation and the state’s rootstock certification program have drastically helped in controlling this and other nematode pests.
“Before irrigation, the roots in sandy soils had to grow deep into the soil for water and that’s where the nematodes thrive,” he said.
With irrigation delivering water (and nutrients when fertigating) to undamaged roots near the soil surface the tree is able to survive without the deeper roots destroyed by the nematode. The Florida rootstock certification program does not allow the sale of any rootstock that is infected with nematodes. The rootstock certification program, coupled with the cultural practices including the use of mowing and herbicides, have helped reduce the damage caused by this worm.
“Growers used to disc as a method of weed control, which cut the shallow roots that were undamaged by the nematode,” Duncan explained.
Nematode-resistant rootstock is another method of control.
The Swingle citrumelo is a rootstock used in Florida for its resistance to citrus nematode and other desirable traits, according to Duncan, who noted also that the Kuharski Carrizo rootstock is resistant to the burrowing nematode and another popular rootstock.
The coffee lesions nematode (Pratylenchus coffeae) also has worldwide distribution in the tropics. In other countries it primarily attacks bananas, coffee and yams; in Florida, it attacks citrus.
“Texas and California fall into the worldwide category, meaning that this nematode isn’t attacking citrus in those states,” he said. “This nematode is just as or more damaging than the burrowing nematode. It attacks the deep and the shallow roots.”
Once harvested, oranges will not ripen further. It’s important to closely monitor the fruit and harvest at peak maturity. Under-ripe fruit will shrivel and sustain damage during packaging. Overripe fruit quickly rots. Inspect oranges on the trees, taste-test and use a laboratory analysis that measures a “soluble solid (or brix)/acid” ratio.
“I recommend all growers sell their best fruit and not rush to market with low-quality fruit,” Price said. “Young trees typically have more cull fruit. Georgia growers have to make a good first impression on their customers so they will continue to want our fruit.”
Satsumas must be hand clipped from trees; otherwise, part of the peel will be removed when plucking it from the tree. Being easy to peel is an advantage to consumers but requires more labor when harvesting.
Citrus production is complex. Best practices can vary from one region of the country to the next so it is critical to work with local experts. The significance of HLB cannot be overstated, especially for growers in the United States. However, for those interested in getting involved in growing oranges, other areas of the country are planting more acreage each year.