Asian citrus psyllid, Diaphorina citri. UF/IFAS/Entomology Photo: Michael Rogers.
In late 2016, as many of us were enjoying the harvests from our backyard citrus, a bacterial plant disease that can affect all citrus, citrus greening, was widespread in central and south Florida but had not made it this far north. That year, the vector, the insect that spreads the disease from tree to tree, had been found in Leon County and a few other surrounding Panhandle counties, but the disease had not. By mid-2017, the disease had been confirmed in Franklin County and we hoped that our cooler temperatures could keep the insect and disease at bay. Well, I regret to inform you that the disease has also now been confirmed in Leon County, growing in a residential yard in Tallahassee. Now that it is confirmed in non-coastal (and cooler) north Florida locations, I thought a review of the signs and symptoms – as well as what to do with your tree if you suspect or confirm greening – would be helpful.
The tricky part about diagnosing citrus greening is that it has symptoms that look very similar to soil nutrient deficiency symptoms, especially when first infected. This is a good time to mention that citrus require certain micro-nutrients for optimal growth and a citrus-specific fertilizer product should be used when applying fertilizer. Both the disease and certain nutrient deficiencies cause yellowing of the leaves. With greening, the yellowing is typically blotchy and/or not in any particular pattern. Nutrient deficiencies typically cause unique patterns of yellowing, such as a V-shape or artistic-like symmetrical patterns on each side of the leaf’s midvein. The soil’s acidity, or pH, can also cause some nutrients to not be taken up by the plant even if they are present. Soil testing, available from your local UF/IFAS Extension office, and scheduled fertilizations with a citrus-specific fertilizer can ensure that nutrients are not to blame for the discoloring of leaves. More advanced stages of the disease cause such symptoms as leaf drop, fruit drop, lop-sided fruit, uneven inner fruit cores, and reduced fruit quality.
Citrus greening symptoms of the fruit. Photo by Brooke Moffis.
A more obvious sign of potential problems for your citrus are the presence of the insect vector, the Asian citrus psyllid. This is a tiny little insect that goes from one leaf to the other sucking up plant saps for food and unknowingly spreading the bacterium responsible for citrus greening. You can monitor for them by looking closely at the new flushes of growth. If the psyllids are present, you will likely notice most their small, peach-colored eggs and/or white, waxy secretions. If found, it doesn’t necessarily mean that your tree has greening, but you will want to minimize the chance that they could carry it to your tree. The psyllids can be treated with pesticides, ranging from the less harsh options (horticulture oils, neem oil, kaolin clay) to the more hardcore stuff (malathion, carbaryl, imidacloprid). Of course, always read the label of any pesticide before use and/or consult a qualified landscape professional for assistance.
Blotchy leaf symptom of citrus greening. Photo by Jamie D. Burrow.
If you suspect your tree is infected, a diagnostic test can be performed by UF/IFAS plant pathologists at the North Florida Research and Education Center (NFREC) in Quincy to confirm. The test does cost $50, which may seem a little steep, but it’s an expensive lab analysis to run and may be worth piece of mind.
If citrus greening is confirmed in your tree, the right thing to do, unfortunately, is to remove and burn the plant material as there is no known cure. While the Florida Department of Agriculture and Consumer Services (FDACS) doesn’t have any removal requirements for infected dooryard citrus, tree removal is best to prevent additional spread of the disease to other trees, especially those grown by commercial producers in our area. This may seem drastic but eventually the health of the tree and quality of the fruit will decline to a point where you will want to remove it anyway. Don’t forget that movement of any citrus plant outside of the state is prohibited for the very reason of preventing spread of citrus diseases.
You may be asking, “Is it okay to replace it with another citrus tree?” The answer is yes you can, but you do risk re-infection and will want to be monitoring the new planting.
You may also be thinking, “What is going to happen to Florida citrus?” That’s a question that many researchers at UF/IFAS are trying to answer. There is some hope that intense irrigation and nutrient management, as well as specific pruning practices, can help infected trees continue to be profitable for commercial growers. Recently, UF/IFAS researchers were awarded several grants to try and figure a way out of this problem. Some of the lines of research focus on exploring the resistance found in different citrus varieties, including an Australian lime that appears to be greening resistant. This could potentially be used as a future rootstock. Another approach is to try and treat the plants with a particular peptide that would prevent the disease from binding in the insect’s gut. Isn’t that amazing?
Until a fix is found, we should be monitoring for this disease in our area and taking steps to reduce its presence through controlling the psyllids and removing infected trees. If you suspect a tree has greening, please contact your local county Extension office to review the symptoms and discuss your options.
Much more information on citrus greening is available at the following Ask IFAS website: https://edis.ifas.ufl.edu/entity/topic/citrus_greening and from this 2017 article – https://nwdistrict.ifas.ufl.edu/phag/2017/03/03/disease-alert-citrus-greening-and-asian-citrus-psyllids-found-in-the-panhandle/.
Q. When is citrus fruit ready to harvest?
Satsuma fruit ready to harvest. Photo credit: Larry Williams
A. Florida uses five indexes to determine maturity of citrus, including soluble solids, juice content, acid level, soluble solids/acid ratio and skin color. But, the home gardener can easily decide when most citrus types are ready to be harvested. As the fruit reaches full size and the skin color changes from green to greenish yellow to orange, simply pick some fruit and taste it to see if it is sweet. If not, wait a little longer (a week or two) and taste test another fruit. Meyer lemons are ready when the skin color changes from green to greenish yellow. Satsuma fruit may be ready to eat before the skin becomes completely orange, especially if the early fall is warm. Kumquats are usually at their peak in taste when they become fully orange.
Citrus fruit does not ripen additionally after it is harvested. So, let it mature sufficiently on the tree.
Harvest season for satsuma is October to December. Harvest season for Meyer lemon is November to March. Harvest season for kumquat is November to April. Most grapefruit have a harvest season from November to May. Harvest season for sweet oranges varies. Early season oranges are harvested October to January, mid-season oranges are harvested December to February and late-season cultivars are harvested March to June. Citrus fruit may mature a little earlier in the harvest season on mature trees and more toward the end of the harvest season on young, vigorous trees.
Q. What cold-hardy citrus is best for North Florida?
A. Citrus species are tropical and subtropical in origin. As a result, citrus is not well suited for extreme North Florida. Commercial citrus production has progressively moved further south in Florida due to historic freezes. So, you’d be wise to choose the more cold-hardy citrus types for our area. But, even cold-hardy citrus can be severely injured or killed by a hard freeze in North Florida.
Some of the better choices for cold-hardy citrus in North Florida include kumquat, satsuma, calamondin and Meyer lemon. There has been some success with grapefruit and sweet oranges in our area. Lemon and lime are much less likely to survive in North Florida. There has been some discussion concerning future success with growing citrus a little more north in its current range related to climate change. There already has been some success with growing the more cold-hardy citrus types such as satsuma and kumquat in middle Georgia. We’ll see how this works out.
More information on cold-hardy citrus is available from the UF/IFAS Extension Office in your County and through this link. https://crec.ifas.ufl.edu/extension/trade_journals/2018/2018_june_coldhardy.pdf
Citrus: Bearing Branches. Image Credit Matthew Orwat, UF/IFAS
Many dooryard fruit growers have asked me this Fall: When is the correct time to prune citrus? How do I prune Citrus right now? The answer may seem obvious, but when we delve into the question further, we find out that it is not.
Two different pruning strategies exist depending upon the citrus plants age. When training young citrus plants, it is essential to develop three to four main scaffold branches with wide crotch angles. This is done by selecting branches growing different directions that intersect with the trunk or each other at the widest angle possible. Other branches need to be pruned off and these need to be left alone to develop into the main scaffold. Once the branching system has been developed, traditional heading back, as seen in peaches and apples, is unnecessary.
Young Citrus Tree with good vase shape
There are several instances in which pruning mature citrus trees is beneficial. First, branches should be pruned approximately one foot off the ground so developing fruit is not sitting on the ground. This also helps with weed control and fertilization. Next, it is important to remove growth that is positioned extremely upward or inward to promote an open, vase-shaped habit. Finally, it is necessary to remove any dead wood resulting from winter dieback.
Many growers are eager to remove branches that have been bent downward by heavy citrus crops. This is not necessary; they will bear well in subsequent years.
The last pruning item to consider is removal of suckers from below the rootstock. If the tree is grafted, this is necessary so that the rootstock does not overtake the scion cultivar. Trees propagated from seedage or cuttings will not need this type of pruning since root suckers will be true to type.
It has been noticed that when trees are not over pruned, they exhibit greater cold hardiness. Keeping that in mind, any pruning of citrus should be done at the beginning of March or later, not in the fall or early winter. With proper pruning practices, gardeners should expect healthy trees with bountiful harvests. For further information please consult the publications listed below or contact your local Extension office.
Citrus Culture in the Home Landscape
Cold Hardy Citrus for North Florida
Louisiana Home Citrus Production Manual
Sugar Belle mandarin cultivar. Mix of sweet Clementine and Minneola varieties. UF/IFAS File Photo.
Florida is known for citrus and many homeowners love to grow and enjoy it. However, a devastating disease known as citrus greening or HLB has taken a toll on commercial and residential citrus since it first was discovered in Florida in 2005.
Sugar Belle is a cultivar of mandarin citrus developed by the University of Florida citrus geniuses and is tolerant of citrus greening disease if it is properly planted and cared for. Tolerance of the disease does not mean that it doesn’t get citrus greening, rather it means that this cultivar can get infected but still be healthy and productive. The fruit of infected trees is safe to eat as the bacterium that causes it does no harm to humans.
Our chilly winters can be detrimental to many kinds of citrus, but Sugar Belle can withstand temperatures down to 14°F once the tree is well established. That is good news for us in the panhandle. Even so, it is best to choose a spot in your landscape with a southern exposure, preferably with a wind block from northwest winds. Avoid low areas as cooler air falls into those areas.
Symptoms of citrus greening on leaves show a blotchy mottled pattern. UF/IFAS photo.
Make your purchase from a certified nursery to make sure you are getting the right cultivar and a disease-free tree. Spring and fall are the best seasons of the year to plant citrus. When planting, make sure to make slices in the rootball if it is rootbound or if circling roots are present. The rootball should be slightly above the ground level after planting. All weeds and grass should be removed under the canopy of the tree to as they compete for water and nutrients with your newly planted tree. Never place mulch against the trunk as it can hold moisture there and promote disease. Water often the first year until well-established; after establishment citrus has some drought tolerance and may only need supplemental irrigation in times of heat and drought.
A good quality citrus fertilizer with micronutrients is crucial for a healthy tree with good quality fruit. The first fertilization should be about 3 weeks after planting and then follow the label directions for subsequent fertilizations. Newly planted trees should be fertilized 6 times in the first year and the fertilizer should be evenly broadcast under the tree canopy.
The only pruning in the first 3 years should be the removal of suckers that grow from the base, water shoots that grow quickly and straight up, and dead wood. Be sure to clean your pruning tools before and after each tree to avoid spreading any possible disease. First rinse off any dirt or other organic matter and then use a 3% bleach solution or alcohol for sterilization.
For more information:
UF/IFAS Research on Development of Sugar Belle YouTube
Citrus Culture in the Home Landscape
Growing Key Limes in the home landscape is not only a fun and unique addition, but is also delicious – any way you slice them.
The key lime, Citrus aurantifolia, originated in southeast Asia. Genetically speaking, the key lime is likely a tri-hybrid cross between the “odd ball fruits”, known as citron, pummelo and a microcitrus species, Citrus micrantha. There is little commercial key lime production nowadays in Florida, but the fruit remains a very popular landscape option.
The key lime is a small, bushy tree that makes harvest and pruning a breeze. Like most citrus, it’s self-pollinating. The key lime is also an ever-bearing fruit, so there is no real seasonal harvest. The tree could technically bloom any month of the year. There are very few varieties, as trees mostly come from true seed or air layering.
Key Lime fruit at various degrees of ripeness. Photo courtesy of Ray Bodrey, UF/IFAS Extension Gulf County.
Climate is an important factor when deciding to plant a key lime. They are sensitive to cold temperatures, especially below freezing. For the Panhandle, it’s wise to keep key lime trees as patio citrus. In other words, keep the trees in pots so that they can be moved indoors for protection during the winter months. In the ground, trees should be planted in an area where there is a significant wind block. Once a few years have passed and tree has become more mature and acclimated to the environment, they may be able to survive on their own, though it is recommended to cover the tree under sub-freezing temperatures. However, it is important to remember that sunlight is a catalyst for citrus fruit production, be sure to plant the tree in an area with full sun.
The usual suspects of citrus insect pests apply to the key lime also. Citrus leaf miner and mites are the most common culprits. Horticultural and insecticidal oils will certainly help to combat these threats. For planting, key lime is well adapted to a variety of soil conditions in Florida. Be sure to water newly planted trees every other day for the first week and then one to two times a week for the first couple of months. Water periodically after that, making sure the soil doesn’t stay completely dry for long periods. A 6-6-6 fertilizer works great for the key lime. Please follow the fertilizer schedule found in the UF/IFAS EDIS publication, “Citrus Culture in the Home Landscape” by Robert E. Rouse and Mongi Zekri: https://edis.ifas.ufl.edu/pdf/HS/HS132/HS132-11822781.pdf
A final interesting thing about the key lime is the ripening stages of the fruit. Because key limes are ever-bearers, blooms can develop at sometimes widely varying times. This causes an uneven development of fruit across the tree. Be sure to wait until the fruit turns begins to turn yellow before harvest. That’s when it’s mature to eat! Fruit can be stored for up to a week in the fridge or can be juiced and stored in the freezer for later use.
Please contact your local county Extension office for more information. Happy Gardening!
Information for this article can be found in the UF/IFAS EDIS publication, “Key Lime Growing in the Florida Home Landscape” by Jonathan H. Crane: https://edis.ifas.ufl.edu/publication/CH092
UF/IFAS Extension is an Equal Opportunity Institution.
The Sunshine State produces a wide selection of citrus, with a number of varieties that can be grown right here, in your Panhandle dooryard. And, what is more satisfying than picking fresh fruit from your very own trees? So, are you looking for a different variety to plant? The ‘Parson Brown’ sweet orange may be of interest. It can certainly add uniqueness to your dooryard citrus grove.
Originating in China, orange varieties began being introduced in Europe in the fifteenth century. As for introduction to America, Columbus brought orange seeds to the new world on his second voyage in 1493. The first plantings in Florida were around 1513 in the settlement of St. Augustine. For the ‘Parson Brown’, a chance seedling originated at the home of Reverend N.L. Brown near Webster in 1856. Sumter and Seminole counties are still home to some of the largest densities of ‘Parson Brown’ orange trees in the state.
Figure 1: ‘Parson Brown’ Sweet Orange. Credit: D.P.H. Tucker, Ray Bodrey, UF/IFAS.
The Parson Brown, however, is often overlooked. The most popular dooryard sweet orange varieties grown throughout Florida are Navel, Hamlin, Valencia and Pineapple. Availability of this variety in our region is not easily found either, as you may have to search to find a tree.
Unlike the short, round appearance of many citrus trees, the Parson Brown tends to grow tall and slim. The Parson Brown’s more upright tree structure is very distinctive. A specimen will certainly stand out in a grove. The fruit and yield rival a Hamlin orange, particularly when grown in heavy, hammock soils rather than sandy soils with low organic content. The variety is also not as marketable as the Hamlin on a commercial level, due to the heavier seediness. You can expect at least 10 seeds per fruit. Average diameter of fruit is between 2 ½” to 2 ¾”. Harvest season for fruit is generally between October and January. Evidence suggests that along with the ‘Sugar Belle’ variety, the ‘Parson Brown’ may be more disease resistant, specifically more tolerant to citrus greening. HLB or citrus greening is a disease that has devastated both commercial production and dooryard citrus across the state.
Contact your local county extension office for more information. Also, for more information on growing citrus in Florida, see the UF/IFAS Extension EDIS publication, “Citrus Culture in the Home Landscape” by Robert E. Rouse and Mongi Zekri.
UF/IFAS Extension is an Equal Opportunity Institution.