Why Are My Oranges Sour?

Why Are My Oranges Sour?

From time to time we get questions from clients who are unsatisfied with the flavor of the fruit from their citrus trees.  Usually the complaints are because of dry or fibrous fruit.  This is usually due to irregular irrigation and/or excessive rains during fruit development.  However, we sometimes get asked about fruit that is too sour.  There are three common reasons why fruit may taste more sour than expected: 1) The fruit came from the rootstock portion of the tree; 2) The fruit wasn’t fully mature when picked; or 3) the tree is infected with Huanglongbing (HLB) a.k.a. citrus greening or yellow dragon disease.

Rootstock

The majority of citrus trees are grafted onto a rootstock.  Grafting is the practice of conjoining a plant with desirable fruiting characteristics onto a plant with specific disease resistance, stress tolerance (such as cold tolerance), and/or growth characteristics (such as rooting depth characteristics or dwarfing characteristics).  Citrus trees are usually true to seed, but the majority of trees available at nurseries and garden centers are grafted onto a completely different citrus species.  Some of the commonly available rootstocks produce sweet fruit, but most produce sour or poor tasting fruit.  Common citrus rootstocks include: Swingle orange; sour orange; and trifoliate orange.  For a comprehensive list of citrus rootstocks, please visit the Florida Citrus Rootstock Selection Guide.  A rootstock will still produce viable shoots, which can become dominant leaders on a tree.  In the picture below, a sour orange rootstock is producing a portion of the fruit on the left hand side of this tangerine tree.  The trunk coming from the sour orange rootstock has many more spines than the tangerine producing trunks.

A tangerine tree on a sour orange rootstock that is producing fruit on the left hand side of the tree.

A tangerine tree on a sour orange rootstock that is producing fruit on the left hand side of the tree. Photo Credit: Matt Lollar, University of Florida/IFAS Extension

Fruit Maturity

Florida grown citrus generally matures from the months of October through May depending on species and variety.  Satsumas mature in October and taste best after nighttime temperatures drop into the 50s.  Most tangerines are mature in late November and December.  Oranges and grapefruit are mature December through April depending on variety.  The interesting thing about citrus fruit is that they can be stored on the tree after becoming ripe.  So when in doubt, harvest only a few fruit at a time to determine the maturity window for your particular tree.  A table with Florida citrus ripeness dates can be found at this Florida Citrus Harvest Calendar.

Citrus Greening

Citrus Greening (HLB) is a plant disease caused by the bacterium Candidatus Liberibacter asiaticus, which is vectored by the Asian citrus psyllid.  The disease causes the fruit to be misshapen and discolored.  The fruit from infected trees does not ripen properly and rarely sweetens up.  A list of publications about citrus greening can be found at the link Citrus Greening (Huanglongbing, HLB).

A graphic of various citrus greening symptoms.

A graphic of various citrus greening symptoms. Photo Credit: University of Florida/IFAS Extension

Satsuma Harvest Season in North Florida

Satsuma Harvest Season in North Florida

Nice crop of satsuma fruit

Nice fall crop of satsuma fruit. Photo credit: Larry Williams

When asked what kind of citrus to grow here in North Florida, my default response is satsuma. I usually get a funny look, followed by an attempt by the person who’s asking to repeat the name satsuma. The individual may ask, “What is satsuma… is that a citrus?” I guess the person expected to hear orange, grapefruit, lemon or maybe tangerine.

Satsuma is a type of citrus, technically classified as a mandarin and is sometimes referred to as satsuma mandarin.  The satsuma mandarin is a good candidate for the North Florida citrus enthusiast for a number of reasons.

  • Historically, mature dormant trees have survived minimum temperatures of 14°F to 18°F when budded/grafted to a cold-hardy rootstock such as trifoliate orange or swingle, a trifoliate orange cross. Young trees are not as cold-hardy but, due to their smaller size, are more easily covered with a cloth such as a sheet or lightweight blanket for protection during freezes.
  • Satsuma fruit are ready to harvest October through December, ripening before the coldest winter temperatures. This is not true with most sweet citrus types such as oranges, which are harvested during winter months. Harvesting during winter works well in Central and South Florida where winters are mild but does not work well here in extreme North Florida. The potentially colder winter temperatures of North Florida are likely to result in the fruit on sweet oranges freezing on the tree before they are ripe, potentially ruining the fruit.
  • Our cooler fall temperatures result in higher sugar content and sweeter fruit.
  • Fruit are easily peeled by hand, have few to no seed and are sweet and juicy.
  • Trees are self-fruitful, which means that only one tree is needed for fruit production. This is important where space is limited in a home landscape.
  • Trees are relatively small at maturity, reaching a mature height of 15 to 20 feet with an equal spread.
  • Branches are nearly thornless. This may not be true with shoots originating at or below the graft union. Shoots coming from the rootstock may have long stiff thorns. These shoots should be removed (pruned out) as they originate.

Satsuma fruit are harvested in fall but trees are best planted during springtime when temperatures are mild and as soil is warming. Availability of trees is normally better in spring, as well. For additional cold protection, purchase a satsuma grafted on trifoliate orange rootstock and plant the tree on the south or west side of a building. There are a number of cultivars from which to choose.

For more info on selecting and growing satsuma mandarin, contact the UF/IFAS Extension Office in your County or visit the following website.

https://edis.ifas.ufl.edu/ch116

Vacation Hitchhikers

Vacation Hitchhikers

Photo from USDA APHIS

Remember last year’s vacation trip?  You picked the perfect location, checked into the hotel and made sure to check every mattress corner for bedbugs.  Bugs can hide in the strangest places.  Now with COVID-19 those people insisting on still taking a vacation are flocking to Northwest Florida.  While some are still utilizing hotels, the majority are pulling into the RV park or campground. They are bringing anything and everything anyone could possibly need for the week, from firewood to camp chairs.  That way no one will have to go to the store.  Somewhere on the vehicle or within all the stuff there may be some hitchhikers, insect stowaways. The problem is that these bugs may be staying even after the human beings head back north.  Florida is notorious for invasive species.  With 22 international airports and 15 international ports in the state, hundreds of foreign insects are intercepted each month.  But, not all the problem creepy crawlers are coming from the south.  Many have been introduced to northern states and work their way here.

One to keep an eye open for is spotted lanternfly (Lycorma delicatula).  The Asian native was first detected in Pennsylvania in 2014.  Since then it has spread to the east and south.  While the insect can walk, jump, or fly short distances, the quickest way for the spotted lanternfly to relocate is to lay eggs on natural and man-made surfaces.  Some of those egg masses may fall off and get left at the park. Next spring after the eggs hatch the nymphs will begin feeding on the sap of numerous plants, often changing species as they mature.  Host plants include grape, maple, poplar, willow and many fruit tree species.

Nymphs in the early stages of development appear black with white spots and turn to bright red before becoming adults.  At maturity spotted lanternflies are about 1 ½ inches wide with large colorful, spotted wings.

Photo from USDA APHIS

At rest their forewings are folded up giving the lanternfly a dull light brown appearance.  But when it takes flight its beauty is revealed. The bright red hind wings and the yellow abdomen are very eye-catching.  Remember, in nature bright colors are often a warning.  Though spotted lanternflies are attractive, they pose a valid threat to native and food-producing plants. The adults feed by sucking sap from branches and leaves.  What goes in must come out.  Sugar in, sugar out. Spotted lanternflies excrete a sticky, sugar-rich fluid referred to as honeydew.  Black sooty mold often develops on honeydew covered surfaces.

Spotted lanternflies are most active at night, steadily migrating up and down the trunk of trees.  During the day they tend to gather together at the base of the plants under a canopy of leaves.  So, you may need your lantern (or head lamp) to locate them.  If you find an insect that you suspect is a spotted lanternfly, please contact your local Extension office of the Florida Department of Agriculture and Consumer Services Division of Plant Industries.

Photo by USDA APHIS

Citrus Rust Mite is a Mostly Cosmetic Problem

Citrus Rust Mite is a Mostly Cosmetic Problem

Citrus Rust Mite “sharkskin” closeup – Image Credit Matthew Orwat, UF / IFAS Extension

In recent years, not a summer has gone by in which I did not see citrus rust mite (CRM) damage in a garden. I thought this year would be the first. Unfortunately, recently I saw my first rust mite damage of the year.

Unlike the myriad of pests that have been recently introduced into Florida from abroad, the citrus rust mite (Phyllocoptruta oleivora) has been documented as present in Florida since the late 1800s. Along with its companion, pink citrus rust mite (Aculops pelekassi) It can be a major summer pest for satsuma mandarins grown in the Florida Panhandle gardens.

Citrus Rust Mite (CRM)  damage manifests itself on fruit in two ways, “sharkskin” and “bronzing“. Sharkskin is caused when mites have fed on developing fruit, and destroyed the top epidermal layer. As the fruit grows, the epidermal layer breaks and as the fruit heals, the brown “sharkskin” look develops. Bronzing occurs when rust mites feed on fruit that’s nearer to mature size. Since the skin is not fractured by growth, the fruits develop a polished bronze look. In both cases, the interior of the fruit may remain undamaged. However, extreme damage can cases cause fruit drop and reduced fruit size. Regardless of the condition of the interior, damaged fruit is not aesthetically pleasing, but fine for slicing or juicing.

“Sharkskin Damage” to fruit caused by past feeding by the Citrus Rust Mite. Image Credit, Matthew Orwat

If a CRM population is present, they will begin increasing on fresh spring new growth in late April, and usually reach peak levels in June and July. By August the damage has often already been done, but is first noticed due to the increased growth of the fruit. Depending upon weather conditions, CRM can have a resurgence in October and November, just as Satsuma and other citrus is getting ready to be harvested, so careful monitoring is necessary. For more information, check out this publication: Guide to Citrus Rust Mite Identification.

Sun spot resulting from where citrus rust mite avoids feeding on most sun exposed portion of the fruit. Image and Caption courtesy of EDIs publication HS-806

If control of CRM is warranted, there are several miticides available for use, but it is not advisable for home gardeners to use these on their citrus plants since they will also kill beneficial insects.  Horticultural oil is an alternative to miticide, which is less damaging to beneficial insects. Several brands of horticultural oil are formulated to smother CRM, but care must be taken to not apply horticultural oil when daytime temperatures will reach 94 degrees Fahrenheit. Application of oils at times when temperatures are at this level or higher will result in leaf and fruit damage.

Although Citrus Rust Mite (CRM) has the potential to be aesthetically unsightly on citrus fruit in the Florida Panhandle, strategies of monitoring and treatment in homeowner citrus production have been successful in mitigating their damage.

Muscadines–Our Florida Wild Grape

Muscadines–Our Florida Wild Grape

Tasty, edible muscadine grapes are ripening in northwest Florida now. Photo credit: Jennifer Shiver

There is something deeply satisfying about plucking fruit off a plant growing outside and tasting it right off the vine/bush/tree. Since childhood, I have reached carefully through the tiny and numerous thorns of blackberry bushes growing in the woods, hoping the berry I’d worked for was more sweet than tart. One vine-ripe fruit that never disappoints, however, is the native muscadine grape (Vitis rotundifolia). Granted, before eating for the first time you have to be aware that the thick skin will give way to a gelatinous goo with several seeds, but their refreshing taste on a hot summer day is unlike any other. Beloved by deer and other mammals and birds of all types, it’s hard to find a lot of muscadine grapes available in the woods because the wildlife has likely beaten you to them. You can find their unique leaves year-round, though, so at least you know where to look once the grapes start to form. I would be remiss if I didn’t mention these grapes also go by the term “scuppernong”, which is a colloquial term for the lighter green/bronze (and more common) muscadines in the southeast.

Muscadines are grown commercially for the wine industry throughout Florida.

While tasty on their own, muscadines are most prized for making jelly and wine. We used to have an older Southern Baptist deacon and neighbor who would slip us both, with a wink and an implied promise not to tell the preacher about the wine. Winemaking in Florida is an old tradition, and several local wineries specialize in these sweeter wines, like Chatauqua in DeFuniak Springs. They are often blended with other fruits like blueberry and strawberry. Our Extension colleagues with the Florida Agricultural and Mechanical University (FAMU) have a widely recognized viticulture program, and I recommend their resources if you are interested in growing muscadines yourself.

As for wild muscadines, you can find the vines all over the place, from shady forests to sunny beach dunes. The vines can be up to 100 feet long, climbing with the help of small tendrils. Inconspicuous greenish white flowers form in late spring, with fruit ripening in late summer/early fall. It serves you well to learn field identification for the muscadine, as it is a sweet treat on a hot Florida day.

Fruit Drop & Fruit Split, the Heartbreak of Citrus

Fruit Drop & Fruit Split, the Heartbreak of Citrus

We’re lucky to live an environment where many citrus varieties can be grown. However, many problems can occur when growing citrus, but none more frustrating than fruit drop or fruit split.

Most citrus varieties are susceptible to fruit drop. This is a major cause of low yield in the Navel orange industry. Quite a few variables can cause the condition. This can be difficult to pin point, however. Ethylene gas production goes into effect when a citrus tree is injured, which can spark fruit drop. Our culprit this year may be the late summer excessive periods of rain, high temperatures and areas of poorly drained soils. Low potassium is thought to also be factor in fruit drop, so be sure to follow a fertilizer schedule every year. Competition between fruitlets and young leaves for carbohydrates, water, and other metabolites can be the reason for fruit drop early in the season, as well.

Figure 1: Fruit Split in Naval Orange.
Credit: Ray Bodrey, UF/IFAS Extension Gulf County

Fruit drop can especially affect mature trees. This could mean up to 25% of fruit loss. Brown rot can accompany this condition, if moisture persists for long periods. Fruit drop is usually associated with the lower, shaded areas of the tree canopy.

Fruit split is more severe in Valencia, Hamlin and Navel oranges. Grapefruit (and other acidic fruits like lemons and limes), Tangerines and Temple fruit are much less susceptible. What is thought to be the primary cause of fruit splitting? High temperatures and heavy rainfall during August can easily give rise to the condition. Excess water taken up by a tree during this time will swell the meat of the fruit causing it to grow quickly. Unfortunately, it is believed that the peel does not grow at the same rate. Damage often occurs as the peel eventually caves under the pressure. Nutritional stresses early in fruit development can also be a factor, as low potassium and copper levels have been correlated. The condition is more likely to emerge when no irrigation practices were in place during dry periods that existed earlier in the year

If fruit split has been a problem this year, ensure a recommended fertilizer program next year. Proper tree siting, nutrition and irrigation scheduling are the best defense against fruit drop and fruit split. Although these measures are not a cure all for the conditions, a healthy citrus tree is less likely to be affected. Contact your local county extension office for more information.

Supporting information for this article is from the UF/IFAS Extension EDIS publication: “Citrus Problems in the Home Landscape” by Mongi Zekri and Robert E. Rouse: http://edis.ifas.ufl.edu/pdffiles/HS/HS14100.pdf & information is also provided by Extension Fruit Crop Specialist, Dr. Pete Andersen with IFAS located at Quincy, North Florida Research and Education Center.

UF/IFAS Extension is an equal opportunity institution.