Update on Avocado and Citrus

Over the past few years, Richard Lyons’ Nursery has reported from time to time on disease problems in avocado and citrus that have imperiled the future of both fruits as commercial crops in Florida. It is time for another update.

Avocados have been hit hard by laurel wilt, a disease spread by Xyleborus glabratus, the redbay ambrosia beetle. The insect, native to Asia, was first detected in Georgia in 2002, and has spread in all directions rapidly since then. Though the beetle’s primary interest is redbay trees, once it decimated those populations, it began to attack avocado, another member of the laurel family.  Originally, it was thought that the ambrosia beetle was the only beetle spreading the laurel wilt disease, but recently several other beetles have been identified in the spread of this fungus.

The quarterly magazine Modern Farmer recently reported that about 40,000 avocado trees have been lost in Florida. That is particularly ominous for Miami-Dade County, where traditionally 98% of the state’s commercial avocados have been grown.

Avocado trees are sitting ducks in the assault by laurel wilt. That’s because their root systems grow shallowly and radiate laterally. It means that in a commercial grove, where the root systems of trees touch—and, in fact, graft with—one another, a pathogen like the fungus that causes laurel wilt is able to spread through the plot fairly quickly. In addition, by the time a tree exhibits a physical manifestation of laurel wilt disease, such as the browning of leaves, it is too late to save the tree.

Accordingly, early detection of laurel wilt has come to be recognized as highly important to the effort to slow the spread of the disease. Research funded by the Florida Department of Agriculture and Consumer Services has led to the use of dogs trained to detect the scent of the laurel wilt fungus before an infected tree shows outward signs. First a drone is flown over an orchard to spot trees with browning canopies; those trees are removed, and the dogs are then released into the orchard to detect any trees in the early stages of infection. Those trees undergo a program of treatment to attempt to save them. However, the cost of identifying and treating diseased trees is high, so while detection via canine olfactory sensitivities is quite helpful, it nevertheless is best recognized as a mechanism that doesn’t stop the spread of laurel wilt disease, but, rather, slows it until a cure can be developed.

Meanwhile, the outlook for citrus in Florida, particularly the southern part of the state, is also tenuous. In recent decades, the family has encountered the one-two punch of citrus canker and citrus greening. The latter scourge, though more recent, is the more threatening, because it is much more likely to kill afflicted trees.

Citrus greening, also known as Huanglongbing (HLB), is caused by a bacterium that was discovered in southern Florida in August 2005 and has proved to be a formidable threat. Leaves of infected trees become chlorotic, or yellow; the visible symptoms of this chlorosis are typically referred to as “blotchy mottle.” In fact, that is probably the most reliable diagnostic symptom of citrus greening disease. The yellowing may show up in a single branch, particularly in a younger tree, and then spread throughout the plant in a year’s time. Developing fruits are misshapen and remain green instead of ripening, and their taste is rendered bitter. The disease, which, like citrus canker, is not harmful to humans, is incurable in plants, and most affected trees die within several years. The drop in orange production has been precipitous. The State of Florida last February lowered its prediction for the 2017-18 season to 45 million boxes; the high-water mark in orange production was 244 million boxes in 1997-98.

Researchers in citrus-growing regions around the world have been working earnestly for methods of cure or treatment of citrus greening. One proposal several years ago involved infusing an infected tree with antibiotics. But that required placing a cover or tent over the entire tree, a labor-intensive and expensive process. There doesn’t appear to be any recent writing on the subject.

In April 2018 it was reported that more traditional applications of bactericides—two brands of oxytetracycline and a streptomycin compound—had had variable results following three years of testing, and success appeared related to the number of annual doses. Other potential treatments have emerged in recent years. One is Benzbromarone, a drug developed to treat gout. Another is Zinkicide, a bactericide specifically created to work systemically within affected trees.

It must be emphasized that even if one or more of these chemicals makes it through the testing and regulatory processes to become commercially available to growers at reasonable prices, they are not cures for citrus greening. They are management techniques that might keep infected trees healthy enough to increase yields. A true cure for HLB does not yet appear on the horizon.

If all the foregoing obstacles weren’t enough, there is an additional challenge for backyard and commercial citrus growers in southern Florida—our alkaline soil. Upstate a number of desirable cultivars are grafted onto rootstocks that perform well in that region’s soils. Unfortunately, those rootstocks are incompatible with our limestone-based soils, and the fruits produced here are pithy, dry, and bitter.

For all the reasons described above, Richard Lyons’ Nursery recommends against planting avocado and citrus species in southern Florida, and it will not again stock them until a cure is found for laurel wilt and citrus greening.

We have Jackfruit

Jackfruit on the tree

Artocarpus heterophyllus (Jackfruit) on the tree.

I know some of you have been waiting since last season ended. The wait is finally over. The jackfruit is back, and we have a beautiful fruit this year.

If you aren’t familiar with jackfruit, this is a tropical treasure. It has a unique flavor somewhere between banana and pineapple mixed with other tropical notes of flavor. The spiny fruits are spectacular in size and can get upwards of 70 pounds.

For a really unique experience, come by our nursery in Miami today and buy some jackfruit for a taste of this Asian treasure.

 

Tropical Fruit – A Tasty Survey, Part VII

This week we look at more of the interesting tropical fruit trees that can be grown in southern Florida.

Ice Cream Bean (Inga edulis)

It’s no mystery how this tree earned its common name: From the sweetness and texture of its popular fruit. Word about I. edulis got out so long ago that its exact native range is not certain, but experts believe it was found from Mexico south through Central America and into the Amazon Basin. In deep soils, the tree can mature to a height of 60-95 ft., but the shallow and nutrient-poor soils of our region modify its size.

The Ice Cream Bean tree produces a flower spike that bears fragrant white blossoms. The fruit is a ribbed cylindrical pod about a yard long. The seeds are surrounded by the sweet pulp, which can be eaten out of hand or used to flavor a number of dishes.

I. edulis is a very versatile plant in the tropics. It makes an excellent shade tree, and that means that it is valuable not only as an ornamental for streets and parks, but in agriculture to protect cacao, coffee or tea plants from intense sun. And its size is easy to control, because it is amenable to being pruned back hard. This species also is a source of construction-grade wood and, in folk medicine, a treatment for various ailments.

I. edulis is often found growing next to rivers or in floodplains that are inundated for several months a year. Nevertheless, it can also tolerate some drought once established. Happily for residents of southern Florida, this species is not particular about soil quality. In fact, as a nitrogen-fixer, it is capable of improving soils.

Macadamia (Macadamia integrifolia)

The guillotine was named for the man who helped develop its prototype. Not everyone would want to be remembered exactly like that. Dr. John Macadam, on the other hand, was a very lucky man. A friend of the 19th-century Australian scientist named a tree genus after him in 1858, and 31 years later the first commercial Macadamia plantation was established. The nut tree has gone on to be cultivated in a number of places around the world, particularly South Africa and the United States. So far, it is the only native Australian plant to become a major commercial food crop.

M. integrifolia is, like the other three Macadamia species, endemic to Australia. It is native to rainforests of southeast Queensland. A small tree that matures to about 30 ft. in southern Florida, it possesses ornamental as well as agricultural value. Its dark green, glossy, oblong leaves—often featuring wavy margins—create an attractive spreading canopy. The tree produces pendulous white to pink flowers, followed by a fruit measuring 1-1½ in. in diameter. Although the fruit’s outer husk is hard, the wall, or shell, of the kernel is even denser, and cannot be cracked by a typical handheld device.

Macadamia is not very particular about soils, although it is averse to heavy clay compositions. Good drainage is a must, and in areas of rocky soil, a deep planting hole should be dug. The species likes ample moisture, even heavy rainfall, but is also tolerant of drought once established. Its tolerance of salt air is rated as good. It should be planted in full sun for best performance.

Jaboticaba (Myrciaria cauliflora)

Jaboticaba is the Brazilian term for four very similar species of Myrciaria that produce one of the more interesting-looking tropical fruit trees in the southern half of Florida. The name of the best-known of those species, M. cauliflora, suggests why: It is cauliflorous, meaning that its flowers and fruits are borne directly on the woody stems and trunk of the tree. Jaboticaba is native to southeastern Brazil, as well as parts of Paraguay, Bolivia, and Argentina. Because of that southerly origin, mature specimens can tolerate periods of brief frost into the upper 20s. The species was introduced to Florida just over 100 years ago, reportedly in Brevard County. It grows very slowly and, in the shallow soils of southern Florida, rarely exceeds 15 ft. (The slow growth rate also makes Jaboticaba popular as a bonsai subject.) While the tree prefers mildly acidic soils, it adapts fairly well to alkaline sites, especially when good nutrition is provided. For best fruiting, trees should be grown in full sun, and the soil at the planting site should be well-aerated. While ample soil moisture is a must for Jaboticaba, good drainage is also essential, so be sure to plant the tree 2-3 in. above the surrounding soil. This genus is not salt-tolerant.

Jaboticaba performs much better in cultivation than under natural conditions. Although a tree may not begin to flower for eight years, given appropriate moisture and fertilization it will eventually flower and fruit several times a year. The flowers are small and white, and the leathery skin of Jaboticaba fruit ripens in a range of color from purplish-maroon to almost black. The period from flowering to fruit harvest is encouragingly short—20-30 days. The fruit, which ripens an inch or so in diameter, has a grapelike appearance, but contains just 1-4 large seeds. The gelatinous flesh is white to pink, and its flavor ranges from sweet to subacid. Since the fruit has a fairly short shelf life, it is usually eaten fresh, but is also used to make jams, jellies, pies, and alcoholic beverages. Fruit skins are known to have medicinal value and are said to be processed for anti-cancer compounds. However, consuming the raw skin more often than occasionally is not recommended due to its high tannin content.

These species are available in various sizes at Richard Lyons’ Nursery.

Tropical Fruit – A Tasty Survey, Part VI

This week we continue our survey of the interesting tropical fruit species that can be grown in southern Florida.

Sapodilla (Manilkara zapota)

This species is not only among the most ornamental of tropical fruit trees, but it is blessed with long life, strength and wind resistance. Because the sapodilla has been popular for many centuries, its native range is a bit hazy; however, it is thought to have been the Yucatan (and nearby parts of southern Mexico), northern Belize, and northeastern Guatemala. It has probably been cultivated all over Central America for millenia, and during the age of colonization, it was distributed into the Old World. For instance, it reached Ceylon (now Sri Lanka) in 1802. Closer to home, it was long ago spread throughout Caribbean islands and nearby land masses, where it is often known as níspero.

M. zapota in southern Florida matures to about 45 ft. in height, with a spread of about 40 ft. It is fairly slow-growing, a feature that contributes to its wind resistance. It features dark, smooth, glossy leaves and a dense crown. One of its most useful cultural traits is its comfort with limestone soils, so long as good drainage is provided. The species is also salt-tolerant and, once established, drought-tolerant. Accordingly, it is a good candidate for installation in poor, unirrigated sites. For optimum performance, it should be grown in full sun. It has a well-earned reputation as an excellent shade tree.

Sapodilla flowers are white, but not particularly showy. They yield sweet-tasting fuzzy, brown-skinned fruits that mature to about 4 in. in diameter. The period from flowering to fruit ripeness is about 10 months. The color of the fruit’s flesh ranges from dark brown to reddish-brown to pale yellow, and the texture is grainy, likened by some to that of a very ripe pear. The fruit is ready for picking and eating when the skin softens. Immature sapodillas have a hard skin which exudes a white latex, called chicle, when cut open. Chicle was an early source of chewing gum. It was introduced to the U.S. in 1866 by the infamous Mexican general, Santa Anna, upon his arrival in, of all places, Staten Island, where he lived in exile for a few years. Later the name of the latex was incorporated into the commercial brand Chiclets.

Elephant Apple (Dillenia indica)

This quaintly-named species is a midsized tree native to a wide swath of southeastern Asia—from the Indian subcontinent south and east into parts of China and Vietnam and then through Thailand to lMalaysia and Indonesia. It was first described botanically in the mid-18th century by Carolus Linnaeus. It is yet another fruit tree that doubles as a very attractive ornamental.

In southern Florida, D. indica can reach about 40 ft. high at maturity. It develops a nice rounded crown, and its leaves are likewise attention-getting—leathery, toothed at the margins, and prominently veined. Its large, fragrant flowers, featuring white petals and yellow sepals, are also appealing. The tree is at its best when planted in a well-drained soil in full sun.

The fruits of this species grow to 4-5 in. in diameter. They’re called Elephant Apples because Asian elephants are crazy about them. As a result, our pachyderm friends are important in the dispersal of Dillenia seeds, if you know what we mean. The reduction in elephant populations might bode poorly for the future of D. indica, but the species has tucked an alternative system of distribution in its back pocket: Although the hard fruits can’t be accommodated by small animals, they do soften on the forest floor during the dry season, after which they can be ingested by squirrels, macaques, and rodents. Happily, the seeds tend not to lose viability over the course of the dry season.

The fruit of the Elephant Apple tree is acidic and fibrous, so it tends not to be eaten out of hand. Rather, it is valued as a component of many food dishes. In India, the pulp is used with spices and coconut in the creation of chutneys. The fruit is also used in drinks, and is also a component of jams, jellies and curries.

A very versatile species, D. indica is said to possess medicinal properties, and its wood is sufficiently strong to be used for gunstocks and light construction.

These two popular species are available in several sizes at Richard Lyons’ Nursery.

Tropical Fruit – A Tasty Survey, Part V

This week we look at more of the interesting tropical fruit species that can be grown in southern Florida.

Loquat (Eriobotrya japonica)

Right off the bat, we have a couple of confessions to make: Loquat is not a tropical fruit, and in spite of its specific epithet ‘japonica,’ it’s also not Japanese. The truth is that it is native to the temperate middle of China. Its pleasing taste led to its introduction to Japan, where it has been cultivated for over a thousand years. It is now just as likely to be called Japanese Plum as Chinese Plum, and Japan is the world’s leading commercial producer of the fruit. So popular is loquat that in Asia alone some 800 cultivars have been developed.

E. japonica grows as a tall shrub or small tree. In our part of the world, it matures in the 10-25 ft. range. The plant has a lot of desirable characteristics: It bears leathery, textured, lanceolate leaves with serrated edges. The leaves are dark green on the upper surface and light green below. Flowers are fragrant, and fruit of the cultivars most commonly found in Florida ripens in the yellow-orange range.

Loquat is a winter-flowering plant. That can make fruit production in the southern Gulf states unpredictable, because frost at the wrong time can kill flowers and developing fruit. Fortunately, that’s a small risk in southern Florida, and fruiting here is often abundant. Depending on the cultivar, the flavor ranges from sweet to subacid to acid.

E. japonica flowers best when grown in full sun. Established plants exhibit some drought tolerance. Fruit is high in Vitamin A, and the plant’s dense wood is valued in furniture-making.

Pineapple (Ananas comosus)

The pineapple is a very interesting plant. People are generally surprised to learn that it is a bromeliad, and, in fact, it has the greatest economic significance of any bromeliad. The plant doesn’t just produce a popular fruit—actually an aggregate, a collection of berries that coalesce into a single body. It also contains the enzyme bromelain, which is processed into meat tenderizer, and its leaves provide a valuable fiber. The genus name ‘Ananas’ comes from the word that the Tupí, a Brazilian indigenous people, used for the plant. ‘Pineapple’ probably arose from an English translation of the term that Columbus coined while under the misconception that he was looking at a conifer.

A century ago, pineapples were grown commercially in Miami-Dade County, generally in the Miami neighborhood known as Lemon City. But because the crop is slow to mature and because land values began to rise, the farmland was sold off for development. Currently Richard Lyons’ Nursery grows an edible pineapple, Ananas comosus (Smooth Cayenne Pineapple), which is very flavorful, but much smaller than the commercially-grown pineapples produced around the tropics.

As an aside, it may surprise some to find out that Hawaii is no longer a significant source of pineapples. Just as in southern Florida, land values in the islands made it uneconomical to farm pineapples commercially.  By 2013, Hawaii-grown pineapples constituted just a tenth of a percent of the world’s production!

Spanish Lime (Melicoccus bijugatus)

Here is another of those species blessed with a multitude of common names. To cite just a few, it is known as Spanish lime, mamoncillo, genip, and quenepa. Native to northern South America and Margarita Island off Venezuela, M. bijugatus has been distributed widely in the New World and as far away as the Philippines. It has been grown in southern Florida for at least 75 years.

The popularity of Spanish lime is based on its value as both an ornamental and a fruiting species. It has become a reliable street tree in many places, including Key West. Happily, it is tolerant of dry conditions, increasingly so as it matures, but does not withstand flooding well. M. bijugatus is also quite comfortable growing in our region’s limestone soils. It grows slowly, and may eventually reach 85 ft. Good horticultural practices pay off with this species. After the first year in the ground, a pruning regimen should be started to encourage lateral branching. As time goes by, pruning practices should also include keeping the canopy open by removing crisscrossing branches and dead wood.

Spanish lime produces fragrant, small, white flowers which attract hummingbirds and bees. This species is almost always dioecious, so fruit production will depend on having both a male and a female tree. Mamoncillo fruit ripens in loose clusters and is popular simply eaten out of hand. The fruit tastes best if allowed to ripen on the tree, and the entire fruiting cluster should be picked after one of the fruits is sampled for ripeness. The skin is green, smooth, thin, and brittle. Consumers usually just rip it open, pop the pulp into their mouths and slurp it off its prominent seed. Unopened fruit keeps well, so it can be carried around for days.

These three species are available at Richard Lyons’ Nursery in various sizes.