Diseases of Citrus and Avocado Trees

As just about everyone knows, southern Florida’s climate permits homeowners to grow
a vast and impressive array of fruit trees.  But the lower end of the peninsula is also a
sitting duck for the introduction of diseases and detrimental insects.  Lamentably,
Richard Lyons’ Nursery must now recommend that you no longer plant citrus and
avocado trees here.

What has led to this sad conclusion?  With citrus, it took a double whammy to make us
throw in the towel.  First came citrus canker, a disease that causes lesions, or wounds,
on the fruit, stems and leaves of many citrus species.  The responsible bacterium does
not carry a risk to human health, but it makes the fruit unsightly and weakens trees.
Dade County first experienced citrus canker a century ago, and it took many years to
eradicate it throughout the southeastern states.  The disease again popped up on the
western side of Florida in the mid-1980s, but was overcome in less than a decade.
Unfortunately, citrus canker made another serious incursion into Miami-Dade County in
1995.  After initial delay, the state took some controversial steps toward thwarting the
disease, but in the wake of the hurricanes of 2005 that spread the bacterium into many
new areas, the federal government ended support for the eradication program.

The second attack on citrus has been infinitely more ominous.  Citrus greening, or
Huanglongbing, also a bacterial disease, is spread primarily by a couple of species of
psyllids (so-called jumping plant lice).  An Asian strain of the bacterium 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.  Florida’s Institute
of Food and Agricultural Sciences (IFAS) advises that the psyllids can be treated by
insectides, but warns that “elimination of the disease from an area has never been
successful.”  And, finally, the agency adds that “[b]ecause of the highly infectious
nature of these citrus diseases fruit crops other than citrus should be considered for
planting in the home landscape.”

When it comes to avocados, the origin of the problem is unique:  It is the only plant
disease or insect pest to invade from north of Florida instead of from the tropics.  It
is known as laurel wilt disease, and it is a fungus that hones in on members of the
lauraceae, or laurel family, which include redbay, swamp bay and, alas, avocado.  It
works by destroying the vascular system which transports water throughout the plant.
The fungus is spread from tree to tree by the redbay ambrosia beetle, an Asian native.
(The beetle itself would likely not kill trees without the disease-causing fungus it
carries.)  Unfortunately, the beetle is commonly found residing in firewood, so it can
be introduced to an area by simply transporting cut wood of laurel family species.

The redbay ambrosia beetle was first detected in the U.S. at Savannah, GA in 2002, where it
probably arrived in solid wood packing materials, and it was found in Miami-Dade
County in swamp bay trees in February 2011.  The bad news outweighs the good news
about laurel wilt disease.  The good news is that avocados are not the preferred host
species for the beetle.  The bad news is that, nevertheless, the beetle has been found in
the commercial avocado grove area of southern Miami-Dade County, and there is as yet
no known effective biological or synthetic chemical treatment for laurel wilt disease.

Spring Has Sprung

The calendar said spring arrived weeks ago.  However, it remained on the cool side until this week.  We have had some rain the last few days which has resulted in a flush of new growth.  The plants which were experiencing the winter malaise have livened up.  There is new growth and the plants are much greener and healthier.  If we continue with these spring thunderstorms, it will definitely mark an early beginning to the rainy season.
This is a great time to plant.  However, I would hold off for another 6 weeks before moving any in ground plants.  If you intend to move plants which are in the ground, start the root pruning process now, and wait 6 to 8 weeks before you actually move them.  Finally, if you haven’t applied your spring fertilizer, now is the time to do it.
Please feel free to drop by the nursery to check out what’s blooming and get ideas to landscape your yard.  We are open every day except Thursdays from 8:00 am to 4:30 pm.

Lady Palm (Rhapis excelsa)

Almost everyone, whether a plant lover or not, knows the Lady Palm — if not by name, at least by sight — for it is one of the most successful indoor palms in use.  Because of its easy adaptability to low light and dry air, it graces interior landscapes in containers of all sizes at malls, offices, hotels and airports.  And yet, until the 1960s it was hardly seen in the U.S.A.

This palm, botanically known as Rhapis excelsa, is no longer found in the wild, but is considered to have been native to southern China, Taiwan and perhaps northern Vietnam.  The genus name is the Greek word for needle, and a form of it is repeated in the name of the Needle Palm, Rhapidophyllum hystrix.  In the 17th century, Rhapis was taken to Japan for use in the palaces of the Tokugawa shogunate, a feudal military government.  Later it was introduced to Europe, and by the end of the 18th century, the Lady Palm was a prized possession of conservatories in northern Europe.  The U.S. was thus a Johnny-come-lately to the appreciation of this species.

R. excelsa is a palmate species belonging to the wide-ranging subfamily Coryphoideae, which includes in its membership Corypha, Licuala, Coccothrinax and Washingtonia, as well as pinnate genera Phoenix and Caryota!  Its glossy blade, or leaf, about 8-12 in. wide, is deeply cut into segments.  It grows 12-13 ft. high and produces multiple thin stems.  Each stem is wrapped in dark fibers which may fall off as they age, revealing a smooth, ringed, bamboo-like cane.  No part of the species bears spines.

As an outdoor plant, The Lady Palm is very undemanding and grows well in a variety of soils, so long as poor drainage and salt are avoided.  Cold is never a problem for it in southern Florida, since it seems to be hardy down to 22°.  For best appearance, it should be grown in filtered light.  Exposure to full sun will turn leaves yellow-green, especially if good soil moisture is not maintained, and the tips of leaf segments will turn brown in the hottest months.

R. excelsa spreads via underground rhizomes which produce new shoots.  The shoots sometimes emerge from the drainage holes of containerized plants and can simply be clipped off.  However, if the owner wants to propagate the new plant and the container is not valuable, the pot can be sacrificed so that a longer piece of the runner can be obtained to preserve some roots.  New plants on the rhizomes of in-ground specimens can be similarly removed.  (A fungicide application to the cut end is also recommended.)  The important thing to remember is to pot up the offset immediately.  If potting is delayed and the rhizome cutting dries out, it will be virtually impossible to save.  The Lady Palm can, of course, also be propagated from seed, but the species seldom produces fruit in southern Florida.  For poorly-understood reasons, 2013 seems to be one of the rare instances in which mature white fruit has been observed on some established plants.

R. excelsa can be grown in containers for a long time, although occasional repotting is necessary once stems fill the capacity of the pot.  But one of the most valued traits of the species as an indoor plant is its slow growth rate, and a specimen may well be kept in the same container for a number of years.  Outdoors as a specimen plant, the Lady Palm is not only striking by day, in or out of the ground, but it can also be shown off well at night with underlighting.  In addition, it can also serve as a very attractive, dense screening element in the landscape.  It has a history of being fairly free of pests and diseases, although indoor specimens should be inspected for red spider mites from time to time.

This popular, dependable palm is available at Richard Lyons’ Nursery in 7-gal. and 15-gal. containers.

Rhapis excelsa (Lady Palm)

Rhapis excelsa (Lady Palm)

Rhapis excelsa (Lady Palm)

White Alder (Turnera subulata)

Meet Turnera subulata, also known as Yellow Alder, White Alder, Yellow Buttercup, Politician’s Flower and Sage Rose.  By whatever name you prefer, you’ll find a reliable, easy-to-grow plant that will provide lots of color in your garden.  T. subulata is a perennial herb that reaches about 2 ft. high and can be grown as a nice low shrub or ground cover.  It is generally considered native to the Caribbean Basin, although some observers have tried to broaden its natural distribution to include Florida, Mexico, Central America and South America.  This popular species not only attracts butterflies, but the brown “eye” inside each blossom lures bees to assist in pollination.  Flowers open at sunrise and fold at dusk, to be succeeded by new ones the next day.

The plant is not at all particular about soil types.  Moreoever, it does not require much in the way of fertilizer to support deep green foliage.  You should grow it in full sun to achieve best flowering and form.  This species has an open growth habit which can become leggy with age.  However, if you prefer a more compact look, simply cut stems back periodically to make your plants branch closer to the ground.  Aside from that exercising that option, maintenance on Turnera is minimal.

In at least two significant ways, T. subulata is superior to Impatiens: It is drought-tolerant once established, a feature of increasing importance now that Miami-Dade County is under permanent watering restrictions.   In addition, it flowers year-round.

T. subulata has proven to have medicinal value as an herbal remedy for coughs and bronchitis.  A study published by a Malaysian university in March 2012 reported that extracts prepared from various parts of this plant — particularly leaves — possess significant capacity to scavenge free radicals and reduce oxidants.

Richard Lyons’ Nursery has Turnera available in 1-gal. containers.

Turnera subulata (White Alder)

Turnera subulata (White Alder)

Turnera subulata (Yellow Alder)

Scarlet Sage (Salvia coccinea)

When Dr. Edwin Menninger bemoaned the “solid green” of Florida’s native flora, he must have forgotten about Salvia coccinea.  If you want to add brilliant color to your home landscape, please consider this striking native shrub.  Commonly known as Scarlet Sage, this herbaceous perennial from the family of lamiaceae is native to a huge range from South Carolina to Texas, then south into Central America and southeast into the Caribbean Basin.  It attains a height of 2-4 ft. and produces triangular leaves on long leafstems.  Bright red flowers roughly an inch long are borne in loose whorls on upright stems.  Over time cultivars have been developed to produce pink, white and bicolored flowers.  In southern Florida the plant blooms most of the year, but in the mid-south, flowering lasts until first frost.  Seeds overwinter in the ground and germinate when warm weather returns.

Scarlet Sage is not a very demanding plant, occurring naturally in dry soils.  However, during sustained rainless spells, flowering is not as prolific.  It performs best in sunny positions, but can tolerate intermittent shade.  S. coccinea makes a good, durable bedding plant and is particularly desirable as a butterfly and hummingbird attractant.  This plant is grown at Richard Lyons’ Nursery in 1-gal. containers.

Salvia coccinea (Scarlet Sage)

Salvia coccinea (Scarlet Sage)

Salvia coccinea (Red and Pink Sage)