Meet Dr. Gary Knox!

Meet Dr. Gary Knox!

Gary Knox is professor of environmental horticulture and Nursery Crops Extension Specialist at the University of Florida/IFAS at the North Florida Research and Education Center (NFREC) in Quincy. Dr. Knox is heavily involved in research and extension on nursery/landscape problems like Rose Rosette Disease, Crapemyrtle Bark Scale, and invasive plants. On a more uplifting note, he also evaluates perennials for their attractiveness to pollinators, and new woody plants for their ornamental qualities and usefulness in Florida landscapes. These plant evaluation activities largely take place in “Gardens of the Big Bend,” a new botanical, teaching and evaluation garden established in 2009 and located on the grounds of NFREC. The Gardens are a collaboration of NFREC with Gardening Friends of the Big Bend, Inc. (GFBB), a nonprofit volunteer group of gardening enthusiasts and Green Industry professionals. Members of GFBB actively volunteer to develop, maintain and fund-raise for the Gardens as well as assist Dr. Knox with research and extension activities.

This 2019 photo shows Gary at the fabulous gardens and fountains of Villa d’Este in Tivoli outside Rome, Italy.

Gary’s current plant passions include magnolia, crapemyrtle, camellia, hydrangea, Southern bulbs, succulents, and palms (so many species, so little time!). It’s no secret that he is particularly fond of magnolias, going so far as to serve four years as president of Magnolia Society International (MSI), the organization supporting magnolia conservation and research. Gary’s roles with UF and MSI have taken him from Cuba to China and England to Ecuador promoting magnolia conservation and research. Furthermore, Gary is a “Johnny Appleseed” of the magnolia world by collecting rare Magnolia species to propagate and share them with botanic gardens in Florida and nationwide to help conserve these species in as many places as possible. The collection of Magnolia species at Gardens of the Big Bend has been named part of the National Collection of Magnolia by the Plant Collections Network, a collaboration of the American Public Gardens Association and USDA.

When not gardening at home, Gary and husband Ken particularly enjoy travel, whether across the country to visit family, or abroad to visit inspirational gardens and historical sites and to meet people from other cultures. Otherwise, you might find Gary meeting friends to play cards and board games, attending civil rights-oriented events, or collecting vintage restaurantware made in his hometown of New Castle, PA. With more than 30 years under his belt at UF/IFAS, Gary is looking forward to retirement, but he’s not quite ready for it yet!

 

Rescue Your Summer Garden with Heat Loving Tropicals

Rescue Your Summer Garden with Heat Loving Tropicals

The dog days of summer are here with high temperatures and humidity. While this sultry weather forces humans to retreat to air conditioning, our gardens suffer because the high night temperatures cause temperate plants to stop flowering, lose vigor and pause growth. By August, many plants in the garden look as bedraggled and wilted as we feel after mowing the grass or trying to weed.

‘Moy Grande’ Hardy Hibiscus (Hibiscus spp.)

All is not lost: the fading flowers and fizzling foliage of traditional garden plants can give way to heat-loving tropicals! Plants that are native to tropical and subtropical climates are naturally adapted to heat, humidity and rain, easily standing up to the worst that our north Florida summers can throw at them. Tropicals offer bright flowers, bold texture and exuberant growth just when the rest of your garden melts in the heat. Tropical plants include trees, shrubs, vines, perennials, groundcovers or annuals, and there are tropicals for full sun, part sun or shade.

Tropical Plants for North Florida

Top tropicals for north Florida gardens are palms, bananas, hibiscus, and gingers. Palms are the iconic symbol of the Tropics. Native subtropical palms can give you the palm vibe without the worry of cold hardiness. These include cabbage palm and related palmettos in the genus Sabal, paurotis palm (Acoelorrhaphe wrightii), saw palmetto (Serenoa repens) and needle palm (Rhapiophyllum hystrix). Non-native European fan (Chamaerops humilis), jelly (Butia spp.), windmill (Trachycarpus spp.), date (Phoenix spp.), Washington (Washingtonia spp.) and other palms also grow well and are cold hardy in north Florida. Most palms grow best in full to part sun but palmettos, saw palmetto and needle palm can handle more shade. Saw palmetto, needle palm and most palmettos grow 3 to 6 ft. tall. European fan, jelly, paurotis and windmill palms grow 10 to 20 ft. tall, while cabbage, Washington and date palms often exceed 40 ft. For best appearance, palms often require special fertilizer (https://edis.ifas.ufl.edu/ep261).

Hardy Yunnan Banana (Musa yunnanensis)

Characterized by their large, bold leaves, bananas are another plant group associated with tropical weather and full sun. Hardier forms of banana that thrive here include Chinese yellow (Musella lasiocarpa), pink (M. velutina), basjoo (Musa basjoo), Yunnan (M. itinerans), and hardy Yunnan (M. yunnanensis). Chinese yellow and pink bananas grow about 5 ft. or more in height, whereas the others have mature heights of 20 ft. or more. Bananas benefit from planting in a location that blocks strong winds so as not to shred the leaves. Depending on the severity of our winter, these bananas may lose some or all leaves but they usually regrow in late spring once warm weather arrives.

The large, colorful and exotic-looking flowers of tropical hibiscus (Hibiscus rosa-sinensis) are associated with the tropics, though this hibiscus is less cold hardy here and is perhaps best enjoyed as a container plant. Other notable hibiscus for north Florida include Confederate rose (H. mutabilis), rose-of-sharon or althea (H. syriacus), and hardy hibiscus (many hybrids of H. moscheutos and other native species). Varying in height from 3 (hardy hibiscus) to 12 ft. (confederate rose), hibiscus thrives in full sun and moist, even wet, soil. Their summer flowers come in colors of white, lavender, pink and red and range in size from a few inches (althea) to the size of dinnerplates (hardy hibiscus)! Except for rose-of-sharon, these hibiscus die back in winter and re-emerge again in late spring.

‘Disney’ Ginger Lily (Hedychium coccineum)

Gingers are also symbolic of the tropics. Many produce complex or colorful flowers and often flowers or other plant parts are aromatic. Ginger lily (Hedychium spp.), spiral ginger (Costus spp.) and shell ginger (Alpinia spp.) have fragrant and colorful racemes or spikes of flowers that appear at the tops of stems 4 ft. to 6 ft. or more tall. Hidden ginger (Curcuma spp.) and true ginger (Zingiber spp.) are lower growing with flowers appearing in “cones” on tops of separate, short stems. Finally, the patterned leaves of peacock ginger (Kaempferia spp.) make a beautiful summer groundcover. Gingers grow best in part sun to part shade.

There are many other tropical plants including coral tree (Erythrina × bidwillii and E. crista-galli), pride-of-barbados (Caesalpinia pulcherrima), fatsia (Fatsia japonica), selloum philodendron (Thaumatophyllum bipinnatifidum), canna lily (the non-invasive Canna × generalis hybrids), peregrina (Jatropha integerrima), elephant ear (non-invasive Alocasia spp. types), Begonia spp. (annual, angelwing and rhizomatous types) and Caladium selections. Bamboos have a tropical look, but many grow aggressively and may be invasive in north Florida. Two recommended clumping bamboos are common bamboo (Bambusa vulgaris; growing 15 ft or more tall) and Chinese garden bamboo (Drepanostachyum falcatum; growing 12 ft. or more tall).

Cockspur Coral Tree (Erythrina crista-galli)

“Tropical” does not necessarily mean “non-native” as there are many Florida natives that provide summer color or texture and are heat loving yet cold hardy in north Florida. These include some palms (cabbage, palmetto, paurotis), ashe magnolia (Magnolia ashei), switchcane (Arundinaria gigantea, a native bamboo), hardy hibiscus (Hibiscus grandiflorus, H. moscheutos and others), golden canna (Canna flaccida), and maypop passionflower (Passiflora incarnata).

Disadvantages of Tropicals
Use of tropicals in your garden does have a downside. Most tropicals are water hogs and need regular irrigation. This isn’t a problem if our area experiences the normal patterns of summer thunderstorms. However, if we don’t receive regular rainfall, tropical plants create the burden of having to water them regularly or else their flowers wilt and leaves droop.

Another disadvantage of tropicals is the “off-season” appearance. Though they thrive in summer heat, they grow slowly during the cooler temperatures of spring and fall and some disappear altogether in winter. Some tropicals are not winter hardy in north Florida and must be replanted each year or undergo elaborate cold protection strategies to help them survive. Other tropicals will over-winter, but often are burned back by frosts, requiring labor to cut back the dead foliage and stems. Finally, tropicals usually require warm weather for growth to resume, and tropicals that die back will produce gaps in your landscape during winter, spring and early summer.

‘Portora’ Giant Elephant Ear (Alocasia sp.)

At the other extreme, some tropicals have such exuberant growth that they are invasive in north Florida. For example, almost all running types of bamboo and many clumping bamboos are invasive, other than those mentioned previously. Also avoid non-native canna (Canna indica), elephant ears (Colocasia and Xanthosoma spp.), Lantana (sterile forms are OK), and some non-native passionvines (Passiflora spp.). If you have questions about a plant’s invasiveness, check the UF/IFAS Assessment of Non-Native Plants in Florida’s Natural Areas, https://assessment.ifas.ufl.edu/.

 

Using Tropicals in North Florida
Tropicals are best used as accent plants to draw attention in summer when they look their best and the rest of the garden looks its worst. When used as accents, place them throughout the landscape so that winter damage or absences aren’t noticed. Concentrations of tropicals in one area will look great in summer but could look like a mass of dead foliage in winter! To create an entirely tropical-looking planting in north Florida, combine tropical plants with cold-hardy tropical lookalikes (a topic for another time!).

Plant tropicals in late spring once temperatures warm because they will grow slowly or even experience damage at temperatures below 50°F. Best practices for tropicals are to place them in the appropriate exposure for the particular plant (sun, part sun or shade) and keep them mulched. One common characteristic of tropicals is their need for soil moisture, necessitating irrigation to supplement rain. A rich soil or applications of organic mulches or compost can provide nutrients for growth, or light fertilizer applications in summer can boost growth.

Tropicals come alive in the heat of summer. When used in north Florida gardens, tropical plants provide pops of color, luxuriant growth and big, bold, dramatic texture that rescue our gardens from the doldrums of summer!

Perennial rhizomatous begonias add bold texture and color to north Florida gardens

Perennial rhizomatous begonias add bold texture and color to north Florida gardens

Article by Dr. Gary Knox, Professor of Environmental Horticulture at the UF/IFAS NFREC Quincy

Introduction

Rhizomatous begonias are a large group of Begonia species, hybrids and selections characterized by large, sometimes-colorful leaves arising from thick rhizomes that grow along the soil surface. White or pink flower clusters that appear in late winter and spring are an extra bonus with these plants. Some types can be used in north Florida as herbaceous perennials that add bold leaf texture and color as well as flowers to shady gardens.

Begonia mass planting

Common rhizomatous begonias such as Begonia nelumbiifolia, ‘Erythrophylla’ (“Beefsteak”), and ‘Ricinifolia’ have long been grown outdoors in south and central Florida gardens as herbaceous perennials. North of these areas, rhizomatous begonias were considered cold sensitive and thus used strictly as pot-grown plants grown indoors or protected over winter. Nonetheless, north Florida trials testing the performance of outdoor, in-ground plantings started in Tallahassee and Gainesville as long ago as the late 1980s and early 1990s. With the proven success of some rhizomatous begonias in north Florida, interest in these plants increased rapidly in the early 2000s. Since then, savvy north Florida gardeners have been delighted by the possibility of using rhizomatous begonias as interesting herbaceous perennials for the shade garden. While temperatures below freezing can damage or kill leaves, these plants will usually produce new leaves from the rhizomes once warmer temperatures return in spring.

Plant Description Under North Florida Conditions

Leaves of rhizomatous begonias are this plant’s most distinctive feature and are why this group is so appealing to gardeners. Leaves often are large, from a few inches wide to almost 3 ft. in diameter (as reported for the cultivar ‘Freddie’ under the right conditions). Leaf shape may be rounded, star-shaped or irregularly edged, and leaf colors include burgundy, red, bronze, chartreuse, silver, and various shades of green including one so dark as to be almost black. Many types have leaves displaying patterns of one or more colors and some have silver or red markings. Undersides of leaves are often burgundy-colored, and leaf stems (petioles) also may exhibit colors other than or in addition to green. Leaves may be smooth, textured, or fuzzy-appearing due to large numbers of sometimes conspicuous hairs. Some types have leaves with an interesting three-dimensional spiral located on top of the leaf where the leaf blade attaches to the stem.

Begonia ‘Big Mac’ foliage

Rhizomatous begonia rhizomes are thickened, fleshy stems 1 to 2 in. or more in diameter that grow, branch and spread horizontally at or just below the soil surface, often in the mulch or leaf duff. Adventitious roots develop along the rhizome, and dormant buds embedded in the horizontal stem can be stimulated to grow new leaves after damage, stress or when divided. With age, as rhizomes grow outward, the oldest part of the rhizome will stop producing leaves and eventually die.

The rhizomes contain water and food reserves that allow this type of begonia to survive environmental stresses like drought as well as leaf loss or damage from cold temperatures. Shoots and roots can grow from the rhizome even if leaves and roots are killed or damaged.

Flowers occur in late winter to spring, depending on the species, cultivar and weather, and are quite showy on some selections. Flowers typically are white to various shades of pink and occur in a cluster (technically called a cyme) held above the foliage, in some cases dramatically high above the foliage. Individual flowers may range in size from 3/8-inch to over 2 inches at their widest point and a flower cluster may contain a few to over 120 individual flowers, depending on selection and growing conditions. A mature rhizomatous begonia may have an extended period of flowering, providing weeks of color. This long floral display results from large numbers of flowers developing sequentially on an individual flower cluster such that new flowers are still forming long after the first flowers have opened. Furthermore, multiple flower clusters appear over an extended time period. Flowers occasionally are pollinated and form winged seed capsules, though seed production and viability are variable. After flowering, the leaves remain a point of interest in the garden due to their size, lush appearance, interesting shapes and colorful patterns.

Cultural Requirements, Use and Maintenance

Rhizomatous begonias grow best in light shade or indirect light but can tolerate morning sun. Plants thrive in rich, organic, well-drained soil that is moist but not wet. A layer of organic mulch or leaf litter often is enough to provide basic conditions for growth in most soils if they are well-drained. Accordingly, organic mulches or leaf litter should be applied regularly around plants. Fertilizer stimulates growth but decomposing organic mulches can provide adequate nutrients, except perhaps with poor or sandy soils.

Newly planted begonias should be watered regularly. After establishment, most rhizomatous begonias benefit from regular watering but only require irrigation during periods of drought or extended dry weather.

An individual plant makes an attractive specimen plant in a container or in the garden. With time, a rhizomatous begonia can spread and, in the garden, develop into a patch. Alternatively, planting large numbers of the same rhizomatous begonia can create a very dramatic garden border, mass planting, or groundcover, especially in spring when all plants are flowering. To achieve this effect more rapidly and with smaller numbers of plants, tips of rhizomes can be pruned to stimulate rhizome branching and result in a denser plant or patch. Rhizome tip pruning should be done after plants finish flowering. Plants can be divided and moved easily since only the rhizome is needed to establish a new plant, but this should occur after flowering and early in the growing season so plants have long enough to establish before cold weather.

For aesthetic purposes, dead or damaged leaves may be removed as needed but especially after frosts and hard freezes. Similarly, leaves that overwinter often become “ratty” in appearance with time and may be removed without affecting plant growth.

Potential Problems

Rhizomatous begonias have few pests or other problems. Mealy bugs can occasionally infest plants. As with other large-leaved plants, wind or physical contact can tear and damage leaves. In north Florida, winter frosts and freezes can damage and disfigure leaves or kill leaves entirely, causing them to lose structural integrity and collapse, appearing mushy. Foliage may be protected during cold weather by frost cloth, sheets or other typical cold protection strategies, though heavy coverings could themselves damage leaves.

Rhizomes themselves usually survive cold weather because they are insulated from low temperatures by being half-buried in the ground and/or being covered by mulch. Adding mulch regularly to rhizomatous begonia plants will provide increased freeze-protection. Also, their typical planting location under tree canopies protects plants from a radiation freeze. Soil drainage is a more important factor for rhizomes since wet soil conditions could lead to rot, particularly in winter.

Common Types and their Descriptions Under North Florida Conditions

With hundreds of species and thousands of cultivars and hybrids, rhizomatous begonias can be overwhelming. Many rhizomatous begonias look alike and even experts have difficulty distinguishing species and cultivars. Many grown in north Florida have their origins in Mexico, Central and South America, though the Begonia Family is huge and species are found nearly world-wide.

Begonia heracleifolia

Technically rhizomatous begonias include Rex begonias, a group derived from Asian native, Begonia rex, and known for their especially colorful leaves. However, most Rex begonias do not grow well in Florida’s heat, high rainfall and high humidity, and so these begonias are excluded here.

Begonias listed below represent types that have proven resilient and usually cold hardy in north Florida USDA Cold Hardiness Zone 8b.

Species:

Begonia heracleifolia: The species boasts star-shaped leaves up to 6 in. across on stiff, hairy, thick leaf stems (petioles) up to 5 in. long. Each of the pointed leaf lobes is edged in dark green and has a chartreuse stripe along the central midrib, adding contrast. Spectacular sprays of pale pink flowers appear in late winter in clusters measuring 3 ½ in. by 4 ½ in. on 6-in. flower stalks (pedicels). Each cluster contains about 30 or more flowers, each about 1 in. across. As the season goes on, foliage gets showier and showier. It often dies down after winter freezes but re-emerges in late spring.

Begonia nelumbiifolia

  1. nelumbiifolia: This cold hardy begonia is known for its exceptionally large, water lotus-shaped leaves, creating a stunning specimen. Individual leaves can grow as large as 18 in. by 14 in. on leaf stems as long as 36 in. but 12 in. by 9 in. leaves are more typical. As temperatures warm, new developing foliage continues to get bigger, growing into very large leaves by fall. There also is a form in which the medium green leaves have red veining. White flowers are displayed above the foliage in mid to late spring in airy clusters measuring 7 ½ in. to more than 12 in. across on stems up to 48 in. tall. Clusters may contain as many as an astounding 120 flowers, each about ¾ in. across at its widest point.

2. popenoei: Huge rounded leaves with red veins and undersides make this a specimen plant which can grow to 3 ½ ft. tall and wide. Hardy with protection, it throws up tall stalks with clusters of white flowers in late winter.

Cultivars:

“Beefsteak”: This catch-all name refers to the original beefsteak begonia, ‘Erythrophylla’, as well as many derivatives that look similar. Beefsteak begonias characteristically have rounded leaves with a glossy green to bronze top surface and reddish undersides. Leaves range in size from 4 to 7 in. in diameter, and flower clusters are on stems up to 18 in. tall. ‘Erythrophylla’ was developed in 1847 and is considered a tough, vigorous plant, hence the common name, “beefsteak”. Given the long history and vigor, ‘Erythrophylla’ and derivative beefsteak begonias have long been shared as pass-along plants, world-wide as potted plants and later as an in-ground Florida garden plant. One type has ruddy, evergreen leaves and long-lasting, bold pink flower clusters. The scalloped 4-in leaves are on short 5 ½ in. reddish leaf stems but are most notable for remaining undamaged by temperatures down to the mid 20s °F, long after all other begonias’ leaves have turned to mush. Mid spring finds this plant topped by numerous clusters of dark pink flowers, with the display lasting 6 weeks or more. Individual clusters are about 8 in. by 5 in. on flower stems about 12 in. tall. Each cluster contains about 20 flowers each about ¾ in. wide at its widest point.

Begonia ‘Big Mac’ in flower

‘Big Mac’: This is a large, vigorous plant with enormous star-shaped leaves having reddish undertones and red leaf stems. The plant grows about 3 ft. tall and 2 ft. wide. Individual leaves may grow up to 18 in. wide on 16-in. leaf stems but typical leaves on younger plants are 10 in. to 12 in. wide. Individual white flowers are an amazing 2 in. wide at their widest point in clusters measuring 7 in. by 12 in. and containing about 75 flowers. Cold winters will knock it to the ground, but this begonia re-emerges again in late spring. This plant was hybridized in 1982 by Paul P. Lowe in Lake Park, Florida.

‘Joe Hayden’: This begonia features dramatic, dark, lobed leaves with burgundy undersides. Leaves are up to 8 in. long supported by leaf stems up to 9 in. long. In spring, the plant is topped by light pink flowers held high above the foliage. Each cluster measures about 5 in. by 7 in. on flower stems up to 26 in. tall. Each cluster contains more than 100 individual flowers, each about ¾ in. across at its widest point. This selection was hybridized in California in 1953 by Rudolf Ziesenhenne, but many similar selections have been made and are often confused with ‘Joe Hayden’.

Begonia ‘Joe Hayden’

Many other cultivars are common, but other cold hardy types suitable for north Florida include ‘Caribbean King’, ‘Caribbean Queen’, ‘Washington State’ and the catch-all ‘Ricinifolia’ types (with large, castor bean-shaped leaves). New breeding by scientists and enthusiasts promises to deliver many more types of rhizomatous begonias with increased foliage cold hardiness and an expanded range of foliage types and colors. A major Texas nursery introduced a series of rhizomatous begonia hybrids marketed as Crown Jewel Begonia™. The series currently features five patent-pending cultivars that are promoted as landscape plants for Zone 8. Additional breeding work is ongoing in north Florida.

Availability and Propagation

Rhizomatous begonias are available from Internet/mail order nurseries, some American Begonia Society members, other gardening groups, and plant societies. The introduction of trademarked rhizomatous begonias like Crown Jewel Begonia™ show promise for wider availability of rhizomatous begonias from nurseries.

Rhizomatous begonias are easily propagated by division, separation of rhizomes, or by rhizome pieces. When planting, place the rhizome or pieces (as small as 2 in. long) horizontally and half buried in a new in-ground location or in a container with potting soil. As with other begonia species, leaves may be used for propagation, though this method usually takes longer to achieve a size suitable for planting in the garden. Plants can be grown from seeds but production time is similarly long.

References:

American Begonia Society. (2020) https://www.begonias.org/index.htm. Accessed 15 April 2020.

Ginori, Julian, Heqiang Huo, and Caroline R. Warwick. (2020) A Beginner’s Guide to Begonias: Classification and Diversity, ENH1317. Environmental Horticulture Department, UF/IFAS Extension. January 2020. https://edis.ifas.ufl.edu/ep581.

Lowe, Paul. (1991) Growing Rhizomatous Begonias in the Ground in Southern Florida. Begonian 58:89. May/June 1991. https://www.begonias.org/Articles/Vol58/GrowingRhizomatousBegoniasFlorida.htm.

Schoellhorn, R. (2020) Personal communication, Alachua, FL.

Sharp, Peter G. (2011) Down to Earth – with begonias. 111 pp. http://ibegonias.filemakerstudio.com.au/PeterSharp/DownToEarthWithBegonias.pdf.

The International Database of the BEGONIACEAE. (2020) http://ibegonias.filemakerstudio.com.au/index.php?-link=Home. Accessed 16 April 2020.

UF/IFAS Gardening Solutions. (2019) Begonias. http://gardeningsolutions.ifas.ufl.edu/plants/ornamentals/begonias.html.

Watkins, Sue. (2020) Personal communication, Tallahassee, FL.

Be on the Lookout for Rose Crown Gall

Be on the Lookout for Rose Crown Gall

Crown gall symptoms on roses caused by the bacterium Agrobacterium tumefaciens (Rhizobium radiobacter) – Photo credits: Kamil Duman

A plant with a mature gall that is potentially releasing the crown gall bacterium into the potting media. Photo credits: Susannah Wright

For gardeners, rose enthusiasts and rosarians, each of the many rose diseases is as important as the others. But we can say for sure Crown Gall is one of the most unsightly of the many rose diseases that can been seen currently.

The disease got this name from the large tumor-like swellings (galls) that typically occur at the crown of the plant, just above the soil level. The cause of crown gall disease is a bacterium that resides in the soil, Agrobacterium tumefaciens (updated scientific name Rhizobium radiobacter).

SYMPTOMS

Galls or overgrowth (1/4 inch to several inches in diameter) of host plant tissue typically form at the soil line but also can form on branches or roots. Galls are initially white, spherical, and soft but darken with age as outer cells die. It can either be almost entirely on the surface of the plant and easily detached or can be almost indistinguishable from normal plant tissue except for its greatly enlarged appearance.

The bacterium that causes Crown Gall disease survives and persists in the soil for up to 3 years. It can invade recent wounds on the branches or roots. Swelling can be seen as early as 14 days following entry of the bacterium into the plant. The tissue near the gall can be crushed due to rapid cell enlargement. If vascular tissue is crushed, wilting can result from the restricted water movement.

 

Early stage symptom of Crown Gall on roses can be noticed as the small white galls. Photo credits: Susannah Wright

The galls can enlarge to a quarter size in a short period of time from the initial small galls. Photo credits: Mathews Paret

ABOUT THE BACTERIUM

Agrobacterium uses its genes as a weapon to attack plants. It enters the plant mostly from the soil through wounds on the roots or lower stem or from the branches during plant pruning. Symptoms are caused by the insertion of a small segment of DNA (known as the T-DNA), from a plasmid, into the host plant cell, which is incorporated into the plant genome. When the plasmid links up with the plants own DNA, the altered plant cells start dividing rapidly and uncontrollably, and the root or stem develops a tumor-like swelling.

Galls can range from pea size to softball size. Tiny cracks from freezing temperatures or wound sites can be the site of gall formation. Once the wound compounds are generated, the bacteria detach from the xylem cell walls and are carried upward with water during evapotranspiration to the wound site where they initiate galls. One of the common ways of the spread of the disease is by pruning infected plants and moving the bacterium accidentally while pruning nearby healthy plants.

The crown gall bacterium is a soil pathogen, which means main inoculum source is soil. The bacterium can overwinter in infested soils, where it can live as a saprophyte for several years. The bacterium can easily during field preparation, pruning and irrigation. Insects, nematodes and grafting materials, can also transfer the bacterium.

The galls will turn dark in color as they age. Photo credits: Kamil Duman

 

HOW CAN YOU MANAGE ROSE CROWN GALL DISEASE

  • Plant only disease-free roses. Check very carefully before you buy plants for any kind of galls in the crown or branches. Use good sanitation practices in handling roses.
  • Plant in clean soil. Avoid areas with a history of crown gall infestation.
  • Avoid fields with heavy infestations of root-attacking insects and nematodes.
  • Select well-drained soil and irrigate from clean water sources.
  • Keep grafts and buds well above the soil line.
  • Destroy diseased plants as soon as you notice them to avoid cross-contaminating other plants, or pruning equipment. Also, do not keep infected plants with healthy plants, as the likelihood of accidental transmission through pruning is high.
  • Avoid mechanical injury to plants from tillage and hoeing. Provide winter protection so that the bark does not crack.
  • Disinfect pruning tools between plants. disinfect budding/grafting tools before and after use. Bleach (10%; equivalent to 0.6% sodium hypochlorite), or quaternary ammonium-based sanitizer are effective as disinfectants. Make sure to prepare fresh stock routinely.
  • If crown gall plants are noted, please let your local county extension agent know about it and they will be able to contact us for additional site-specific management plans if needed.

Gall formation at pruning sites indicating contamination of the plant during pruning. Photo credits: Kamil Duman

 

 

Authors: Kamil Duman, Susannah Wright, Fanny Iriarte, Barron Riddle, Gary Knox and Mathews Paret, University of Florida – NFREC, Quincy, FL

 

 

Plant Cupheas for Summer Flowers, Hummingbirds, and More

 

Cuphea ignea
Photo courtesy: Gary Knox

Cupheas are perennials that produce bright orange, red, yellow or purple flowers all summer and fall.  Some species are called cigar plants due to their tubular, cigar shaped flowers tipped in red or yellow (like a lit cigar). Others are sometimes called firecracker plants because their cylindrical flowers are bright red or orange (looking like a firecracker). By any name, their nectar-filled, tubular flowers are widely known for attracting large numbers of hummingbirds, butterflies and bees. In addition, young stems of some species are reddish, further adding color and contrast to the usually narrow, lance-shaped green foliage.

 

As a group, cupheas grow best in full to part sun (the brighter, the better) and well-drained, moderately fertile soil. Cupheas are drought tolerant once established, but grow faster and larger with regular moisture and occasional fertilization. Their origins in warm climates allow them to thrive in heat, but likewise make some species sensitive to cold winters. Those that are frost tender along the Gulf Coast are best placed in a sheltered location in the garden. Cupheas are pest and disease resistant and are not invasive in Florida. They are not truly deer resistant, yet reports suggest cupheas are not favored by deer.

Cupheas are great summer performers in bright, hot and dry locations. Flowering begins in summer and continues through fall until short days and cool weather reduce flowering or frosts cause dieback. Along the Gulf Coast, cool winter weather slows them down, so re-growth doesn’t occur until mid to late spring, and flowering usually doesn’t begin until days and nights are warm. Growth and appearance of many cupheas are improved if plants are pruned or cut to the ground in late winter.

Over 200 species of Cuphea are native to Mexico and the warm-temperate and tropical Americas. Of these and their hybrids, the cupheas listed below are great summer-flowering perennials for the northern Gulf Coast.

 

Cuphea micropetala
Photo courtesty: Gary Knox

 

Cigar Plant (Cuphea ignea)

This fine-textured plant produces red to orange tubular flowers about an inch long. This cigar plant is hardy to about 20°F. It grows about 2 feet tall and 3 feet wide along the Gulf Coast, though it would be a larger, evergreen shrub in warmer climates. This cuphea tends to have lanky growth, so occasional summer pruning will stimulate branching which results in more dense growth.

 

Cigar Plant or Candy Corn Plant (Cuphea micropetala)

Flowers are 1.5 inches long, emerge pale yellow and gradually turn orange from the base upwards, offering a colorful, two-tone effect. Foliage is hardy to 25-30°F and this cigar plant is root hardy to at least 15°F. Stems should be cut back to ground level in late winter to keep the plant tidy. Clumps spread slowly outward by rhizomes, and the plant will reach 3 feet tall and wide along the Gulf Coast.

 

Cuphea schumannii
Photo courtesy: Gary Knox

 

Orange Cigar Plant or Schumann’s Cuphea (Cuphea schumannii)

This sprawling, floriferous cigar plant prefers moist, well-drained soil to thrive. Barrel-shaped, 1- to 1½-inch blooms are orange and yellow and sometimes have small purple petals at the tips. Flowers cover the branch terminals in the heat of summer and into fall. This plant is hardy in Zones 8 to 9 (at least down to the mid 20s°F). Unlike many other cupheas, leaves of orange cigar plant are oval- to heart-shaped. Stems grow 2 to 3 feet tall and readily flop or fall over. Plan to give orange cigar plant lots of room to sprawl through the garden!

 

Cuphea ‘David Verity’
Photo courtesy: Gary Knox

 

‘David Verity’ Large Firecracker Plant (Cuphea ignea × micropetala ‘David Verity’)

This floriferous hybrid produces flowers that are dark orange with a short yellow-orange flared tip and purple filamentts. Well-adapted to the Gulf Coast, this plant is foliage hardy down to 25-30°F and root hardy to at least 15°F. In Zone 9 this plant will grow as an evergreen shrub up to 4 to 5 feet tall and wide, but it will be smaller in areas where frost or freezes occur. This selection is believed to be a hybrid between Cuphea ignea and C. micropetala that was given in the mid 1970s to David Verity, then the manager of the UCLA Mildred Mathias Botanic Garden. It was subsequently named for him when later brought into commercial production.

 

‘Vermillionaire®’ Large Firecracker Plant (Cuphea ‘Vermillionaire®’)

This new hybrid appears to be a superior cuphea because it grows as a naturally compact plant that produces more flowers than other selections. ‘Vermillionaire®’ grows about 24 inches or more tall and wide with a compact, mounding habit. Orange tubular flowers are produced continuously until late fall. This cuphea is too new to know the full extent of its hardiness, but it is expected to be a perennial in Zones 8 and higher.

 

Mexican Heather (Cuphea hyssopifolia)

Unlike the previous cupheas, this plant has small purple flowers, and some selections sport white flowers. Another difference is Mexican heather’s finely textured, bright green leaves. Gulf Coast Zone 8 plants are usually killed to the ground in winter, often recovering by summer but resulting in a compact plant growing less than 24 inches tall and wide. In Zones 9 and higher, Mexican heather is a larger-growing semi-evergreen tropical shrub. Reported pests are leaf-chewing beetles (Altica and Colaspis spp.) and the twig-dwelling lesser snow scale (Pinnaspis strachani). Mexican heather works well for edging beds or sidewalks, helping to define and soften pathways. Cultivars include Allyson, Lavender Lace, Purple Nurple™ and the white-flowered Monga (Itsy Bitsy° White) and ‘White Whispers’.

Bat-Faced Cuphea
Photo courtesy: Gary Knox

Bat Face Cuphea (Cuphea llavea)

Each 1-inch flower consists of a purple tube lipped with two red, upright lobes. By viewing the flower with its tip facing you, it takes only a little imagination to see the two red lobes resemble large “ears” above the purple “face” of a bat, hence the name. Along the Gulf Coast, bat face cuphea grows mound-shaped 8 to 24 inches tall and wide, depending upon the selection. It is very heat and drought tolerant but requires better drainage than the other cupheas. Bat face cuphea is evergreen down to the upper 20s°F and root hardy into the lower 20s°F. Improved forms of bat face cuphea include the cultivars, Flamenco Samba, Georgia Scarlet, Mellow Yellow, Miss Priss, Tiny Mice®, Sriracha™ Pink, Sriracha™ Violet, Torpedo, Vienco° Lavender and Vienco° Red.