Begonia Production Guide

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CFREC-A Foliage Plant Research Note RH-91-18

R.W. Henley, A.R. Chase and L.S. Osborne University of Florida, IFAS Central Florida Research and Education Center - Apopka 2807 Binion Road, Apopka, FL 32703-8504

BEGONIAS (Foliage types)

Botanists have described over 1,000 species of Begonia, belonging to the begonia family, Begoniaceae, from the tropics and sub-tropics of both hemispheres. Most of the cultivars in commercial production are complex hybrids of several of these species, a condition which makes them difficult to describe because the genetic backgrounds of most cultivars are not reported in widely distributed horticultural literature.

The term "foliage begonias" is used to indicate those begonias which are utilized primarily for their attractive leaves. The flowers which occur on these begonias, although they may be attractive, are incidental to the decorative foliage. The foliage begonias include: Rex begonias, some of the other rhizomatous begonias, iron cross begonia, some of cane begonias (including angel-wing begonias), and a few other miscellaneous begonia categories. This publication does not include information on the culture of wax-leaved begonias, Rieger begonias, and tuberous-rooted begonias.

Most foliage begonias are sold in pots ranging from 3 to 8 inches across. The greatest volume is grown in 4-, 5-, and 6-inch pots for mass market outlets. A few growers finish plants in 8-inch azalea pots for the commercial interiorscape market. There is also a limited retail store market for small begonias in 2 1/2- to 3-inch pots. Some cultivars which have leaves or stems that reflex or cascade are finished in 6-, 8-, and 10-inch hanging baskets. The brittle nature of begonia foliage and stems makes it more difficult to handle and ship than many others foliage plants. Packaging and shipping begonias should be done before plants become overgrown to minimize the risk of mechanical damage. Very large plants should be produced exclusively for local market.

Most foliage begonias, especially the Rex types, are very useful design elements because of the large selection of colors and patterns available. Although the majority of the foliage begonias are used as containerized specimens at tabletop level or on the floor, large plants can be massed in commercial planting in raised or ground level beds with breath taking results. In many cases the foliage begonias are an excellent alternative to some of the flowering potted plants because they offer different colors, textures and a product which outlasts most floral products by a considerable margin. Indoors most of the foliage begonias do best when the light levels are 150 to 500 foot-candles and the relative humidity is 30 percent or more.

CLASSIFICATION

Nomenclature of the begonia hybrids is quite variable among some producers. Because there are several hundred cultivars of foliage begonias in the trade, many with similar characteristics, and cultivar names have been lost and mixed during the many years, this group has been hybridized by both amateur and commercial horticulturists. It is understandable why there is confusion with nomenclature. It is also probable that some of the plants in cultivation were never given names by their originators. To further complicate the issue a number of growers have renamed plants with names to facilitate their marketing without concern for the legitimate (original) name.

The American Begonia Society, Inc. is a plant society, composed primarily of amateur horticulturists, which serves to stimulate interest in the cultivation of begonias. The Begonia Society also serves as the International Registration Authority for cultivars of Begonia. Registration of new cultivars is one of the best ways of documenting cultivated plants with detailed descriptions which facilitate the use of proper cultivar names in the future.

Due to the thousands of cultivars recorded from years of hybridizing, it is useless to attempt to develop a meaningful list of begonia cultivars in this publication. Instead a system of classification utilized by horticulturists based on type of root stock is provided. The system includes three major categories as outlined below:

The foliage begonias, as discussed in this publication, includes primarily Rex begonias, other rhizomatous begonias and some of the cane type begonias.

PRODUCTION

Although making controlled crosses and producing plants from the resulting seed is the primary means of obtaining new hybrids, most foliage begonias are propagated from leaf or leaf-chip cuttings. Whole leaf cuttings involve removing most of the petiole and lightly pressing the leaf blade at approximately a 45 degree angle into a clean peat-lite medium contained in either a community flat or a cavity tray. After the base of the leaf cutting roots, a number of small plantlets form from tissue next to the leaf veins.

A number of the foliage begonias will also form roots and plantlets on the leaf blade if cuts are made through the large veins over the leaf blade (lamina) and the point of each cut is kept in contact with the rooting medium. As clumps of plantlets grow from leaf cuttings they can serve starter plants for finished product or some of the plantlets can be separated and grown further to be used as transplants. A few of the plant tissue culture labs have grown foliage begonias successfully through the plug stage, but most have abandoned the crop because it can be propagated relatively easily and more economically through use of leaf cuttings. The cane type begonia are also easily propagated from stem cuttings (terminal stem cuttings, single node cuttings, and multiple node cuttings).

As with many other foliage plant crops, a few firms have emerged as propagation specialists, rooting the leaf cuttings and selling established plugs to plant finishers. Because the propagation process requires a high level of sanitation and greenhouse management, many growers prefer to start with plugs and concentrate their efforts on finishing high quality potted begonias.

Most of the foliage begonias grow well under temperatures of 62 to 85°F, actually the middle to lower end of the range is reported to be best. The light intensity for production should range between 2000 and 2500 foot-candles. Slightly brighter light levels will result in somewhat more compact plants but the intensity of foliage color patterns in some cultivars will be "washed out". Plants should always be forced in greenhouses as opposed to shadehouses because the greenhouse environment permits better control of water falling on the plants. Plants maintained with wet foliage usually acquire bacterial leafspot, a very serious disease discussed thoroughly later in this publication.

Proper plant spacing through all stages of plant production is crucial to production of healthy plants. Crowding causes longer petioles, more open plants and frequently results in development of bacterial leaf spot. Wider spacing permits the plants to dry off quickly after irrigation, especially if the greenhouse is well ventilated.

Growers are encouraged to use drip irrigation or some form of sub-irrigation on potted plants to prevent bacterial leaf spot, a disease which has seriously limited the production and utilization of Rex begonias until recent years. Avoid use of overhead irrigation systems if possible.

Foliage begonias have fine textured root systems, a condition which makes them vulnerable to mechanical damage during the potting process if liners are handled carelessly or potting medium is compressed excessively. Care should also be taken to set liners in the finishing containers so the plant crown is approximately the same level as it was in the liner container. Plants set too deep frequently fail due to poor root zone aeration and subsequent root rots. Plants set too high can succumb from lack of water.

Begonias grow well in many of the commercially prepared peat-based potting mixtures which have good aeration and water holding properties. Growers should use the cleanest mixes they can obtain for begonia production. Plants grow well with fertilization from a 3-1-2 or 2-1-2 ratio complete fertilizer with a minor element supplement at the rate of 2.3 pounds of actual nitrogen per 1000 square feet per month. Precautions should be taken to avoid accumulation of soluble salts in the root zone which will damage the fibrous roots.

Crop schedules for foliage begonias are dependent upon cultivar, initial plug size, pot size, number of plugs per pot, temperature, light intensity and other environmental factors. Growers use different planting densities. In general, one plug is used per 4- and 5-inch pots. Two plugs per 6-inch and 3 plugs per 8- and 10-inch pot or hanging basket.

Reference to University of Florida/IFAS Pest Control Guides

BACTERIAL PROBLEM

1) Xanthomonas leaf spot (Xanthomonas campestris)
 
Symptoms -
Begonias are commonly infected with this bacterium although some producers do not recognize the symptoms as a disease problem. Marginal necrosis and speckling are the most common symptoms. All types of begonias have been found susceptible to this pathogen.
Control -
The best way to control this disease is to establish plants that are free of the disease for cuttings. All symptomatic plants should be collected and destroyed. Minimizing overhead irrigation will also reduce disease development and spread. Using slightly higher than recommended rates of fertilizer also have been shown to reduce disease severity.

Reference to University of Florida/IFAS Pest Control Guides

FUNGAL PROBLEMS

1) Botrytis blight (Botrytis cinerea)

Symptoms -
Botrytis leaf blight usually appear on lower leaves of cuttings in contact with the potting medium. The water-soaked lesion may enlarge rapidly to encompass a large portion of the leaf blade or even the entire cutting. The area turns necrotic and dark brown to black with age. When night temperatures are cool, day temperatures warm, and moisture conditions high, the pathogen readily sporulates on leaves, covering them with grayish-green dusty masses of conidia.
Control -
Controlling Botrytis blight of foliage plants is particularly important during the winter months in Florida. Methods which improve foliage drying and reduce moisture condensation on foliage during the nights reduce the need for fungicide application.

2) Myrothecium leaf spot (Myrothecium roridum)

Symptoms -
Lesions generally appear at edges, tips and at broken leaf veins of plants. Necrotic areas are dark-brown and initially appear water-soaked. Examination of the bottom leaf surface generally reveals sporodochia which are irregularly shaped, black and have a white fringe of mycelium. Sporodochia form in concentric rings within the necrotic areas.
Control -
Using fungicides when temperatures are between 70 and 85°F, minimizing wounding, and fertilizing at recommended levels contribute to minimizing severity of Myrothecium leaf spot of foliage plants.

3) Pythium root rot (Pythium splendens)

Symptoms -
Cuttings usually show poor rooting and have yellow leaves. Examination of the stem and roots reveals a mushy black rot extending from the cut end into the upper portions of the stem and leaves. Root and stem rots usually occur in patches on a propagation bench where it spreads into uninfected cuttings.
Control -
Control should be based on use of disease-free propagation material, sterilized potting media and raised benches. Preplant treatments with fungicides or postplant treatment can be very effective in control of Pythium root rot. Reducing water applications to the minimum level for good rooting also reduces root and stem rot diseases.

4) Rhizoctonia aerial blight (Rhizoctonia solani)

Symptoms -
A mass of brownish mycelia covers the infected plants. Growth of mycelia from the potting medium onto the plant can escape notice and give the appearance that plants have been infected from an aerial source of inoculum. Close examination, however, generally reveals the presence of mycelia on stems prior to development of obvious symptoms. Rhizoctonia mycelia are usually reddish-brown in color and have the consistency of a spider web.
Control -
Chemical control of diseases caused by Rhizoctonia has been investigated on many plants using a variety of fungicides. The fungicide most widely used for soil drenches control of Rhizoctonia diseases.

5) Southern blight (Sclerotium rolfsii)

Symptoms -
The pathogen attacks all portions of the plants but is easiest seen on the leaves and stems. Initially, symptoms on stems are confined to water-soaked areas near the soil-line. Another symptom is a white, relatively coarse mycelia grown in a fan-like pattern on the surface of leaves or the potting medium. The sclerotia of the fungus form in this mycelia. They are white but turn dark brown when mature and are the size of a mustard seed. A cutting rot can develop on contaminated plant material especially during warm months.
Control -
All infected plants and the pots they are in should be removed from the growing area and destroyed as soon as they are found. There are not chemicals which are safe, effective and labeled for this disease on fittonias.

Reference to University of Florida/IFAS Pest Control Guides

INSECT AND RELATED PROBLEMS

The major and related pests of this plant species include aphids, moths (worms), fungus gnats, mealybugs, mites, shore flies, snails, slugs, thrips, and whiteflies. Mealybug, and mite infestations are typically the result of bringing infested plant material into the greenhouse. Aphids, moths, fungus gnats thrips and whiteflies have the ability to fly and thus invade the greenhouse from weeds and other infested plants outside. In the control section for each pest, a few of the many registered and effective pesticides will be listed. For a complete listing, please consult the references at the end of this report.

1) Aphids

Symptoms -
Aphids are pear-shaped, soft-bodied insects which vary in color from light green to dark brown. Infestations may go undetected until honeydew or sooty mold is observed. Aphids can cause distortion of new growth or, in extreme cases, infested plants can be stunted.
Control -
Aphids are relatively easy to control with many registered materials. Phytotoxicity to this plant has been caused by many different chemicals. Please conduct your own tests to see what is safe under your conditions. Root aphids have been controlled with soil drenches.

2) Caterpillars (worms)

Symptoms -
Infestations are easy to detect because worms, their excrement and the damage they cause, are usually quite visible to the unaided eye. Damage appears as holes in the center or along the edges of leaves. Damage by worms is often confused with slug or snail damage. The only way to determine which pest is involved is to find a specimen. Old damage can be distinguished from new by the calloused appearance of the older damaged areas (worms are usually gone by this time).

3) Fungus gnats

Symptoms
- Fungus gnats are small black flies (1/8 inch long) and are frequently observed running around the soil surface or on leaves and are often confused for Shore flies (see later section). The adults have long bead-like antennae and their legs hang down as they fly. These insects are very weak fliers and appear to "flit" around randomly. The larvae are small legless "worms" with black heads and clear bodies that inhabit the soil. The larvae spin webs on the soil surface which resemble spider webs. Damage is caused by larvae feeding on roots, root hairs, leaves in contact with the soil and lower stem tissues. Feeding damage may predispose plants to disease and they are often found in close association with diseased plants or cuttings. Adults do not cause any direct damage, but are responsible for many consumer complaints to growers. Adults emerge and fly around in retail shops, homes, or offices and are therefore a nuisance. For further information please consult Extension Entomology Report #74 (Management of fungus gnats in greenhouse ornamentals).
Control -
Reduce the amount of water applied to each pot where possible. Avoid algae growth where possible. Soil drenches or soil-surface sprays are effective at controlling the larvae. Nematodes that seek out insects in the soil are sold commercially and have been shown to control these pests without causing any negative effects to the host plants. Adults are very sensitive to most chemicals.

4) Mealybugs

Symptoms -
Mealybugs appear as white, cottony masses in leaf axils, on the lower surfaces of leaves and on the roots. Honeydew and sooty mold are often present and infested plants become stunted, and with severe infestations, plant parts begin to die.
Control -
Systemic materials are preferred. Control of root mealybugs is accomplished with soil drenches with an insecticide. When pesticides are applied to the soil, care must be taken to assure that the pots have good drainage and that no saucers are attached, or phytotoxicity may result.

5) Mites (Broad mite)

Symptoms -
Mites are very small and go unnoticed until plants become severely damaged. Broad mites cause foliar necrosis of the vegetative shoot apex. Initial symptoms of injury show new leaves cupped downward, puckered, stunted and have serrated margins. Broad mite eggs are covered with many tubercles which give them the appearance of being jeweled.
Control -
The critical point in any control program is thorough coverage with the pesticide. The best control program is to minimize the possibility of introducing mites into the growing area on infested plant material.

6) Shore flies

Symptoms -
Shore flies small black flies (1/8 inch long) and are frequently observed sitting on the tips of leaves or on the soil surface feeding on algae. The adults have very short antennae. These insects very strong fliers and exhibit directed flight (straight between 2 points). The larvae inhabit the soil and are small legless "worms" with clear bodies and no obvious heads. No known damage is caused by larvae. This insect is believed to feed only on algae. Adults do not cause any direct damage, but may be responsible for spreading plant pathogens, reducing value by defecating on the leaves (small black to green spots) and for many consumer complaints to growers. Adults emerge and fly around in retail shops, homes, or offices and are therefore a nuisance.
Control -
Reduce the amount of water applied to each pot where possible. Avoid algae growth on walkways, benches, and cooling pads. Chemicals are not believed to be very effective in the control of this pest.

7) Snails and Slugs

Symptoms -
Snail, slug and caterpillar damage are similar and determining which pest is present can be difficult. Snails and slugs are voracious feeders, with small stages feeding on surface tissue and larger ones eating irregular holes in foliage. Generally, the culprit can be found on close examination of the plant. Slugs often live under benches or in dark, moist protected places close to the damage. These pests are nocturnal and can be found feeding at night.
Control -
Sprays or baits applied to moistened soil around plants are effective. Repetitive applications are necessary. Good sanitation with removal of extraneous plant material and debris which might shelter these pests aids in control.

8) Thrips

Symptoms -
Thrips are small (less than 1/20), thin insects. Adult thrips can be identified by a long fringe of hair around the margins of both pairs of wings. Color varies between species with western and other flower thrips being yellow to light brown and banded greenhouse thrips and a few other thrips that feed mainly on leaves being dark brown to black. Feeding takes place with rasping type mouth parts. Infested leaves become curled or distorted, with silver-gray scars or calloused areas where feeding has occurred. Thrips can transmit the tomato spotted wilt virus to many different ornamentals. Any unusual symptoms should be investigated.

9) Whiteflies

Symptoms -
Infested leaves often have small yellow spots where adults or immature whiteflies have fed. When populations become dense the leaves become yellowed and lower leaves are covered with black sooty mold. The immature stages of the sweetpotato whitefly are small scale like insects and can be found on the undersides of infested leaves.
Control -
Many materials are registered and effective at controlling whiteflies. To minimize additional resistance problems, one of the insecticides should be applied two times per week throughout one life cycle (3 weeks) to control an established infestation. Monitor the population to determine if the particular insecticide being applied is reducing whitefly numbers. Some populations may be resistant to one or more of these insecticides. If the infestation persists, use another compound following the same schedule. Do not apply tank mixes as they may enhance resistance. If low numbers of whiteflies persist, apply one of the above insecticides once per week for 3 weeks then switch insecticides. Undersides of leaves must be covered thoroughly to achieve satisfactory control. For additional information on this pest please consult Plant Protection Pointer #73 (Sweetpotato whitefly on ornamental plants)

Pesticides should be applied according to label directions.

Regardless of the pesticide or mixture of pesticides used, it is
strongly recommended that the effects be evaluated on a few
plants, under your particular conditions before treating all plants.

Mention of a commercial or proprietary product in this paper
does not constitute a recommendation by the authors,
nor does it imply registration under FIFRA as amended.

Reference to University of Florida/IFAS Pest Control Guides

REFERENCES

1. Anonymous. The Begonian. The monthly magazine of the American Begonia Society, Inc. (John Ingles Jr, Membership Secretary, American Begonia Society, 157 Monument, Rio Dell, CA 95562-1617)

2. Bailey, L.H. Hortorum staff. 1976. Hortus Third. MacMillan Publishing Company, Inc., New York, NY. 1290 pp.

3. Chase, A.R. 1990. Phytotoxicity of bactericides and fungicides on some ornamentals. Nursery Digest 24(5):11.

4. Conover, C.A. and R.T. Poole. 1990. Light and fertilizer recommendations for production of acclimatized potted foliage plants. CFREC-Apopka Research Report RH-90-1.

5. Marousky, F.J. 1979. Effects of ethylene in combination with light, temperature and carbon dioxide on leaf abscission in Fittonia verschaffeltii (Lem.) Coem. var. argyroneura (Coem.) Nichols. Proc. Fla. State Hort. Soc. 92:320-321.

6. Poole, R.T. and R.W. Henley. 1989. Production of foliage begonias for the interiorscape market. Proc. Fla. State Hort. Soc. 102:280-282.

7. Price, J., D.E. Short and L.S. Osborne. 1989. Management of fungus gnats in greenhouse ornamentals. Extension Entomology Report #74.

8. Shaw, D. Michael and A.R. Chase. 1991. Effect of fertilizer rate of susceptibility of 'Mikado' begonia to Xanthomonas campestris pv. begoniae. CFREC-Apopka Research Report RH-91-9.

9. Short, D.E., L.S. Osborne and R.W. Henley. 1984. Phytotoxicity of insecticides and miticides to foliage and woody ornamental plants. Extension Entomology Report #57.

10. Short, D.E., L.S. Osborne and R.W. Henley. 1991. 1991-1992 Insect and related arthropod management guide for commercial foliage plants in Florida. Extension Entomology Report #52. 13 pp.

11. Short, D.E., J. Price and L.S. Osborne. 1989. Sweetpotato whitefly on ornamental plants. Extension Entomology Report #73.

12. Simone, G.W. and A.R. Chase. 1989. Disease control pesticides for foliage production (Revision #4). Plant Protection Pointer. Extension Plant Pathology Report #30. [also in Foliage Digest 12(9):1-8]

13. Son, K.H. and D.Y. Yeam. 1987. Effects of light intensities and temperatures in various indoor situations on growth of some foliage plants. J. Korean Soc. Hort Sci. 28(2):173-184.