Wax Plant (Hoya) Production Guide

CFREC-A Foliage Plant Research Note RH-91-35 L.S. Osborne, R.W. Henley and A.R. Chase

University of Florida, IFAS Central Florida Research and Education Center - Apopka 2807 Binion Rd., Apopka, FL 32703-8504

WAX PLANT (HOYA)

Wax plant belongs to the genus Hoya, a member of the milkweed family, Asclepiadaceae. Wax plants grown in the foliage plant industry are primarily cultivars of one species - Hoya carnosa. The preferred common name of the species is wax plant, but wax vine and porcelain flower are occasionally used. The fleshy leaves and flowers, which are covered with a semi-glossy layer of waxy substances known as the cuticle, account for the common names given to the group. A few other species, such as H. australis, H. bella and H. multiflora, are produced by a few nurserymen.

The wax plant is a semi-woody vine with nearly oval or ovate-shaped leaves 2 to 3 inches long arranged oppositely along the stems. The flowers develop in clusters 2 to 3-1/2 inches in diameter. The individual flowers (florets) are attractive and consist of five white to pink symmetrical outer lobes, about 5/8-inch across, and an inner structure which is red or partly red. The inflorescences develop from the ends of short spur-like branches along the vines. These spurs increase in length slowly with each successive cycle of bloom.

Wax plant is a minor foliage crop, constituting less than one percent of the total foliage plant product mix grown in Florida. Although the plant is well adapted to interiors with 125 foot-candles or more of light for approximately 10 hours per day, it is not a favorite of many growers because of its lengthy production schedule. It is most commonly grown in 3-inch square pots, but a few producers offer it in 4-inch and larger pots. The plant is most attractive when finished in hanging baskets which display the trailing habit of the vines and the attractive flowers which appear periodically on older plants. Occasionally wax plants are cultured as totems, a form which is usually not cost effective for the commercial producers because of the lengthy growing period and labor required to train the vines on a pole or slab.

CULTIVARS

There are several cultivars of Hoya carnosa which are grown by commercial growers in Florida. Those cultivars of wax plant which have been cultivated with some frequency are as follows:
Table 1:

Horticultural name	                    	Common name
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Hoya carnosa					Wax plant

Hoya carnosa `Argentea Picta' (pat. 3307) 	Hindu rope (R)

Hoya carnosa `Compacta'	

Hoya carnosa `Mauna Loa' (pat. 3054)		Lura-Lei (R)

Hoya carnosa `Compacta Regalis' (pat. 3306)	

Hoya carnosa `Krinkle 8' (pat. 3008)		Krinkle 8 (R)

Hoya carnosa `Krinkle 8 Variegata'		Variegated Krinkle 8

Hoya carnosa `Rubra' (pat. 3105)		Krimson Princess (R)

Hoya carnosa `Tricolor' (pat. 2950)	

Hoya carnosa `Variegata'			Variegated wax plant

Hoya purpurea-fusca `Silver Pink'		Silver pink wax plant

PRODUCTION

Wax plant is propagated from cuttings which are harvested from stock vines. Normally single-node cuttings are made with a cut approximately 1/4 inch above each pair of leaves, leaving a longer stem section below the leaves to anchor cuttings which are usually direct stuck. Cuttings root in 3 to 4 weeks and a single shoot usually develops from one of the buds on each cutting approximately 4 to 6 weeks later. Roots form along the stem section below soil level with the greatest number of roots developing at or near the node (point where leaves are attached to the stem). Cuttings should be positioned so the node is at the soil surface to ensure maximum rooting. Avoid sticking cuttings too deep as shoot development will be inhibited or prevented if buds are positioned below the soil surface.

Wax plants develop best under light intensities of 1500-2000 foot-candles and temperatures of 68 to 75°F. Summer rooting and growth of wax plant can be reduced if temperatures are excessively high due to poor ventilation or inadequate cooling. If greenhouses are run very cool in winter, plants will become dormant. An acceptable production temperature range is 68 to 90°F.

After cutting material is harvested from stock plants, water management becomes one of the most critical factors in propagation. As long as greenhouse relative humidity is high (75 percent or more), the unrooted cuttings should not be misted frequently. Simply apply enough water overhead to keep the soil surface moist, not soggy. After roots develop to the bottom of the pots, the watering frequency should be reduced to permit the potting medium to become relatively dry before the next irrigation.

Most wax plant growers prefer liquid fertilizer application over incorporated slow release products so the fertility level of the potting medium can be adjusted easily as the crop irrigation frequency is changed. Fertilizers with a 2:1:2 or 3:1:2 ratio with microelements added are a good choice. Apply fertilizer at the rate of 2.9 pounds of actual nitrogen per 1000 square feet per month.

Potting media should contain a high percentage of organic material, such as fibrous peat, to provide good water holding capacity and some coarser particles, such as pine bark, perlite and calcined clay to assure good drainage and aeration. Several of the commercially available preblended soilless mixes are suitable for growth of high quality wax plants.

Production schedules vary considerably depending upon cultivar, temperature and degree of water management. The flat-leaf, all-green types grow more than twice as fast as plants with variegated, reflexed leaves and short internodes. It takes approximately 5 to 11 months to produce a finished 3-inch pot of wax plant with a 6 to 8-inch long vine from an unrooted, single- node cutting. One or two cuttings are stuck per 3-inch pot and 3 to 4 single-node cuttings stuck per 4-inch pot.

FUNGAL PROBLEMS

Reference Pest Control Guides Here

1) Botrytis blight (Botrytis cinerea)

Symptoms -

Botrytis infections are typified by large grayish areas on leaf margins or centers. The leaves in the center of plants is commonly infected since moisture levels are highest here. Affected leaves collapse and turn mushy and the dusty gray to tan spores of the pathogen can be easily seen with a 10 x hand lens. This disease is most common during the cooler and lower light periods of the year (winter in Florida).

Control -

Reducing humidity through irrigation management (amount and timing) as well as venting greenhouses during the late afternoon have been used to control this disease on crops in the Northeast. Many plants other than Hoya spp. can also be infected with Botrytis cinerea and control measures should be extended to all susceptible hosts. Examples of other hosts include lipstick vine, African violet, English ivy and the majority of flowering crops such as Lisianthus, marigold, and roses.

2) Stem and root rot (Phytophthora, Pythium and Rhizoctonia spp.)

Symptoms -

Stem and root rot on Hoya spp. sometimes go unnoticed until symptoms are quite advanced. This is probably due to the waxy nature of the plant which retards wilting even when all roots are rotted. Lesions on the stems are usually brown to black and can be mushy or dry. Roots are gray to black and can also be mushy or dry. If plants are infected with Rhizoctonia sp., leaves can also be infected and the weblike red-brown mycelium of the pathogen can spread across the potting medium surface and leaves.

Control -

Cultural disease control is the most important step[ in reducing problems with stem and root diseases. Reduce water applications to plants suspected of stem or root rot disease and be sure to start with fresh potting medium, pots and pathogen-free cuttings for each crop. Depending upon the cause of the stem or root rot, a fungicide may be chosen for control. Since symptoms caused by these organisms are similar and fungicides used for their control differ, the exact organisms involved in each disease must be accurately determined. Pythium, Phytophthora spp. and Rhizoctonia root rot can be controlled with soil drench applications.

INSECT AND RELATED PROBLEMS

Reference Pest Control Guides Here

The major arthropod pests of this plant species include aphids, moths (worms), fungus gnats, mealybugs, mites, scales, and thrips. Mealybug, mite, and scale infestations are typically the result of bringing infested plant material into the greenhouse. Aphids, moths, fungus gnats and thrips 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. The aphid most often observed feeding on wax plants is the Oleander aphid, which is bright yellow with dark brown appendages. Infestations frequently result from insects flying into the greenhouse from infested milkweed or Oleander plants. These infestations often go undetected until honeydew or sooty mold is observed. Aphids can cause distortion of new growth or, in extreme cases, infested plants will 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) 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.

3) 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.

4) 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.

5) Scales

Symptoms -

Infested plants become weakened or stunted and begin to die. Scales can be found feeding on leaves, petioles, or stems. They are usually distinct from the plant material on which they are feeding. Their shape (round to oval), size (pinpoint to 2 mm long), and color (light to dark brown) are quite variable and many scales are hard to distinguish from the plant material on which they are feeding.

Control -

See Mealybugs

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) Thrips

Symptoms -

Thrips are small (less than 1/20), thin insects. Adult thrips can be identified by a long fringe of hairs 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.

Control -

Many materials are registered and effective at controlling thrips.

Reference Pest Control Guides Here

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.

REFERENCES

1. Anonymous. 1984-1985 Florida Foliage Locator. Florida Foliage Association. 160 pp.

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

3. Chase, A.R. 1983. Phytotoxicity of some 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 potted foliage plants. CFREC-A Research Report RH-90-1. 13 pp.

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

6. 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. 32 pp.

7. Short, D.E., L.S. Osborne and R.W. Henley. 1991. 1991-92 Insect and related arthropod management guide for commercial foliage plants in Florida. Extension Entomology Report #52. 13 pp.

8. Simone, G.W. and A.R. Chase. 1989. Disease control pesticides for foliage production (Revision 4). Plant Pathology Extension PPP#30. Plant Protection Pointer 30. 54 pp.