Aralia Production Guide

CFREC-A Foliage Plant Research Note RH-91-5

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

Reference to University of Florida/IFAS Pest Control Guides

ARALIA

The aralia family (Araliaceae) is composed of 84 genera of herbs and woody plants ranging from vines to trees (2), including the genus, Polyscias. Within Polyscias, there are approximately 80 species of trees and shrubs indigenous to Polynesia and tropical Asia, most of which are commonly called aralias. Many aralias are useful interior plants and landscape plants in tropical areas of the world. Leaves of Polyscias are arranged alternately on the stem and are usually compound. Several cultivars have attractive variegated foliage.

Although there are several plants outside Polyscias which have aralia as part of their common name, this publication will be limited to aralias within Polyscias. Nomenclature of Polyscias has not been well defined until recently. The L. H. Bailey Hortorum staff (2) listed 4 species and 9 cultivars and Graf (6) listed 5 species and 8 cultivars. More recently, Burch and Broschat (3) studied the aralias grown in south Florida and described 8 species and 21 cultivars. Commercial producers of interior foliage plants in Florida listed for sale 6 species and 7 cultivars in 1985 (1) and this has fluctuated slightly since that time. It is estimated that one can find 25 or more species and cultivars of polyscias in Florida nurseries, the landscapes of southern Florida and in private collections.

Several of the most popular polyscias are described below:

Polyscias balfouriana (Refer to P. pinnata)

Polyscias crispa `Chicken Gizzard' (Chicken Gizzard Aralia)

The chicken gizzard aralia is also known as celeryleaf aralia. This upright plant branches rather freely and bears leaves which are pinnately divided with usually more than 3 rounded leaflets that have 2 or more lobes.

Polyscias crispa `Palapala' (Palapala Aralia)

Palapala aralia is similar in branching habit and leaf characteristics except the leaflets are attractively patterned with dark green, golden yellow and ivory. Propagators should know that `Palapala' is patented (plant patent number 3775).

Polyscias filicifolia (Fernleaf Aralia)

The fernleaf aralia is a distinctly upright shrub which branches freely. It bears pinnately divided leaves which resemble the fronds of some ferns.

Polyscias fruticosa (Ming Aralia)

Ming aralia is one of the most popular of the polyscias with its upright-spreading growth habit and fine-textured, pinnately-divided leaves. Because of the wide crotch angle of the branches and the openness of the fine foliage, the trunk and many of the attractive branches are exposed, lending additional beauty to the plant.

Polyscias fruticosa `Elegans' (Parsley Aralia)

The parsley aralia is an excellent dwarf cultivar with leaves that resemble some of the finely-divided strains of parsley. It produces an abundance of side shoots and compactly-arranged, small leaves that make it a good choice for small pots in the 4 to 8-inch diameter range.

Polyscias guilfoylei `Blackie' (Black Aralia)

Black aralia is a strongly upright, sparsely branched plant with very dark green, pinnately-divided leaves. The leaflets have a unique, but not especially decorative, wrinkled surface texture.

Polyscias pinnata `Dinnerplate' (Dinnerplate Aralia)

The dinnerplate aralia is predominantly upright and open. The pinnately-divided leaves usually have 3 or more large, rounded leaflets which accounts for the cultivar name.

Polyscias pinnata `Marginata' (Variegated Evergreen Aralia)

The cultivar `Marginata' is similar in growth habit to `Dinnerplate' except the leaflets are smaller, usually more numerous, and have an irregular white margin. This plant is occasionally listed as P. pinnata `Tricochleata'.

Polyscias pinnata `Pennockii' (Pennock Aralia)

The leaf size and shape of the Pennock aralia is like the cultivar `Marginata', but the leaflets have an attractive blend of ivory, yellow and dark green patches.

Polyscias tend to be produced predominantly in south Florida due to their slow growth rate and their application in landscaping. The products grown in south Florida nurseries tend to be in the 6 to 14-inch pot, diameter range. In recent years there has been increased interest among central Florida nurserymen to produce polyscias in 4 to 8-inch diameter pots. The plants are excellent interior plants, well adapted to light levels of 125 foot-candles or higher. The upright forms are used as specimen shrubs by commercial interiorscapers. Some of the dwarf cultivars with an upright- spreading branching habit, such as P. fruticosa `Elegans', are good choices for 4 to 8- inch pots. The ming aralia and its dwarf cultivars are excellent candidates for bonsai.

Polyscias can be propagated from softwood terminal cuttings under intermittent mist or hardwood cuttings (cane) without foliage. Cuttings should be stuck in a well drained nursery mix with high water-holding capacity. Rooting hormones will enhance the rooting process. Direct-sticking technique is preferred because plant roots should be disturbed as little as possible during propagation. Heavy misting during propagation is discouraged because best rooting occurs in a medium which is not waterlogged.

Some growers propagate polyscias successfully under polyethylene film tents erected over greenhouse benches. This technique provides elevated daytime temperatures, increases the humidity and minimizes the amount of water applied during rooting. If possible, provide a root zone temperature range of 70-75°F during propagation.

Calcium and magnesium are normally applied by blending dolomite at the rate of 4 to 10 pounds per cubic yard of potting medium to adjust the pH to approximately 6.0. The amount of dolomite used will depend upon the initial acidity of the medium. A fertilizer with a 3-1-2 to 2-1-2 ratio should be used at the rate of 2.5 to 3.0 pounds of actual nitrogen per 1000 square feet per month once the propagules have rooted. Light level range for good nursery growth and dark green leaf color is 1500 to 4500 foot-candles. Plants grow best at temperatures of 70 to 85°F.

PHYSIOLOGICAL PROBLEMS

1) Rapid loss of older leaves

Symptoms -

Older leaves become chlorotic and abscise or abscise without chlorosis. This usually occurs in late autumn or winter when plants are abruptly exposed to chilling temperatures (40-55°F) or ethylene from improper combustion of fuel used to heat greenhouses or plastic lined shadehouses. Severe defoliation can occur if plants are permitted to dry excessively.

Control -

Prevent exposure to chilling temperatures in production areas or during shipment. Plants usually recover slowly from this type of injury. Have all heating equipment properly vented and maintained prior to heating season. Also, avoid drought conditions.

2) Slow growth and slow loss of lower (older) leaves

Symptoms -

Poor root development, slow growth and often some loss of older leaves occurs and is a condition which often progresses to include root rot diseases (discussed later).

Control -

Use sterilized or new and well drained potting medium. Avoid setting plants too deeply in potting medium and overwatering.

3) Pronounced "birdnest" type growth and stunting of tip growth

Symptoms -

A proliferation of short shoot growth at shoot tips can occur. Plants do not resume growth for a considerable length of time.

Control -

4) Poor rooting response

Symptoms -

Stem cuttings root very slowly and often with poor rooting percentage.

Control -

Provide a root zone temperature range of 70-75°F. Use of hormone powder or hormone quick-dip is suggested. Avoid use of cuttings or cane which has been store for long periods.

Reference Pest Control Guides Here

BACTERIAL PROBLEMS

1) Xanthomonas leaf spot (Xanthomonas campestris pv. hederae)

Symptoms -

Xanthomonas leaf spot of Aralia has become more common during the past five years. Lesions are initially tiny, corky appearing areas which are seen on the lower leaf surface and can be easily mistaken for edema or phytotoxicity. Lesions generally enlarge to 1/8 to 1-1/4 inch in diameter and become black with a chlorotic margin.

Control -

See those listed for Alternaria leaf spot with respect to irrigation methods and host nutrition.

Reference Pest Control Guides Here

FUNGAL PROBLEMS

1) Anthracnose (Colletotrichum gloeosporioides)

Symptoms - Lesions are initially water-soaked and surrounded by a yellow halo. Eventually, they can reach 1 inch in diameter and turn tan to black in color. The tiny black fruiting bodies of the pathogen are readily detected in the lesions on the upper leaf surface. Most lesions occur on leaf margins or in wounded areas.

Control - Elimination of overhead watering and exposure to rainfall can reduce disease incidence and severity.

2) Alternaria leaf spot (Alternaria panax)

Symptoms -

Alternaria leaf spot is most commonly found on scheffleras, but is also known to occur on Polyscias spp. Lesions are initially tiny translucent areas which later turn tan and have a chlorotic halo. Sometimes a reddish-purple pigment is associated with leaf spot of variegated Polyscias balfouriana. Lesions on Polyscias fruticosa can enlarge to 1/2 inch and cause severe defoliation within 5 days of infection.

Control -

Alternaria leaf spot can be controlled with elimination of overhead irrigation and exposure to rainfall. In addition, use of greater than recommended levels of fertilizer result in reduced severity of Alternaria leaf spot on several other members of this plant family including schefflera, dwarf schefflera and false aralia.

3) Pythium root rot (Pythium spp.)

Symptoms -

Pythium root rot of many foliage plants is most often caused by P. splendens. Plants appear stunted, chlorotic and wilted even when soil moisture is high. Roots are usually rotted, brown to black and mushy. The outer portion of the root tissue (cortex) is easily pulled away from the inner core leaving a fine hairlike root system which can be seen when plants are removed from their potting medium. Since these symptoms can be caused by many different soil-borne pathogens, a precise diagnosis can only be made when the roots are culture indexed for these organisms.

Control -

Cultural control of soil-borne diseases is based on use of pathogen-free seedlings or cuttings, pots and potting media. Grow plants on raised benches away from the native soil, since it can be a source of infection or can become contaminated and infect future crops. Soil drench applications of several fungicides are effective in controlling Pythium root rot.

4) Rhizoctonia aerial blight (Rhizoctonia solani)

Symptoms -

Aerial blight can begin as discrete lesions anywhere on plant foliage. The spiderweb-like mycelia of the pathogen develops all over the aerial portions of the plant and can cover infected plants completely. Infected tissue wilts and turns necrotic rapidly. Mycelium of Rhizoctonia is usually tan to reddish-brown.

Control -

Cultural controls for Rhizoctonia aerial blight are the same as those mentioned for Pythium root rot, since both are soil-borne fungi.

Reference Pest Control Guides Here

INSECT AND RELATED PROBLEMS

The major arthropod pests of this plant species include fungus gnats, mealybugs, mites, and scales. Mealybug, mite, and scale infestations are typically the result of bringing infested plant material into the greenhouse. In the control section for each pest, a few of the many registered and effective pesticides will be listed. The list by Short et al. (1984) should be used only as a guide to the sensitivity of foliage plants to pesticides. Another publication by Short et al. (1989) provides a summary of insect and mite management information for foliage plants.

1) 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.

2) 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.

3) 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.

4) Mites (Twospotted spider mite)

Symptoms -

Two-spotted spider mites are very small and go unnoticed until plants become severely damaged. Damaged foliage begins to turn yellow or become speckled due to the feeding of mites. Webbing, loss of leaves and plant death can occur when mite populations reach high levels. Often the presence of this pest is overlooked because the cast skins and webbing produced by this mite are confused for dust on undersides of leaves. Mites have round pale yellow to reddish eggs deposited on the under surfaces of leaves; nymphs and adults have two dark patches on either side of their bodies.

Control -

The critical point in any control program is thorough coverage with a pesticide. The best control program is to minimize the possibility of introducing mites into the growing area on infested plant material. Biological control programs have worked in small scale studies but remain unproven in commercial greenhouses.

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

Phytotoxicity data for this plant are limited. If a pesticide is required, small group of plants should be tested for phytotoxicity prior to treating the entire crop (See Chase et al. 1981).

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 Pest Control Guides Here

REFERENCES

1. Anonymous. 1985. Florida Foliage Locator 1985-1986. Florida Foliage Association, Apopka, FL. 188 pp.

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

3. Burch, D.G. and T.K. Broschat. 1983. Aralias in Florida horticulture. Proc. Fla. State Hort. Soc. 96:161-164.

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

5. Chase, A.R., T.J. Armstrong and L.S. Osborne. 1981. Why should you test pesticides on your plants? ARC-Apopka Research Report RH-81-6.

6. Graf, A.B. 1978. Tropica. Roehrs Company-Publishers, East Rutherford, NJ. 1120 pp.

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

8. 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.

9. 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.

10. 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]