Pilea Production Guide

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CFREC-A Foliage Plant Research Note RH-91-28

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


PILEA

The genus Pilea, a member of the family Urticaceae, contains over 200 species of herbaceous perennials and annuals found in the tropics except Australia. Plants have opposite, solitary leaves with three primary veins (nerves) from the leaf base, but some lack veins. Only a few of the Pileas are regarded as ornamental for their foliage and growth habit. Their flowers are not attractive.

Those species or cultivars which have been cultivated with some frequency in Florida foliage plant nurseries are listed below:

Pileas have limited application as foliage plants because of their fragile stems and foliage and their need for rather high humidity levels for long term survival indoors. They are grown primarily as small potted plants, 3-inch being the most popular size, and hanging baskets, usually 6- and 8-inch for the trailing types. Pileas have also been used successfully in dish gardens and terrariums. Occasionally, some of the trailing pileas have been used as ground covers in interior plantings. Pileas are estimated to account for less than half of one percent of the total foliage plant mix computed on a crop value basis.

Pileas are propagated by cuttings which root easily and finish quickly. Within a temperature range of 65 to 85F and under a light intensity range of 1000 to 2000 foot-candles, 3-inch pots can be rooted and finished in a 3-to 5-week period with 2 to 3 cuttings per pot. Pileas grow best in a well drained potting medium rich in organic matter. Many of the commercially formulated or nursery blended peat-like mixes with good aeration characteristics can be used for production of pilea. A low pH should be adjusted to 5.0 to 6.0 with dolomitic limestone. Plants should be fertilized with a liquid or soluble formulation with a 3-1-2 or similar analysis ratio at the rate of 1.7 to 2.3 pounds of actual nitrogen per 1000 square feet per month. Microelements can be added at the time the potting medium is formulated or during plant production as a liquid supplement.


PHYSIOLOGICAL PROBLEMS

1) Pale coloration of foliage

Symptoms -
Plants growing under excessively high light develop light colored foliage. This is primarily a problem that occurs in the spring as light intensity increases.

Control -
Provide recommended light intensity.

2) Plants stunted

Symptoms -
Plants growing in poorly aerated potting mixes fail to develop roots beyond the upper layer of medium and top growth is severely restricted.

Control -
Use a high quality potting medium with good aeration characteristics. Use only moderate pressure when firming potting mix. Avoid keeping the potting medium excessively moist.

Reference Pest Control Guides Here


BACTERIAL PROBLEM

1) Xanthomonas leaf spot (Xanthomonas campestris)

Symptoms -
This disease is most frequently encountered on aluminum plant, but also occurs on other species. Symptoms on aluminum plant are dry, tan, irregularly shaped lesions primarily found in the white areas of the leaves. In advanced infections, the lesions fall away leaving ragged holes in the leaf blades which can appear similar the insect feeding damage. Lesions on species other than aluminum plant are somewhat similar except they tend to be dark brown to black and may be angular in shape since they rarely spread across leaf veins.

Control -
Chemical control of this disease is rarely successful and cultural methods should be the first line of defense. Elimination of overhead watering and/or exposure to rainfall aid in control of disease development and spread. However, once infection occurs, lesions can expand even when leaves are kept dry. Discard all plants infected with this pathogen and never use infected plants for stock since the disease is easily carried on tissue even though no symptoms are evident.

Reference Pest Control Guides Here


FUNGAL PROBLEMS

1) Anthracnose (Colletotrichum spp.)

Symptoms -
Anthracnose of Pilea species can occur most readily during the rooting process. Many leaves can be affected and cuttings can be lost due to leaf abscission (drop). Single lesions can appear anywhere on the leaf and are water-soaked, roughly round, and sometimes contain the fruiting bodies (acervuli are black, appear in concentric rings and are the size of pepper grains). If the lesions dry out, they turn tan to gray and papery in texture. Large, well-established plants are also susceptible to Colletotrichum sp.

Control -
Use only disease-free stock plants for cuttings since infected plants rarely give rise to healthy new plants. Minimizing the amount of water applied to leaves can reduce disease as can wide spacing of plants which enhances rapid drying of the foliage.

2) Myrothecium leaf spot (Myrothecium roridum)

Symptoms -
Brown to black circular lesions form on leaf margins and centers. The lesions may have concentric rings of light and dark tissue or they may be water-soaked and uniformly black in color. The lower surface of the lesion frequently has the fungal fruiting bodies present, which are irregularly shaped, black and have a white fringe around the borders.

Control -
Small plants are highly susceptible to this disease and may be lost if precautions are not taken. Disease is worst during periods of the year when air temperatures are between 60 and 90F. Little, if any, disease occurs at other times.

3) Pythium root rot (Pythium spp.)

Symptoms -
Pythium root rot of 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 other portion of the root tissue (cortex) is easily pulled away from the inner core leaving a fine hairlike root system when plants are removed from the 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 infections or can become contaminated and infect future crops. Drench applications of several fungicides are effective in controlling Pythium root rot. Be sure to check labels prior to applying these compounds, since all are not registered for use on Pilea spp.

4) Rhizoctonia aerial blight (Rhizoctonia solani)

Symptoms -
Rhizoctonia aerial blight and leaf spot occurs on the majority of the foliage plants produced. Symptoms of aerial blight can begin as discrete lesions anywhere on the plant foliage. The spider web-like mycelium of the pathogen develops all over the aerial portions of the plant and can cover infected plants completely. Affected tissue wilts and turns necrotic rapidly. The 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 pathogenic fungi. Chemical control of this disease can be achieved with applications of a fungicide which is labeled for ornamental crops.

5) Southern blight (Sclerotium rolfsii)

Symptoms -
Southern blight disease appears much the same on one host as another. The pathogen generally attacks the crown of the plant first, sometimes leaving the roots intact and causing girdling and collapse of the tops only. Sclerotia, the fruiting bodies of the pathogen, form all over the infected tissue and appear as small mustard seed-sized bodies. They are first white and turn brown as they mature. The white fan-like mycelium of the pathogen also forms over the plant, potting medium and even sides of benches.

Control -
Chemical control of Southern blight is difficult, since the fungicide may stunt growth of plants. Always discard plants suspected of Southern blight infection and use pathogen-free potting media and pots, since the organism lives in soil and can transfer from one crop to the next on recycled materials and equipment.

Reference Pest Control Guides Here


INSECT AND RELATED PROBLEMS

The major arthropod pests of this plant species include aphids, moths (worms), fungus gnats, mealybugs, mites, scales, thrips, snails and slugs. 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. 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).

Control -

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 and false spider mites)

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. False spider mites (Brevipalpus spp.) are red in color and sedentary. Eggs are bright red and oval-shaped and are laid on both surfaces of leaves. Initial infestations are indicated by faint brown, scruffy flecks, later becoming bronze or reddish in color. Basal leaf areas are affected, vegetative shoot apexes may be killed, and severe leaf drop may occur.

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) 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

7) 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.

8) 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.

9) 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.

Control -
Many materials are registered and effective at controlling thrips.

10) 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 for the above list 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 the 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 Pest Control Guides Here


REFERENCES

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

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

3. 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.

4. Conover, C.A. and R.T. Poole. 1981. Effect of soil compaction on physical properties of potting media and growth of Pilea pubescens Liebm. 'Silver Tree'. J. Amer. Soc. Hort. Sci. 106(5):604-607.

5. Conover, C.A. and R.T. Poole. 1990. Light and fertilizer recommendations for production of acclimatized potted foliage plants. CFREC-A Research Report RH-90-1. 13 pp.

6. Poole, R.T. and C.A. Conover. 1977. Influence of medium, container size and water regime on growth of Pellionia pulchra N.E. Br. and Pilea involucrata (Sims) Urb. Proc. Fla. State Hort. Soc. 90:319-320.

7. Poole, Richard T. and Charles A. Conover. 1984. Growth of foliage plants in various ratios of peat and sand while fertilized and irrigated at different levels. CFREC-Research Report RH-84-3.

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

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. 1989. Disease control pesticides for foliage production (Revision #4). Plant Protection Pointer. Extension Plant Pathology report #30. 54 pp.