Calathea Production Guide

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CFREC-A Foliage Plant Research Note RH-91-9
R.T. Poole, 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


CALATHEA

The genus Calathea is comprised of some of the most attractive species of foliage plants. Calathea insignis, also called Rattlesnake plant, is a bushy species with narrow, tapering erect foliage, wavy at the margins, yellow green with lateral ovals, alternately large and small, of dark green. The underside is maroon. Calathea makoyana, Peacock plant, has oval leaves, with opaque, olive green lines and oval areas alternately short and long, in a translucent field of yellow green. The pattern is repeated on the underside of the leaf with a purple red color. Calathea roseo-picta has elliptical leaves, 6 x 9 inches, with a dark green upper surface, red midrib, a red zone fading to pink near the margin. The lower surface is purple. Calathea louisae has leaves broadly ovate, dark green with light green splotches along the midrib. It is also purple underneath. Calatheas are closely related to, and often confused with species of Maranta, Ctenanthe and Stromanthe.

Although very attractive plants, calatheas are frequently omitted from lists of popular foliage plants. Good quality calatheas can be produced but careful attention must be given to the production environment.

Calatheas should be grown with 1000-2000 ft-c. Lower light levels can cause pale leaves with indistinct markings, while higher light levels result in tip necrosis and sometimes bleached areas on the leaf. Three pounds of nitrogen per 1000 square feet a month should maintain good growth and color. With cool temperatures the rate should be reduced, but frequent irrigations might necessitate an increase of fertilizer. Inadequate rates result in loss of color and may cause spotting. A ratio of 3-1-2 (N-P2O5-K2O) should be used. High potassium can cause leaf spotting and reduce color intensity. The nitrogen source should be at least 50% urea or ammoniacal with higher percentages preferable. Good quality calatheas have been grown when the electrical conductivity of the leachate from the soil medium was 1,000 mhos/cm. Micronutrients, 1/2 pounds/yd3 of MicroMax or equivalent, will improve plant color and quality. Tissue analysis revealed that good quality calatheas contained about 3% N, 0.5% P, 3% K, 0.5% Mg and 0.1% Ca. Micronutrients were Cu, 6 ppm, Fe, 130 ppm, Mn, 500 ppm and Zn, 40 ppm. A medium with high water holding and cation exchange capacities, such as a peat:sand mix (3:1 by volume) provides a good base for calathea growth. Calatheas are damaged by fluoride and the pH should be maintained near 6.5. Seven pounds of dolomite per cubic yard can be added to maintain the proper pH in most potting media. Large plants are more susceptible to high summer temperatures. When plants are small, they are tolerant of 100F maximum, but when large, temperatures above 90F will reduce quality.

Calatheas are produced by divisions or tip cuttings, with nodes to form the roots. Mist and reduced light are important during the early stages of propagation.


PHYSIOLOGICAL PROBLEMS

1) Marginal or tip leaf necrosis

Symptoms - Leaves are necrotic at tips or margins.

Control - Several factors may be involved including light, pH, or excess fertilizer. Maintain light levels between 1000 and 2000 ft-c and keep pH near 6.5. If excess soluble salts are detected, leach pots several times.

2) Chlorosis

Symptoms - Plants have light green leaves.

Control - Increase fertilizer, especially nitrogen, may need iron.


BACTERIAL PROBLEMS

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1) Pseudomonas leaf spot (P. cichorii)

Symptoms - Lesions are water-soaked and turn dark green to black depending upon the cultivar. They may have a yellow halo but this is not common. C. roseo-picta and `Vandenheckei' appear to be especially susceptible to this bacterial pathogen and spots may reach 1 inch in diameter. There are rarely more than two spots on a leaf although loss of the leaf often occurs if it is infected when in the whorl.

Control - Avoid overhead watering as much as possible to reduce conditions for infection and spread of the pathogen. Preventive applications of a copper bactericide may aid in disease control but none are labeled for this plant at this time.

2) Pseudomonas blight (Pseudomonas sp.)

Symptoms - This bacterial disease has become a problem for calathea growers only during the past year or two. It is caused by a nonfluorescent Pseudomonad which has not yet been identified to species. Symptoms start as water-soaked areas along the leaf veins and are especially visible on the leaves as they unfurl. The lesions are clear appearing and run together readily. When completely mature, the lesions are tan to brown and somewhat papery in texture. C. roseo-lineata is very susceptible to this pathogen, with severe symptoms developing even when drip irrigation is employed.

Control - Due to the serious and potential systemic nature of this disease, infected plants should be destroyed. Although tissue culture plants may be free of the disease when purchased they are as easily infected as cuttings.


FUNGAL PROBLEMS

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1) Alternaria leaf spot (Alternaria alternata)

Symptoms - Alternaria leaf spot of Calathea spp. is characterized by small (less than 1 mm in diameter) lesions which are initially water-soaked. These lesions turn reddish-brown, may reach 1/8 inch in diameter and are roughly circular. Lesions generally do not have any type of halo surrounding them and coalescence is rare. Although closely related, Maranta leuconeura cultivars have not been found susceptible to A. alternata. Calathea bella, C. insignis (rattlesnake plant), and C. picturata `Argentea' are each susceptible to this disease with C. bella very susceptible.

Control - Alternaria leaf spot can be controlled through a variety of methods. Total elimination of water on leaves is sufficient to completely control Alternaria leaf spot of calatheas. In addition, many fungicides provide some control of Alternaria leaf spot on these plants with the exception that C. bella is so susceptible that no fungicide applications result in a significant degree of control. The fungicides listed for Helminthosporium leaf spot are effective in controlling Alternaria leaf spot as well.

2) Helminthosporium leaf spot (Drechslera setariae)

Symptoms - Helminthosporium leaf spot is frequently a problem for calathea producers. The lesions first appear as tiny water-soaked areas which turn chlorotic and finally necrotic lesions are normally large (1/2 inch wide). In severe cases, lesions coalesce and form large irregularly shaped areas which are tan with a chlorotic halo. Maranta spp. are also highly susceptible to this pathogen.

Control - Minimizing the period of time leaves are wet can dramatically reduce disease severity. This can best be accomplished by eliminating overhead watering or at least applying water early in the day to allow rapid drying of foliage. Plants which are watered in the late afternoon may remain wet for the entire night, allowing germination and infection of many fungal spores.

3) Fusarium wilt (Fusarium oxysporum)

Symptoms -This disease can be common on calatheas propagated from cuttings. Cutting bases may rot or lower leaves can wilt and turn yellow. Larger plants show signs of wilting and yellowing of lower leaves and the vascular system is brownish.

Control - Drench treatments may aid in reducing disease spread but complete control can only be achieved if the infected planting material is destroyed. Be sure to obtain an accurate diagnosis since nematode infection and root rot due to other soil-borne fungi could appear similar.


VIRAL PROBLEM

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1) Cucumber mosaic virus (CMV)

Symptoms -CMV causes minor symptoms on calatheas. The most obvious symptoms of CMV infection are the bright yellow patterns formed on the leaves. These patterns are generally jagged and alternate with the normal coloration of the affected leaf. Marantas are also susceptible, with symptoms generally more dramatic than those on Calatheas.

Control - Although the symptoms of CMV are sometimes noticeable, there is no evidence that the damage caused is other than aesthetic. The only recommended control is destruction of plant material showing these symptoms. Propagation of material with CMV will transfer the virus to new plants.


NEMATODE PROBLEM

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1) Burrowing nematode (Radopholus similis)

Symptoms - Symptoms include lesions on roots and root rot which lead to reduced plant vigor and poor growth. Both roots and tops appear stunted.

Control -

INSECT AND MITE PROBLEMS

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The major arthropod pests of these plants include caterpillars, mealybugs, mites, and scales. Mealybug, mite, and scale infestations are typically the result of bringing infested plant material into the greenhouse. Adult forms of caterpillars 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. Because the potential for phytotoxicity exists, a small group of plants should be tested for phytotoxicity prior to treating the entire crop (See Chase et al 1981). The list given in this section should be used only as a guide to the sensitivity to pesticides.

1) 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. If leaves have been fed upon while in the rolled stage the damage appears as a line of equally spaced holes once the leaf opens. 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 -

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 antennas 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 (Tarsonemid)

Symptoms - Mites are very small and go unnoticed until plants become severely damaged. The mite, Steneotarsonemus furcatus, can be a serious problem. The early signs of damage appear as water-soaked lesions or a necrotic line that parallels the margin of the leaf. Severe infestations will kill the plant (See Denmark and Nickerson 1981).

Control -The best control program is to minimize the possibility of introducing mites into the growing area on infested plant materials. All plant material, including material received from tissue culture laboratories, should be examined for the presence of this mite.

5) Mites (Two-spotted spider mite)

Symptoms -Two-spotted spider mites are very small and go unnoticed until plants become severely damaged. Affected plants turn yellow or speckled due to the feeding of this pest. Secondly, the plant responds to mite feeding by exuding a sticky substance which can accumulate in large quantities on the lower leaf surface. 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 the 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.

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 are 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 antennas. 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) Slugs

Symptoms - 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.


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.


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REFERENCES

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

2. Chase, A.R. 1986. Fertilizer level does not affect severity of Helminthosporium leaf spot of calatheas. CFREC-Apopka Research Report RH-86-19.

3. Chase, A.R. and R.T. Poole. 1988. Nutritional responses of five Calatheas. Proc. Fla. State Hort. Soc. 101:323-325.

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

5. Conover, C.A. and R.T. Poole. 1982. Influence of nitrogen source on growth and tissue nutrient content of three foliage plants. Proc. Fla. State Hort. Soc. 95:151-153.

6. Conover, C.A. and R.T. Poole. 1984. Relationships of dolomite and superphosphate to production of calathea. CFREC-Apopka Research Report RH-84-16.

7. Denmark, H.A. and J.C. Hickerson. 1981. A tarsonemid mite, Steneotarsonemus furcatus DeLeon, a serious pest on Maranta sp. and Calathea sp. (Acarina: Tarsonemidae). Proc. Fla. State Hort. Soc. 94:70-72.

8. Poole, R.T., A.R. Chase and C.A. Conover. 1988. Chemical composition of good quality foliage plants. Revision. CFREC-Apopka Research Report RH-88-6.

9. Poole, R.T. and C.A. Conover. 1979. Melaleuca bark and solite as potential potting ingredients for foliage plants. Proc. Fla. State Hort. Soc. 92:327-329.

10. Poole, R.T. and C.A. Conover. 1985. N, P, and K fertilization of Brassaia actinophylla,Calathea makoyana and Chrysalidocarpus lutescens. J. Environ. Hort. 3(1):1-3.

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

12. 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.

13. 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.

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

15. 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 12(9):1-8].