Yucca Production Guide

CFREC-A Foliage Plant Research Note RH-91-36 R.T. Poole, A.R. Chase and L.S. Osborne

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

YUCCA

Spineless Yucca (Yucca elephantipes) has rigid sword-like leaves, with soft points. Leaves are closely spaced on the trunk, usually 1-2 feet in length, but larger specimens can have 4 foot leaves. Commercially available plants are usually 2-6 feet tall cane or tips. Yucca will tolerate low temperatures and humidity, but when placed indoors, they should be kept in high (150 or more ft-c) light.

Yucca are easily propagated from fresh healthy cane. Almost any size cane will produce good plants, but young cane with small diameter and old cane with large diameter should be avoided. Removal of about 1/4 inch from the lower portion of the cane immediately before propagation will improve percent survival. During production, Yucca can be grown in full sun and will have more breaks, but better color and appearance are produced if plants are maintained in 50-60% shade (6,000-7,000 ft-c) and fertilized with 3 pounds of nitrogen per 1,000 ft2 a month from a fertilizer with a 3-1-2 (N-P2O5-K2O) ratio or 7 grams of a slow release fertilizer, 19-6-12 per 8 inch pot every 3 months.

Potting media utilized for Yucca must be supportive of the canes, yet provide good aeration. Such mixtures usually contain some sand, such as a 3:1 peat:sand mixture, which helps hold canes straight, yet provides good water and fertilizer retention. Media should be amended to include a moderate level of micronutrients such as 1 lb Micromax/yd3 and sufficient dolomite to adjust medium pH to 5.5 to 6.5. Elevating pH levels above 6.5 have been shown to cause iron deficiencies. Suggested air temperatures for best growth range between 65 and 95°F.

PHYSIOLOGICAL PROBLEMS

1) Necrotic tips and edges.

Symptoms -

Leaves have necrotic areas at the tips and along the margins.

Control -

Possibly caused by fluoride. Reduce superphosphate in the medium and increase pH by additions of lime. May also be caused by water stress and high soluble salts.

2) Leaf blanching.

Symptoms -

Upper leaves with large white areas.

Control -

Caused by movement of plants from lower light areas (usually from propagation areas) to high light areas for production. Move plants to 50-60% shade level.

FUNGAL PROBLEMS

Reference Pest Control Guides Here

1) Coniothyrium or brown leaf spot (Coniothyrium concentricum)

Symptoms -

Coniothyrium leaf spot first appears as tiny clear zones in older leaves of yucca. Lesions turn yellow and finally brown as they mature. Lesions are generally elliptical and scattered across the entire upper leaf surface. After about 4 months, black perithecia or pycnidia form in the sunken lesion centers and are easily seen with the naked eye. Sometimes a chlorotic halo and/or dark-purple or black margin forms around older lesions which rarely exceed 1/2 inch in diameter.

Control -

The most important aspects of control are removal of older infected leaves and elimination of overhead watering and exposure to rainfall. Since most yuccas are grown exposed to both overhead watering and rainfall, regular applications of fungicides are needed to prevent this disease.

2) Cytosporina or gray leaf spot (Cytosporina sp.)

Symptoms -

Cytosporina or gray leaf spot of Yucca aloifolia (Spanish-bayonet) has not been adequately described. Symptoms include tip and marginal necrosis with a predominantly gray color and brown margin. Lesions often reach 3 inches, have concentric rings of light and dark tissues and are most common on older leaves. The pycnidia of Cytosporina sp. can be found in these lesions.

Control -

Use the methods and fungicides described in the UF/IFAS Control Guide for Coniothyrium leaf spot to control Cytosporina leaf spot of Yuccas.

3) Fusarium stem rot - (Fusarium spp.)

Symptoms -

One of the most common diseases of rooted yucca cuttings is caused by Fusarium spp. Soft rot of stem ends develops with destruction of leaves as well. There are two types of fruiting bodies for the pathogen which are commonly produced on the infected tissue. These are the bright red perithecia which are round and relatively easy to see with the naked eye and the powdery clusters of conidia which are ochre-colored.

Control -

4) Southern blight - (Sclerotium rolfsii)

Symptoms -

This pathogen attacks all portions of the plant but is most commonly found on stems. White, relatively coarse mycelia grows in a fan-like pattern and may be seen on the soil surface or stems. The round sclerotia form almost anywhere on the plant or soil surface. Sclerotia are initially white and cottony and approximately the size of a mustard seed. As sclerotia mature, they turn tan and eventually dark brown and harden.

Control -

Although this disease can be avoided through cultural methods, it continues to cause losses in production of foliage plants today. Chemical control of Southern blight has been investigated on several foliage plants as well as non-ornamental crops.

INSECT AND RELATED PROBLEMS

Reference Pest Control Guides Here

The major arthropod pests of this plant include mealybugs, scales, thrips and weevils. In the control section of 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 prior to treating the entire crop. The list in this section should be used only as a guide to the sensitivity to pesticides.

1) 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.

2) 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

3) 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.

4) Weevils

Symptoms -

Damage by the `Yucca Weevil', Scyphophrus acupunctatus, is most extensive in the cane. The white grub-like larvae tunnel under the bark which can girdle and therefore kill the plant and also tunnel in the tip killing the growing plant. Secondary infections by various pathogen often result from feeding damage.

Control -

Reference Pest Control Guides Here

PHYTOTOXICITY PROBLEMS

Phytotoxicity data for this plant are limited. If a pesticide is required, a 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.

REFERENCES 1. Chase, A. R. 1990. Phytotoxicity of bactericides and fungicides on some ornamentals. Nursery Digest 24(5):11.

2. 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.

3. 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.

4. 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]