A Visit with Louis Vogelpoel

Prior to my journey to South Africa in December 1999, I had never met Dr. Vogelpoel.  Even though he didn't know me personally, he arranged for Wally and I to have a guided tour of Table Mountain put on by the people at the Kirstenbosch Botanical Garden.  This represents the generosity that is typical of Dr. Vogelpoel.  Unfortunately, he had a bit of a problem with an insect pest the prior fall so there wasn't as much to see in his shadehouse as one would normally see.  For this reason coupled with the fact that I had a new and unfamiliar camera, there aren't a lot of photos of Dr. Vogelpoel's orchids. In some respects, I have something better to show you instead.  During the early 1980's,  Louis wrote a small publication titled, "Disa uniflora, Its propagation and cultivation."  This was published by the new Disa Orchid Society of South Africa.  It has been long out of print and when Wally and I visited, I asked Louis whether or not he was planning on doing a reprint and if he wasn't, did he mind if I scanned it and put it on my web site.  He was most generous and said that he would happily give his permission.  So rather than bore you with poor photos, I am presenting this copy of his publication for your information.  First though, a picture of Louis after leading us all over Table Mountain and a view of some of the plants in his shadehouse.

Disa unifora 

 Its propagation and cultivation   By  Dr. Louis Vogelpoel

Introduction

During the past three decades great strides have been made by a handful of Cape growers in the propagation, cultivation and hybridization of Disa uniflora and allied species. ^1-5 Thanks to the pioneering efforts of Mr. Helmut Meyer of Stellenbosch and Mr. K. C. Johnson of Somerset West, the secrets of successful cultivation were dis­covered. Success was based upon a thorough grasp of the characteristics of the natural habitat. Techniques have been greatly improved and extended by the efforts of dedi­cated and enthusiastic newcomers to this field. An historic milestone was the first Disa show, held at Kirstenbosch in December 1980. This was the first time that a show limi­ted to Disas was held and over 900 plants were exhibited. It was such a success that Disa growers formed the Disa Orchid Society, dedicated to the promotion of all as­pects of Disa cultivation and hybridization. Award judging, registration and docu­mentation of new hybrids are among the Society's important functions.

In December 1982 the Society staged the second Disa show, which was even more successful because of the improved standards of culture and the many new hybrids in­troduced. However, numerous visitors were disappointed that they could not acquire seed or plants; therefore, the Society has decided to make seedlings and plants avail-able at its future shows. This service should stimulate many to grow the much-coveted "Flower of the Gods".

The Disa, like all indigenous orchids, is totally protected and the only legitimate way to obtain seed or plants is from licensed growers.

The Disa, however, is no ordinary orchid and success in growing it to perfection demands a large measure of dedication and enthusiasm from its owner. For this reason, the author has compiled this booklet with the support of the Disa Society, to describe the basic principles and techniques for successful cultivation and propa­gation. If these are understood, followed and adapted to local conditions, the grower will not only be rewarded but could become the victim of an incurable obsession called “Disamania". The Disamaniac becomes intensely proud of this Western Province orchid, and so contributes to its conservation by being fully committed to meticulous breeding and hybridizing programs, and conscious of the privileges and responsi­bilities of his or her work.

Local habitat and ecology

In order to grow Disas successfully it is essential to understand the local habitat and ecology.

Disa uniflora is confined in nature to the sides of streams and waterfalls in the moun­tains of the South Western Cape. Although a winter rainfall area, the mountains in this region are frequently moistened by southeaster clouds during the dry summer months, which help to sustain streams throughout the year. Disas grow in dense colonies just above the mid-summer water level. During winter the colonies are exposed to heavy rains and are often completely submerged in running water. They grow in various media such as sand and moss, but the root systems are usually firmly embedded in a fibrous mat provided by ferns, restios, Ericas or palmiet. Wherever they grow, water is moving through the root system and good drainage ensures adequate aeration. The streams flow over Table Mountain sandstone rock and sandy, acid soil of poor quality. The water is always cold, even in mid-summer. Sunlight, direct or filtered, during some portion of the day is essential for flowering spike formation and full development of the color of the flowers. Flower spikes are thus much more numerous after veld fires which clear away the shade-producing overgrowth. Conversely, when the overgrowth gets old and dense, very few flowers are seen, but meanwhile the Disa colonies conti­nue to maintain themselves by vegetative, stoloniferous growth.  

Although Disa uniflora flowers from December to March, often in extreme heat and is able to tolerate many hours of full sun, the plants always grow in a cool, well drained sub-stratum with a root system that is constantly kept wet. As the plants usually occur near free water, a fairly humid microclimate is maintained and with filtered sunlight, Disas are able to resist the desiccation seen in the dry veld (unenclosed country) nearby.  

There is no true dormant season with Disas as is the case of most terrestrial orchids. Even when the flowering stem dies back and the leaves wither, there is continuous ac­tivity below the surface with the formation of a new tuber and stolon production. Even­tually several new plants emerge, growing slowly in winter but rapidly as the days become longer to culminate in spike formation in mid-summer. There is always circu­lating air and frequent exposure to strong winds. Nutrients are provided by decaying humus, bird and animal droppings and some trace elements are leached from the sandstone. Due to the excellent drainage system, these nutrients are continuously sup­plied in weak concentrations.

Basic cultural requirements

1.   Water and pH

Mountain, rain or soft borehole water with a neutral or low pH is ideal. Municipal water can be fatal if the pH is high and chlorination excessive, but in most Western Cape towns the quality is acceptable.  

2.   Drainage and Growing Medium

Good drainage is absolutely essential to prevent fatal waterlogging, "souring" and the development of toxic anaerobic conditions in the root zones. A porous medium consis­ting of coarse river or other sharp sand or live sphagnum free of decaying organic mat­ter to allow unimpeded entry of water, oxygen and nutrients has been found best. Very fine sand and the presence of soil and particularly clay must be avoided.

3.   Temperature

A cool root environment ranging from 10⁰C-20⁰C is desirable.⁶ The air temperature, however, may occasionally exceed 30⁰C and be tolerated, provided adequate humidity and free air movement are ensured.

4.   Humidity and Air Circulation

Humidity above 50% is ideal and this can usually be maintained in the disa house by keeping the surroundings damp. Hot, desiccating winds are harmful. Stagnant air seems to induce fungal attack, so free air circulation should be encouraged.

5.   Light

Subdued sunlight giving approximately 50% shade is required in summer to produce strong flower spikes and pigment development to give rich colors.

6.   Feeding

Nutrients and trace elements given frequently in weak concentration is preferable to heavy dosages at long intervals.

It is only by appreciation of the importance of these factors and close adherence to the recommendations that one can hope to cultivate Disas successfully. The safety mar­gin is narrow and neglect of the basic requirements will quickly lead to disappoint­ment. The danger of fungal attack is ever present and apt to occur in plants with poor root systems, growing in a "sour" or badly drained medium. The objective should be to attain the perfection and soundness seen in the disease-free Disa populations found in nature.

Propagation

In nature, dense colonies of Disa uniflora become established by vigorous vegetative propagation. This results from a characteristic sequence of events. (Fig. 1) Firstly, a new tuber is produced annually by each mature plant so that by the time the flowered spike and the previous year's tuber die back, a new shoot and root system arise from the new tuber. This new plant, genetically identical to the old, emerges alongside the old spike in early autumn. Secondly, Disa uniflora and its allied species produce sto­lons or under-surface runners from the tips of which new tubers, complete with leaf growth and roots, emerge. Thirdly, some plants may produce a mass of new plantlets at the base of a dying flowering stem.

Although a single seed capsule may contain a thousand or more seeds, reproduction from seed plays a minor r6le in nature as evidenced by the paucity of fertile seed cap­sules. However, cross-pollination by hand between species and subsequent propa­gation by seed is the only way to produce Disa hybrids, while intra-specific pollination can be used to improve desirable features.  

GROWING FROM SEED

Fertile seed can be obtained by applying a  ripe pollinium or pollen sac to the stigma of a flower at its peak. Cross-pollination is preferred; but pollinating a flower with its own pollinium ("selfing"), is necessary to bring out recessive genes of interest. After pollina­tion the flower rapidly fades and the seed capsule develops. About 5 to 6 weeks later the ripe capsule will split to release the seed. This is the time to harvest the capsule and place it in a small, open container to dry before separating the seed.

Seed should be sown soon after harvesting as it gradually loses viability after a few months. Viability can, however, be extended to about a year by storing in a deep freeze, although germination percentage will by then be somewhat reduced.⁷ Sowing in late summer or early autumn has the added advantage of producing strong seed­lings, before the cold winter months set in.

SOWING PROCEDURES

Disa uniflora is unique amongst the commonly grown orchids in that germination in sterile flasks on nutrient agar is unnecessary; germination is excellent when sown on a damp surface of boiled sphagnum moss or imported peat moss. If the sphagnum is not boiled, it may grow so vigorously that the tiny Disa seedlings are smothered.  

The following procedure has proved itself and is recommended. (Fig. 2)

A 13 cm pot with ample holes for drainage is filled with clean riversand to a depth of about 4 cm and the sand firmed down. Over this is placed a 2 cm layer of clean boiled sphagnum moss previously soaked in water. A thin layer of small polystyrene granules can be introduced at the sand/sphagnum interface to ensure good aeration. The seedbed thus prepared is now watered from below, by standing the pot for a short while in shallow water. After allowing excess water to drain from the pot, sprinkle the seed sparsely over the surface; the pot is then covered with thin transparent plastic, such as "Gladwrap", and kept in place by a rubber band. A few puncture holes in the cover will reduce condensation of moisture in the pot. Whenever necessary the pot is henceforth watered from below as described. The water level in the shallow container in which the pot stands, must be kept just below the top of the sphagnum layer, otherwise the seedbed will be disturbed. The seedbed must never be allowed to dry out but, equally important, the pot must not be left standing in stagnant water. A wick can be used to slowly siphon off the water from the container. Watering in this way, approximately every five days, should be adequate, especially if the pot is kept covered. The cover also appears to suppress algal growth which can be harmful.⁸

Germination is rapid and protocorms should appear 4-6 weeks after sowing. Soon the first leaf emerges and after three months plants will normally have two leaves ap­proximately 1-2 mm in length. Feeding from below with a weak nutrient solution can now be commenced. Use a quarter-strength balanced chemical mixture. Trace ele­ments can also be supplied from preparations such as Kelpak or Marinure and other similar products. The seedlings grow rapidly until the onset of winter, when growth ap­pears to remain static for several months. Growth can be forced with heating, high humidity and artificial lighting, but is not recommended because of the risk of encour­aging fungal attack and algal overgrowth. With the advent of spring, growth accele­rates and small roots start developing, and by early summer the seedlings are ready for pricking out into community pots. The glass or plastic covering should be removed a few months after sowing, to prevent plants becoming spindly, and to harden them be­fore planting out.

PRICKING OUT

This should be done when leaf length reaches about 0,75 cm and roots are growing ac­tively. Community pots are prepared in much the same way as the seedbed pot (Fig. 3). A 13 cm pot is filled to about three-quarters with the same grade of coarse, washed riversand medium which is watered and firmed down. A 1 cm layer of either living sphagnum or sterilized imported peat is then added and lightly pressed down. After making the medium damp, small clumps of approximately five seedlings are pricked out, settled in the new medium and treated with a weak nutrient solution. It is advanta­geous to cover the pots with transparent plastic or glass to ensure high humidity for a month or so. When growth can be observed, the cover should be removed. Strong Disa seedlings with leaf length of 1-2 cm should be produced 9-12 months after sowing. Dilute feeding from below at weekly intervals is necessary while the pots are covered, but once the covers are off, feeding from above, using a simple atomizer, is preferable.

Seedlings grow rapidly in their second year and the more vigorous plants will begin to multiply vegetatively.  

VEGETATIVE PROPAGATION

Active vegetative reproduction is evidenced by the appearance of new leaf shoots near the older plant, usually in late summer and early autumn. Well established plants should be divided at this stage. By tipping the contents of the pot into water, the medium falls away from the root system. The old plant, whether immature or a dying flowering stem, can be discarded and the new plants that have arisen vegetatively can be carefully divided and potted into fresh medium. One or more plants can be placed in each pot and allowed to grow to maturity. Care should always be taken in handling the roots and tubers as these are very brittle and fragile and the plant is set back seriously if these are broken. The great advantage of a sand medium is the ease with which re-potting is accomplished.

Cultivation

Success in growing Disas depends on providing the basic growth requirements out­lined above. In addition, constant vigilance throughout the year, which includes check­ing for fungal attack and pests, while maintaining scrupulous cleanliness and hygiene in the growing area, is mandatory. This demands a high standard of devotion and any would-be Disa grower who cannot commit the necessary time and care to growing this noble orchid is advised not to embark on the project.

GROWING AREA

A structure should be prepared so as to give sufficient light, maintain humidity and al­low for air circulation. The grower could construct or adapt a simple structure, for example by enclosing a pergola with 40/50% shade cloth, with or without transparent fiberglass roofing. The sides can either be left open or closed in with shade cloth, or even partially enclosed with fiberglass, provided there is an opening below bench level to permit fresh air circulation at all times.

The plants in their containers can be placed on benches, made either from a dipped metal mesh or corrugated asbestos, the valleys being filled with sand. The latter will have the effect of drawing off excess water from the pots, provided there is capillary contact between the internal and external sand.⁹ Furthermore, damp sand serves to maintain humidity and keeps the root system cool.  

A useful method for beginners having only a few pots, is to place four pots in a hang­ing basket lined with hessian and containing a mixture of coarse sand and peat. Pots can be embedded in this mixture and the evaporation of water from the surrounding medium and hessian will provide the ideal temperature and humidity. Disas can be grown very successfully in this manner.

GROWING MEDIA

Many years of experience have proved that thoroughly washed medium to coarse riversand, free of all organic matter, gives excellent results. 10 By using appropriate sieves, sand fractions of different sizes can be separated and stored. In addition, some growers prefer to sterilize the sand with heat or chemically.

The following potting procedure is recommended (Fig. 4). The bottom of the 13 cm pot is first covered to a depth of 2-3 cm with polystyrene or stone fragments of about the same diameter, then follows a 1 cm layer of coarse pebbles or stone chips of about 5 mm diameter; this in turn is followed by medium to coarse sand 1-2 mm in diameter, until the pot is filled to about three-quarters of its depth. This sequence of particle sizes will prevent the loss of the finer fractions through the large drainage holes in the bot­tom of the pot. If the pot is now immersed in water, the contents will settle into place. The plants can then be positioned and the roots suitably spread, after which the pot is filled with the same grade of sand. Finally, a 1 cm layer of pebbles about 5 mm in diam­eter is used to cover the sand. This will serve to reduce evaporation from the surface and discourage the growth of algae and moss. If live sphagnum moss is available, it provides an alternative to the pebbles; it has the advantage of creating humidity and is an excellent growing medium for Disa roots.  

A mixture of imported peat and coarse sand (1:3), materials like osmunda or palmiet fiber, even pots filled with live sphagnum moss only, can be used as alternatives, but medium to coarse sand as described above remains the medium of choice from the point of convenience and easy availability.

The pot size for mature plants should not exceed 15 cm and to promote good internal aeration, extra holes can be drilled in the sides near the base. Plastic pots have been found best.

WATER AND pH

Disas require a moist medium at all times but over-watering should be avoided even where drainage is perfect. Rain, river or borehole water is ideal whereas municipal water, with a high pH and chlorine content, can be rapidly fatal. It can, however, be rendered less harmful if allowed to stand in an open tank for de-chlorination. Sea sand and builders' sand are totally unsuitable. Likewise sand containing limestone particles should be avoided. Generally speaking, a mildly acid root environment has been found to suit Disas. Depending on the growing area, watering must be done daily, sometimes twice a day in very hot weather. If an automated sprinkler system is used, care will be needed in the flowering season, since wetting the flowers may cause un­sightly spotting and fungal attack on pollinia, stigma and ripening seedpods. The ideal, as is the case with most orchids, is a good watering in the morning which allows the leaves and flowers to dry quickly.

TEMPERATURE

The root system must be kept as cool as possible at all times and this can be achieved by placing the pots on a bench covered with stone chips or sand. Evaporation from the damp medium and surrounding plant pots will reduce the temperature and provide the necessary humid micro-climate. A fairly wide latitude for air temperature is per­missible and temperatures occasionally well above 30⁰C are tolerated, provided humidity and free air circulation are ensured. Desiccating dry winds over an extended period can do much damage, and frost is reported to be fatal.¹¹

HUMIDITY, AIR CIRCULATION AND LIGHT

A sand covered bench and moist greenhouse conditions should give the necessary humidity which ideally should be between 50% and 70%. When temperature and light intensity are high, humidity must also be kept high.  

Adequate light intensity is important for Disa spike development, and filtered sun­light is essential to ensure a strong, fibrous stem and optimal color development of the flower. The full potential of the color is only realized when the flower is exposed to sunlight at some stage, preferably the morning sun; 40% to 50% shading is ideal. Suc­cessful spike formation of Disas can be achieved when grown under glass or fiberglass roof, but over-heating combined with high humidity lead to soft stems that require stak­ing. Such plants may produce excellent flowers although the full color potential is not always attained. The plants are also more vulnerable to fungal attack and adapt poorly when removed from the hothouse conditions.

FEEDING

Clean coarse sand, peat or even fibrous materials used as a potting medium contain practically none of the nutrient elements essential for plant growth. It is thus important that these be supplied artificially on a regular basis, with perhaps some reduction during the cold winter months, when plants are almost dormant.

Various brands of mixed fertilizer salts comprising nitrogen (N), phosphate (P) and potassium (K) are available; some conveniently include the various essential trace ele­ments. These nutrients must be dissolved in water before application. Some growers apply the nutrient solution directly into the potting medium, while others prefer to wet the leaves with the solution, so-called "foliar feeding". Excess solution will run off but some will also find its way into the pot. Although nutrients can be absorbed rapidly by the leaves, it is best not to water the plants for 24 hours after feeding, otherwise the nutrients will simply be washed off or leached out.

Fertilizer mixtures, such as Chemicult, Lush etc., vary in strength but it is best to avoid those that are too concentrated, as Disa leaves are very easily scorched by strong solutions. It is advisable to start by using one level teaspoon per 10 liters of water but Disas will tolerate twice this strength in the case of some brands. The addi­tion of one drop of a concentrated wetting agent per liter of nutrient solution will re­duce the risk of fertilizer burn marks on the leaves. There are a number of organic fer­tilizers on the market, such as Sea-Gro, Nitrosol etc. and the occasional addition of a teaspoon of any of these to 10 liters of the fertilizer salt solution has given good results. Trace elements can also be supplied by preparations such as Kelpak or Marinure.

The above recommendations are made on the assumption that the nutrients will be applied weekly, either as a mist spray or with a watering can, at the rate of about 1 liter per square meter of bench area. The best time for application is early in the day. Excessive use of the organic based nutrients must be avoided, as it increases the risk of fungal and bacterial attack, which could lead to root rot and other diseases.

The temptation to over-feed or "force" Disas with strong mixtures should be resisted in favor of a policy of frequent feeding with very dilute solutions.

RE-POTTING

Re-potting is best done either in autumn or spring, or at any time if the plants look pale and sickly, possibly due to a medium which is stale, densely packed or "sour". It is usual to find that mature plants require re-potting every two years but the criterion should be the condition of the root system. If, on inspection, the roots appear inactive and there is a large proportion of black, dead roots, then obviously re-potting is indi­cated.

When coarse sand is used, it will fall rapidly away from the fragile root system and tubers upon tipping the contents of the pot into a bucket of water. All that is needed is gentle shaking, removal of dead roots and old tubers followed by careful re-potting.

Another advantage of sand is that it can be washed clean, dried and stored for future use. Like with many other orchids, re-potting the Disa seems to infuse new vigor into the plants.

The best first-aid treatment for a sick plant is to remove it from its medium, trim off all dead roots and leaves, soak for a short while in a fungicide and then re-pot in clean riversand. Withhold all food until the root system recovers.

Growing Disa species and their hybrids

The Disa species, which have been found to hybridize with Disa uniflora, are Disa tripetaloides (pink, aurata and alba forms), D. cardinalis, D. racemosa, D. caulescens, and D. venosa. All these can be grown using the same cultural methods as for Disa uniflora. However, D. racemosa and D. venosa; which inhabit marshy seepage areas rather than stream-sides and waterfalls, are more difficult to maintain in cultivation and are somewhat more susceptible for fungal attack. Fortunately, the growing conditions and methods described for Disa uniflora can be used with all Disa hybrids made thus far.

Diseases and pests

FUNGAL DISEASE

Undoubtedly the most serious hazard for Disas is a virulent rot, presumably fungal, which may strike the leaf axil, crown, tuber or the whole root system. The plant rapidly disinte­grates, the stem collapses and when the medium is examined, the tubers and roots have usually disappeared or turned into a glutinous mass. The disease can spread in epidemic proportions and can wipe out a good collection of seedlings and mature plants. The cause of this rot, whether fungal or bacterial, has yet to be identified, and a disheartening feature thus far has been the failure of any available fungicide to cure this infection, once estab­lished. The experience has been shared by most Disa growers. ¹²

The best safeguard against fungal infection is constant vigilance and the regular use of a variety of fungicidal sprays on the assumption that prevention is better than cure. However, since using clean sand medium, free of decaying organic matter, and regu­lar feeding with dilute nutrient solutions to ensure vigorous, healthy plants, the inci­dence of disease has dropped markedly. Furthermore, observance of cleanliness and good hygiene, re-potting of weak plants, removal of dying leaves from the base of the stem and prompt removal, isolation or even destruction of all diseased plants and avoidance of over-watering go a long way towards preventing fungal diseases.

Many orchids are known to be susceptible to Phytophthora cactorum.'² This fungus attacks the leaves, pseudo-bulbs, rhizomes and flower buds. Affected areas on the leaves are purplish-brown or black. Fusarium and Pythium species are also known to attack but should be susceptible to the appropriate fungicide.

When using a new unproven fungicide, it is wise to experiment on a few plants. This is to ensure that the fungicide itself does not kill the Disa. Hitherto Dithane, Captan, Funginex, Benlate, Bayleton-A have proved safe, but Benlate given in full strength can result in severe chlorosis of the leaves of seedlings and young plants.

BACTERIAL DISEASE

Bacterial Soft Rot (Erwinia carotovora) can cause amber colored spots to develop on leaf blades, which then turn brown. 12 The whole leaf is involved and becomes chestnut-brown. If not arrested, the rot may involve the entire plant and destroy it. This infection usually occurs only through wounds and care should be taken not to bruise plants and to re­move damaged portions. Other bacteria, such as Pseudomonas catdeyae¹² are known to cause deadly rots in orchids. We need to determine which are relevant to Disas. Physan 20 is an excellent bactericide, but should be

used with extreme caution as it could burn the delicate Disa plant.

VIRUSES

These have never been recognized in Disas and could not be identified in suspect plants when these were tested by Dr. W. Stouta­mire. 14

INSECT PESTS

Some growers have reported heavy damage from red spider and thrips. These, and also greenfly  which  occasionally  attack  the plants, respond readily to the usual control methods.  However, systemic insecticides are best avoided when the flower spike is developing. Pedicel and bud growth can be distorted and seriously malformed flowers may result.

A most serious problem is damage caused by the minute larvae of a galimidge fly, belonging to the genus Cecidomyidae. It was first recognized by Mr. K. C. Johnson in 1965. Research workers at Stellenbosch then identified the fly after pupation of the lar­vae, and found that Lebaycid was the antidote. From early spring onwards, the flies lay their eggs on the young flowering stalks or in the undeveloped flower bud. Minute, bright yellow larvae, covered in clear sticky mucus, cause the plant tissue to collapse, and the plant then becomes rapidly susceptible to fungal attack. If the larvae are not destroyed, the tip of the flower spike may be seriously damaged, with resultant malfor­mation of the flower buds. The only effective treatment appears to be Lebaycid, which should be administered at monthly intervals from August onwards.

SCALE INSECTS

Attack from various types of scale insects has not been encountered.

CATERPILLARS

A variety of caterpillars, including the boll-worm, can be eliminated by dusting with contact insecticides or stomach poisons.

SNAILS AND SLUGS

Fortunately these do not appear to attack the roots, leaves or stems of Disas, but enjoy the buds leaving nasty perforations on one's choicest blooms. Slugs hide under the pots or amongst the stones in the bottom of the pots. Snailbait is best applied around the pots.

Helpful hints for maintaining good hygiene

Attention to cleanliness is essential in growing Disas and good hygiene minimizes the need to use fungicides and insecticides, which could harm the plants and flower growth.

1.   Inspect all gifts and purchases from whatever source for pests, fungal diseases, snails, mites, weevils, and aphids. Deal with these immediately and keep in quarantine if necessary.

2.   Algae can be a danger to small seedlings in seedbeds. Use only clean pots, gutters, water tanks in the disa house. Sowing medium must be fresh and sterile. Sphagnum moss should be boiled. Keep medium damp, not wet. Water intermittently, cover with glass or "Gladwrap". Use algaecides with caution.

3.   When transplanting small seedlings, first dislodge algae by rinsing in a jet of water from a pressure-spray bottle.

4.   Remove all dying or dead leaves from plants, remove weeds, old flower heads etc. and then gather up all the refuse and remove it from the disa house.

5.   At the first sign of disease or pest outbreaks remove, isolate and apply appropriate treatment to affected plants.

6.   Avoid growing other plants, creepers, vines in the vicinity if they are prone to fungal and pest attack. Attend to plants under the staging and ensure that they do not become infected.

7.   Periodic scrubbing and disinfecting of floors and staging with a disinfectant, such as Jeyes Fluid, keeps down spores.

8.   Disinfect or sterilize old pots and stored potting media. Riversand can be contami­nated, so it is sound practice to disinfect with Jeyes Fluid mixed in water (one table­spoonful per five liters of water) a week or so before use.

9.   If the potting sand contains significant amounts of organic matter, it is wise to wash the sand thoroughly so as to float off the organic matter. The addition of ordinary washing detergent greatly facilitates the washing process.

Acknowledgements

The author is indebted to Prof, S. Cywes, Prof. E. R. Orchard, Mr. S. A. Sutherland and Mr. D. W. van deer Merwe for valuable assistance with the manuscript and to Mrs. B. Anderson for help in its preparation.

References:

1) Johnson, K. C., Disa uniflora and its hybrids. Amer. Orchid Soc. Bull. 38: 136 1969

2) Vogelpoel, L., Disa uniflora, its propagation and cultivation. Amer. Orchid Soc. Bull. 49: 9611980.

3) Vogelpoel, L., Disa species and their hybrids. Amer. Orchid Soc. Bull. 49:1084, 1980

 4) Vogelpoel, L. Disa Hybrids 1981. Proc. of the Tenth World Orchid Conference, Dur­ban 1981 pp 65-71. L. Backhouse (Pty) Ltd., Pietermaritzburg.

5) Winter, J. H. S. Disa uniflora at Kirstenbosch. Veld & Flora 87: 24 1981

6) Van der Merwe, D. W. & Anderson, B. D. Disa uniflora - observations on water tem­perature and pH readings in Disa-bearing streams. Unpublished observations.

7) Orchard, E. R. The effect of refrigeration on the viability of Disa uniflora seed.

8) Van der Merwe, D. W. Unpublished observation.

9) Meyer, H. Personal communication.

10) Personal communications: B. D. Anderson, 0. P. H. Augustyn, S. Cywes, J. Holmes, C. J. Lotter, H. Meyer, P. Noone, E. R. Orchard, D. W. van der Merwe, J. van Niekerk,  J. H. S. Winter.

11) Stoutamire, W. Disa uniflora and Disa Veitchii. Amer. Orchid Soc. Bull. 46: 438 1977.

12) Van Heerden, H. D. The phytosanitary requirements for the importation, distribution and growing of orchids in South Africa. Lecture. Plant Protection Research Jnstitute.

13) Burnett, H. C. Diseases caused by fungi and bacteria. Handbook on Orchid Pests and Diseases. 1975. American Orchid Society, Inc., Cambridge, Massachusetts.

14) Stoutamire, W. Cultivating Disas in Ohio. Amer. Orchid Soc. Bull. 50:1195 1981.

For further information please contact:

Dr. L. Vogelpoel

7 Sunnybrae Road

Rondebosch 7700  S.Afrioa Tel: (021)6891919

Cape Town,  Republic of South Africa

HOME                TOP OF PAGE