THE SCHLUMBERGERA SEASON
by Dick Kohlschreiber Epi Gram - South Bay Epiphyllum Society
All that is known about Black Spot.
By Harry Mays Alsterworthia International 1(2)3-5
Notes on Colorful, Graceful Euphorbia francoisii
By Pete Boudraint National Capitol C&S
The species Euphorbia francoisii is native to the island of Madagascar. It is a leafy miniature species related to such well-known euphorbia species as E. cap-saintmariensis, E. cylindrifolia and E. decaryi. As is true for most euphorbias the inflorescence is not the noteworthy aspect of the plant. Rather the leaves and stems are the conspicuous features of these plants. With E. francoisii attractive cream color stems emerge from a geophytic caudex, or from a tangle of fat roots if the plant is a cutting. The branches sprawl gracefully in a random fashion making each plant a unique living sculpture. The uniqueness of each francoisii plant's leaf coloration and branch architecture is what I like most about this species. Every plant is a beautiful ever-changing, singular expression of Nature's wondrous and artistic hand. From the scientific angle this is due to the fact that they are hexaploids. I have 14 francoisii plants- I believe I could identify each one of my plants based on seeing only a single leaf sample. That statement is biased however considering that I chose my plants to differ from one another.
E. francoisii leaves typically exhibit very attractive color variegation. The variegation emerges and radiates throughout the leaf as it matures. The variegation is genetic. Unlike other leafy Euphorbia species E. francoisii is evergreen. This means that the full splendor of francoisii plants can be enjoyed throughout the year. Other Madagascan euphorbias I have such as neobosseri, sakaharensis and capuroni shed their leaves for the winter, only the spiny branches remain for appreciation. I have not noticed an apparent dormancy period but I have noticed periods where the emergence of new leaves stops and older leaves wither and drop. I have not determined a cause for this seemingly random phenomenon; it might just be due to my cultural regime. The leaf shape can be the more usual lanceolate form or spade shaped. I've even heard of lyre shaped leaves. The leaves are glabrous (no fine hairs), smooth (not bumpy or rough in surface texture) and typically flat in cross section. In their degree of succulence the leaves are what I describe as leathery. The margins of the leaves are often wavy. The leaf margins sometimes are a different color than the rest of the leaf. If the unique leaf coloration and shape from one plant to the next were not enough the individual leaves on a single plant can vary in color and shape. Temperature
E. francoisii is quite comfortable in normal indoor temperatures. From my experience in growing a limited number of euphorbias I've concluded that for most species optimal growth occurs when temperatures are warm, above 78 degrees lets say. This was born out when I moved my two largest francoisii plants into the greenhouse this summer due to lack of space on the windowsill. The growth rate of the two plants in the greenhouse is greater than that of the windowsill plants. E. francoisii does not require cool temperatures for its growth cycle or flowering as some of the cactus and crassula species do.
The orthodox view holds that E. francoisii can, and should, be grown in a shaded or bright indirect light situation. This probably is good advice for southern Californians or Floridians however the light intensity that comes through a window or that arrives at the high latitudes many of us live at is muted enough to be tolerable to a francoisii. And remember the more light that a francoisii gets the more intense the leaf color and variegation will be. More light will bring forth red tones in the leaf veins, or a suffusion of white variegation or even a darkening of the leaf. I give my francoisii's on the windowsill as much sunlight as is possible. The 6 plants in the greenhouse sit on the lower bench which is shaded dappledly by the upper bench. As with so many aspects of our hobby keep adjusting the light exposure for your francoisii plants until they produce a coloration that you find appealing and is a light intensity your plants can thrive under. (Remember the goal of the c&s hobbyist in my humble opinion is to appease both the hobbyist's aesthetic pleasure and the plants' well being. Don't you agree?)
I haven't had extensive experience growing francoisii's but I tend to believe that they can grow in any reasonable soil mix that c&s hobbyists have available. Currently all of mine are in a mix that I bought as "Bonsai Soil for Tropicals" at a local nursery. C&s books state that francoisii's grow in sandy soil in the wild. Of course we shouldn't try to replicate that soil medium for our domesticated plants.
Beyond Euphorbia francoisii, my other favorite species are Portulacaria afra, Euphorbia capsaintmariensis, Euphorbia cylindrifolia v. tubifera and many species of Sulcorebutia and Rebutia. Whatever your favorite species are give them the special attention that will allow them to give many rewards back to you.
7704 Quaint Court
Bowie, MD 20720-4316
THE SCHLUMBERGERA SEASON:
by Dick Kohlschreiber Epi Gram - South Bay Epiphyllum Society
I have long advocated that if you are interested in epies, you should also collect the other epiphytic cacti. During the Fall and Winter months, when very few of your epies are in bloom, you can have color in your plant collection with Schlumbergera plants. And if you have to bring your plants into the house, Schlumbergera make good house plants and don't take up as much room as epi plants. If you have hybrids of several of the different Schlumbergera species, you can have flowers for 4-5 months (September - January).
If you are really interested in Schlumbergera, you should have the book CHRISTMAS CACTI, The genus Schlumbergera and its hybrids by A.J.S. Mc Millan and J.F. Horobin. This book is filled with beautiful pictures and illustration and has the best information about this genus. It will soon be out of print so get it while you can.
From this book you can find out that Schlumbergera grow in a highly scenic part of Brazil where they inhabit the coastal states of Sao Paulo, Rio de Janiero and Espirito Santo and adjacent parts of the land-locked state of Minas Gerais, in the hills and mountains. One of the most fertile collecting grounds for Schlumbergeras has in the Organ Mountains in state of Rio de Janeiro. The plants bloom in the cool month of May which is the beginning of Brazil's Winter season. They grow not only in the trees but also on the rocks and cliffs of the mountains.
The species within the genus Schlumbergera include:
Schlumbergera microsphaerica (S. obtusangula)
There are some names for interspecific hybrids which you should be aware
Schlumbergera xbuckleyi - cross of S. russellliana and S. truncata.
Schlumbergera x reginae - cross of S. truncata and S. orssichiana
Schlulmbergera x exotica - cross of S. opuntioides and S. truncata.
Some of these species are very difficult to grow. A true S. russelliana is seldom found in collections but Schlumbergera x buckleyi is one of the best growers and very long lived. This is the original ``Christmas'' cactus and plants have existed as family heirlooms for several generations.
I have had not had good luck growing S. kautskyi but have better luck with S. orssichiana and even better luck with the orssichiana crosses. Most of the material of S. orssichiana that was collected was thought to be virused and that may account for it not growing well.
I had never seen S. microsphaerica growing until I went to Germany and most of the plants there were grafted. I have been very frustrated with trying to grow S. opuntioides and have become convinced that I probably treat the plant too well and it doesn't like that. I like this plant because the joints (segments) look like small opuntia pads. But the large plants I have seen of S. opuntioides always look like they are grown very hard - in full sun and not much water.
I was always told that the ideal mix for Schlumbergera was a ``Cornell'' mix which is 2 parts of peat moss and 1 part perlite. I would use the raw peat and mix it with the perlite and found that it was very hard to get the peat moss wet and once it was wet, it never dries out. Now I'm just using a commercial potting mix (Potting Mix) and the #2 perlite and this seems to work well. The potting mix is actually a composted peat.
Schlumbergera are easily propagated. You're better off to just use single segments. Twist off the segments, let them callous for a week and then either just lay them on your planting mix or insert them in the mix.
Like most epiphytic cacti, Schlumbergera like water but don't like to be soaked especially when it's cold. They can grow with very little light and that's why they make good house plants. It has long been thought that Schlumbergera plants bloom when there are fewer hours of light. One year, I put some of my plants in a closet for a month and they survived but still bloomed at about the same time they always did. Then I read that you should cut back on the watering of the plant and that would stimulate the plant to bloom. I didn't water for a month and the plant bloomed about the same time it usually did.
All that is known about Black Spot.
By Harry Mays Alsterworthia International 1(2)3-5
If you have ever kept gasterias and/or aloes you will no doubt be acquainted with black spot. Even if you have no personal experience of it, you may well have heard of it in discussion and you may have noted that whilst some people may claim to know what causes it and what should be done to get rid of, or prevent it, facts do tend to conflict and undermine ones confidence in perceived knowledge. Much of what is said is based on (incomplete) empirical evidence; very little science is evident. The proposed causes of black spot range widely. The following is a distillation of views presented by a variety of sources.
Stress is sometimes cited as a factor contributing to black spot. Given that stress weakens a plant and therefore makes it less resistant to pathogens, this seems to be a reasonable line of approach and it may contribute to an explanation of why some plants may be subject to black spot in opposing conditions, hot-dry and cold-damp, both of which can be stressful to the plant, particularly in prolonged periods. However, it does not explain what is causing black spot, only what might be facilitating its development.
Cultural conditions are sometimes proposed as causes of black spot - too much sun and lack of ventilation can result in surface tissues being damaged, feeding with a high nitrogen fertiliser and over watering can result in soft tissue, which is more vulnerable to pathogens, but there is often a lack of consistency in the results with only a few plants being affected. Other growers in the same area experiencing about the same cultivation conditions have indicated that they do not experience black spot.
It is known that deficiencies in soil can cause blemishes in plants ipso fact black spot is caused by soil deficiency. This is speculation. Others have pointed out that gasterias which have not been repotted for many years must have depleted nutrients, but they show no signs of black spot, whereas plants in much fresher compost and, therefore, with nutrients have developed black spot.
Glasshouses do not have uniform conditions throughout. Corners, particularly right angled corners, can be damper than the centre, the north side can be damper than the south (opposite way in the southern hemisphere) and under the staging, particularly on the north side, can be much damper and at a lower temperature than above staging and above suspended shelving. You can easily verify this for yourself by installing a series of maximum and minimum thermometers at various points in your glasshouse and recording and comparing the temperatures at different locations at the same time. Air at higher temperatures holds more moisture than air at lower temperatures, consequently plants under the staging are likely to experience more condensation than those at the higher, hotter levels. In one glasshouse a difference of more than 10 Fahrenheit was found between under the staging and on suspended shelving on the north side. Furthermore, condensation lingered longer by two to three hours in the corners compared with the sides and southern end. It also lingered longer on the north side. In the evenings the reverse occurred. Condensation formed in the corners and at the north end two or three hours before it became evident at the south end and sides.
Dampness is frequently proposed as a cause of black spot and claims made that removal of plants to a dryer part of the glasshouse is a reliable preventative measure. A contrast has also been drawn between winter, when it is much damper and the development of black spot has been observed, and summer, when it is much dryer and the development of black spot has not been observed. Unfortunately there is conflicting evidence as some growers have seen the development of black spot in the dry conditions of summer but not in damp winters. One Gasteria disticha in its younger days when grown on the staging in the centre of the glasshouse suffered from black spot. In its old age, when it became a large clump and remained in old compost in a tray under the staging for a long time, with less light, cooler conditions, higher humidity and low nutrients, it was free of black spot.
Another popular proposed cause is fungus and, apparently less frequently, bacteria. Perhaps these should be considered together with dampness because fungus and bacteria are known to flourish in damp conditions. However, many gasterias, which are inevitably kept in damp conditions in winter when rain, cloud cover and short days maintain a high atmospheric humidity for long periods without any significant sun, do not develop black spot, whereas plants in the summer with long day length and clear sunny skies and much lower humidity do.
The suggestion has been put forward that some gasterias are naturally prone to the development of black spot and others are not, but reports from different people do not support an agreed list of species which are, and which are not, prone to its. Furthermore, some cultivators have found that only one plant of a species has developed black spot whilst others of the same species have not. Perhaps even more revealing is the observation that, where a large plant has been split into several individuals, observation of their progress over a number of years has revealed that only one or two have developed black spot, the majority of the same clone having remained free from it. Black spot does not seem to be contagious and rampant.
Does black spot occur in habitat? One visitor, who has made several excursions to South Africa, reported that he had rarely seen black spot on the Gasteria species he had observed west of the Eastern Cape and then north to the Orange River. In one year a few black spots were observed on Gasteria pillansii in the Hells Kloof area when it had been exceptionally dry for several months. On another occasion, in the same area in an exceptionally wet year, leaves of G. pillansii were highly turgid, some were splitting and some showed signs of rot, but black spot was seen only occasionally
In the search for more authoritative information David Cumming, who has made many field trips in South Africa, was contacted. He says that black spot "appears to be widespread and common, especially in the Eastern Cape. Astrolobas seem the most 'infected' followed by gasterias. It seems to me to be stress related, just as many diseases are in humans, which leads me to think that it may be an opportunistic pathogen rather than a primary cause of disease. In cultivation many of my gasterias that were more neglected than others displayed black spot, but on now receiving better care have recovered."
Earnst van Jaarsveld indicated that black spot is caused by a fungal disease, by a Montagnella species, which is common all over South Africa. As a preventative measure he sprays every 3 to 6 months with copper oxichloride or Captan, but notwithstanding regular spraying some plants still get some spots.
A study of Montagnella was carried out in South Africa some years ago, but it was never published. The report of the study must be lurking somewhere on the shelves of a university or botanical garden, but all attempts to locate it (and the author) have failed. Unfortunately not all important information is published for the benefit of a wider audience.
Doug McClymont of Zimbabwe was also consulted. "My experience has been with aloes and as a semi-hobby, not as a full time researcher, so I have no replicated experiments to quote, all my recommendations coming from personal observation and a suck it and see philosophy!
"The black spots I have dealt with have proved to be a minefield in many ways. Perhaps some of my general observations may be of use. The black spots on aloes generally develop in high humidity conditions, overcast, temp minimum > 18 deg. C, rain every day etc., but also when there has been a significant insect (especially Mirid) attack and even more confusing only on senescing leaves on some cultivars?! We get two main types of leaf spot, but their epidemiology has never been researched. The two types are: Montagnella maxima Mass. and Placoasterella rehmii (P. Henn) Theiss & Syd. Certainly I have experience that these are not controlled by systemic fungicides such as benzimidazoles or triazoles as I have an excellent granule mix of cyproconazole and disulphoton that ensures season long control of rust and all sucking pest and, surprisingly, including mirids who just eat the waxy cuticle of the leaves. I definitely get markedly less black spot with this annual treatment, but I am sure that this does not actually control the black spot per se, but the mirids who injure the leaf. These injuries are then colonised by the black spot organisms. So, no injuries less black spots. However, insects or not, under very moist conditions the spots come booming back and the only success I have had is with copper oxychloride or cupric hydroxide sprays. Wettable sulphur does have an effect, but not as good as the copper. The senescing effect is marked and I am sure triggered by some metabolic change. The lower leaves senesce and the black spot overwhelms them irrespective of spraying which is a real pain when trying to exhibit a show entry. I am sure there is some relationship there, perhaps extra ethylene production in the leaf on senescence, which is perfect for the spot, I don't know.
"What I do know is keep the insects off, spray regularly with copper in very wet conditions and the black spot is markedly less. In drought seasons it may disappear almost completely. I am afraid I haven't really answered your queries and I don't have any rigorous scientific replicated data to supply, but I trust my observations over the last 23 years on aloes may be of some help."
In an attempt to obtain some scientific evidence the Plant Pathology Division of the Royal Horticultural Society was contacted.
Leaves of Gasteria disticha with black spot on both sides, samples of the roots and the soil in which they were growing were sent to them to see if they could establish the cause of the black spot. They carefully examined the material and concluded that the spots were not the result of cultural practice such as the amount of sunlight, watering and feeding. They incubated areas of tissue around the black spots, but were unable to isolate any fungal or bacterial pathogens; they did add that the isolation of bacterial and fungal pathogens was difficult. They also carried out a search of the literature for diseases in Europe, but were unable to find any information on Montagnella species, presumably because it is not a factor in Europe. The best suggestion they could offer was to use the fungicide mancozeb, which is available in garden centres as Bio Dithane 945, as it had proved effective in controlling leaf spotting in a wide range of plants.
It is worth bearing in mind that for some people black spot does not develop on their plants, notwithstanding their cultural conditions may not be quite up to the standards conceived as being ideal for the prevention of
black spot. "I find black spot to be rare in my greenhouse in spite of damp conditions in winter and poor air flow because vents have to be kept closed to isolate the interior from the low outside temperatures." "I never get Black Spot and grow all my Gasteria in shade."
So where does all this leave us? The conflicting information from growers does suggest that there is no one set of conditions under which black spot develops. The causes of black spot appear not to have been finally established, but many perceive that fungi are the culprits though fungicides seem to do no more than control them; they do not eliminate them. Stress would also seem to be an important factor. Good husbandry may be the best preventative measure, which means growing plants hard in the growing season with plenty of moving air, good light, but not necessarily full sun, adequate water and nutrients for growth and repotting as dictated by growth. This should result in a "hard" plant which is better protected from insects and any pathogens the damp, dormant period can throw at it. It should help considerably to keep the floor, staging etc clean at all times and the plants dry during dormancy and during dull, cold, damp weather. From hereon you are on your own. Conditions do vary from year to year so these alone could influence the occurrence of black spot more than the removal of a plant from one position to another in the same glasshouse. Careful observation over a number of year will be necessary to come to any reliable conclusions.
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Acknowledgement, with appreciation, of information received for
incorporation into this article from:
1. A number of growers in different countries.
2. David Cumming, South Africa.
3. Ernst van Jaarsveld of the National Botanic Gardens, South Africa.
4. Doug McClymont, Zimbabwe.
5. Dr. A. J. Jackson, Plant Pathologist, Royal Horticultural Society.