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From worchard@ups.edu Mon Dec 16 15:42:53 1996
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To: Aaron Hicks <ahicks@nmt.edu>
Subject: Disas, culture and agriculture
OK, AJ, here it is in a plain brown wrapper!
Wally
_______________________________________________________________________ ___
DISA CULTURE
This deals with the culture of the better known Disa species and hybrids
which grow in winter rainfall areas around Cape Town, South Africa. The main
species of interest are Disa uniflora, D. racemosa, D. tripetaloides, D.
aurata, D. cardinalis, D. venosa and D. caulescens.Many other Disas are
known, though few are commonly cultivated and many grow in drier conditions
and have rather different cultural requirements (e.g. D. sagittalis).
Media
Disas need excellent drainage, and a constantly moist, aerated medium. New
Zealand sphagnum moss is excellent, but breaks down quite quickly. Coarse
sand (not beach sand!), sometimes mixed with peat or fern fiber works well
for some growers. Perlite:vermiculite: peat in a 1:1:1 mix is convenient and
good. Algal growth on the surface can be reduced with a layer of small
pebbles. A layer of pebbles or styrofoam chips in the bottom of the pot
helps promote drainage. Experiment with media to find the one which suits
your plants and growing conditions the best.
Pots
For mature plants, 3 to 4" square plastic pots are fine; for seedlings,
smaller pots are ok, but they should be reasonably deep to conserve moisture
and allow room for the roots and tuber. For specimen plants, bigger pots can
be used. Netting pots with NZ sphagnum as a medium can be used to encourage
vegetative multiplication of valuable clones.
Water quality and watering
Water quality is absolutely critical in Disa culture. The water should have
a low concentration of dissolved mineral salts and should be low in chorine.
Some tap water is ok, but most is not. Rainwater or reverse osmosis water is
recommended where there is any doubt about tap water; well water is
sometimes acceptable. An acidic pH (4.5 to 6.0) is preferred.
The medium should never be allowed to dry out. Hydroponic systems have been
used, but regular watering works just as well. Water 3 to 7 times a week in
summer, and 1 to 4 times a month in winter. As with most orchids, watering
is best done early in the day so that the leaves can dry out. It is
important to cut down winter watering, otherwise problems with fungal rot
can be expected. Disas succumb rapidly when mineral salts accumulate in the
medium; regular, thorough watering from above will help to prevent this from
happening.
Fertilizer
Use very dilute (about 1/10th strength), balanced fertilizer containing all
trace elements on a regular basis during the spring to fall growth phase.
Moderate to high nitrogen is recommended; I like Dynagro 10:5:5 and use one
quarter teaspoon per gallon of water, weekly in the growing season. With
this fertilizer the sphagnum moss medium seems to hold up better than with
others I have tried. Dynagro Protekt is supposed to prevent heat stress, and
Superthrive vitamins can be applied occasionally. A handheld conductivity
meter ($45-50) is a useful aid in monitoring water quality and fertilzer
concentration. Water should be below 100 microSiemens/cm, fertilizer
solutions below about 300.
Temperature and humidity
Disas like plenty of air movement and relatively cool temperatures,
especially in their root zones. They are stressed when the temperature goes
above 80F; also the humidity should ideally be kept above 50%, especially in
hot weather. Shade netting in summer helps keep the temperature down and
humidity up. A sharp frost will damage the leaves, and a hard, extended
freeze is likely to kill the plants, but they will happily tolerate winter
temperatures just slightly above freezing.
Lighting
During the growing season bright, filtered sunlight is important for Disas.
They can also be grown under lights. My plants stay outdoors, half under a
deck and behind shade netting from spring to fall, and come into the garage,
under fluorescent lights, from late October to March.
Repotting
Mature Disas need annual repotting since the old plant, tuber and roots die
and rot. Repotting is usually done in the fall, after flowering, or whenever
there are indications of root problems. Healthy roots are pale and very
brittle; dead roots are brown and soggy. These should be removed, and the
plant should have a thorough washing before repotting.
Pests and diseases
Disas are susceptible a virulent fungal rot, in which the whole plant and
root system decomposes into a soggy black pulp. Correct culture reduces the
chances of this, but routine fungicide application at least from fall
through spring is recommended. Among the fungicides which have been used are
Subdue, Banrot, Captan, Benomyl, Dithane, Funginex, Benlate and Bayleton-A.
As mentioned above, watering should be severely curtailed in winter in order
to minimize the danger of bacterial and fungal infections. Bacterial soft
rot has been treated with Physan 20. Insect pests and their treatment
include Aphids (Malathion, Sevin, Orthene), thrips (Cygon, Lebaycid),
gallmidge fly larvae (Lebaycid) and earwigs, which eat the flowers at night.
Regular removal of dead and dying leaves reduces the risk of disease.
Growth cycle
Winter. Plants show little or no green growth during the coldest months, but
mature plants can have significant underground activity in the way of
developing tubers and shoots.
Spring. With the advent of warmer weather and longer days, leaf growth
begins to accelerate.
Summer. As the weather warms up, growth continues and spikes may start
developing. The hybrids tend to flower early, along with species such as D.
tripetaloides. D. uniflora flowers quite late, typically in July and August
on the US West Coast. Flowers may last for six weeks.
Fall. After flowering, the plants die back. With good management, other
plantlets are already present, and a new tuber has been produced from which
a strong new plant will sprout. Even unflowered plants may die back as the
weather gets cold, but provided a new tuber has been produced, a healthy new
shoot can be expected to grow in the spring.
Propagation
Mature Disa plants often produce several new plantlets annually, and these
provide a simple way of increasing a collection. These new plantlets can
grow from new tubers, as keikis alongside the main growth, or from long
underground runners (stolons). Disas can be grown from seed to flowering in
3 to 4 years. Seed can be sown on boiled, damp moss, on peat, or on a
sterile nutrient agar medium, which is quicker. One quarter strength
Murashige and Skoog formulation, or similar mixes, with added banana pulp or
powder, work well for sowing seed and replating.
General
Despite trying to follow other people's proven growing methods, I have had
my share of setbacks. It pays to experiment to find the best growing medium,
watering regimen, fertilizer, lighting etc for your locale. Unfortunately,
you will probably lose a few plants along the way!
Wally Orchard
839 Harvest Ct SE
Tumwater, WA 98501
Tel: 360 705 4229; Fax: 360 705 4206; E-mail: worchard@ups.edu
_______________________________________________________________________ ____
Wally Orchard
Department of Chemistry 839 Harvest Ct S.E.
University of Puget Sound Tumwater, WA 98501
1500 N Warner
Tacoma, WA 98416
E-mail: worchard@ups.edu Tel: 360 705 4229
Tel: 206 756 3834 Fax: 360 705 4206
Fax: 206 756 1304
_______________________________________________________________________ _____
________
re: germination of disa seed:
Date: Mon, 19 Jan 1998 23:25:32 +1200
From: CESAR ZAPATA <dioza@ibm.net>
To: "Aaron J. Hicks" <ahicks@rt66.com>
Subject: Re: Disa seeds
Dear Aaron,
We must soak the seeds until we see a noticeable swelling
probably 24 hours. I have done this on several disa seeds
sent to me from South Africa. These are seeds that were almost
a year old and only the batches of seed that show swelling
when soaked have germinated. This has been my standard test
on disa seeds to see if they are still alive.
I have noticed that the disa seeds are germinating while still
in the seed capsule. This might be the main reason why most
dried disa seeds do not germinate mainly because they have
pre-germinated in the capsule and then dried out to die. When this
kind of seed gets to the recepient, of course nothing will
germinate.
Cheers,
Cesar Zapata
P.O. Box 11969
Wellington
New Zealand
Date: Wed, 21 Jan 1998 00:26:25 +1200
From: CESAR ZAPATA <dioza@ibm.net>
To: "Aaron J. Hicks" <ahicks@rt66.com>
Subject: Re: Disa seeds
>I take it this is only for seeds sown on sphagnum, rather than _in
>vitro_, or does this work well for flasking?
The test is only for sowing seeds in sphagnum. When flasking it is
easier to just flask it and wait for it to germinate. It is very tricky to
sterilize disa seeds and I just follow sterilization for phalaenopsis
seeds which is one minute in 5 percent commercial bleach.( that is: 5
percent by volume on the commercially available bleach Chlorox or Janola
which in turn are about 4 percent sodium hypochlorite)
I have not heard or read of any literature about disa seeds
germinating when the seedpod breaks while still on the seedpod. This will
be a first. Next time I will document this using slide photos. By the way
this observation is for Disa uniflora.
Cheers,
Cesar
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