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Cattleya Culture - Part 4

NED NASH

The following article first appeared as part of a five-part series in the American Orchid Society BULLETIN Vol 52 1983. While it is over 25 years old remains an excellent source of information for today's orchid growers. It has been edited to conform to modern taxonomic nomenclature, insecticide/pesticide and potting media availability.

CATTLEYAS in modern collections are fortunate in suffering from very few pests. Their tough, leathery foliage is not as attractive to sucking pests as a tender phalaenopsis or masdevallia, for instance. Sensible use, as needed, of today's readily available insecticides will take care of any minor infestations.

It is never a good idea to spray insecticides as a prophylactic measure for the simple reason that one is encouraging the creation of resistant strains of insect by this type of usage. An analogous situation exists with antibiotics. Most doctors will not prescribe their usage as a preventative measure, only when the substance is indicated for by a disease.

I should stress very early on that although today's insecticides are of relatively low-toxicity, great care must be exercised with their use. The storage and preparation of any insecticide should be according to the instructions on the label. Full clothing, gloves and a mask should be worn when spraying to avoid any splashing or drift. The insecticide concentrate should be poured into the water to avoid splashing of concentrate on the mixer. A good point to remember about most insecticides is that they will accumulate in the body over a period of years and will not be broken down. If they reach a critical concentration after many years, the symptoms of insecticide poisoning may appear. Always be careful and alert while using insecticides!

Things were not always so easy for Cattleya growers. Before Dr. Knudson's work on asymbiotic germination enabled us to grow large populations of hybrids from seed, jungle-collected species were grown in vast numbers. Before the turn of the century, large consignments of plants would be imported for use in cut-flower production. In many cases, the plants would be forced for several years until their jungle vigor was exhausted. When this occurred, the plants were discarded and fresh ones imported. This practice, besides constituting ecologic rape, led to the importation of many jungle insects along with the plants.

In those days, the science of pest control was not as sophisticated as it is today. Most pesticides were either basically petroleum distillates that would essentially smother the insects, or nerve poisons that were as fatal to people as they were to insects. Leo Holguin tells some very entertaining "horror stories" about life with cattleyas before OSHA, EPA, etc.

Many older growers remember the nicotine smoke bombs that were so effective against aphids and other sucking pests. One simply lit the fuse and vacated the greenhouse. Before the smoke bombs were manufactured, liquid nicotine sulphate was used to produce the fumes. The boiler would be started, thereby heating the under-bench steam pipes. Men with paintbrushes and buckets full of nicotine sulphate would be stationed at the far ends of the steam lines in the greenhouse. They would then more or less simultaneously paint the nicotine onto the hot steam pipes as they backed quickly out of the house. The rising fumes worked well on insects, but they rapidly turned the slower painters green!

Perhaps the most severe measure was the use of cyanide crystals on wet walks. Mason jars with perforated lids were filled with cyanide crystals. The concrete walkways in the greenhouse were hosed down and the men were stationed at the far end of the house. Again, the men walked quickly backward, sprinkling the cyanide crystals on the wet walks. The use of cyanide naturally made the men nervous, and one would occasionally drop his jar. Leo has always said it was interesting to see just how fast the men could move if they wanted to!

Nicotine painting and cyanide sprinkling were extraordinary measures for extraordinary infestations. A more common practice was the use of Red Arrow, which was basically an oil preparation. All cattlcyas (millions and millions of them, as Carl Sagan would say) were routinely stripped of the dead sheathing on the bulbs and scrubbed with a toothbrush dipped in Red Arrow to take care of minor scale infestations. This was generally done every year to every mature plant. Red Arrow was also used as a dip for a pest we thankfully do not have to deal with anymore. The "orchid beetle" was a tiny (1/8") weevil-like insect that would bore into both flower buds and pseudobulbs. Flats of plants would be brought out of the greenhouses and the entire flat dipped into a tank of Red Arrow solution.

Another serious pest of that era that has been eradicated on the mainland is the "Cattleya Fly". This insect inserted its eggs into the new growths of cattleyas. The grubs would feed on the developing growths until ready to hatch, whereupon they would emerge as flying adults. Control of these flies was possible only just as they emerged from the bulbs. Fortunately, this event tended to be synchronous throughout the house. By placing a sample plant in a glass box, the emergence of the tiny flies could be closely monitored and measures taken at the correct time. Much experimentation with available insecticides was necessary before truly effective methods were found. Initially, Black Leaf 40 spray in conjunction with nicotine smoke was used. Later, both DDT and Chlordane were tried with DDT found to be the most effective. It took nearly two years before the pest was eradicated from the Armacost range. Because the pest attacked the new growths only, ruining them in the process, one of the remedies (?) was to walk the aisles of the houses looking for the characteristic swelling of the new growth and simply cut off the new growth. This pest still pops up occasionally in tropical areas where plants are grown out-of-doors the year around. Ease of access to the plants makes it nearly impossible to adequately control the pest in these situations.

A third serious pest that has become relatively scarce today is boisduval scale. This rapidly spreading soft scale forms cottony masses on the underside of the leaf where it joins the bulb. Boisduval scale is a fairly ravenous scale and its depredations can be observed as yellowish blotching on the upper surface of the leaf. Thanks to Cygon, a systemic pesticide, boisduval scale is not the serious problem it was twenty-five years ago [other systemic insecticides that are effective against this scale insect are Orthene, Safari and one of the neonicotinoids like Merit]. Because boisduval scale spreads unbelievably quickly, entire blocks would become infested before it was noticed. The infestations necessitated not only a Red Arrow scrub, but a cyanide treatment as well. Today, when the rare infestation is found, a single thorough spraying with an effective systemic is usually sufficient to mop it up.

Malathion, Orthene or one of the neonicotinoids are the insecticides of choice today for most sucking insects. The tough foliage of cattleyas is not too adversely affected by the oil carrier (Malathion), and Malathion is effective against scale and mealy bugs, as well as aphids. Mealy bugs arc usually a more serious problem on young seedlings and dwarf hybrids because of their softer foliage. Wettable Malathion or Orthene powder may be indicated in these cases, as they do not utilize the oil carrier. Aphids tend to attack only the flower buds, and these are easily damaged by either the oil base or the physical force of spraying. Insecticide residues are also not desirable on the flowers. We use a Carmel Fogger in these situations. A Carmel Fogger is essentially a gasoline-powered ramjet that produces a dense fog of insecticide. The stream of fog is directed up into our fanjets and the house quickly fills with the fog. This is quite effective against aphids and does not seem to affect the flowers.

An important point to remember is that one application of an insecticide will rarely take care of the problem. Most commonly used insecticides affect one stage of an insect's life-cycle. For this reason, three to four applications at seven- to ten-day intervals are recommended. We have not found systemic insecticides to be generally effective for cattleyas (except Cygon for boisduval scale). I suspect it is because cattleyas grow so slowly that the systemic is poorly or weakly distributed throughout the plants [Editor's note:  Orthene an the newer neonicotinoid have proven effective in Cattleyas but were not available when this article first published].

Soil-dwelling pests are a relatively minor problem for cattleyas. Snails and slugs do not care for the tough foliage, but they do relish flower spikes and buds! Regular applications of metaldehyde granules or one of the "green" alteratives will stop this pest. Sowbugs and/or millipedes will occasionally infest potting medium. A Diazinon drench will take care of this type of problem. Sowbugs can wreak havoc on mounted orchids by eating the fresh root tips. Spraying with Diazinon or Sevin will prevent this.

Perhaps no other subject raises so much controversy as virus in cattleyas. With the recent thrust in research and the many articles being written by people of much greater expertise, I will not dwell too long on this subject here. Yes, virus is a serious problem in many Cattleya collections around the world. No, it cannot at this time be reliably cured. Yes, it is really easy to spread it from plant to plant. No, you cannot reliably diagnose a virused plant from foliar symptoms (although you can make a good guess). Yes, you must disinfect your cutting tools between each plant (heat is the only sure method). No, virus does not necessarily affect the vigor of a plant, although it may. Unfortunately, the more we learn about virus, the more plants we find infested with it, plants apparently "free" of the disease. This, to me, is the most disturbing aspect of the virus problem. How many "Typhoid Marys" are there throughout the orchid world?

The next article in this series on the culture of cattleyas will deal with growing conditions and flowering. — Armacost & Royston, 3376 Foothill Road, Box 385, Carpinteria, California 93013.