Good basic greenhouse hygiene is something every grower should practice. Not only does it provide for a more healthful environment for your plants, but it also keeps the entire collection looking better. Plant diseases are caused by bacteria, fungi and viruses, and they can start at any time or from any place, but they are most prevalent in an unsanitary environment.
Even by keeping your growing area perfectly clean (free from dead and decaying material), it will not keep your plants entirely free from disease, but it will lessen their chances of being attacked. By eliminating breeding grounds for bacterial and fungal rots, we are better able to ensure the good health of our plants, and unless an infected plant is introduced into the collection, they will remain clean for longer periods of time. (Chapter 3, “Air and Light – The Correct Balance” details how those two elements are an important and necessary part of maintaining good plant hygiene.)
Plant hygiene is particularly important to observe, since in the United States as in many other countries, we no longer have the availability of useful pesticides. We must now contend with those which have a very limited effectiveness against the relentless attacks from the same diseases and pests with which we have been forced for years to contend. For those few remaining effective pesticides we still are able to use, history has shown us how quickly they become ineffective because of the pesticide resistance plant pests are rapidly able to generate. Unfortunately, the evolution of effective pesticides has now been essentially halted and our arsenal of chemicals used to maintain our pesticide rotation cycles continues to diminish.
Although some of the more effective pesticides are still being manufactured, present laws mandate they can only be used for those pests or diseases, and for those plants that are specifically listed on their labels. If they are not listed for a specific use, it is illegal to use them for any other, and there are only a few which still specifically list “orchids” on their labels. Fortunately, there are some jurisdictions that allow the use of pesticides on orchids when the label reads, “ornamentals.”
Most all of the traditional pesticides have been eliminated from our arsenal, and those which have replaced them are questionably with scarce justification for their use. These “soft” pesticides as they are now called, must be applied to directly contact the pests or the diseases, and they have little or no residual effect. In other words, you may need to repeat the spraying again tomorrow, or even as quickly as the original application has dried if you failed to make direct contact with the contaminant.
Realistically, the Neem oils and the insecticidal soaps are a comparative joke when held against the effectiveness of our better chemical pesticides. Paradoxically, soft pesticides now must also be applied at far more frequent intervals and unfortunately, there are some which are limited in their use to only a single application on a crop, and tough decisions must be made to decide on which ‘problem’ to target.
Beside mandated reasons for protecting the environment from damage by persistent chemical residues, (which has been difficult to substantiate with hard evidence over the longer term), we are unable to get useful pesticides because it no longer is practical for chemical companies to continue making and developing them, since the enormous costs and the numbers of years required to prove their efficacy can no longer be justified. (Common sense tells us that if “soft” pesticides were truly effective, most every chemical company would be vigorously promoting their virtues.) In addition, the threats of liability lawsuits, which have bankrupted some of the largest companies, continually hang over their heads.
While there has been great press recently, in many different countries in fact, to discredit the use of pesticides in the name of protecting the environment, there are few reliable sources which provide direct evidence to support any substantive, permanent or long-lasting damage, despite what you constantly see and hear in the media. Any prudent person can realize how the excessive use of most any product might have some cumulative effect by its application, but the constantly hyped drive for environmental protection has become more of an emotional issue with many people, and is mindlessly used in a multitude of instances where there is no justification for its mandated implementation.
The desire to protect the environment is unquestionably, a noble cause, and is certainly one which we must all strive to ensure. The problem we now must face however, is how to answer the question of whether we should save our orchid plants, or to engage in a systematic but futile attempt to slay a non-existent dragon, as a means to ‘conserve’ the world.
THAT IS the question we must confront.
I see the answer in a clear and uncluttered picture, simply by weighing the causes and effects of the two opposing ideas. Since there is no irrefutable evidence to show how the few chemicals we use in our greenhouses and in our homes has negatively impacted our environment over the long term, I choose to protect our orchids.
I recommend the prudent use of the most effective pesticides for each targeted pest problem as a means of effective control and elimination of those problems. The protection of our orchid plants must be guaranteed, until we see verifiable evidence of just how harmful these current pesticides actually are. This idea must be adopted since it is supported by the Test of Logic.
As much as I would like to do so, I have not recommended particular pesticides for specific uses (however, see the last paragraph in this chapter), although in a few cases I have done so. One of the reasons for this is that they are not all registered for use in every state of the U.S. Secondly, within a few more years it is highly doubtful that many of them will still be made and thirdly, the ones we have available today are continuously being re-evaluated by government mandate to determine if they are still necessary. The spiraling costs of that very expensive re-evaluation practically insures, that for whatever it is that replaces the chemicals we have today; new and different evaluations and restrictions for their use will be accorded them in the future.
Agriculture of all kinds today, including horticulture, is faced with some of the most serious threats ever encountered. It is imperative now, that orchid growers learn to practice the most sanitary cultural techniques they are capable of providing for their plants. While this may sound like a portentous message, it is important that the realities of the situation be understood. The problem we must face when pesticides are no longer effective is a question no one seems to have yet answered. The possibilities of replacing your orchids have been radically reduced, and they continue to diminish with each passing day.
Your actions must be pro-active. Help is not on the way.
While some plant diseases are fatal, others are not. Some will hardly be noticed while others can be devastating, and certain plants are more vulnerable to attack than others. Common garden and greenhouse pests seldom attack a healthy plant. Those that are sickly or less healthy than others are the first to suffer from attack by insects and rots. This attack may help you to identify those plants in poor health.
Depending upon the numbers of invading pests, or by the fact that it has become a breeding grounds for disease, the plant in question could be very sickly, or just slightly below its peak of health. In any case you should eliminate the invading force and then examine the plant for signs of poor roots, blocked drainage, or whatever else might be the cause of its poor condition.
Plants which are chronic subjects of insect or disease injury are weakened internally, and in most cases are not worth the time and energy required to try to keep them in good health. Your time is much better spent caring for those which respond, rather than by devoting it to nursing those that show no lasting improvement.
Fungal and bacterial diseases first show up as semi‑transparent, or water‑soaked spots. These spots will later turn brown and appear sunken as the tissues in the surrounding areas collapse and then die. Frequently, the spots will enlarge extremely rapidly, and with some diseases the spread is so rapid that the whole plant may be engulfed overnight. Droplets, often too small to be seen by the naked eye, ooze to the surface, while the fungus spreads its growth inside the tissues of the leaves and rhizome as it consumes the plant’s tissues.
Reproductive spores develop in the oozing droplets, and from there they are spread to other healthy plants by insects, humans, tools, or simply by water splashing from irrigation. If the surface where these spores land remains wet, they can enter the plant through mechanical injury, insect bites, or even through the plant's stomata. Once inside the plant they can rapidly infect the new host, and within a short time many plants in your collection can be lost.
Standing water on the leaves of a Paphiopedilum is an invitation to the spread of these types of diseases. Generally, night temperatures over 65° will prevent most diseases from gaining a foothold, however this is not always the case, therefore it is a good practice to water early in the day so the plants will be dry when temperatures fall at nighttime.
Not all diseases are readily visible. Some bacterial and fungal rots begin within the root system, or in the rhizome of the plant. From there they can multiply and rapidly attack the basal portion, then quickly spread out to the leaf tips. By the time the disease is noticed, the plant may already be dead. If the plant has many large new growths, rapid action by the grower, by quickly removing the affected parts, might save some of the as yet unaffected tissues.
To determine which tissue is free from disease, diseased parts must be cut away with a sharp knife, until clean white tissues are seen. Purple, brown or darkish flesh still contains diseased tissue which will continue its spread unless cut off well past the darkened area.
Treatment for these types of diseases calls for the same basic action. Infected plants should be isolated and then their diseased parts removed. The clean cuts should be dusted or painted with an appropriate fungicide. Perhaps the whole plant might be soaked in a fungicidal bath, or sprayed with a liquid solution of it. When dry, the plant should be repotted in fresh compost and placed in shade, with more warmth and humidity. Since these diseases are spread by infected cutting tools and by our hands, the greatest of care for sanitation must be maintained during these procedures.
While relatively few diseases attack paphiopedilums, there are some common types. A few pose serious threats and must be treated without delay in order to protect the health of your entire collection. The following sections detail the most common problems, and the successful methods used to treat the plant, and to arrest the spread of the disease.
Root Rot, Rhizoctonia solani, causes a gradual decline in the health of the plant. Leaves turn pale; they become desiccated and curl inwards. New growths are smaller, and dark lesions may show up on the surfaces of the leaves. Unpotting will reveal a thick, solid mass of dark webby growth throughout potting soil and the root system; often it firmly engulfs the roots. Only the central core of the root remains, and there will be no live roots. The brown and solid packed root ball will have to be cut away with a knife in order to release the plant from its grip.
When allowed to progress to this stage, the plant is probably too weakened to be saved, especially if the fungus has invaded the rhizome of the plant. If it has not, and it is possible to cut away all he infected parts, then drench or soak the plant in Natriphene if you can find it, or Banrot, and then repot it into fresh medium. Following this treatment the plant will need extra care in the form of elevated humidity and temperatures, and more shade.
This is generally not a contagious disease, but rather an isolated infection. To guarantee that this fungus will not return, and to supplement your first treatment, drench the plant, pot and all, two or three additional times at weekly intervals. Be sure to follow the directions for the mixing the fungicide, and to prepare a fresh batch for each time.
Brown Rot, Erwinia cypripedii, is usually a fatal bacterial infection which gains entry into the plant through injury, or possibly through the stomata. It begins as a small brown spot in the leaf, and then it rapidly spreads throughout the rest of the plant. As soon as it reaches the basal portion of the plant, or its crown, the plant will die.
The spread of this disease is so fast, it can destroy a multiple‑growth plant within 24 hours. Often, the crown of the plant will be completely rotted and collapsed, while the outer portions of the leaves still remain healthy looking. This disease is the most serious threat to Paphiopedilum growers and it is responsible for more losses than any other single disease.
Treatment, when it is possible, is to remove the infected growths, sterilize the knife with flame for each cut, and then dispose of the infected parts in a safe place outside your growing area and far away from the rest of your plants. First, cut away all dark tissue, well into clean white flesh, and then soak the plant in a fungicide solution for several hours. Allow the plant to dry completely before repotting. You should also thoroughly spray the surrounding plants, pots and bench area with the same fungicidal spray. At intervals of one week, again spray the infected plant and the same bench area with three additional treatments.
Bacterial Brown Spot, Pseudomonas cypripedii, is another dreaded disease of paphiopedilums. It is highly contagious and spreads rapidly throughout the collection when unchecked. Its symptoms are like those of Erwinia cypripedii, and its treatment is the same. Symptoms first appear as soft, water-soaked spots along the upper surfaces of the leaves. Spreading rapidly, it soon enlarges to cover the whole section of the leaf or leaves until it reaches the crown, where it then kills the plant.
Damaged areas always exude droplets of moisture teeming with infectious bacteria, which pose a serious danger to surrounding plants because they can be carried to them by splashing water. The plant should be carefully removed to an isolated place, where it can then be treated in the same manner as the above disease, Erwinia cypripedii.
Leaf Die‑Back, Glomerella cincta, is a fungus which starts at the tip of the leaf, and then proceeds along to the central, or basal portion of the plant. Often it is caused by an injury and it spreads slowly, in a straight line, across the leaf towards the base of the leaf. On one side of the line is clean healthy tissue and on the other side the leaf becomes hard and brown. The dead portion dries up just behind the line of demarcation. This is not a serious disease, just an unsightly one.
Treatment consists of cutting off the diseased area, well into clean flesh. This should be done soon after the disease is recognized to prevent more spores from forming and causing the spread of the fungus to other plants. Dip, or spray the plant with a fungicide, and then paint the exposed cut with a paste made from the same fungicide. Keep the plant dry for several days and only water directly into the pot for the following week.
Fusarium Wilt is a fungus caused by Fusarium oxysporum. It travels through damaged roots and into the rhizome of the plant where it causes healthy tissue to turn purple, or pinkish in color. The entire rhizome might be discolored, or perhaps just a small band may be seen traveling through the rhizome along its longitudinal axis. Its spread will cause serious damage to the plant and most likely it will cause its ultimate death.
Frequently this disease is not even noticed because the plant only gradually becomes desiccated, but when the leaves take on an unhealthy color, it will more clearly indicate its presence. Unfortunately, the only way the rhizome can be examined is by cutting through it, and it is then that the discoloration will be seen. Once you have seen the outward symptoms of this disease it will be easier for you to recognize it in other plants when it occurs.
The diseased plant should be unpotted and the root ball examined to see if there are any live roots. Cutting through the rhizome will disclose the tell‑tale discoloration which will confirm that this is indeed the disease. The only effective method of saving the plant is to cut across the rhizome until clean white flesh is found. Usually, by the time this particular disease is recognized, the damage has spread throughout the plant, and little uncolored flesh will be found.
If even the slightest streak of color through the rhizome is visible, treatment will be almost impossible. Perhaps you might save the plant by soaking it in a fungicide for the recommended interval. This drenching treatment can be repeated at three-, or four-day intervals, for three treatments after it has been repotted.
Flower Blight, Botrytis cinerea, infrequently is found in Paphiopedilum collections, but it is in the air we breathe and it occurs in all places. This fungus first appears as numerous random spots, speckled about on the flower. They are very small spots, only about the size of an “o”, but if conditions remain favorable, they will increase in numbers until the whole flower becomes spotted.
At first glance it appears there are small insects like aphids, but upon closer examination, they are found to be sunken, water‑soaked spots, which then turn black within a day or two. This fungus is rampant under cool, damp and airless conditions, and it can infect the whole greenhouse within one or two evenings.
Treatment first consists of removing all infected flowers and disposing of them safely out of the growing area. To prevent Botrytis from reoccurring, increase the temperature to approximately 60°‑65°F., and lower the humidity, and more importantly, remove any decaying plant material from the growing area. Spray flowers and foliage with a fungicide labeled for Botrytis cinerea, at the recommended rate, and increase the air circulation, (this is important).
There are other types of damage, which occasionally affects our plants. Flower sheaths which turn brown and die before the flower emerges, thereby preventing the plant from blooming, can be caused by water from irrigation, air pollution, excessive humidity or by fluctuations in temperatures, as well as by temperatures which are too cold both day and night.
Water left in the leaf axils at night, in a plant with a developing flower, also promotes this problem. It can affect a flower at any stage of development, but it primarily affects those with flower spikes due to open within a few days. Lowering the humidity and raising the temperature is part of the treatment, and if the problem seems to occur during a certain time of the year, or with a certain species of plant, a preventative application of fungicide when the flower bud is forming might prevent further occurrence of this seldom seen disease.
Until recently, rust fungus was a disease unknown to attack Paphiopedilum orchids. As a matter of fact, I am the only person I have ever known to encounter the disease, and it effectively wiped out my entire collection of Paphiopedilum orchids. The disease is difficult to detect at first and even the most insignificant lesion on a plant is enough to halt its growth and to cause it to soon die. It spreads rapidly in warm weather and high humidity.
In 1984 I imported some paphiopedilums from Thailand and when they were inspected at the plant quarantine in Los Angeles, one of the inspectors noticed a tiny rust-colored lesion on a plant of P. ‘ang thong’. Since it was so unusual, he asked to keep the plant for the pathologist to examine, and I requested a report of that necropsy. One never came and I assumed it was a false diagnosis.
The following year in September, I returned from a trip to Peru and found that several benches of plants in my greenhouse displayed signs of severe damage. After close examination of the plants I realized they were infected with rust, and while I used several different fungicides, one or more of which seemed to have eradicated the problem, I learned later they had not actually stopped the spread of the disease.
Rust first appears as a small, rust-colored mark or lesion on a leaf margin, or on the developing bracts of a flower stem. Usually it is so small as to be unnoticed, or to be confused with a spot of dirt, and it remains on the margin, not visibly invading the leaf structure itself. A lesion only a few millimeters long can cause the death of the plant. Even vigorous and actively growing plants can be halted in their tracks, and excising the infected parts the moment it is noticed will not guarantee it will survive.
Plants that have been infected with the disease show signs of desiccation, severe stress and unhealthiness. They appear as if salt had been poured on them.
The worst part is that there is no way to eradicate the disease once it is established. Rust sporolates; it produces spores which cannot be contained, and even if every plant is disposed of, the spores remain within the vicinity of the growing area to ultimately infect any new Paphiopedilum plants brought into their contact. Those spores are air-borne and could find their way outside of the greenhouse and into any newly constructed greenhouse near your property, so the possibility of salvaging your plants is not an option. Neither is the idea of removing your healthy plants to someone else’s greenhouse since they might carry the spores and spread the disease to a different area.
After the applications of pesticides I thought I had solved the problem, but in reality, it was the cooler temperatures beginning in October, which stopped the active spread of the disease. When the warmer temperatures and higher humidity the following August and September returned, nearly half my plants became infected. The following September I lost the remainder of my collection. Soon thereafter, I was forced to tear down my greenhouse.
(I continue to be amazed by the irony of my situation.)
Since viruses (not, ‘viri’) appear to attack almost every living thing, it is only natural to assume they also would be a cause for concern to Paphiopedilum growers. While it has been shown that indeed there are viruses which attack these plants, in reality this is not easy to confirm. Either the incidence of infection is extremely small, or else there are only a few types causing serious infection. Perhaps it is because we fall to recognize them as being a virus.
Cymbidium Mosaic Virus and Tobacco Mosaic Virus are two of the most common plant viruses attacking orchids. They are easy to spot in other plants, by their vertical striping of yellow or brown, and by their sunken tissues, which are spotted and have irregularly broken lines. Concentric rings of necrotic tissue, which has turned black or brown, also appear as symptoms of these two diseases.
In paphiopedilums, we seldom find these symptoms, but they sometimes do show up. Healthy plants are able to mask the effects of a virus and can appear unaffected. Later, when the plant becomes stressed, these symptoms can appear and it will not be known if the infection was new, or if the plant had carried the disease for some time.
Once the plant becomes infected with a virus, there is no known way to isolate the disease from the host plant without killing the plant by the treatment. Any plant known to carry a virus should be destroyed, but unless it is tested, it cannot be positively determined. Plants suspected of having virus should be isolated as much as possible, and then watched closely for its outward signs, particularly during times of stress, such as during repotting or dividing.
Little work has been done with orchid viruses, and it is not possible to tell if the disease can be transmitted through open wounds, or by such methods as pollen transferal to an uninfected plant. Prevention is the best method for keeping your collection clean, which means isolation of suspected plants as well as sterilization of cutting tools, and by the control of insect vectors.
At different times, the leaves of some plants will exhibit a plaited or accordion effect, longitudinally along a newly developing leaf. The leaf usually appears folded as it emerges from the center of the growth, but it tends to flatten somewhat as it expands and elongates. Frequently the folding involves all the leaves of the growth, and seldom will this particular fan develop a flower. Subsequent growths from this affected plant will usually be normal in appearance.
The cause of this distortion is unknown, but might be traceable to improper nutrition, possibly because of an under-developed root system. Polyploidy is frequently suggested as being responsible for this curling-leaf in complex Paphiopedilum hybrids, and while it seems to mar the appearance of the plant, it does not seem to cause any lasting damage.
Other noticeable damage occurs when two or three leaves of a new growth show streaks of white or creamy coloring. A truly variegated Paphiopedilum is rare, and is not the same thing. When longitudinal stripes of varying widths suddenly appear between the newest leaves, it is an indication that there was some sort of mechanical injury. Metaldehyde granules have been known to cause this effect when broadcast about over the tops of the plants. When the granules become lodged in the leaf axils of the new growths, and they remain there for weeks or months, the chlorotic spots and striping continues until the pellets are removed physically.
No serious damage seems to be caused by such discoloration, but since there is a loss of chlorophyll, the plant's health has not been improved. Metaldehyde snail poison is best placed carefully about the bases of pots and along the benches, rather than by being indiscriminately broadcast.
Salts from dissolved solids in the water supply, from fertilizers or from ingredients within the potting media itself, are taken up by the plant and can pose a dangerous threat to its health. Salt damage is one of the most frequent causes of injury to paphiopedilums. It is first seen at the tips of the leaves, where it accumulates to toxic levels, and then it causes the cells in the surrounding tissues to rupture. First, small pits appear on those leaf surfaces, and later, the whole leaf tip becomes brown and desiccated. Frequently, this is mistaken for infectious rotting.
Salt damage spreads slowly. Older leaves are affected first since they have had longer to accumulate the salts. Healthy tissues surrounding the infected tissues do not exhibit the typical ‘water-soaked’ appearance of a bacterial infection, and the plant itself will otherwise seem to be in good health. Some species of paphiopedilums, such as those in the Brachypetalum section, are very susceptible to salt damage, and they might even be used as indicator plants for the other plants in your collection.
Treatment for the problem is easy, but it must be done carefully. The potting mix should be covered with a thin cloth or a fine net, such as a woman's nylon stocking, (to keep it from floating away), and then the entire plant should be immersed in a bath of fresh water for 4 to 8 hours. After it has been removed from the bath, cut off the damaged tissue, well into clean material, and paint the wound with a fungicide paste. Too lengthy a soaking may rupture the plant's tissues and could cause death of the plant. (Remember that orchids have fixed stomata, and they cannot close them to keep from absorbing too much water.)
If the damage continues, soak the plant again in a water bath. You will then want to determine if your plant has continued to receive more salts, or if it is still suffering from the initial buildup. Take appropriate remedial action in either case.
Overdoses of fertilizer can have the same appearance as one of the more serious rot infections. Since rot infections demand immediate treatment, treat your plant for that disease unless you can determine if the damage is fertilizer‑related. If it is caused by an overdose of fertilizer the plant will respond to the same water-bath treatment as described above. An overdose of fertilizer will show up within a day or two, by blackened leaf tips, or even by the loss of many of the newer leaves of your plant. Their softened, or collapsed texture and blackened coloration is an indicator of fertilizer damage.
The choice for repotting plants damaged by this problem will depend upon the density of your potting material, since excess fertilizer salts can be easily washed out of fir bark, but not so easily with more dense soils. For denser mixes, perhaps several leaching treatments at weekly intervals will wash away excess salts.
The loss of lower leaves is a common problem and usually is the result of root damage. Their appearance is similar to salt damage, but there are no sunken pits, or perhaps the ones you might see are the results of past damage from salts. The effect is exhibited by the gradual dying-back of the lowest leaf, or several leaves. The tips are the first part of the leaf to shrivel, and then the rest of it begins to turn brown. There is no water‑soaked margin where it meets the healthy tissue; you will only see healthy tissue on the one side, and dead tissue on the other.
Additional clues might help you to identify this problem. Was the plant recently repotted? Is the mix still healthy and functioning properly? Knock the plant out of its pot to make this determination. Was it recently sprayed with an insecticide or fertilized while being under water-stress? Are there any insects in the pot or on the plant? You can train yourself to notice the tell‑tale clues and then make the appropriate remedial treatment.
Since older growths have ceased their active growth, the plant’s energy is directed toward the making of new growths. Frequently, older growths have lost many of their roots and cannot produce sufficient food to maintain either the new growths, or for their own maintenance. Subsequently, the oldest leaves sacrifice their food reserves in order to guarantee the plant’s further existence.
Lower leaves are also the first to drop when the plant is stressed. Extra care should be afforded large, older plants exhibiting leaf drop, since they can become your specimen plants.
Paphiopedilums with this problem need not be isolated since it is not a contagious situation. Treatment is to give the plant extra shade and to raise the humidity in its proximity. Misting is beneficial, as is increased air movement.
Fortunately, there are few pests which pose a threat for Paphiopedilum growers. The most common pests that attack these orchids are easily controlled by simple means. Few other plants have such a natural resistance, or such low susceptibility, as do paphiopedilums.
Ants are responsible for most of the common pests in seen the growing area, and by keeping ants under control it is easy to keep most insects out. Aphids, mealy bugs and scale are the most common pests, and the ants which feed on their secretions, bring them into the growing area. Mites, thrips and centipedes are secondary pests, as are slugs and snails. Keeping greenhouse pests under control requires timely action, since most of them multiply rapidly and can cause considerable damage within a short period of time. The minute you first notice a pest, is when action is required. Do not wait a few days, when you might have more time.
Under most greenhouse conditions, certain pest populations can double every few days, necessitating repeated and prolonged treatment, which makes them considerably more difficult to eradicate without immediate action. In order to ensure proper control you must be able to correctly identify the pest, and to select an appropriate pesticide. The pesticide must then be applied at the recommended rates and frequencies, and continued inspections must be made to determine the results of that treatment.
Aphids are soft‑bodied, sucking insects that suddenly appear, slowly crawling over our flowers and buds. In heavy infestations, they might also attack the soft parts of a new leaf or the succulent flower stem. There are both flying, and non‑flying aphids, and some females produce living young which only require six to ten days to reach adulthood. Aphids are seen in two colors, black and green, and there are numerous different species. While ants usually bring aphids inside our greenhouses, they may enter through the ventilators, open doors, or cracks in the wall, flooring or the roof.
Because they are so small and easily camouflaged, they are not readily noticed. When detected, and they are approached for closer examination, they drop to the ground rather than flying off. In small collections, they can be disposed of with a stream of water from the misting nozzle, or by touching them with an alcohol-soaked cotton ball.
For a more positive control on a few plants, the aerosol from a can of fly spray can be used, but for a larger infestation, an appropriate insecticide must be used. Wettable powders should always be used instead of liquid insecticides which have petroleum distillates (Xylene) as a base. This will help to prevent foliage or flower-burn on some of the more delicate species. Mix according to label directions and take safety precautions seriously. Clean up spills and dispose of empty containers properly.
Mealy bugs are more of a problem to control than aphids, since they are able to hide in the folds and sheaths of the flowers and leaves, or even in the mix itself. Mealy bugs are small white, segmented and whiskery insects, covered by a powdery wax. Some species produce live young while others lay eggs which they confine in a white cottony egg sac. They also secrete honeydew which attracts ants, and it causes a black sooty mold to grow wherever it touches our plants.
Mealy bugs first appear as small white, powdery, or cottony specks along the stem of the flower, or in and around the flower itself. Sometimes they appear under leaves, or in the axils of the leaves. Whenever you notice a white powdery substance you should inspect the folds and sheaths of flowers and stems, and poke below the surface of the potting mix for traces of these pests. Look carefully under the leaves, and spread open the leaf axils to see if there are others hiding in these places.
Mealy bugs must be killed by contact with a pesticide spray, which should be directed into these hiding places. Because of the waxy substance which coats their bodies, they are difficult to control unless a spreader‑sticker is added to the insecticide spray which will help it to penetrate that coating. If there are only a few plants infected, a cotton ball soaked in rubbing alcohol can be an effective eradicant.
After treatment you will notice that the mealy bugs seem to have remained, however after five to seven days they will have dried up and will not ooze body fluids when crushed. After several greenhouse irrigations they will eventually be washed off the plants. For control, the same sprays may be used as for aphids. Follow-up treatments should be done at three-, to four‑week intervals.
Although scale insects are common pests, both in the garden and the greenhouse, they usually do not cause problems for Paphiopedilum growers. They are serious pests however, and once they gain a foothold it can be most difficult to eradicate them. Scale cannot move about like flying or crawling insects do, but they can be brought into the growing area by ants, or on newly acquired plants. Even while the young stages of scale are free moving, they seldom travel from plant to plant. Two kinds of scale attack greenhouse plants, including Paphiopedilum orchids; they are soft scale, and armored scale.
Soft scales, of which there are several types, usually are larger than armored scales. They vary in size from 1/8 to 1/4 inch in length. Soft scales have a waxy coating and cause damage by sucking the plant's vital juices. They also excrete a sticky substance on which a black sooty mold grows, making for a very unsightly plant. They produce either living young or eggs, depending on the species. The young emerge from under the female and will crawl to any spot on the plant where they then penetrate the plant tissues and begin their adult life of destruction. Soon they form their own protective shell and start to reproduce.
Armored scales have a hardened shell over their bodies, which are usually less than 1/8 inch in length. Females of the common types of armored scales have grayish, oval shells, like an oyster. Males are smaller and are more elongated; often they occur in cottony masses. Armored scales do not secrete honeydew, but they do suck the plant juices. Some species inject a toxic substance into the plant, injuring it further.
Since scale insects can attach to any part of the plant, including the flower, insecticide coverage must be thorough. The addition of a wetter-sticker improves coverage, but all surfaces of the plant must be covered with spray. Adult scales are difficult to control because of their protective covering, but juvenile stages are easily killed before they have a chance to form their shell. Eggs, and living young under the protection of the female's shell are likewise difficult to kill, and continued applications of an appropriate pesticide will need to be made.
Complete eradication might take several months, since some egg‑laying species may hatch over a period of many weeks. With little residual action from insecticides, it will not guarantee coverage for long, therefore, repeated applications would be necessary. After this treatment it would be wise to continue a regular schedule of control for scale insects to ensure that you did not miss any, and which would necessitate a repeat of the lengthy sequence.
For control of scale, four or more applications at weekly intervals are to be followed by a two‑week break, and then the series of four applications should be repeated. After they are killed, the adult scales remain on the plants in many cases. To see if they are still alive, they can be squeezed or crushed to see if any body fluids remain within them. Those still alive will have fluids. It is a wise practice to always inspect newly acquired plants for these pests, since they can be very problematic to eradicate.
Several species of spider mites and false spider mites are known to attack Paphiopedilum orchids. Both are tiny and are very difficult to see without magnification, but their damage is readily noticeable. Red spider mites, and the two‑spotted mites are the most common mites seen, and both can be recognized by the webbing they spin. Mites usually live on the bottom surfaces of the leaves where they suck the plant juices and they leave tiny, silvery spots to indicate their damage. Their presence is not usually noticed until it becomes a heavy infestation and visible damage has occurred. In a heavy buildup, you can see tiny mats of webs, spun from leaf to leaf, and upon closer examination the mites themselves can be seen scurrying along on them.
Red spider mites are completely red, while the two-spotted mite has a large, dark spot on either side of its pale greenish-colored body. Both mites multiply extremely rapidly and can double their population within three to five days. They favor warm, dry conditions. Limited control may be achieved by physically washing them off the plant using spray from a misting nozzle.
False spider mites pose a greater hazard to Paphiopedilum growers, but because they are seldom encountered, they pose less of a continued threat than do spider mites. False spider mites are extremely small, and can be seen only under high magnification. Their damage is similar to that of the spider mites, but it usually occurs in clusters which form pits on the upper surface of the leaves. False spider mites do not spin webs. Frequently their damage causes the loss of a leaf or several leaves before their presence is noticed, and by the time action is taken, the plant can be in serious trouble.
Control for all types of mites is not difficult as there are miticides which kill all stages of growth; from the egg, to the larva and the adults. Coverage is the biggest problem, and with the addition of a spreader-sticker, your chances for control will be better. Be certain to follow label directions, to measure the spreader sticker carefully and to spray when the temperatures are cool. Keep in mind that some sprays can cause leaf-burn, especially when temperatures exceed 75°F.
Thrips are tiny chewing insects with narrow, tapered bodies about one twenty‑fifth inch long. They disappear rapidly at the slightest disturbance. Thrips are seldom a problem for Paphiopedilum growers, however at times they love to chew on succulent flower parts. Damage, in the form of irregular scars, or from tiny dots of excrement, is probably the first signs you will notice of their presence. Some species puncture the flower parts with their ovipositor in order to lay their eggs, in which case the tiny area surrounding the puncture will appear water-soaked.
Control is affected by spraying all the flowers with an appropriate pesticide whenever their presence becomes a problem. (The word ‘thrips’ is both singular and plural.)
Both centipedes and millipedes are long worm‑like pests, with dozens of legs and long antennae. They are fast moving and will curl-up at the slightest provocation. Few growers realize their threat. Each can be a bothersome pest to Paphiopedilum growers, not for the damage they might do to the orchids themselves, but for the destruction of the growing medium, which then causes the decline of the plant from the loss of its roots.
They can both be found in pots, and in seedling flats where they feed on the organic potting material. Damage is quick, for they can reduce a pot of compost to a pot of excrement in a short time. Some species feed on the roots themselves, but damage usually occurs when the roots are smothered and killed from the lack of aeration. Control is affected by drenching the pots with an appropriate pesticide at intervals of two months.
Both slugs and snails are serious pests if not kept under control. In one evening, either can do considerable damage, not only to young seedlings, but also to flowers, buds and to new growths. Even the tiny Bush snail is feared, because it is so easily hidden, and once seen, the grower worries for months that the pest is down inside his pots, chewing all the roots. Snails come out at night and leave their silvery trail of slime, to let us know where they have been, but never telling us where they are. They lay their eggs below the surface of the soil and are most active during warm weather.
Control can be had with the use of baits or granules, especially the more potent 7% granules of Metaldehyde, carefully spread around the pots and benches, just after the last irrigation has dried. Withhold water for as long as possible after application, since water seems to render baits less effective. Care must be exercised not to let any granules of Metaldehyde fall into the crowns of paphiopedilums, since it is known to cause loss of chlorophyll when it lodges within the leaf axils.
In areas where they are still available, liquid pesticides that kill snails can be used as a pot drench, administered through the watering hose and covering the benches and outside surfaces of the pots and plants. A drench may not be necessary if only a few slugs or snails are seen; however it is wise to maintain a continuing program directed at controlling these pests.
New labeling requirements, along with heightened public awareness and agricultural worker education, have served to alert people that pesticides are potentially dangerous. Whenever any agricultural chemicals are used they should be treated as if they were potentially lethal, because some of them might be. Even if it does not say so on the label, you should be fully dressed and wear eye protection whenever you use pesticides. If the label states that you need further protection, follow the directions. Any spills must be washed up and the container disposed of according to the label.
Store all chemicals in a secure place, out of the reach of curious children. It may not occur to you, but there are millions of curious children running around out there, who find things that you leave lying around. Not many of them know enough to understand the danger these chemicals hold.
Pesticides last longer when stored in a dark and cool place, which means somewhere other than in the greenhouse. All labels must be protected from damage since many of the pesticides you buy will last for many years. Pesticides must never be stored in any container other than the original one, and once they are mixed for use, any leftover preparations must be immediately and properly disposed of.
I would strongly recommend you keep any pesticides that you now possess, since the likelihood of obtaining more of the same becomes reduced each day. The trend to produce ‘soft’ pesticides continues, and you will be glad if you still have ones which are effective.
Orthene® (Acephate) is a useful, broad-spectrum (kills many insects) systemic (is absorbed into the plant tissues) pesticide which has not yet been targeted for elimination, mostly because it is not registered for use on food products, only for turf, trees and ornamentals. While it has displayed burning and leaf-scorch (phytotoxicity) on some species of plants, it is long lasting and very effective. It is very inexpensive (particularly for a pesticide), it has a disagreeable odor when in the dry form, nonetheless, its use can be recommended after test-applications are made on expendable plants. Orchids are listed on the label, and for the most part, those few plant types which are adversely affected are few and far between. (Do not exceed directions for re-applications).
One last note to consider. Rubbing alcohol is an effective insecticide against many animal pests. Besides its use with a ball of cotton, the use of a small, plastic hand sprayer, filled with rubbing alcohol and sprayed with direct contact onto targeted insect pests is every bit as effective as the use of practically all the “soft” pesticides. For five bucks you can buy the alcohol and a sprayer which can last for many months of use. (Save your money and buy some more orchids.) Keep in mind however, that some plant species might be damaged by alcohol, particularly by other and more concentrated forms of it. It is prudent to test its use before any full-scale applications are implemented, and be careful to not allow it to puddle in any quantity on the surfaces of your plants.