Listing from the shipment that just arrived from Brazil.

The main objective was to restock for the Redland Festival but as many people are not coming, we are sending it so people can reserve items before the event. Shipping will be a few weeks from now, as plants are still being potted and starting to root. Hurricane Ian will likely slow us down for a few days, and we also might lose power and internet. As always, keep in mind that some of these are in very limited (I mean VERY limited) quantities and might not be available in the future. We are also excited we had a chance to get  many of the most recent high quality seedlings from Brazil, mainly purpuratas and walkerianas.

We still have to go through the purpurata and walkeriana items in more detail, so might release an addendum to this list in the future.  With this said, here is the list and if you are interested in ordering just send me an email to info@mirandaorchids.com (or reply to this one) with the items listed.

By Ron McHatton with Photographs by Greg Allikas

Summer presents challenges in the form of increased pest activity, fungal and bacterial problems in traditionally wet areas and desiccation in those areas with Mediterranean-like climates where summers are typically quite dry. Careful observation of your plants is the best way to identify small problems before they become big problems, and in the summer, the time between these two events is dramatically shorter due to higher temperatures.

Pest Control

For small collections, the best thing to do is to physically wipe insects of and clean the plant. Isopropyl alcohol and a cotton swab are effective against most pests and if you want to increase its effectiveness, a drop of Ivory dishwashing liquid added to the alcohol helps wet the typically waxy surface of orchid leaves. If you haven’t been watching carefully and the infestation gets out of control, you might have to use chemicals. Few pesticides are specifically rated for use on orchids, but you can use any that are labeled for ornamentals. Use care and follow the label directions. This is not a situation where if a little is good, more will be better.

In areas with dry summers, mites can be a serious problem, especially on phalaenopsis. These creatures attack the surface of the leaves producing a sort of rough silvery appearance. Mites are not insects and insecticides offer little or no control. Mites do not like humid conditions so efforts to increase humidity are beneficial. Light infestations can be controlled by thoroughly cleaning plants but in hot, dry climates light infestations rapidly become serious and control is best accomplished by the use of a miticide.

In areas with wet summers, wet foliage and high humidity encourage the spread of fungal and bacterial diseases. Bacterial diseases do not respond to fungicides and vice versa so it’s important to know which disease you are dealing with. Perhaps the easiest way to distinguish between the two is by smell. The most common bacterial disease in orchids produces a foul smell often likened to dead fish. If you’ve ever had cut flowers stand too long in water, you know the sort of smell we’re talking about.

Diseases can spread quickly. Bacterial diseases kill plants especially rapidly and time is of the essence. Both bacterial and fungal diseases are spread by splashing water, and this includes rainfall. Use a clean cutting tool such as a single-edge razor blade, cut off the infected tissue as well as at least an inch (2.5 cm) of clean, green area and then treat the cut surface with a fungicide. Even if the problem is bacterial, you don’t want a fungal infection to start in the wound. Cinnamon — the common spice — is effective against fungal diseases and can be used to coat the cut surface. It’s perhaps not as effective as a chemical fungicide but it’s readily available and does work.

Where it’s wet, keep your plants as dry as possible. Alternatively, provide a lot of air movement. When you water, try to do so as early in the day as possible. This will allow adequate time for the foliage to dry before nightfall.

In dry-summer areas, the bane of orchid growers is extremely low humidity, and this leads to two issues. The first of these is an increase in the rate at which plants dry out and the other is the ever-presence of mites.

Summer Sun

How does sun affect orchids? Solar radiation is much more intense in the summer and plants that have been thriving in full sun all winter may need a little extra protection (shade) when the sun is at its strongest or, often during the late afternoon, when the temperatures are highest. Orchids are easily sunburned and you should take care when moving plants around, especially if you are moving plants grown inside during the winter to a spot outside for the summer. Sunburn, while not in itself a serious problem is irreversible and will make your plants look ugly. In serious cases the plant can be killed outright and any leaf damage is an invitation to a secondary infection in the damaged area.

Capitalizing on the High-Growth Season

Because of increased light and temperatures, your plants will benefit from more fertilizer (increased frequency, not concentration). This is especially true for those varieties that put out new growth during this time. Avoid fertilizers that contain significant amounts of urea (formulations with more than 20 percent nitrogen). Urea nitrogen is much less readily available to orchids in soilless mixes than ammoniacal and nitrate forms.

By Thomas Mirenda

Family Gatherings and Grilling Bring Together the Holiday Spirit

Summer fun reaches its peak in July, with the hot weather finally arriving and sunscreen flying off the shelves. For kids, it just doesn’t get any better than July — barbeques, cooling off in the sprinkler or pool by day and backyard fireworks displays by night. Occasionally, there will be the unusual child who gravitates away from all the hullaballoo in the backyard and finds that shady spot where orchids are growing. With bursts of Epidendrum and brassia flowers and huge cornet like scapes of glowing encyclia and myrmecophila blossoms reaching skyward, many a budding interest in orchids has been ignited by the fascinating array of plants in bloom this month. Keep an eye out for those young ones who see the miracles of nature as more than rivals for the glitzy fireworks, but as the true marvels they are. Take the time to nurture and perhaps share a plant or two with a youthful relative or neighborhood nature child.

Heat

With temperatures often rising into the 90s, many orchid plants are stressed. Large and tender new growths generated this past spring are maturing and hardening off but are still susceptible to sunburn, heat stress and fungal infections. Therefore, the bulk of our activities this month are related to minimizing the effects of heat on our plants.

Read About Plants

Many orchids, particularly those from seasonally dry forests, such as encyclias, myrmecophilas and brassavolas, seem to do well in the summer heat. Even the many deciduous Dendrobium species and hybrids that require cool winter temperatures are growing rampantly now. Their adaptations of extreme succulence and large pseudobulbs give them the ability to withstand heat and dryness better than orchids from more seasonally uniform habitats like montane tropical rainforests, such as miltonias, many paphiopedilums, pleurothallids and even phalaenopsis. These orchids tend to have smaller pseudobulbs, or none, and have less succulent foliage. For these plants, shade and hydration during the summer heat is a real necessity.

Cooling Plants

Basically, there are three strategies for cooling off your plants: shading, misting and air flow. All of these strategies either separately or combined can ease the stresses of summer heat on orchids significantly. But taken to excess, these heat defenses can do more harm than good.

Shading

Most of our orchids benefit from some shading during the hottest months, but many also need bright light to grow strongly and store enough nutrients to bloom once their new growths have matured. Cattleyas, cymbidiums, standard dendrobiums and vandas will languish with weak and spindly new growths if kept constantly in deep shade. For such plants, misting and air flow are better strategies for cooling. For phalaenopsis and most pleurothallids, deeper shade gives better results.

Misting

Many high-light orchids, notably vandas and cymbidiums, benefit from a fine cooling mist at the height of the day’s temperatures. Feel your orchid’s leaves on a hot day. If they are hot to the touch, they have shut down and are in danger of burning. Just a quick wetting down with a light mist is often enough to cool the leaves down. Cymbidiums in particular seem to grow better when cooled in this way. Automatic misting systems are available for both outdoor and greenhouse growers. Still, beware of wetting down leaves in full sun, as the water can overheat or act like a lens. This usually happens only under glass or on window sills where the air flow is poor. The other danger with misting is waterlogging your plants. Don’t mist so much that your plants never dry between waterings. Also, remember that water sitting in the new growths of your phalaenopsis plants at night is a sure recipe for the dreaded crown rot.

Air Flow

Perhaps the most important and overlooked aspect of cooling is air movement. A beam of light hitting a thermometer will make it register much higher than the actual ambient temperature. The same is true of leaves. If light hits the same portion of a leaf on a hot day with no breeze to cool it, it will overheat and burn quickly. But if a light moist breeze is caressing your plants, it will dissipate this heat. This can also be done to excess, for example, if the air movement is too strong, it can prevent plants from taking in carbon dioxide, or cause desiccation.

Microclimates

Put maximum/minimum thermometers and monitor the light and air flow in various spots of your growing areas. You’ll be surprised at how much they can vary. You might find, for example, that the sunny south side of your greenhouse near the exhaust fan is a prime spot for dendrobiums. Or the cool, breezy spot under the beech tree is ideal for the miltoniopsis. There is a copper beech tree near our facility here in Washington, DC., where legend has it that Abraham Lincoln used to like to sit and write because it was 10 degrees cooler under that tree than anywhere else in the infamously torrid DC summer. There may be spots like that in your own back yard. Seek them out. Those are great spots to summer your orchids.

Fertilizing

Even though your plants have been growing so well these last few months, beware of fertilizing on hot days. When plants overheat, they shut down metabolism and basically stop growing. If their medium and roots are imbued with plentiful, but unused, fertilizer, it can sour your mix and burn your roots. Take the time to leach your plants of excess fertilizer salts, and use plant foods sparingly (if at all) during excessively hot weather.

—

Originally published in Orchids Magazine – July 2006

Thomas Mirenda is the orchid collection specialist at the Smithsonian Institution and an AOS judge. 3000 Cedar Lane, Fairfax, Virginia 22031

Growing orchids outside isn’t much different than indoor orchid care.

Your plants need the right temperatures, lighting, humidity, and water, as usual. You may find that you need to water more frequently outdoors, perhaps even daily. This depends a lot on wind conditions and humidity. If your climate’s temperatures don’t agree with what an orchid needs, keep it indoor!

Very few orchids like direct sunlight; and a shade cloth or a shade tree is usually required that provide alternating light and shade as the sun moves across the sky, provided the light doesn’t stay in one place long enough to cause sunburn!

Pay extra attention to your plants outside as it’s much easier for bugs to get at them, and you’re more likely to have to deal with things like caterpillars! One recommendation is to spray outdoors orchids with a mix of water, horticulture oil or neem oil and several drops of liquid dish detergent every 3 weeks to keep insects away. Also keeping orchids raised off the ground helps to control pests.

Repotting

You should only repot orchids when you NEED to repot orchids. Many orchids resent the root disturbance that comes with repotting, so it is not a good idea to repot needlessly. The following reasons are the only times you should consider repotting : 1)The potting mix has broken down; 2)Your plant has a health problem, so the roots need to be examined; 3)The plant was accidentally dropped and got damaged or unpotted in the process; 4)The plant has outgrown it’s pot. (“Outgrown” orchids like to be tight in their pots and thrive best when this is the case. In fact, Cattleya alliance plants actually bloom best when they are 1 or 2 growths off the edge of the pot, so repotting them sooner deprives you of a nice display of flowers.)

When to Repot

Consider the growth habits and culture of your orchids. The optimal time to repot is after the plant has bloomed and is beginning a new growth cycle. The emergence of a new leaf, new roots, or a new pseudobulb signals this time.

Early Spring

This is the best time to repot most orchids as the days are getting longer; you see new growth; and they are no longer blooming. It the time to check your Brassavola (Winter – Spring) , Cattleya(Spring/Fall), Catasetums, Cymbidiums, Dendrobiums, Epidendrums, Encyclia, Ludisia(Winter-Spring), Masdevallia, Oncidiums, Paphiopedilum, Phalaenopsis (Spring-Summer), Sophronitis, Stanhopeas (Spring/Fall)

Repot in Fall

Doritaenopsis (Fall-Winter), Miltonia, Miltoniopsis, and Vanda.

Other Times Repotting May Be Necessary

Repotting may be required if an orchid is infested with bugs. If bugs keep recurring it is sometimes because they have taken their operations underground and are munching on the roots or in the media. Removing all of the old mix, carefully cleaning and examining the roots and repotting in fresh mix is often a critical step in eradicating a persistent pest issue.

Pot Size

Should be selected according to the size of your plant’s root mass and growth habit. When potting epiphytes (tree-dwellers), these are lateral or shallow rooters, so choose pots that are not as deep as they are wide. When potting terrestrial types (ground dwellers), they will want to root deeply, so choose pots that are deeper than they are wide. If the current pot is the right size, then you should clean it and re-use it!

—

From the April 2013 issue of Orchids Magazine
Prepared by the AOS Education Committee with Photographs by Greg Allikas

ASK 10 ORCHID growers how to sprout backbulbs and you’ll likely get a dozen answers. These include everything from the sphag-n-bag method to potting the backbulbs as you would a front division and hoping for the best.

The theory behind the sphag-n-bag method (and its corollaries) is that by keeping the backbulbs in a constantly humid environment, but not touching wet potting mix, dormant eyes will eventually break. The method varies, ranging from placing the backbulbs in Ziploc bags or large plastic pretzel jars to suspending the
backbulbs in a dry cleaning bag over moist potting medium and hanging the whole affair from the bottom of a greenhouse bench (popular when I first started growing orchids in the 1960s). But they all rely on nearly 100 percent humidity.

Other methods that involve potting the backbulbs in one fashion or another, including laying the backbulbs on a tray of moist medium, are based on the theory that
contact with moist medium will eventually trigger growth.

By Susan Jones

Planning for the optimum health and blooms of your orchids through winter and into spring is as important as their day-to-day care. Preparing now for orchids’ seasonal nutritional needs can boost their resistance to damage from pests, disease and winter temperatures in the coming months

Overall Health

Orchids will fare better in encounters with pests, diseases and temperature extremes if they are in a good state of overall health. A plant suffering from underor over-fertilizing, or stressed from lack of water is much more likely to be injured by any additional strain.

Orchids grown under less than ideal conditions are more likely to be a target for infection or infestation. Make an extra effort now to get plants and their greenhouse or growing area in good shape for the shorter, darker days ahead by removing old foliage, weeds and dying flowers. An autumn cleanup can minimize or prevent the pest and disease problems that can crop up in the darker and more crowded conditions that often characterize the winter growing area.

General Nutrition

Light levels and temperatures begin to fall at this time of year, and your orchids’ nutritional needs change accordingly. Orchid growers can take the following steps now to help prepare their collection for optimal health through the months ahead.

If your orchids will winter outdoors, fertilizing properly can help them resist cold, insect and disease damage, as well as give them two to three additional degrees of cold resistance. This can mean the difference between a dead orchid and an unscathed plant or one that just loses a few leaves.

Use a fertilizer low in nitrogen (which should be nitrate nitrogen, not urea nitrogen) and high in potassium; the numbers on the label should read something like 10-5-20. Watering and fertilizing should be reduced in frequency for the cooler autumn season, and orchids that bloom during the winter and into spring should be given a couple of doses of blossom booster in October and November; bloom boosters should have a higher middle number, such as 10-50-10.

Ideally, this change in fertilizer should start by mid-November and continue through the end of January. This regime will sacrifice plant growth in December and January in favor of plant protection, but it can help keep the plant healthier overall.

Some growers recommend using Dyna-Gro Pro-TeKt (0-0-3), a liquid nutritional potassium-silicon supplement for plants. The product is supposed to improve heat and drought tolerance in orchids, as well as boosting their resistance to pests, disease and environmental stress.

Specific Genera

Seasonal nutritional needs differ among various orchid genera, and may diverge still further depending on local climatic conditions in disparate geographic regions. The following guidelines may require modification to accommodate individual growing conditions.

Cattleya: Watering and fertilizing frequency should be reduced, as the plants dry out more slowly in the cooler temperatures and shorter days.

Bud sheaths may yellow at this time of year as temperature fluctuations can cause water to condense inside the sheath. Should you notice condensation in the sheath, it should be opened or removed to allow the developing buds adequate air circulation and prevent bud blast caused by rots. Simply slit open the sheath and carefully peel it down toward the pseudobulb, exercising caution so as not to damage the delicate bud primordia within.

Dendrobium: Autumn and winter needs vary according to the species or hybrid parentage in this diverse genus. Dendrobium phalaenopsis and Dendrobium canaliculatum hybrids will benefit from a fertilizer with a low nitrogen formula for optimal flowering.

The leaves of Dendrobium nobile types and their hybrids begin to yellow and drop at this time of year in preparation for their winter dormancy. Plants should be given plenty of light and good air circulation and kept dry from November through February. Mist occasionally if their canes become overly shriveled.

Paphiopedilum: Generally, these do not require a great deal of fertilizer. This is especially important with the cooler-growing bulldog types to reduce nitrogen levels at this time of year for best flowering. (Bulldog Paphiopedilums have plain green leaves as opposed to the mottled-leaf types. One of the best-known bulldog-type hybrids is Paphiopedilum Winston Churchill.) Watch for water accumulating in the growth around the sheath or for late-season warm spells, as either can rot the sheath and destroy the developing inflorescence. While Paphiopedilums should not be allowed to dry out entirely, water needs are significantly reduced in the cooler days. Overwatering can cause root rot or Erwinia problems.

Phalaenopsis: Growth slows and inflorescences begin to appear. Reduce watering and fertilizing frequency, and apply a bloom-boosting fertilizer. Many growers also recommend applications of epsom salts (magnesium sulfate) to Phalaenopsis at this time of year to prevent yellowing and loss of lower leaves and to enhance blooming.

Once buds are evident on the inflorescences, keep temperatures and humidity consistent to prevent bud drop. Phalaenopsis grown in the greenhouse are especially prone to bud blast in February and early March, when the heat is still coming on at night and the greenhouse temperatures rise during the day.

Vanda: Aside from Neofinetia falcata, vandaceous orchids generally do not tolerate autumn and winter’s cooler temperatures (below 60° F [16° C]) well and need to be carefully protected from chills.

Vandaceous orchids still need as much light as possible as the days become shorter and light levels fall. Reduce the frequency of fertilizing and watering to accommodate the slower growth period they are entering.

Starting the first week of October, Julie Rosenberg at R.F. Orchids in Homestead, Florida, recommends feeding vandaceous genera a blossom booster fertilizer exclusively, once a week for four to six weeks, at 1 teaspoon per gallon of water (15 ml to 3.8 l), with normal watering between. In November, begin fertilizing every other week, using a balanced 20-20-20 fertilizer at 1 teaspoon per gallon (15 ml to 3.8 l), substituting bloom booster every fourth feeding.

Preparing now for orchids’ seasonal nutritional needs can mean happier, healthier and more productive plants year round.

—

Reprinted from the OCTOBER 2003 issue of Orchids — The Bulletin of the American Orchid Society. Copyright American Orchid Society — aos.org

By Paul J. Johnson, PhD

Scale is probably the most important insect pest of cultivated orchids in northern climates. According to a Florida Department of Agriculture and Consumer Services publication, there are at least 27 species of scale identified from cultivated orchids. Fortunately, only the most common soft scale, usually referred to as brown scale or brown soft scale, regularly survives in the north on indoor or greenhouse plants. The soft brown scale (Coccus hesperidium), and possibly the similar elongate soft scale (Coccus longulus), seem to be the most observed species. Boisduval scale (Diaspis boisduvali), an armored scale, can infect orchids in the greenhouse and the home, and should be guarded against.

Boisduval scale is the most common type of scale found on orchids and can multiply rapidly.

The adult brown scale is recognized by light yellowish to dark brown oval to circular shells appearing on leaves, petals, sepals, petioles, pseudobulbs, and sometimes rhizomes and roots. Mature female Boisduval scale are rounded and lightcolored, while aggregations of males are identified by their cottony appearance, which may cause them to be confused with mealybugs if not examined closely. The immatures, or crawlers, of all species are tiny and yellowish to pinkish, and not easily seen without a magnifier.

The most common way of acquiring scale is purchasing an infested plant. Scale is easily transmitted to clean plants when plants are crowded and crawlers move from plant to plant. Colonization by windblown crawlers may occur when plants are outdoors, but this can also happen indoors and in greenhouses when crawlers float on currents from circulation and heater fans. This can produce pockets of infestation where air currents are weakest when crawlers settle on plants.

Life Cycle

Scales have three life stages: egg, larva (or nymph) adult. Eggs are laid under the female’s shell and remain there after she dies. These hatch into mobile nymphs, called crawlers, that can move between plants. After finding a suitable place, crawlers settle to feed. The females then form a light yellowish protective scale covering, which enlarges as the insect grows and darkens to tan or brown as it matures. Male Boisduval scale form an armored scale while those of brown scales are small winged creatures. The primary role of males is to mate and die.

Scales have short life cycles, but may cycle many times a year. Typically, a month or more is required for completion of a scale generation, but a mere two to three weeks is possible in favorable conditions. The overlapping generations create the biggest scale-management problem. All control methods are at their greatest effectiveness against crawlers. By the time the scale has matured the hardened shell, it is too late to easily kill those adults with chemicals. Also, the largest dark brown colored scales with a powderlike substance inside are dead and the shells are often full of eggs.

Management

Scale management is usually a protracted and serious effort, and never fun. Light infestations restricted to one or a few plants can be treated with household products rather than concentrated insecticides. When possible, immediately isolate infested plants from others to prevent the crawlers from moving among them.

The key to control is persistence. Management methods least toxic to people, pets and plants are the most time consuming and laborious. Chemical methods, including oils, soaps and synthetic insecticides are progressively more toxic and expensive, but less work. Regardless of method or chemical used, remain vigilant and expect to make at least two to three applications 10 to 16 days apart.

Due to plant costs, owners’ personal attachment to orchids, and many growers’ desire to avoid insecticides when possible, a number of effective home remedies for scale are available. However, noninsecticidal treatments may not be highly effective for eliminating scale – they should be viewed as controls, not eradicators. Also, many chemicals for home use are toxic to humans, pets and plants even in diluted forms, often proportionately more toxic than the feared insecticides.

Rubbing Alcohol

A popular home remedy is swabbing plants with isopropyl (rubbing) alcohol. Do not use other alcohols such as ethanol or methanol; they will penetrate the plant tissues and cause considerable damage. On hard-leaved plants, remove scale by gently rubbing with fingers or an infant’s soft toothbrush, with or without alcohol. Afterward, repeat the alcohol treatment to remove recently hatched crawlers. Pay particular attention to the mid rib, other veins and leaf edges. (On soft-leaved orchids, such as some Oncidiinae, isopropyl may damage the leaves.)

Another method is to spray alcohol with a misting bottle or small pump sprayer. When so applied, a few drops or a short quirt of liquid soap are added to the alcohol. Some growers also like to add some horticultural oil, mineral oil or neem oil to this solution. Use caution, as a detergent that is too strong or applied in excessive amounts, or use of an ammonia-based chemical cleaner, may damage your plants particularly buds and flowers. Also, alcohol sprays are not effective against eggs beneath scale coverings, hence physical removal of scales by hand is suggested.

When air movement increases evaporative cooling, rapid evaporation of alcohol may over-cool plant tissues, creating zones of dead mesophyll cells that can become necrotic. On warm or breezy days, especially with low humidity, wipe residual alcohol with a tissue instead of allowing it to evaporate.

Repotting During

Extreme infestation, scale may develop on roots and rhizomes. Consider replacing the potting medium, which can harbor eggs and crawlers. Dispose of it in a compost pile or in the garbage. When repotting, a close inspection, and, if necessary, a gentle clearing and spraying of the roots is essential.

Oils, Soaps and Sterilants

Horticultural, neem and mineral oils, and insecticidal soaps form the next stage of chemical control. All of these solutions are generally considered safer for humans, pets and plants than insecticides. None provide absolute control over pests, but frequent applications reduce insect populations to below self-sustainable levels in small orchid collections.

Oil solutions smother insects, so complete coverage of all sprayed plants is essential. These oils are mixed with water and a plant-safe detergent for enhancing spreading and sticking. Never apply these solutions to plants on hot days (over 85 F).

Insecticidal soaps, while considered safe, may still damage some plants, particularly tender new tissues, and when the soaps are mixed with hard water. They can also cause allergies and respiratory problems for users.

Insecticides

Persistent or heavy scale infestations may require the use of synthetic insecticides. Few insecticides are tested on or specifically registered for use on orchids, but several common, inexpensive, home-and-garden chemicals are labeled for ornamental plants.

Some of the more effective insecticides available to home growers are Orthene (wettable powder), Malathion (liquid), Diazinon (liquid) and Carbaryl (water-based emulsifiable concentrate). Always follow label directions and never exceed the minimum recommended concentration given in mixing directions. Orchids are tough, but sensitive to many chemicals. While certain species may not react to a given formulation, others might, so advance testing is advised.

In the home, growers who must apply insecticides during inclement weather need special care for applications. If outdoor spraying is not an option, spray plant(s) inside a large plastic bag, remove the bag after the spray has settled, and let the plant(s) ventilate where fumes will not invade the home or work area.

Never apply any liquid pest treatment in direct sunlight or high heat. To prevent burning of tissues, always shade plants until the solution dries.

Growth Regulators and Chitin Inhibitors

Insect-growth regulators, such as Enstar II, are synthetic forms of insect hormones that interrupt normal development in insects, including scale. While there is little reliable information on their use on orchids, there have been no plant health problems noted thus far. An increasing number of growers are reporting satisfactory results with Enstar II.

Azadirachtin (Azatin and Neemazad) is a plant-derived (neem tree) chemical or botanical insecticide. It inhibits development of chitin, a primary component in insects’ exoskeletons, causing mortality. There is little information available on its use on orchids, but it is approved for a wide variety of ornamentals and is labeled for greenhouse applications.

Final Considerations

Heavy infestations of scale may require other control methods. In such situations, a synthetic insecticide may be useful. On the extreme side, for a plant showing signs of decline from scale, consider whether the low likelihood of rejuvenating the plant justifies the expense and effort of continued treatments. After all, the destruction of a sick plant can be used to justify the purchase of a new and healthier one.

To minimize risks of developing a treatment-resistant pest population, change methods and chemicals occasionally; do not use the same chemical mix more than three to four times sequentially. For example, if an insecticide was used for previous treatments, switch to an oil, soap or different insecticide.

Never use an insecticide not labeled for ornamental plants, and do not use less than the minimum concentration of a mixture. Too little of a chemical enhances resistance, while too great a concentration may damage plants. Never use chemicals as a routine preventative; this wastes chemicals (and money), and allows resistant pests to develop. Continue manual removal of scales during treatment – removing egg-laying adults is as important as killing nymphs. Finally, always monitor the cycling of the scale population to optimize spray effect and minimize total number of sprays.

—

Reprinted with permission from the SEPTEMBER 2003 issue of Orchids — The Bulletin of the American Orchid Society. Copyright American Orchid Society — aos.org

By Susan Jones

A danger to orchids any time the weather is rainy or damp for extended periods, black rot can quickly destroy an entire plant if left unchecked. Caused by one or both of the fungi Pythium ultimum and Phytophthora cactorum, black rot affects a wide variety of orchids. Cattleyas seem to be particularly susceptible.

Black rot moves quickly through a plant and can decimate an orchid collection if not treated.

Life Cycle

The fungi that cause black rot in orchids can live only in environments where water is available to them. They consist of spores capable of independent movement, called zoospores, which swim through the water. If that water happens to be sitting on an orchid leaf, the zoospores can penetrate the plant tissue and begin the next stage in their life cycle. At this point, the fungus develops a vegetative part or mycelium consisting of hyphae (thin, thread-like tubes), which spread quickly through the affected plant tissues. Once this occurs, the visible signs of infection – small, watery, translucent spots – expand quickly and change to brown and then black. Left untreated, the affected plant or plants may infect others and will probably die themselves.

Symptoms

When the fungus attacks seedlings, it is usually at the soil line. This can cause the little plants to topple and die, and is referred to as damping off.

In mature plants, the disease can strike at any point on the plant (leaves, pseudobulbs or roots), but often starts in new leaves or growing leads, and progresses downward through the plant until reaching the roots..

As its name implies, black rot shows up as dark blackish spots or lesions on the affected plant part. The black spot or spots enlarge rapidly and can spread throughout the plant. If allowed to reach the crown of a monopodial (single-stemmed) orchid, the rot will kill the plant. Affected leaves may turn yellow around the infected area, and the lesions themselves will be soft and exude water when pressure is applied.

Prevention

Unsterilized pots, media or water sources, as well as water splashed from affected plants nearby, are all excellent means of spreading the fungus. In addition, plants that spend time outdoors should be elevated 3 to 4 feet (90 to 120 cm) above the ground to avoid splash contamination. Do not allow your orchids’ leaves to remain wet for any extended periods. Good air circulation in the growing area is key, and can help plants dry quickly after watering or rains. The addition of a fan or fans to the growing area can improve the airflow and help prevent rots. At first signs of infection, segregate all affected plants to avoid contaminating healthy plants. Finally, some growers recommend the use of a high-calcium fertilizer in the spring to help avoid black rot in new growth.

Black rot is easily spread by splashing water.

Mechanical Treatment

To stop the spread of black rot in your orchid, begin with a sterile knife and cut out the diseased portion of the plant. Remove all infected plant material, taking out a small amount of healthy tissue bordering the infected area as a safety precaution. Examine the cut portion carefully. It is sometimes possible, especially in pseudobulbs, to see a brownish discoloration extending into the interior of tissue that appears healthy on the surface. In sympodial (many-stemmed) plants such as a cattleya, it may be necessary to cut below the leaves and into the pseudobulb to stop the spread of the disease. If the plant is badly infected, cut into the rhizome, growth by growth, until you reach healthy tissue. For a monopodial orchid such as a vanda or phalaenopsis, remove the infected portion of the leaf, or the entire leaf if necessary, to halt the spread of the fungus before it reaches the crown. Place the plant in an area that receives good air circulation to allow the cut to dry.

Chemical Treatment

Once the infected plant parts have been removed, a fungicide should be applied to protect the remaining healthy tissue. Cinnamon is an excellent fungicide, and ground cinnamon may be applied straight from the spice jar directly to the exposed area where infected portions of the plant have been excised. First Rays Orchids also recommends mixing cinnamon with either casein-based glue (such as Elmer’s) or cooking oil to form a thick paste. This paste is fairly waterproof and can be used to cover the wound.

Another poultice that was developed specifically for use on orchids is StopRot. The product contains a Bordeaux mixture in lanolin. The Bordeaux, a mixture of copper sulfate and lime, has fungicidal properties. The lanolin seals the wound to keep moisture out.

Whatever method is chosen, be sure to cover all of the exposed (cut) area with the fungicide or sealant, so that no new infection can be introduced to the open wound.

Drenching the affected plant with fungicide is also an option. Drenches of a protectant fungicide such as Truban or Terrazole are recommended if the disease is diagnosed early. For more advanced cases, a systemic fungicide such as Aliette or Subdue is more effective. Captan, Dithane M-45 and Physan 20 have also been recommended by some growers for control of black rot.

To protect seedlings against damping off, water with the fungicide of choice (at the dilution rate for seedlings specified in the product’s instructions) as soon as they are deflasked and potted in compots. Afterward, treat with a preventive fungicide at two-week intervals.

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References

• Simone, Gary W., PhD, and Harry C. Burnett, PhD. 1995. Diseases Caused by Bacteria and Fungi, in Orchid Pests and Diseases. American Orchid Society, West Palm Beach.
• CLAN Tropicals and Orchids R Us, Inc. 2001. Common Rots: What To Do When Your Plant Falls Victim. Camp Lot O’Noise Tropicals, Sarasota.
• Fortner, Linda. 2002. The Orchid Garden: Wilting Flowers. Suite101.com.
• Home-made Remedies and Treatments. First Rays Orchids, Pennsylvania. First Rays Web site
• StopRot. Flora Laboratories Web, Mentone, Victoria, Australia. Flora Laboratories Web site
• Thoerle, Lisa, Ed. 1995. Deflasking: Editor’s Column, Fred Paget’s Section. National Capital Orchid Society Bulletin 49(3). Canadian Orchid Congress Web site.

Susan Jones was the editor of Awards Quarterly and assistant editor of Orchids. American Orchid Society, 16700 AOS Lane, Delray Beach, Florida 33446

Reprinted with permission from the OCTOBER 2002 issue of Orchids — The Bulletin of the American Orchid Society. Copyright American Orchid Society — aos.org