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Strategies for Bio-Rational Control of Orchid Pests


Aphids: These tiny, soft bodies insects suck plant juices causing distortion of shoots and spikes.  They have been shown to carry virus.  Females are born pregnant and can give birth to 3 - 6 young per day.  These insects feed in the plant phloem and leave sticky honeydew attracting ants and sooty mold.  Ant control can be a critical factor in some cases.  Aphids quickly develop resistance to insecticides.
Aphids seem to prefer Oncidiinae, congregating on nearly spent flower spikes but preferring the flower buds on reed stemmed Epidendrums.   Washing removal of the pest is a very effective control both in the home collection and in the yard.  Cut fading bloom spikes to remove the population as aphids are rarely found on orchid leaves.

Strategies

Windowsill collection - less than 50 plants:  Wash flowers using a steady stream of warm water.  Remove infected bloom spikes.  Inert ingredients in sprays will frequently damage flowers.  

Small greenhouse or climate controlled light room: Wash heavily infected plants. Remove nearly spent bloom spikes. Be sure to inspect foliage plants and weeds, as they can be a repository for residual populations. Use neem oil or summer horticultural oil as initial knockdown agent. Remember that contact pesticides are only as effective as the spray technique! Insecticide must contact insect! Be thorough!

Alternate - use Lady Beetles for initial knock down and follow with the introduction of Aphidius colemani or another parasitic wasp to maintain control.  Lacewing (Chrysoperla rufilabris) is effective here too, as is Aphid Predatory Midge (Aphidoletes aphidimyza)

The Good Guys:

Lady Beetles (Coleomegilla maculata or Hippodamia convergens): Adults can consume 50 - 150 aphids per day and can be kept in the refrigerator for short periods of time.  Periodically warm and mist them to maintain.  They are about 6 mm in length and are brightly colored orange, red or pink.  They tolerate a wide range of conditions, however they will disperse even in the presence of large aphid populations.   Mist plants before release.  Release at dusk and apply to the base of plants for best results.  Use a twice-weekly release.  

Aphidius colemani: This is a small predatory wasp that lays its eggs in the aphid body. The eggs hatch inside and the larva spins a cocoon, which swells the body of the aphid. The adult emerges leaving a hard shell called an aphid mummy. Look for mummies when scouting. Larval development takes 2 weeks at 70F. This wasp does not go dormant in cool temperatures in fact it is most effective from September - March. Optimum is 50 - 70F, tolerates cool temperatures and low light.
Aphidoletes aphidimyza: This is a small midge or fly (3mm), which produces a bright orange larva. Females lay 100-200 tiny orange eggs near aphid colonies. Each larva eats about 50 aphids per day. Short winter days can induce dormancy. Use supplemental lighting in the greenhouse to avoid this. One 60 watt bulb per 30 feet or one 100 watt bulb per 65 feet is adequate. Optimum is 73-77F, but is OK to 60F, 80-90% RH

Mealy Bug: If you have Phalaenopsis you know mealy bug. This soft- bodied insect sucks phloem plant juices, but has not been implicated in virus spread. There are two different varieties that are common. The Long- tailed Mealybug has the typical cottony looking, waxy coating and has several long filaments that form a 'tail'. They give birth to live young. Citrus Mealybug have no long tails, are oval and pinkish in color. It has short filaments that radiate out from the body. Eggs are laid in cottony 'nests'.

Strategies:

Windowsill collection - less than 50 plants: Quarantine new purchases for several weeks before introducing them into the collection area.  Use this time to closely inspect the plant and flowers for crawlers (mealybug young).  It is easier to control mealybug on one plant!!  Use a warm water stream and a rubber dental pick to remove.   or remove with the pick alone.  Check under twisty-ties and edges of pots!  Spraying with alcohol is not very effective.  If an insecticide is used make sure to get thorough coverage.  Mealybug gets into flower parts and inside sheathing.  Palms are particularly difficult in this respect.  Use summer horticultural oil or neem oil for control.  Follow label directions

Small greenhouse or climate controlled light room: Spot treat heavily infested plants with a combination of washing and the above-suggested insecticides. Use summer horticulture oil or neem oil for a rapid knock down as a cover spray. Avoid pyrethrum and pyrethroid use if you desire to establish a predator. Insect growth regulators (Enstar II) and 'leaf systemics' (Marathon II) can be effective aids in population control, but can affect predator populations adversely. Mealybug can be a very persistent problem if allowed to go unchecked. They will start to infest non-plant areas and might necessitate stripping down the greenhouse and thorough steam cleaning. Very low temperatures can control this pest as well. Don't let this pest get out of hand! Mealybug has demonstrated living off a host plant for 23 days!

The Good Guys:

Lacewing (Chrysoperla rufilabris): Lacewings are general predators and feed on aphids, scale, thrips, spider mites, and small caterpillars as well as mealybug.  They are about  inch in length and have transparent green, veined wings.  Larva, known as aphid lions, will consume 200-300 aphids.  They are frequently distributed as eggs and after hatching the larva remain active for 10 -14 days.  Unfortunately, they are not known to colonize in greenhouse conditions.  Adults disperse after hatching.  Typical application is 5, 000 eggs per 1-6 sq feet twice a week.  Optimum conditions, 60-80F
Mealybug Destroyer (Cryptolaemus montrouzieri): This is a great predator of Citrus Mealybug.  Both adults (3mm) and larva feed on mealybug and do not do well where populations are low.  Optimum conditions, 75 - 80F, 60% RH.

Soft Scale: Orchid growers encounter two basic types of soft scale - soft brown scale and hemispherical scale. There are many species of both that are common. Soft scales are small round or oval 'bumps' (1/16 to " in diameter) found on stems and leaves. They are phloem feeders of plant juices and are usually discovered by the sticky honeydew they excrete. Adults are immobile and are covered with a protective waxy shell. They are most vulnerable for control in the juvenile or 'crawler' stage. Soft scale usually have one generation per year.

The Good Guys:

Metaphycus helvolus: These are tiny (1mm) black and yellow wasps that lay their eggs on newly hatched crawlers and young scale.  Adults emerge from the body of the adult scale leaving a characteristic hole.  Release should coincide with a flush of new crawlers for best results.  They are well adapted for greenhouse conditions.

Lacewing is a good general predator of soft scale, too

Armored scale - Boisduval Scale: Boisduval scale can be extremely difficult to control.  They prefer cattleyas but can be found on Angraecum, Cymbidium, and occasionally Oncidium.  They feed in a more isolated area of the leaf structure and are not affected by systemic insecticides such as Marathon (Imidacloprid).  The males and females look very different from one another.  The females are solitary, small round, beige discs about 1 - 2 mm in diameter.  The males tend to congregate in protected areas of the plant as in under the sheathing, along the rhizome, and at the leaf juncture in cattleyas.  Males are thread like and white.  A congregation will resemble mealybug 'cotton' so look carefully. (Mealybug does not prefer cattleya, so that is a clue).  Typically, there are several generations per year.

The Good Guys:

Rhyzobius (Lindorus) lophanthae - The Scale Destroyer:  This is a small beetle (2mm) with black wing covers and a burnt-orange head, thorax, and abdomen.  Females lay hundreds of eggs under the scales.  Larva feed on scale eggs and crawlers for about two weeks before pupating.  Adults are voracious feeders of all stages of scale.  They prey on mealybug and soft scale as well.  Optimum environment 75-80F (ok down to 40F)

Strategies:

Windowsill collection - less than 50 plants: Quarantine and inspect plants before introducing them into the collection.  Thoroughly wash insects off of plant using warm water and a little finger pressure.  A used toothbrush is also helpful, but take care that the plant tissue is not damaged.  Spray with a summer horticultural oil or a neem oil product by the label directions.  Make sure coverage is complete.  Examine plants on a regular basis to keep this pest in check.
Small greenhouse or climate controlled light room:  Pay attention to spacing of plant material.  Crawlers are less apt to spread when they cannot reach the next plant over.  Wash and spot treat the most infected plants.  Use oil products for initial knock down.  Repotting and thorough cleaning of the plants will help control this pest.  Introduce Metaphycus and or Lindorus.  Be persistent!

Spider Mites: Spider mites can be one of the most devastating pests in a plant collection. Two Spotted Spider Mite (Tetranychus urticae) is one of the more common found. They are very tiny and feed on plant sap, usually by the thousands. Most plants have a population of mites at all times. When the natural balance of mite predators and mites get out of balance, plant health is affected. Look for spider mites by performing a 'beat test'. Hold a sheet of white paper under the leaf of a plant. Tap briskly. An examination of the paper with a hand lens will reveal tiny red mites, or wipe the paper to crush the mites and count the red streaks left behind to give an indication of population numbers. On foliage plants, spider mites will form webbing, but on orchids the visual signs are more subtle. Look for a matt surface where once there was a glossy leaf. Heavy infestations will show minute pitting and this pitting can sometimes take on a rusty color.

Strategies: 

Windowsill collection - less than 50 plants:  Try to maintain higher humidity, especially during the winter months.  Water plants in the sink or bath tub where they can be cleaned with a spray of water.  The use of summer horticultural or neem oil can be effective.  Avoid insecticidal soaps as they are less effective.  Avoid pyrethrum and pyrethroids as they frequently kill more mite predators than mites.  Organophosphates are also not good control choices.  Try introducing predatory mites.  There are a variety of beneficial mites that will work in the home situation.  Mesoseiulus longipes is effective at lower humidity and warm temperatures.  For areas of higher humidity, Phytosieulus persimilis is the better choice.  Predatory mites are frequently available in mixtures of several varieties to cover a wider range of conditions.

Small greenhouse or climate controlled light room: It is sometimes easier to maintain a higher humidity in the small greenhouse than in other growing situations. However even in greenhouses frequent watering down of floors will be needed to raise humidity levels. Light rooms will need a more aggressive method. The use of humidifiers or hydro-fogging machines is usually necessary to counter the drying effects of the lights. The ever-present population of spider mites usually necessitates a more pro-active approach to managing this pest. A plan of regular scouting, the application of summer horticultural oil or neem oil, and the periodic application of predatory mites are usually very effective.

The Good Guys:

Phytosieulus persimilis: This mite is the most commonly used beneficial mite in the world. They reproduce faster than spider mites and can rapidly bring an outbreak under control.  Optimum environment, 65-80F, 60%RH

Mesoseiulus longipes: Tolerating a lower humidity than 'persi', makes this mite very effective in the home growing area. Optimum environment, 70-90F, 40%RH
Neoseiulus fallacies: This mite can survive lower temperatures and the absence of prey. It has some pesticide resistance. It has the ability to provide quick knock down of spider mite outbreaks. Optimum environment, 50-80F, 60-90RH
Stethorus punctillum: This is a tiny lady beetle, 1.5mm or smaller. It is shiny black and will lay its eggs in spider mite colonies. It can rapidly suppress a population. This is a North American native.
Minute Pirate Bug - Orius insidiosus: MPB (2mm) is a generalist predator. It is useful in controlling, thrips, aphids, mites, whiteflies, and small caterpillars. It can go from egg to adult in less than 3 weeks at 77F. It kills its prey by sucking out the body contents. Both adults and nymphs are predaceous. Adults can survive on pollen in the absence of prey. Optimum environment, 70-90F, day length 11+ hours.

Pesticides:

Summer horticultural oils are highly refined parafinnic oil.  They require thorough application and kill pests by smothering.  The advantages are even removal of both pest and prey insects and the inability of the pest to develop resistance.  Use according to package directions.  A rapid drying of the material will decrease the possibility of phytotoxicity.  It has no residual action to affect future applications of beneficial insects.  Constant agitation is necessary when using oil products.

Neem oil products can be very confusing. Most common products are hydrophobic extracts of cold pressed oil from neem tree seeds and are non-toxic to mammels. Check the package lable for restrictions. Some products contain a higher percent of azadirachtin, which is an insect growth regulator and will add that benefit to your application. Avoid the use of 'pure' neem oil products, as emulsifiers are needed for uniform applications of the product. The undiluted product has a shelf life of about two years.

Azadirachtin by %: Aza-Direct (1.2%), Azatrin (3%), BioNeem (0.09%), Neemix (0.5 or 4.5%), Ornazin (4%)


Supplier:

IPM Laboratories, Inc.
Locke, NY 13092-0300
www.ipmlabs.com
315-497-2063

Listing of Commercial suppliers:

http://www.cdpr.ca.gov/docs/ipminov/ben_supp/ben_sup2.htm

References:

Natural Enemies Handbook, Flint, Mary Louise and Dreistadt, Steve H., University of California Press