Even the best growers will have some insect problems from time to time on their orchids. Insect pests are controllable, just follow some simple rules and you will be in control rather than the pests being in control.
Some very general information that will help you take charge:
- Be observant – Take time to look at your plants. The insects do not usually sit up on top of the leaves waiting to be found. They hide under the leaves, in the leaf axils, in the crown of the plant, on the flower sheath, etc. etc. Pick up your plants, look at them from all sides. The sooner you find the infestation the easier it is to control.
- Identify insects correctly – This is absolutely critical, it does not do any good to spray aphids with a miticide. You must spray spider mites with a miticide, insects with an insecticide and fungus diseases with a fungicide. Actually makes sense doesn’t it.
- Know the life cycle for each type of insect – The most important aspect of insect control is the stage of development they are in. Some stages of growth cannot be controlled by simply spraying with chemicals (or SOAP) as the stage is resistant in some way. For example, Mealy bugs are virtually impossible to control in the egg sack, adults cannot be controlled without very strong (and dangerous) chemicals. If you know when Mealy bugs are in the juvenile or crawling stage, then most SOAP or chemical sprays will kill them.
- Cleanliness – Yes, just like the old days you have to keep the growing space clean. Insects hide and grow in old leaves and flowers that have fallen to the ground. Molds, fungus and fungus gnats love a moist decaying area below the pots. By keeping the area clean, the only place the insects can be are on your plants then you will find them and have control again.
- Complete the control program – Along with using the correct pesticide for each pest problem, make sure that if the insect pest life cycle requires three applications, then you must do three applications to get close to 100% control. By reducing the applications you may leave one generation of pests to re-infest your orchids. Remember most pesticides will not kill every stage of an insects life cycle.
- Isolate new plants to your collection – When you have an insect free collection it is important to try and keep it that way. If possible, any new plants should be grown in an isolated environment until you are sure that there are no new pests to infest your orchids. It is also important to screen windows and vents to prevent pests from entering your plant growing area. Remember also that yellow clothing attracts many types of insects, so going outside in yellow then coming into your growing area could in fact bring in aphids, thrips, and whitefly. (Royal Blue is very attractive to thrips.)
Types and Uses of Pesticides
ALL pesticides are dangerous but all can be used safely. Use common sense, follow directions, wear protective clothing and READ THE LABEL. There are five main types of chemicals or insect controls:
- Contact sprays are just what they say. If you don’t actually hit the pest, it will not die. These chemicals are a problem because most pest are hidden or in hard to reach areas. The contact sprays have no residual effect, a short time after spraying the chemical has broken down and will not kill anything.
- Systemic sprays absorb into the plant (and into you!) so there is some residual action. In other words, after the spray is applied the pest may absorb the poison by eating the leaf or leaf juices or by running across the residue on the leaf. The residue may last in the plant for up to 10 days. Systemic sprays are far more dangerous to the user. A child (or pet) eating a leaf several days after application can be poisoned. Most chemicals purchased in the garden stores have some residual (systemic) action.
- Soaps – so called safe chemicals, they are all in the contact type. Safers Soap (Trounce) is a product designed especially for the home owner to have an effective pesticide that is safe to use in the home.Because it is a contact type, more frequent applications are necessary or complete control is impossible. You have to hit every insect to kill them. Soaps actually work by dissolving the epidermal protection around the pest so they freeze to death. (You can hear them shivering and thus know it is effective.) Ivory liquid soap at the rate of 1 tablespoon per gallon is just as effective as Safers Soap. Some damage to flowers may occur from the use of soap sprays.
- Oil Sprays – a new generation (redeveloped) of safe pesticides. They are actually a finely refined vegetable oil and are generally non-toxic to plants.One of the current product names is Sunspray 2E which is simply a refinement of the old Dormant Oil. This product is also a contact spray that suffocates the insect by filming over breathing apparatus. The Oil sprays are very effective but, as with Soaps, more frequent spraying will be necessary as you have to hit every insect to kill them. Too heavy a concentration may also seal up the plant stomata thus causing some damage to the plant.
- Biological Controls – A word of warning, the introduction of Biological Controls will not be the end of your pest problems. For one thing, to most people ‘a bug is a bug’ and there is no such thing as a good one. Also to successfully use ‘Bio’ there has to be some pests present so the good bugs have something to eat.There is a biological control available for each insect pest but conditions have to be just right for them to be effective and Biologicals are generally quite expensive.
Insects To Be Concerned About
The list is extensive so don’t give up now. All of these insects will not be on your plants (may never be).
I will list the more common ones first. Remember correct identification is the key to control – Do you have a magnifying glass? Many are very small and hard to see.
I will identify a control chemical in each case but make sure the specific chemical is in fact licensed for use on orchids in your area. In the United States there are far more pesticides registered than in Canada.
Learn the life cycles for each pest. It is essential to recognize the life cycle for each pest involved in the program. The life cycle will determine the frequency of any spray program.
- 300-600 eggs in loose cottony sacs. (eggs covered in waxy ovisac that acts as water repellant)
- eggs hatch every 2 weeks.
- crawler migrate actively.
- 4 stages of growth in female.
- 5 stages of growth in male (tiny fly-like insect).
- total cycle lasts 30-70 days (depending on temperature).
- located in out-of-sight places – roots (root mealybugs are different species) and leaf nodes
- spray control programs 10-14 days apart.
- applied to crawler stage.
- Malathion, Orthene (wettable powder), SOAP, Sunspray Oil.
There are many varieties of scale, two main classes are listed below.
1) Soft Scale:
- 2-6 millimetres long.
- 1000-2000 eggs.
- eggs hatch in 1-3 weeks.
- crawlers migrate over the leaf and stem.
- feeding begins after a few days.
- two weeks later they molt to a second stage.
- after second molt, the males become minute, two winged fly-like insects.
- complete generation is from 40-80 days.
- contact insecticides will not kill adults as they are protected by the scale’s hard surface.
- spray at 7-10 day intervals at least 4 applications (2 with systemic 14-21 days apart).
- same sprays as with mealybugs.
2) Armoured Scales: – Boisduval, Florida, Red, Greedy Scale
- smaller than soft scales.
- 1-3 millimetres in length.
- some species produce live young.
- 20-400 eggs.
- each generation may take 60-120 days to complete.
- eggs and adults are generally resistant to pesticides.
- crawlers do not travel as far as soft scales.
- spray at 10-14 day intervals (same sprays as Mealybugs).
Two-Spotted Spider Mites
(Note: This is different from the False Spider described later.)
- life cycle – from egg to adult 7-10 days.
- 0.5 millimetres in length (usually located on the underside of the leaf).
- clear white spots represent the eggs.
- 100 or more eggs produced by each female.
- increased temperature speed maturity.
- eggs and adults are difficult to control
- larval and protonymph stage easiest to control.
- mites produce extensive webbing.
- spray with Kelthane, Pentac, SOAP, Sunspray 2E Oil.
- increased humidity reduces population.
Western Flower Thrip
- most serious threat to orchids as the Western Flower Thrip is the vector for Tomato Spotted Wilt Virus.
- thrips can also seriously damage flowers and leaves.
- tiny slender insects 1.5-3 millimetres in length.
- usually dark brown as adults but yellow as young crawlers.
- white streaked areas on the flowers the most observed symptom.
- reversed foliage is a silver color after thrip infestation.
- eggs hatch in 5-7 days.
- several nymphal stages before adulthood.
- new generations every 20-35 days.
- spray every 5-7 days with Orthene, SOAP, Decis.
- thoroughly spray all parts of the plant including leaves, stem, flowers, and buds.
- lay live young.
- generally green in color but may come in shades of black, brown or red.
- usually found in colonies with all stages of growth,
- they love the flowers and flower spikes or new growth on plants.
- aphids secrete a honeydew that drips onto lower leaves.
- flying stage common in spring and late fall looking for new plants to infest.
- spray every 7 days with any insecticide. SOAP is very effective.
False Spider Mite
- should be called Phalaenopsis Mite.
- 0.3 millimetres in length (not visible to eye).
- red in color.
- usual sign is yellowing of lower leaves.
- green leaves will have darkened sunken area usually on bottom of leaves.
- slow reproducing pest but extremely difficult to see, therefore infestation can be extensive.
- eggs hatch in 30 days.
- adult female only lays 25 or so eggs at one per day.
- every leaf must be thoroughly sprayed top and bottom.
- spray twice at 10 days apart.
- spray with Kelthane, SOAP, or Sunspray Oil.
- both species will be treated the same in the description although they are separate species.
- Whiteflies generally only are attracted to the soft or fine leafed orchid varieties.
- pure white in color, adults are approximately 1.5 millimetres long.
- nymphs (4 stages) are small, white, oval shaped generally found on lower leaves.
- Pupa stage can be seen on the undersurface of the leaf as “white flat rings”.
- adults lay 200-400 eggs in a 20-50 day life cycle.
- sanitation (removal of weeds) is essential in controlling whitefly.
- spray every 4-7 days for at least 3 applications.
- Orthene (wettable powder), Ambush, Enstar, SOAP, or Sunspray Oil are effective controls.
- underside of leaf is critical spot to ensure control.
- generally a sign that plants are being kept too wet. They breed and grow in moist wet decaying situations.
- little or no damage to roots or orchids (unless severe infestation).
- noticed as small black flies around your face.
- larvae is a very small white worm on the media surface after watering.
- life cycle is 12-30 days.
- adults may carry plant fungus diseases.
- two applications of a drench through the medium with SOAP (1 tbsp/gal water).
- keep plants dryer.
- remove any wet mossy areas under growing bench.
Slugs and Snails
- have soft unsegmented bodies.
- secrete a slimy substance.
- can elongate and contract their bodies thus fitting into very small spots.
- feed at night on flowers and leaves.
- love moist dark areas (under flats, pots, etc.).
- best control is good sanitation
- baits are very effective
- beer in shallow saucers will attract the slugs at night.
- they can be destroyed the next morning.
- slug baits on the market are very good but dangerous to pets.
- Fossil Flower (Diatomacious earth).
Gordon Heaps, Orchid Society of Alberta
Gordon Heaps is Supervisor of operations at Muttard Conservatory in Edmonton with extensive experience in the interior landscaping industry. He served as President of the Orchid Society of Alberta for two years, 1991 to 1993.