Orchid
Pests and Diseases
The best defense is a
healthy plant.
Orchids can grow and flower
for many years if their basic needs are
met. Healthy plants are
less likely to became infected with disease or be
attractive to insects. Pests
can arrive with new plants so always quarantine them
away from your established
plants for a few weeks.
Some diseases are a direct
result of poor growing conditions. To keep your orchid healthy,
learn its identity and then
research its basic requirements. You need to consider:
Potting mix and watering
– most tropical orchids need well-drained, specialized potting mix. Be
careful
not to over water and, when
you do water, make sure the water runs through the pot and out
the bottom. Don’t let
the pot sit in water.
Light –
grow at the correct level for the orchid
species.
Temperature – some like it hot, some like it cool. Know
which your orchid prefers.
Humidity – most orchids prefer 40-60% humidity.
Humidity
in winter is usually lower. Excessive
humidity can encourage
disease.
Air circulation – all orchids appreciate exposure to moving
air.
Fertilizer – For most species, less is better.
Fertilize
with a weak balanced fertilizer solution.
The following symptoms may
indicate that you need to change the care of your orchid:
|
Symptoms |
Cause |
|
Leaves wilted, older leaves turn yellow and drop off, pseudobulb shriveled |
Look at the plant’s roots. If they are
firm, the plant needs to be watered more frequently. If the roots
are dark and mushy, the plant has been overwatered. Cut
off the blackened roots and repot plant in coarser
mix. Water less frequently. |
|
Leaves are dark green, new growth is small, no flowers form |
Orchid needs higher light level. Leaf color is bleached and may have dark spots that are not soft (sunburn) Orchid is getting too much light. |
|
Leaves are yellow and new growth is small |
Plant needs fertilizer, but also check
night temperature – it may be too low. |
|
Leaf tips are burned, roots withered, especially tips, there may be a white crusty buildup on potting mix or pots |
Too much fertilization or water used is too
salty. Rinse potting mix thoroughly several times with
deionized water. Never use water softened by sodium exchange
on orchids. |
|
Flowers suddenly wilt or buds drop off before flower opens |
Ethylene in the air can cause wilting
(improve ventilation, remove wilted flowers and any fruit), as
can excessive temperature fluctuation. |
|
Poor growth, leaves fall prematurely |
Night temperatures may be too high. |
Orchid diseases –
fungal, bacterial, viral
Symptoms of disease are
blackened areas on leaves or stems, brownish spots turning black or
brown and
black streaking on leaves. Often
the area will be soft and increase in size. Light brown or pinkish spots
may also appear on flowers.
Roots will appear dark and may smell rotten. If disease is suspected:
|
1.
Cut off the part of the plant showing symptoms and discard. Cut at
least ½” into healthy tissue. It
is imperative that the cutting tool be sterile and that it be
resterilized after each cut. This can be done
by passing the tool through a flame or soaking in a 1:9 dilution of
bleach (rinse thoroughly before
use). Dust cut areas with a fungicide. Consider spraying plant with
fungicide to prevent reinfection. |
|
|
|
2.
If the base of the plant or roots are affected, repot using new potting
mix after cutting off affected part
and dust the cut areas with a fungicide. Consider using a fungicide as
a soil drench. |
|
3.
Increase air flow around the plant and decrease humidity, at least
temporarily. Check humidity requirements
for your species and make sure humidity is not too high. Allow humidity
to fluctuate
during the day so the plant can dry out. |
|
4.
Modify watering and misting schedule so the foliage stays wet for only
a short period. |
|
5.
Isolate the plant from your other orchids until you are sure it is free
of disease. For all your plants,
always clean up leaf debris and cut off wilted flowers. |
Sanitation may stop a minor
infection. If fungicide treatment is necessary, make sure you follow
label
instructions for dilutions,
safety, and treatment schedule. Fungicides which might be used on
orchids are
Truban, benomyl and Banrot. For best results, consult additional
references
before deciding on a
fungicide treatment. It is
best to confirm the identity of the fungus infecting your orchids. Your
county
extension agent can help
you send samples for analysis and provide recommendations. If you have
a viral
infection, there is no
treatment. Isolate the plant immediately and discard if viral infection
is
confirmed.
Orchid pests
Several small invertebrates
attack orchids. Most damage the orchid by attaching to it and sucking
out
water and nutrients. Only
slugs and snails will eat holes in the leaves. Before purchase, check
plants
for
insects. Look not only at
the leaves but also at the nooks and crannies between leaf and
pseudobulb and
Under any papery coverings
on the flower stalks or stems.
Some insects you may find
on your orchids are:
Small insects
that may be hard to see
|
Mites |
You
will see stippling or irregular pits on undersides of leaves, sometimes
with fine Webbing.
Foliage may have silvery areas that turn brown and sunken. If you rub a White
cloth on the underside of the leaf, it may come away streaked with
brown. |
|
Aphids |
You
may see punctures on leaves and sometimes flowers, new growth is
stunted. Aphids
secrete a sugary liquid and sooty mold, a black fungus, may grow on it. |
|
Insects you will see easily |
|
|
Mealybugs |
Soft-bodied
insects that are covered with a waxy, cottony secretion which looks like White
fuzz. They may hide under papery coverings of pseudobulbs and in other sheltered
spaces. |
|
Scale |
Hard-shelled
insects which look like bumps on leaves and pseudobulbs. |
If the infection is minor and
you can see the insects, you may be able to physically remove them with
a
cotton swab dipped in
alcohol. Hard-shelled scale may need to be scrapped off. Aphids can
sometimes
be removed with a stream of
water. Monitor the plants closely. Unhatched
eggs may
result in a new
insect infestation.
Insecticides will also be
effective. Make sure you test the insecticide on one plant before
spraying all
your orchids. Several
sprayings may be necessary, as eggs hatch over a series of weeks. For
best
results,
consult
references and make sure you follow insecticide label instructions for
dilutions and safety. Your
county
extension agent can help you identify insect pests. Insecticides which might be
used on
orchids
are
insecticidal soap, Orthene, carbaryl
(Sevin), malathion and Neem.
References:
All About
Orchids,
Ortho books,
1999.
All About
Orchids, Charles
Marden Fitch, 1981. Doubleday &
Company, Inc.
Home Orchid
Growing, Rebecca
Tyson Northen, 4th
Edition, 1990.
Prentice Hall
Press.
http://www.theaos.org/orchids/index.shtml
and http://www.orchidlady.com/