Pests &
Diseases
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Prevention
Thrips
Mealybugs
Mites
Diseases
1.
Preventive measures are important. Keep the plant area clean, isolate new
plants from old ones until you are sure they are problem-free. Sterilize
pots and saucers that are to be re-used. Use sterilized or pasteurized soil.
2. Common
insect pests are thrips and mealybugs. Mites are also a danger.
3. The
most common diseases are fungal, especially powdery mildew.
4. Pests
and diseases can be attacked with chemical pesticides, more natural and
traditional treatments, and now, in the cases of insects and mites, natural
predators and parasites.
Occasionally a grower's collection of gorgeous plants is suffers an outbreak
of pests or disease. Growing indoors does not make our plants immune to the
horrors that all gardeners will sometimes find in the outdoor garden. Little
bugs and tiny disease spores have no problem getting indoors.
Prevention
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Prevention of pests and diseases is of prime importance. The little extra
work that prevention involves is well worth it in ensuring a healthy
collection. An infestation is a disaster which may necessitate measures as
drastic as throwing the whole collection out. We have learned from
experience to practise prevention.
The first
important preventive measure is to inspect all plants regularly for possible
problems. When buying new plants or accepting them as a gift inspect them
also and particularly carefully. All newly acquired plants should be
isolated from the rest of the collection (preferably in another room) for a
minimum of six weeks. This gives insect eggs a chance to hatch or disease
spores a chance to do their work and you can then determine if your new
plant is infested before exposing your other plants to the danger. While it
is in isolation like this you will want to tend your new plant using
different tools from those used on the main collection. Always wash your
hands after handling the isolated plant.
Keep
other plant materials out of the plant room. (Some African violet growers
would say out of the house not merely out of the room.) The little pests
that love your garden plants would love that special opportunity to come
indoors and devour your African violets too. Never bring your outdoor plants
or their cut blooms into the plant room. Transfer of minute insects is
almost inevitable and some of them can be extremely destructive of African
violets. The same applies to cut flowers and plants from nurseries.
Commercially grown flowers are often infested. Your Valentine's Day roses
may look and smell wonderful; however, tiny blossom thrips love roses too
and they also love African violets. Keep them away. Outdoor pests get a
wonderful opportunity to come indoors when you proceed to the plant room
directly from gardening outdoors. They can travel on your hands, hair and
clothing. You should wash and change before attending to the indoor plants
after being outdoors, or, if you are a good scheduler, plan your plant room
visit to be after your regular bath and change.
Observe
good general cleanliness in the plant room. Keep your shelves clean. Use
only pots and saucers that have been washed, rinsed, soaked for a minimum
often minutes in a chlorine bleach solution (1 part bleach to 15 parts
water), and rinsed again. This prevents eggs and spores from old plants from
transferring themselves to your new ones. Wash all other planting equipment
— scoops, knives, tweezers, etc. — after each use.
Space
your plants well on the shelves. Crowding them, allowing them to touch, will
reduce air circulation and increase the opportunities for spores of fungal
disease to take hold.
Your
growing medium should be sterile or pasteurized. If the package does not
indicate that it is, ask your supplier. Otherwise it can be another source
of insect eggs and disease spores.
Thrips
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Just a
few words about the more common African violet pests: The pest that seems
to appear most often in our area is thrips. Thrips are tiny insects,
off-white to beige-brown in colour and 2 to 4 mm. in length. While they
survive on the leaves of plants that are out of bloom, they are most evident
on blooming plants. They look like little bits of thread scurrying across
the petals of the blossoms and into the area of the anthers.They love to eat
the protein-rich pollen hidden in the yellow anthers and often spill it on
the petals. If you don't see the insects directly, spilt pollen is a
possible indicator of their presence.
Once
established, thrips are very hard to eliminate and any plant with them is an
eyesore which cannot be enjoyed. The standard, non-chemical way of treating
plants with thrips is to disbud them preventing bloom for a period of six
months. Unfortunately, a bug or two may survive and when the blossoms appear
again so do the bugs. Safe insecticides such as insecticidal soap are of
limited effectiveness and the bugs often elude the more toxic chemical
insecticides although there are good reports about one or two of the
strongest available.
Mealybugs
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Both
foliar and soil mealybugs will infest African violets if given the chance.
Foliar mealybugs look like minute balls of cotton hiding near the bases of
the leaves from which they suck the juices. Soil mealybugs suck the juices
from the roots and bear a resemblance to small particles of perlite or
grains of rice.
Foliar
mealybugs can be controlled though not eliminated by picking them off by
hand and/or wiping them away with a swab dipped in alcohol and rinsing with
lukewarm water. The usual approach to soil mealybugs is to use a soil drench
made of a chemical insecticide. This may be only partially effective as the
bugs can usually find an area of soil that the drench has not reached and
weather the storm in this haven.
Mites
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Mites,
not insects but eight-legged spider relatives, are the final common pest.
Broad mites are tiny but barely visible and range in colour from dark green
to amber. They hide on the undersides of leaves where they suck the juices.
Leaves curled under at the edges and becoming brittle are signs of their
presence.
Their
distant kin the cyclamen mite is the most dangerous of all African violet
pests. They are invisible to the naked eye and can just barely be seen with
a hand-magnification lens with a power of 1Ox. For such tiny creatures the
damage they do is remarkable. The first sign of their presence is a fuzzy
whiteness in the centre of the plant. Infected leaves curl upwards. A
seriously infested plant will die within weeks. While chemical miticides are
available, it is very difficult to defend against a mite infestation. Most
experienced growers advise that you isolate the first affected plant you
spot until an expert can examine it. If the expert confirms your suspicion
that you have mites throw out the plant. Watch the rest of your collection
carefully. If you have caught them early, the mites may not have a chance to
spread. If they have spread, your choices are to use a miticide or dispose
of all your plants. Most local experts say to do the latter as the safer
alternative. Start collecting again after cleaning and sterilizing the plant
area and your tools. Better still, acquire new tools.
In recent
years, African violet growers have been turning to natural predators and
parasites of the insect and mite pests as a safe way to control the
problems. There are other insects and mites which can be introduced into the
plant collection to eat the problem insects as prey. Nematodes can also be
introduced which parasitize them. These little marvels are available
commercially, but can be hard to get and they are expensive.
Diseases
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Disease
can also affect the African violet, but it is not a frequent occurrence if
proper growing conditions are maintained. Most common are the fungal
diseases including different forms of mildew, especially powdery mildew,
botrytis blight and crown rot. The one most frequently encountered is
powdery mildew which is hard to avoid as the spores are everywhere. It looks
like white powder sprinkled on the leaves. Fortunately, it is easily treated
by dusting the leaves with flowers of sulphur, then gently brushing off the
sulphur in a few days after it has done its job. There are also several
modern chemical treatments.
Bacterial
and viral diseases do occur in African violets but are not a frequent
problem.
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