Pests and Diseases
page addresses the most common pests and diseases of African violets. If one
of these titles interests you, click on it to go directly to that section.
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 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.
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.
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, 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.
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.