Growing African Violets, part 6 – Pests and Diseases

 The great things about African violets are that they are relatively easy to grow and they will bloom nearly year round, allowing even the harshest climates to experience a little bit of summer all the time.    The not so great thing is that they are prone to diseases and pests.  Virtually all the common problems, however,  can be avoided with proper growing practices we’ve been discussing.  When disease and pest problems occur, they are serious.

Brown center and collapsing leaves indicating Crown and Root Rot

One of the most serious conditions is Crown and Root Rot.  This is first noticed when the crown of the plant becomes mushy , the older stems droop because their attachment to the crown is compromised, and new growth is stunted and eventually turns black and dies.  Crown rot is caused by a fungus that takes hold when plants are allowed to remain too wet, either through over-watering or poorly draining pots or potting mix, or when  African violets are planted too deep. 

The only cure for Crown and Root Rot is prevention.  I have never succeeded in saving a violet once evidence of Crown Rot exists.  It is best to put the rotting plant and soil into a sealed plastic bag and throw it in the garbage.  If you are using a porous, clay type pot, it is recommended that you even destroy the pot because of the difficulty of killing any of the Phytophthora fungus that causes the rot.    If you don’t wish to throw the pot, you need to give it a good long soak totally submerged in a 10% bleach solution for enough hours to allow the bleach to completely permeate the pot, usually around 12 to 16 hours.  Then,  remove the pot from the bleach solution and soak it in clean, clear water for that same amount of time.

If you must try to save the affected violet, completely isolate it from all other plants.  Trim off all decaying tissue from the plant and the roots,  dust the plant and root ball with plant grade sulfur, then replant in a sterilized pot with very porous, sterilized potting mix that has been treated with an anti-fungal such as Benomyl.  I don’t know about you, but that violet would have to be pretty precious for me to bring Benomyl into my home in any form.



Botrytis lesions on leaves



Botrytis blight is another disease caused by a fungus.  Its first appearance may be in the form of lesions on the underside of the leaves that are similar in appearance to water damage.  The leaves and stems turn a dark, greenish-brown color and may begin to look like they have a fuzzy coating on their surfaces.  Flowers will develop brown spots or the entire flower will turn brown and appear wilted.    Botrytis is also difficult to treat but, unlike with Crown Rot, you may have a chance of saving your violet. 

First, isolate the violet from all other plants.  Violets are not the only plants affected by Botrytis and it can be spread through air movement.  Remove, bag, and destroy all dead and dying tissue from the plant.  Make sure the remaining plant has good air circulation around it.  Botrytis must be treated with a fungicide.  Both Benomyl and Captan are effective against Botrytis.  Again, unless this is a very special violet, I would opt for throwing it out and starting over rather than using fungicides in my home environment.



Powdery Mildew

Powdery Mildew can appear similar to the gray mold of Botrytis, but instead of being spots of fuzzy gray mold on the leaves, Powdery Mildew generally is a white, dusty appearing powder that covers the entire plant.  Left untreated, Powdery Mildew will cause discoloration of the leaves and flowers, as well as distortion of the flower and stem.  Powdery Mildew is more common than Botrytis in most home environments and can almost always be prevented with proper watering and adequate air circulation. 

Again, isolate the affected plant(s) to prevent the spread of Powdery Mildew.  Remove any dead or dying tissue and place the plants in an area where the humidity is consistently less than 60% and the temperature stays at a consistent 70 degrees.  If the infection is particularly bad, or if you see no improvement after two to three days of the reduced humidity and consistent temperature, spray the entire plant with Lysol disinfectant spray.  The Lysol will cause discoloration of the flowers, but will not do any harm to the plant and is safer for you than chemical fungicides.  Plant grade sulfur dusted on the entire plant, or a mixture of one teaspoon of baking soda mixed in one quart of room temperature water and sprayed over the entire plant can also be used in place of fungicides.  If these treatments do not cause noticeable improvement within the first week of treatment, your only other option will be to treat with Benomyl or Captan if you want to save the plant.



Center showing cyclamen mite damage

Cyclamen mites are partial to African violets as well as cyclamen.  They are microscopic spider-like pests and, next to Crown Rot, are the most serious thing that can happen to your African violet.  Damage to your violet is the first indication that mites are at work.  They prefer the new growth, so damage will show up first in the center of your violet, with stunting of the new leaf growth, curling of the edges of the leaf and a very hairy appearance on new leaves.  Flowers will also become stunted and deformed and will not open fully, if at all.

Mites prefer very high humidity and low temperatures.  They don’t like light, so they hide in the leaf folds or right up against the crown of the plant.  They suck the sap from the plant, and in the process inject a toxic substance that causes the growth deformities that are the hallmark of mite infestation.

Isolate the plant at the first sign of infection, as mites spread very easily from plant to plant.  Because greenhouse conditions are often perfect for the development of mite infestations, it is a very good idea to isolate any new violets you bring home for several weeks, until you can see for sure that new growth is normal. 

The only way to get rid of mites is to spray them.  You can try spraying with Azadirachtin (Neem), which has some systemic insecticidal properties but works primarily by making your violet taste bad to the mites, but will not kill them immediately.  I’ve had minimal success with this, but it is a more human friendly approach than chemical miticides.  Generally, if you want to save the plant, you will need to resort to chemical miticides, such as Bonide Mite-X or Dicofol.  Whatever product you use must be rated for indoor, household use.

You’ll need to spray all surfaces of the plant, making sure to get into the folds of the leaves and the undersides, especially where the leaves attach to the crown.  Spraying needs to occur once every four days for three times, or every fourth day over a twelve day time period.  Then watch closely for signs of continued infestation.  It’s important to keep the plant isolated for the entire time until you clearly see healthy new growth.



Mealybug on back of leaf

Mealybugs are tiny bugs that collect on the undersides of leaves and near where the stem attaches to the leaf or to the crown.  They are visible to the human eye and look like a tiny speck of cotton or white dust.  Root mealybugs look essentially the same, but are found collected in the root ball of the violet.  They suck the juices from the plant and will eventually kill the plant if left untreated.  As they feed, they excrete honeydew, which makes a sticky mess on the leaves and on the surface of the plant’s table or stand. 

The best way to treat mealybugs is to never bring them home in the first place.  Inspect all plants carefully for those tiny white fluffballs, including looking at the root ball, either by lifting it out of the pot or inspecting through the drainage holes.  The adult bugs have a waxy coating that makes them impermeable to contact pesticides, so the best way to treat them is to physically remove them with a cotton swab dipped in rubbing alcohol.  The immature mealybugs do not yet have that coating, so they are susceptible to insecticides and can be destroyed with insecticidal soap, which is generally rated safe for use in a home.

Whenever you trim tissue from your plants, it is critical that you disinfect your equipment between plants to avoid spreading even more disease.  You can do this by wiping or rinsing in a 10% bleach solution.  Ready to use disinfectant wipes may also be used if you can get to all surfaces of your tools adequately.  It’s also important to wash your hands between plants to avoid carrying any unwanted “stuff” from one plant to another when you are having disease or pest problems.

There are other common African violet problems that are not disease or pest related, but rather are caused by improper environmental conditions.  Buds may turn brown and fall off before opening if the temperature is too cold, if they are over-watered, or if the humidity in their environment is too low.  Exposure to fumes from gas fired cook stoves or heaters will also cause the flower buds to drop before opening.

A rust colored spot that appears where the stem or the leaf touches the pot is called petiole rot, but is not a bacterial or fungal rot.  These spots occur when the leaf or stem touches fertilizer salts that have accumulated on the rim of the pot.  This can be prevented by proper fertilizing and leaching the soil periodically, as well as using a salt –free source of water.

Cold water damage

Yellow or white spots or lines on the leaves of African violets is caused by contact with cold water.  Keeping the leaves dry when watering and using room temperature water is guaranteed to avoid this problem.

Truthfully, African violets are pretty cheap and readily available.  The only violet I’ve had that I attempted to treat disease or pests in has been the one I received from my mother-in-law’s collection when she passed away in 1982.  I’ve always kept several starts of the plant growing so that I was less likely to lose it.  Other than that, I’ve opted to throw and replace if I see any signs of problems.  I think that has not only saved me a lot of time and headache, but has also saved many of my healthy plants in the long-term.

If you follow the guidelines for appropriate water, temperature, air movement, humidity, and fertilization and repot your African violets whenever they need it, they will reward you with years of trouble-free blooms.