African Violet Diseases & Insect Pests
African violets are easily the most popular flowering houseplants in America. Their popularity arises from the fact that they are easy to grow and can bloom for 10 to 12 months of the year. They commonly have disease and pest problems, but most of these can be avoided by following the recommended cultural practices to keep plants healthy as described in HGIC 1550, African Violet.
Crown & Root Rot: One of the most serious fungal problems of African violet is usually first noticed when the crown and roots of the plant turn soft and mushy. The older leaves droop, and the younger leaves in the center of the plant appear stunted, turn black and die. The fungi Pythium species and Phytophthora species can cause this problem, especially when plants are watered excessively, have poor drainage, or are planted too deeply. Any of these conditions can contribute to rotting of the crown and roots.
Prevention & Treatment: Prevent disease by always using sterilized potting soil mixes and clean containers when planting. Do not plant African violets too deep. Discard severely affected plants.
Botrytis Blight: Botrytis blight is caused by the fungus Botrytis cinerea and often first appears as small water-soaked lesions on the underside of the leaf. Leaves, stems or flowers appear blighted and turn dark brown to gray, often with a fuzzy coating on the surface.
Prevention & Treatment: Collect and discard all dead and dying plant material. Provide better air circulation, and avoid getting the flowers and foliage wet. Botrytis often follows mite injury, so controlling this pest aids in controlling this disease.
Insects & Related Pests
Cyclamen Mites: Mites are not insects but are more closely related to spiders. Cyclamen mites (Steneotarsonemus pallidus) are one of the most serious pests of African violets. They are extremely small (approximately 1/100 inch long) and cannot be seen with the naked eye. Typically, damage to plants is the first indication of their presence. They feed on new growth (i.e. leaves in the center of the plant). Symptoms may include severe stunting of leaves in the center of the plant, sometimes with leaf curling. New leaves are often very hairy, making them appear grayish. Flower buds may also be stunted and misshapen or even fail to open.
Cyclamen mites develop most rapidly with high humidity (80 to 90 percent) and a temperature of 60.8 ° F. To avoid light, they favor the plant crown or leaf folds located in the area where the petiole (stalk that attaches the leaf to the stem) joins the stem. As such, damage is usually seen there first. Mites feed by sucking sap from the plant. During feeding, they inject a toxic chemical that disrupts normal growth patterns. With heavy infestations, leaf and flower buds may die. If ignored, the entire plant or just the center of the plant may die. Even after infestations are controlled, some symptoms will remain. A return to a normal appearance requires time and a gradual pruning of distorted leaves.
Prevention & Control: Space plants so that they do not touch to prevent the spread of cyclamen mites. Also, be careful not to touch infested plants before working with non-infested plants. Isolate infested plants. Badly infested plants should be discarded. Pots of discarded plants should not be reused until they have been soaked for 30 minutes in a solution of 1 part household bleach to 9 parts water.
For valuable plants, spray with a miticide that is labeled for use on house plants. Take the plant outside during mild temperatures and spray with an insecticidal soap, or products containing sulfur or tau-fluvalinate. Two or three sprays at three day intervals may be required for mite control. See Table 1 for examples of brands and products. Follow label directions for use and safety of all products.
Mealybugs: Several kinds of mealybugs are pests on African violets. They include the citrus mealybug (Planococcus citri) and the Comstock mealybug (Pseudococcus comstocki). Mealybugs are about ¼ inch in length. They have soft bodies and are covered with a white waxy material that makes them look cottony. They are found on leaves, stems and in leaf-crotches. They feed by sucking plant sap. Their feeding causes stunted and distorted leaves. Heavy infestation can cause leaf and plant death. As they feed, they excrete honeydew (a sugary material) that can coat the leaves, making them sticky.
Prevention & Control: Avoid bringing these pests into the house by inspecting a new plant carefully, including the bottom of the pot, for mealybug eggs. Light infestations of mealybugs can be controlled by removing them with a cotton swab dipped in rubbing (isopropyl) alcohol. Repeat as needed.
Heavy infestations are more difficult to control. The waxy material that covers mealybugs protects the adults from insecticides. The immature nymphs are susceptible, however. House plant insect sprays, such as insecticidal soap or pyrethrins are the least toxic insecticides, but sprays with acetamiprid, cyfluthrin, imidacloprid or permethrin will control mealybugs. Take the plant outside during mild temperatures to spray. Two or three sprays at three day intervals may be required. Alternatively, soil-applied insecticide granules or plant spikes containing imidacloprid will also control mealybugs. See Table 1 for examples of brands and
products containing these active ingredients. Follow label directions for use and safety of all pesticides.
Failure to Flower: African violet flower buds may fail to open, turn brown and fall off. Unfavorable environmental conditions such as low temperatures, poor soil aeration, wet soil or excessively dry air contribute to flower failure. Blossoms will drop if there is the slightest presence of cooking gas.
Petiole Rot: The symptom of petiole rot is a rust-colored spot that appears where the stem of the leaf touches the pot. This is not a disease but is caused when fertilizer salts accumulate on the rim of the pot and the soil surface. Avoid over-fertilization of plants, and be sure to use a salt-free source for watering, such as, rainwater. Tape on the rim of the pot will prevent this problem. Leach out the remaining salts in the soil, by flushing the container with plenty of fresh water.
Water Spots: Yellow or white ring and line patterns on African violet leaves can be caused by contact with cold water. Keep the leaves dry when watering to avoid this problem.
Table 1. Pesticides to Control Insect Pests & Mites on African Violets.
|Pesticide Active Ingredient||Examples of Brands & Products||% Active Ingredients||Pests Controlled|
|Natural, Less Toxic Pesticides|
|Insecticidal Soap||Bonide Insecticidal Soap RTU
Espoma Earth-tone Insecticidal Soap RTU
Safer Brand Insect Killing Soap Conc.
Garden Safe Insecticidal Soap RTU
Whitney Farms Insecticidal Soap RTU
|1% potassium salts of fatty acids||Mites, mealybugs, aphids, whiteflies|
|Neem Oil||Natural Guard Neem RTU
Monterey Neem Oil RTU
Garden Safe Fungicide 3 RTU
Bonide Neem Oil RTU
extracts of Neem Oil
|Mealybugs, aphids, whiteflies, Mites|
|Safer Brand neem Oil RTU||Mealybugs, aphids, whiteflies|
|Ferti-lome Triple Action Plus RTU||0.9% Neem Oil
0.20% Pipernyl butoxide
|Mealybugs, aphids, whiteflies|
|Pyrethrins & Neem Oil||Bon-Neem Fungicide, Miticide, Insecticide RTU||0.02 % Pyrethrins
0.90% Neem Oil
|Mites, mealybugs, aphids, whiteflies|
|Pyrethrins Neem Oil Insecticidal Soap||Safer Brand End All insect Killer RTU||1% Potassium Salts of Fatty Acids
0.9% Neem Oil 0.012% Pyrethrins
|Mealybugs, aphids, mites, whiteflies|
|Pyrethrins & Sulfur||Bonide Eight Insect Control home & Garden
Espoma Earth-tone 3-in-1 Disease Control – Kills Fungus, Insects & Mites RTU
|Mites, mealybugs, aphids, whiteflies|
|Pyrethrins & Canola Oil||Espoma Earth-Tome Insect Control RTU
Monterey Take Down Garden Spray RTU
1.00% Canola Oil
|Mealybugs, aphids, whiteflies, mites, thrips|
|Bonide Mite-X RTU||0.40% Cottonseed Oil
0.20% Clove Oil
0.10% Garlic Oil
|Mites, aphids, thrips|
|Pyrerthrins||Garden Safe Houseplants & Garden Insect Killer RTU||0.02% Pyrethrins
0.20% Pipernyl butoxide
|Contact & Systemic Insecticides|
|Acetamiprid||Ortho Rose & Flower Insect Killer RTU||0.006% Acetamiprid||Mealybugs, aphids, whiteflies|
|Permethrin||Spectracide Immunox 3-in-1 Insect & Disease Control & Fertilizer for Gardens RTU||0.02% Permethrin
|Mealybugs, aphids, whiteflies|
|Imidacloprid||Bayer Advanced 3-in-1 Insect & Mite Control RTU||0.012% Imidacloprid
|Mealybugs, aphids, whiteflies, leaf miners, thrips, beetles, scale crawlers, mites|
|RTU = Ready to spray (a pre-mixed spray bottle)
Note: Spraying of houseplants is most safely done outdoors during mild temperatures. Once plants are dry, they may be brought back indoors. Granular products are sprinkled on the soil surface and watered in.
White Substance at Base of Stem: Mealy Bugs
Question: My violet hasn’t looked very happy lately. The leaves look dull and a bit limp. There is a white substance around the base of the stem, which makes me suspicious. Could this be a pest problem that’s causing my plant to look this way, and how do I get rid of it?
Answer: It sounds like your violet may have mealybug. If you see slow-moving, white, waxy, insects hiding within the leaf axils of your plant, you may have foliar mealybug. Sometimes, they’ll look like litte bits of perlite–if it “squishes” it’s mealybug; if it’s crunchy, it’s perlite. That white substance around the base of your plant may very well be a mass of mealybug eggs. Soil mealybugs are harder to see, since they are smaller and they do most of their damage within the soil, to the plant’s roots. They, too, can leave egg masses on the soil surface, at the plant base. You’ll know for sure by taking the plant out of the pot and examining the root ball. You’ll see white patches, like “confectioner’s sugar” on the root ball or inside of the pot. These will be the egg masses of soil mealybug.
In either case, you’ve got a problem to deal with. Mealybugs can be difficult to get rid of without taking extreme, or costly, measures. If it’s not a valuable plant, and you don’t want to risk the problem spreading to the rest of your collection, it may be best to simply discard the plant. Too often, growers will take half-measures in an effort to save one plant, meanwhite letting it spread to the remainder of their collection. After (sometimes years) of battling, the original plant, as well as many others, end up being discarded anyway.
Should you want to keep the plant and fight the problem, be prepared to spend some time, effort, and money. To begin, you will need to use chemicals to eliminate the problem with certainty. Unfortunately, many of the chemicals that are proven to work can be either too toxic to wisely use in the home, too costly, or both. Chemicals such as Cygon, diazanon, or Malathion, once popular, and perhaps effective, are just too toxic to safely use in the home (though many of us did). Today, the insecticides of choice areMarathon and its liquid form, Admire. Both contain the active ingredient imidocloprid (look for this on the label if using another product). Though still toxic, and to be used with caution, it is much safer for home use than what’s been used in the past (it’s the same ingredient in the liquid flea medication you may be applying to your pet). Unfortunately, both are quite expensive for the small grower–$100 or more per container, making it impracticale for many small growers and hobbyists. Don’t waste your time and money on less expensive, less toxic, products like insecticidal soaps intended for in-home use. They are ineffective (regardless of what the label says) for problems such as mealybug.
Marathon come in a granular form (it looks like sand) and can be added to your soil mix when repotting the plant. For best results, prepare your plant by removing as much unnecessary foliage and roots as possible. Even better, remove all of the root ball and soil, leaving only the crown of the plant. Then wash the plant, using a mild dish detergent and room-temperature water. Fill a pot with soil and sprinkle the granular Marathon over the surface. As a precaution, wear protective gloves (and mask) while doing this. Next, moisten the soil, press the crown into it, and firm soil around it. Place in a clear container (like a large baggie), seal, then wait 4-6 weeks until rooted. Until you’re certain the plant shows no signs of mealies, keep it separated from your other plants. You might also want to start again from a leaf cutting, taking the same precautions.
Should you want to avoid using chemicals entirely, wash the crown in mild soap and room-temperature water, and reroot as described above. Though not foolproof, if you’ve done a thorough job of washing, you may be lucky enough to have eliminated your this way.
A dense colony of mealybugs.
Mealybugs are common pests of houseplants. They are pink, soft-bodied insects covered with a white, waxy, cottony material. The white “fluff” helps protect them from excessive heat and moisture loss. Unlike their relatives the scales, most species retain their legs throughout their life and can move around. Females are rounded, wingless, and about 1/16″ long.
The citrus mealybug (Planococcus citri) is the most common species found on plant foliage. It feeds on a wide variety of plants, and especially likes soft-stemmed and succulent plants such as coleus, fuchsia, croton, jade, poinsettia and cactus. In my greenhouse I also find them consistently on rosemary, citrus, and bird of paradise. Other mealybug species such as longtailed mealybug (P. longispinus) or cactus mealybug (Hypogeococcus festerianus) occasionally occur on specific host plants. These species remove plants sap from aboveground plant parts, especially stem tips, leaf junctures and new growth.
Citrus mealybug, the most common species of mealybug found on houseplants.
Their feeding weakens and stunts plants, and causes foliar yellowing, defoliation, wilting and general plant decline. In some cases, plants can be killed. Citrus mealybugs inject a toxin while feeding that causes plant malformation. Mealybugs also excrete honeydew, which allows for the growth of sooty mold.
Some mealybugs are root-feeders. The ground mealybug (Rhizoecus falcifer) is the most common soil mealybug, occurring on the roots of many house plants, especially African violets. Feeding on the root hairs results in yellowed leaves, wilting, stunting and bloom reduction. A few mealybug species will move to roots when growing conditions are less favorable, but return to stems and leaves when plants are actively growing.
A female mealybug and her cottony egg mass.
Female citrus mealybugs lay up to 600 small (1/100 inch or 0.3 mm long), yellow eggs within a protective mass of white, cottony threads. The longtailed mealybug does not lay eggs but produces live young, similar to aphids. After depositing the egg mass or live young over a period of 5–10 days, the female mealybug dies. The immatures search for feeding sites on which to settle. Male nymphs settle and spin an elongated, white waxy cocoon. Females have three instars and are mobile throughout their lives.
Citrus mealybug egg mass with newly hatched nymphs.
The best method for detecting infestations of mealybugs on leaves and stems is visual inspection – just looking at the plants. Both the insects themselves and the eggs in their masses of waxy threads may look like white cotton on the plant. On some plants mealybugs concentrate on the growing tips, and on other plants they are more dispersed. The longtailed mealybug frequently conceals itself in leaf whorls.
Underground infestations are more difficult to detect. Yellowed or wilting foliage may indicate the presence of mealybugs on the roots. Small white cottony masses around the drainage holes of pots also indicate the presence of mealybugs, but in many cases infestations can be confirmed only by removing the root-ball from the pot to observe mealybugs on the roots.
Mealybugs on a hibiscus flower bud.
Mealybugs are difficult to get rid of because immatures typically wedge themselves in stem crotches, leaf folds, or other tight locations where washing or pesticides cannot reach them. The best way to control mealybugs on houseplants is to prevent them from being established in the first place. Carefully inspect all new houseplants before introducing them to your home, and keep them separate from other plants for a week or so if possible. Mealybugs can easily crawl from one plant to another, especially when leaves or branches overlap, so one contaminated plant could spread mealybugs to all your houseplants. Check under leaves, in new leaf folds, and around the growing tips for signs of infestation. Mealybugs like lush foliage, so avoid over-fertilizing with excess nitrogen.
A citrus mealybug nymph crawls along a leaf.
If mealybugs are present on only a few, small plants, you can try to reduce or eliminate infestations by washing off the plants. A moderately strong spray of warm water will dislodge most of the mealybugs. Alternatively, you can try wiping the insects and egg masses off the plants with a cotton swab or cloth dipped in rubbing alcohol. This is most effective on large-leaved plants (but test first on a small area to make sure the alcohol won’t damage the plant; it may take a day or two for symptoms to show). Washing rarely eliminates all the pests, so it is important to check the plants periodically and wash again or use other controls when more are noticed.
A mealybug crawls on a red coleus plant.
It may be helpful to prune out heavily infested plant parts when such pruning won’t damage the appearance of the plant. Dispose of plant cuttings immediately, since mealybugs can survive on detached plant parts for as long as those parts have moisture. Consider discarding a heavily infested plant and replacing it with a new, pest-free plant as one way to deal with a severe mealybug problem. Root infestations are particularly difficult to control, so this is often the most practical way of eliminating root mealybugs.
Chemical controls can be used to treat mealybugs. Less toxic alternatives such as insecticidal soap or horticultural oils can be effective, but must be applied to the hard-to-reach places the mealybugs inhabit to kill the insects. These may require several applications to achieve control. There are several registered insecticides available at garden centers that will control mealybugs. Read the label carefully to make sure the material is effective for mealybugs and for instructions on how to apply the pesticide.
A citrus mealybug.
A number of natural enemies, including several parasitic wasps and predators, are known to attack mealybugs. Some are used for control of mealybugs in commercial greenhouses, but most are not appropriate for use in the typical home. The mealybug destroyer, Cryptolaemus montrouzieri, is a small lady beetle that is a very effective predator, especially when mealybug numbers are high and many egg masses are present. It can be purchased commercially and should be released at the rate of 2-8 adults per plant. However, it will take some time for the beetles to reduce mealybug populations and may not eliminate it entirely.
– Susan Mahr, University of Wisconsin – Madison