African violet crown rot

African Violets for Everyone

The leaf you grow from should be fresh and healthy. It is a common mistake to try to grow a new violet from an old outside leaf from the mother plant. Un­fortunately such leaves, although the plants can most easily spare them, are often too old to have babies. If they are really old they may root but never put up a plantlet at all. It is also best not to use the leaves from near the centre of the mother plant. They would grow well, but their removal will mar the original plant. Maximise your chances of success by choosing a leaf that is neither the oldest nor the youngest on the plant. For a variegated leaf African violet choose a leaf showing a lot of green.
Prepare the leaf by checking that it is healthy and clean, cut the stem to a length of 10-20 mm, cutting at an angle so that the cut edge, from which all roots and plantlets will come, is maximised. If the leaf is wilted or soft, recut and submerge in water for an hour or so to make it crisp again.
Plant your leaf in good quality African violet potting mix. Only place the cut end about 10 mm under the surface of the mix. You may need to support the leaf with a plant label or similar. If too large cut of the top. While a leaf will root successfully in water, it will later have to be moved to potting mix, or any plantlets it does produce will be weak and possibly lack the strength to grow on to satisfactory mature plants.
Occasionally new growers may find that leaves rot when grown in potting mix. If you find this a problem, dilute the mix with extra perlite and vermiculite, or try a mix of those two ingredients alone.Hormone rooting powders and solu­tions are unnecessary as African violets produce roots and shoots with ease.
Only use a small pot for your leaf. A 60 to 70 mm pot is plenty big enough. To propagate miniatures, use the smallest size. Leaves under propagation need water, and light just like full grown plants so place accordingly and set up with a wick if that is how you intend to water. Don’t fertilise for the first couple of weeks, until you believe the leaf has produced roots. You can determine that by lightly tugging to see if there is any resistance. After that fertilise, ei­ther with the standard African violet fertiliser, or with a higher nitrogen fer­tiliser to promote more rapid growth.
Don’t try to propagate in the coldest months of the year, unless your grow­ing area is really warm. This particularly applies to variegated leafed African violets. If their leaves are planted in late autumn or during winter, they may produce plantlets that are all white. Of course, if you are given a leaf of a cultivar that you would really like to grow, you will accept and plant it, no matter what the season. Growing the leaf in terrarium-like conditions (even if that just means covered with a plastic bag) may help to keep it from suffering from the cold weather.
If the worst happens, and you start spring with a pot full of little white plantlets that simply won’t colour up, repot the lot, including the mother leaf, into a larger pot, removing a little of the old potting mix when you do so. This will encourage new growth in the clump of plantlets and that growth will be greener in the warmer season.

African Violet (Saintpaulia spp.)-Root and Crown Rot

See:

Greenhouse Plants, Ornamental-Pythium Seed Rot, Damping-off, and Root Rot

Cause Pythium ultimum, a fungus-like organism that is a common soilborne pathogen. The disease can be severe in overwatered soils or media with poor drainage. It survives unfavorable periods in soil and infected plant debris. Under favorable conditions, such as cooler soil-media temperatures, spores germinate and infect roots. Crowns and leaves or petioles in contact with the media can also be invaded. Leaf cuttings are also susceptible. After infection, the fungus-like microorganism spreads mainly in the inner tissues of the root and stems. A thick-walled survival structure, oospore, are produced that can persist for several years. Movement of infected plants and/or soil can spread this fungus-like microorganism. African violets are more susceptible when grown in high intensity light for prolonged periods or when infested with root knot nematodes. Most cultivars are susceptible.

Symptoms Plants suddenly wilt and die. Sometimes only the lower leaves and petioles become necrotic and dry. Plants are easily separated from the pot and media when the crown has decayed. Roots and root crowns become brown, soft, and mushy.

Cultural control

  • Sterilize rooting media and potting soil before planting. Also disinfect any tools and equipment that might be used and contaminate the media.
  • Avoid overwatering but keep soil evenly moist by sub-irrigating. Let plant get dry between waterings when not flowering.
  • Destroy diseased plants.
  • Fertilize only when plant is beginning to flower.
  • Avoid reusing pots or trays from a previous crop for propagation. If pots must be reused then wash off all debris and soak in a sanitizing solution or treat with aerated steam for 30 min.

Chemical control Soil drenches are useful before disease develops. Best used in conjunction with cultural control methods. Rotate fungicides from different groups that have a different mode of action for resistance management.

  • Banol at 2 to 3 fl oz/10 gal water. Group 28 fungicide. 24-hr reentry.
  • Banrot 40 WP at 6 to 12 oz/100 gal water. Group 1 + 14 fungicide. 12-hr reentry.
  • Mefenoxam 2 AQ at 0.49 to 0.98 fl oz/100 gal water as a soil drench. See label for media incorporation. Group 4 fungicide. 48-hr reentry.
  • MetaStar 2E at 0.5 to 2 fl oz/100 gal water. Group 4 fungicide. 48-hr reentry.
  • Proplant at 2 to 3 fl oz/10 gal water. Group 28 fungicide. 12-hr reentry.
  • Subdue MAXX at 0.5 to 1 oz/100 gal water. Group 4 fungicide. 48-hr reentry.
  • Terrazole 35 WP at 3.5 to 10 oz/100 gal water. Group 14 fungicide. 12-hr reentry.
  • Truban 30 WP at 3 to 10 oz/100 gal water. Group 14 fungicide. 12-hr reentry.

Biological control

  • Prestop (Gliocladium catenulatum strain J1446) at 1.4 to 3.5 oz/2.5 gal water as a drench. Do not use with other products in the tank. 0-hr reentry. O

Reference Thompson, H.S. 1958. Pythium rot of Sainpaulia, the African violet. Canadian Journal of Botany 36:843-863.

Root and Crown Rot of African Violets

Root and crown rot of violets, and most other plants, can occur if their roots are kept too wet. Disease fungi may or may not be present for rot to occur. Leaves of plants with rotted roots and crowns usually turn yellow, mushy, and fall off. It’s normal for old leaves to have this same sequence of events, but they will be more numerous on plants with a rot problem.

Because the first symptom of root and crown rot is droopy leaves, a natural reaction is to water the plant more because it seems to be wilted from lack of water. But watering can be a big mistake. When a plant’s root system is constantly saturated with water, the roots can lose the ability to absorb water and oxygen. Under these wet conditions the roots and/or crowns tend to decay.

There are several ways to avoid creating rot conditions. Be sure the potting mix isn’t too heavy. Also, the mix should be free from disease organisms. Perlite added to the mix can help prevent oversaturation. Water the plant when the soil feels dry to the touch, but be careful not to allow the soil to dry out completely. The pot should have good drainage and shouldn’t sit in water. Prevention is the easiest and most successful “cure.”

This article originally appeared in the February 7, 2003 issue, p. 7.

African Violet (Staintpaulia)

Saintpaulia ionantha

Crown Rot (fungi – Pythium spp., Phytophthora spp., Fusarium spp.): Crown rot is probably the most serious disease of African violets and may cause loss of entire groups of plants. Older leaves droop and younger leaves showing stunting. Roots are killed rapidly and appear brown. Unless treatment is administered before massive root death, the plant will have to grow an entirely new root system before recovery occurs. Two alternatives are available for infected plants: One is to discard all affected and exposed plants and the other is to use fungicide drenches. Drenches should be administered when the first evidence of disease occurs. Caution should be used in getting the right dosage levels since excessive levels of some chemicals may damage plants. Preventive measures include using sterilized soil and avoiding plant introductions that may harbor crown rot organisms.

Botrytis Blight (fungus – Botrytis cinerea): Leaves, flowers and petioles develop small water-soaked spots that enlarge rapidly. A grayish fungal growth may be seen upon close examination of diseased tissue. The disease is more severe when atmospheric conditions are cool and damp, poor air circulation exists and when light intensity is low. All disease tissue should be removed as this serves as a source for new spores. Surface sterilize the area surrounding the plants with a household cleaner or bleach.

Powdery Mildew (fungus – Oidium spp.): A white powdery type substance may be observed on leaves, petioles, petals or flower stems. It is more easily seen on dark blossoms than white ones even though the white varieties may be slightly more susceptible. Spores of the fungus are air-borne from one plant to another. Control with fungicides is very effective. If the systemic fungicide is used, one may have to spray blossoms since the fungicide is not translocated to floral parts when the pot drench method is employed.

Petiole Rot (Physiogenic): An orange to brown, rust colored spot appears where the petiole touches the pot. The petiole and leaf may collapse. This damage results from salt accumulation on the rim of the pot and the soil surface. Use rain water or another salt-free source of water and avoid over fertilization. Construct a collar from aluminum foil to be fitted around the rim of the pot.

Ring Spot (Physiogenic): Light brown rings form on leaves with some running together to form irregularly shaped spots. This condition is caused by cold water coming in contact with the leaves. In some cases, damage may occur even if warm water is used. Such a possibility exists when a breeze blows across the wet area and produces an evaporative effect. Water should be kept off leaves.

Root Knot (nematode – Meloidogyne spp.): Galls form on roots of plants causing the root system to be inefficient in absorbing and translocating water and nutrients. This condition can be prevented by using nematode free propagating stock and a sterilized potting medium. The nematode may also be transmitted by petiole cuttings from infected plants. Do not use infected plants for propagation.

Crown Gall (bacterium – Agrobacterium tumefaciens): Fleshy galls form around the base of the plant with a profusion of leaves being produced at that point. Natural infection seems to be slight but infected tissue is perpetuated by some who sell this unusual looking plant under the name of “Witchcraft”. Infected plants should be discarded.

Viruses (virus – several): Infected plants have distorted leaves that are mottled in color. Infected plants are not killed but should be discarded because they may serve as a possible source of infection for other plants.

Growing African Violets

Circular 660 View PDF picture_as_pdf Proper culture and a desire for house plants are the keys to a well grown African violet like this.

Prepared by Paul A. Thomas, Extension Horticulturist-Floriculture

  • Classification and Varieties
  • Conditions for Culture
  • Common Insects and Problems of African Violets

Once found only in the coastal woods of east Africa, African violets (Saintpaulia ionantha) are now among the most popular indoor plants. They are easy to grow and offer a wealth of beautiful flowers. For the indoor gardener with limited space, African violets have an added attraction — with sound cultural practices, they can be grown quite successfully on window sills.

Classification and Varieties

African violets are available in a wide range of colors and types. You may choose from several hundred varieties depending upon the flower color, form and plant characteristics you prefer.

Flower color varies from blue to violet, lavender, pink, red-violet, blue-violet, lavender-pink and white. Flowers may be single, double, semi-double, star-shaped, fringed or ruffled. Some varieties produce flowers with two or more rows of petals on one color with the rest fringed in a different color. Leaf types are described as plain, quilted, spidered, ruffled, fringed, scalloped, spooned, pointed and variegated.

Several hundres varieties of African violet exist.

Conditions for Culture

Light

African violets grow well, stay healthy and produce abundant flowers when they get the right amount of light.

Intensities of 1,000 foot-candles of light for 6 to 8 hours per day give good results. This compares to the light intensity of a sunny, east or west window or a bank of four fluorescent shop lights. Violets also will tolerant low light levels (200 to 500 foot-candles).

South or west windows offer the best light in winter. During warmer seasons, windows with east or north exposures are best.

Insufficient light is probably the most common reason for failure of African violets to flower. If violets are growing in too little light, the leaves become darker green and thin, petioles or leaf stems are very long and weak, and the plants flower very little if at all.

Violets exposed to too much sunlight will have pale yellow-green leaves. Bleached-out, burned or dead areas also may be present. A little study and testing may be needed to determine if the light intensity or duration is sufficient in your home. Where plants must be grown in windows with bright light, you may need to use a very sheer curtain to diffuse and reduce the light reaching the plants. In an excessively high light intensity, plants can be scorched or at best will be quite compact because of short stems and slower growth.

African violets can be easily grown using artificial light. An intensity of approximately 600 foot-candles for 14 to 16 hours per day is recommended. Inexpensive timers are available to automatically turn lights on and off.

Fluorescent lights are most frequently used and can be arranged in tiers or attached to shelves for a convenient and attractive light source. The tubes should be 12 to 15 inches above the tops of the plants. A shelf containing two or more 20- to 40-watt tubes will grow numerous plants. Several companies manufacture fluorescent tubes specifically designed for plant growth. The light emitted contains more usable radiant energy. In most cases, however, indoor gardeners enjoy success with less expensive “Cool White” tubes. One or two incandescent bulbs may be used with the fluorescent tubes.

Standard incandescent bulbs alone are not recommended as a light source because of their poor light spectrum and the heat they produce. Specially designed incandescent spotlights are available for plants in 75 and 150 watts. They provide useful levels of light energy when located about 12 to 18 inches away from the plants.

Healthy violets require proper temperature, light and humidity.

Temperature

The most attractive violets are grown at a nighttime temperature of 65° to 70°F and a daytime temperature of 70° to 90°F. Plants grown at temperatures below 60°F will be deformed. The leaves may curl down, cup and become brittle. Flowers may be deformed and discolored. Also foliage maybe a light green at cooler temperatures, especially when grown under correct light conditions. Plants growing in drafts or touching glass window panes may have injured foliage.

For best results, avoid placing the plants where temperatures are above 90°F or below 60°F.

Humidity

Humidity, or the amount of water vapor suspended in air, is important to good violet growth. Even though violets grow and flower in humidity ranges of average homes. The most successful plants are grown in a higher humidity. Devices are available that increase the humidity in the home and benefit both plants and people.

Where a few plants are concerned, humidity may be increased by setting the pots in watertight metal or plastic trays filled with water and gravel or pebbles. Maintain a shallow level of water in the tray. Do not allow the pots to sit in water; set them on pebbles or on inverted shallow pot saucers.

Misting is not recommended.

A recent trend for easier control of humidity is to plant violets in large glass goblets, aquariums or terrariums.

Soil Moisture

Soil moisture and proper watering are critical to your success in growing African violets. Plants can die from too much or too little water. How often to water and how much vary depending on the soil, pot and plant sizes, and environmental conditions. For this reason, you’ll have to learn the moisture requirements of your plants and develop an individual watering schedule.

Moisture meters and devices are available which measure soil moisture. While some of these are fairly reliable, an easier (and less expensive) method is to simply touch the soil surface with your finger tips. Allow the soil to become slightly dry between waterings, but don’t allow it to become excessively dry as wilting can cause root damage.

Apply water until it drains out the bottom of the pot. Pour off the excess after 20 to 30 minutes.

Cold water (55°F or below) splashed on the leaves causes light green, discolored areas called ring spot. If the temperature difference between the leaves and water is as little as 10°F, damage can occur. But damage can be prevented if the water is brought to room temperature.

Many violet growers prefer to water from the bottom rather than the top of the pot. This works well, but it doesn’t leach salts that can accumulate in the soil. All plants should be watered occasionally from the top with warm water to remove dust and to wash out salts.

Plants in containers without drainage holes are much more subject to overwatering problems such as root rot or stem rot.

Plants in high light and low humidity require more frequent watering than those in low light and high humidity. A coarse, well-drained soil mixture requires more frequent watering than a heavy, poorly drained soil mixture.

Maintaining the correct soil moisture becomes more of a problem as plants outgrow their pots. Crowded plants should be repotted into the next larger size pot.

Soils

African violets grow in a very wide range of soils and soil mixtures. Gardeners get the best results with well drained, well aerated soil that contains a high percentage of humus or organic matter. Generally, a mixture of 1 part leaf mold, 1 part peat moss, 1 part sand and 2 parts loamy top soil gives good results.

Artificial mixes such as peat-vermiculite and peat-perlite are excellent for growing violets. They are relatively clean and will be free of most insects and diseases. A mixture may consist of equal parts of soil, peat moss and horticultural perlite. Vermiculite may be substituted for perlite.

Some violet growers prefer the artificial mixtures because they are consistent in quality, while sand and soil can vary. Violets grow best in a sterilized potting soil or commercial African violet soil mixture.

Potting

When potting, remember that violet leaves, stems and root systems are very tender and easily broken.

Older plants usually have more than one crown. After you have gently removed the plant from the pot, divide the crowns by cutting through the root ball with a sharp knife. Be careful not to destroy all the roots or to shake all the soil from the root systems.

When repotting, partially fill the pot with soil. Set the plant so the crown is slightly above the soil level (approximately ¼ to ½ inch below the rim of the pot.) Gently firm the soil around the old root ball.

Remember plants do better in pots with drainage holes. A thin layer of gravel, pieces of stockings, or pieces of broken pots should be used to prevent soil from washing through the holes.

Fertilization

Violets, like most plants, respond well to regular doses of fertilizer. Most violet hobbyists prefer to use liquid or water-soluble fertilizers such as 20-20-20 every four to six weeks. Dry fertilizers and slow-release or encapsulated fertilizers can also be used. With a dry fertilizer, be sure the soil is moist before you use it.

Regardless of which kind of fertilizer you use, read and follow the manufacturer’s recommendations.

Plants in less than ideal conditions or in non-active stages of growth may require less fertilizer. African violets are very sensitive to a build-up of soluble salt which can damage plant roots. Many indoor gardeners get the best results using one-third to one-half the recommended amount of fertilizer; however, too little fertilizer may cause a slow-down in growth and/other deficiency symptoms. Note, too, that excess fertilizer can result in symptoms that sometimes mimic deficiencies. A soil test will be your best guide in figuring out the problem.

Violets can be propagated through leaf cuttings.

Propagation

African violets are easily propagated by division (see Potting). You also can get more violets with leaf-petiole cuttings; however, this takes longer to produce a flowering plant. African violets can be grown from seed, but only a few varieties will come true. A flowering plant can be produced from a leaf cutting or a seed in about 10 months under good growing conditions.

The most trouble-free method of propagating violets is to make a greenhouse with two 8 x 12-inch clear plastic storage boxes. Fill the bottom of one box with 4 inches of potting soil. Moisten the soil and then stick overlapping violet leaves about ½ inch into the soil. Place the clear plastic bottom of the other storage box on top and tape the sides. Place the sealed box in an east or south window. Young violet plants will appear in 8 to 10 weeks and be ready for transplanting in three months.

When potting newly rooted cuttings, it is wise not to add fertilizer. However, when dividing or shifting large plants to larger pots, you may want to use ¼ to 1/3 teaspoon of a complete African violet fertilizer for each 5-inch pot volume of soil mixture. Thoroughly mix the fertilizer into the soil to prevent root injury. A slightly acid soil mixture (pH 6.0 to 6.5) will give best results.

Common Insects and Problems of African Violets

Aphids Insect, usually green or black, 1/8″ long, called plant lice. Injure plants by sucking the plant sap. Check with your county Extension agent for the latest and safest recommendations on chemicals.*
Cyclamen Mites Extremely small insects, not visible with magnification. Insects feed on growing tip of plants. Corky layers develop over injury causing puckering, twisting and distortion of leaves in center of plant. Leaves may be excessively hairy, stunted and hard. Severe infections cause a mass of tiny, hairy and distorted leaves in center of plant. See above.
Red Spiders Injure by puncturing and sucking sap. In large numbers, develop a web over leaves, flowers, etc. Plants appear stunted. Insects small, reddish in color and visible with naked eye. If in doubt shake leaf on white piece of paper. Insects visible crawling. See above.
Mealy Bugs White cottony mass of eggs and insects in crown of plant. As population increases, insects distribute themselves on stem and underside of leaves. Insects feed by piercing and sucking sap. Insects about ¼” in length with a waxy coating. See above.
Botrytis Blight A disease infecting flowers, leaves, petioles. Causes decay, flowers develop water-soaked appearance. Affected plant parts become covered with gray mold. Improve air movement, reduce humidity. See above.
Root and Crown Rot Attacks stems, leaves and petioles in contact with soil. May cause complete wilting of plant if entire stem is attacked. Individual leaves wilt if infected. Use sterilized well-drained soil. Use clean plants. Discard badly diseased plants. See above.
* Specific chemicals are omitted from this publication because of frequent changes in pesticide development and regulation.

Mealy bugs feed on plant stems and leaves.This plant shows typical symptoms of cyclamen mites.

Status and Revision History
Published on Feb 24, 2009
Published with Full Review on Feb 14, 2012
Published with Full Review on Feb 01, 2016

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