African Violet Production Guide
Return to: MREC Home Page
AFRICAN VIOLET
CFREC-A Foliage Plant Research Note RH-91-1
This publication is a revision of AREC-A Foliage Plant Research
Note RH-85-D.
R.T. Poole, L.S. Osborne, and A.R. Chase
Professor, Environmental Horticulture, Professor, Entomology,
and Professor, Plant Pathology, respectively.
University of Florida, IFAS
Central Florida Research and Education Center - Apopka,
2807 Binion Rd., Apopka, FL 32703-8504.
Reference to University of Florida/IFAS Pest
Control Guides
Although Saintpaulia ionantha (African violet) is not
considered a foliage plant, it is grown under environmental
conditions that are very similar to those used to grow foliage
plants. African violets are hairy herbs from the Gesneriaceae
plant family discovered in Tanga, East Africa, growing at
elevations of 100 feet or higher. Leaves usually grow in a
rosette pattern. The green leaf blades are nearly orbicular to
ovate, grow to 2 1/2 inches long, with long and short appressed
hairs intermixed on the upper surface. Lower leaf surfaces are
paler green or light purple. Flowers are borne 8 to 10 on
peduncles rising above the upper leaf surface. Flowers can be
single, semi-double or double in regard to number of petals.
African violets have always been very popular with consumers
and today are still near the top of the list when number of
flowering plants sold yearly is considered. Thousands of
varieties of African violets exist and new hybrids are being
developed constantly throughout the world. In recent years,
commercial hybridizers have strived to produce new cultivars that
produce a massive flowering display at time of sale. On the other
hand, hobbyist breed for plant size and form, flower color and
shape, frequency of bloom and light tolerance.
African violets available in central Florida include standard
size and miniature cultivars. Standard size plants can be
purchased as liners in cavity trays or as finished plants in 3,
4, 6 or 8 inch containers. Miniature African violets are sold in
1 or 2 1/2 inch pots. African violets are considered to be the
most popular flowering indoor plant, but sales are well below
those of throw-away flowering pot plants such as Chrysanthemum
and Poinsettia.
PRODUCTION
Light intensity strongly influences appearance of African
violets and is very important in production of quality plants.
Listing a specific light level for African violets is difficult
because of variation between cultivars, but a range of 1000 to
1200 ft-c is satisfactory for most cultivars. Cultivars that
produce dark green leaves with long petioles may require higher
light levels, especially if few flowers are produced, while
plants with light green foliage may require lower levels.
Good overall growth can be obtained with a fertilizer regime
that provides a 3-1-2 ratio of N-P2O5-K2O at a level that
provides about 1200 lbs N/A/yr, 2 lbs N/1000 square ft-month or 3
lbs/yard or 4 grams/6" pot 19-6-12 every 3 months. Both
liquid and slow-release fertilizer sources are acceptable
provided the proper rate is supplied during the growing period.
Micro-nutrients should be added to the potting medium during
preparation or included with the fertilizer program.
African violets are well suited to production in artificial
potting media composed primarily of peat moss mixed with
vermiculite, pine bark, perlite or styrofoam beads. Care must be
taken, however, to be sure plants receive sufficient water, since
drying out will suppress growth and flowering. Soil pH should be
in the range of 5.5 to 6.5 and soluble salts levels below 500 ppm
at initiation of growth. The best way to irrigate African violets
is by use of capillary mats, since this keeps foliage dry and
prevents leaf spotting. Use of a perforated black overlay product
is recommended to obtain desirable leaf shape. Plants grow and
flower best at high relative humidity. Suggested air temperatures
for growing African violets are between 70 and 85°F. Lower
temperatures reduce growth rate as do temperatures above 85°F.
Care must be exercised in selecting cultivars to grow in Florida,
since some are heat sensitive and will not produce marketable
plants in summer, even if maximum temperatures of 85°F or below
are maintained. Atmospheric mercury did not affect blooming of
violets.
PHYSIOLOGICAL PROBLEMS
1) Chlorosis
- Symptoms -
- Leaves are light green or medium green with chlorotic
edges.
- Control -
- Increase fertilizer level or decrease light intensity if
blooming is satisfactory. Also, check to be sure
micronutrients were included in the potting medium or are
included in the fertilizer program. Sometimes different
cultivars grown side by side will have one with superb
quality and another with off color because of different
nutritional or light requirements.
2) Leaf spotting
- Symptoms
- - Primarily circular shaped spots which are light yellow
or green appear on the upper surface of leaves. Spots can
appear on margins or blades and are sometimes irregular
or donut-shaped and white.
- Control -
- Water that is colder than the leaf surface will cause
spotting and is most common in Florida during winter.
Deep well water is usually near 70°F and rarely causes
problems, except when it is stored outdoors in tanks. Be
sure temperatures of overhead water applications are near
leaf surface temperatures.
3) Long petioles
- Symptoms -
- Leaves appear on extended petioles which give the plant
an undesirable shape.
- Control
- - Long petioles are usually caused by low light, medium
high fertilizer rate and optimum irrigation level. The
easiest way to control this problem is to lower the
fertilizer level. In some cases, selection of cultivars
that do not have the tendency to produce stretched
petioles should be considered.
4) Flowering problems
- Symptoms -
- Plants may not produce flowers, or may produce only a
few, or flowers produced may not open properly.
- Control -
- Plants produced under low light may not bloom profusely,
and therefore at least 1000 ft-c is required. Excessive
light will cause plant yellowing, dwarfed plants and will
also reduce flowering. In summer, excessive production
temperatures may cause flowers to abort or open
improperly. The only control for this problem is to
reduce greenhouse temperatures or select different
cultivars.
BACTERIAL PROBLEM
Reference Pest Control Guides Here
1) Bacterial blight (Erwinia chrysanthemi)
- Symptoms -
- Erwinia chrysanthemi can infect all tissues of
African violet. Root infection is characterized by a
rotted, water-soaked root system. A crown rot is also
found sometimes. Infected petioles and leaves are greasy
brown to black. Wilting and complete collapse of plants
are symptoms of advanced disease.
- Control -
- Although there is a wide range of susceptibility levels
to bacterial blight in African violet cultivars, most are
moderately susceptible. Since bacterial diseases are so
difficult to control with the bactericides currently
available, avoiding the disease is very important.
Minimize irrigations to reduce water splashing of
bacteria and discard all plant materials which are
suspected of bacterial infections. This pathogen infects
a wide range of other foliage plants.
FUNGAL PROBLEMS
Reference Pest Control Guides Here
1) Botrytis blight (Botrytis cinerea)
- Symptoms -
- Lesions usually appear on the leaf underside, especially
on petioles near the pot rim or in contact with the
potting medium. A small, water-soaked lesion can rapidly
enlarge and extend into the blade or petiole causing its
collapse. Sporulation on necrotic leaf or flower tissue
is characterized by a powdery grayish-green mass of
conidia.
- Control -
- Avoid the following conditions - low light, high
humidity, poor air circulation and warm days with cool
nights.
2) Phytophthora stem and root rot (Phytophthora
parasitica)
- Symptoms -
- Phytophthora stem and root rot appears very similar to
bacterial blight caused by E. chrysanthemi. Mixed
infections with the two pathogens sometimes occur.
Culture of the pathogen is necessary prior to developing
a control program for either disease.
- Control -
- Avoid overwatering since water-logged roots are easily
attacked by P. parasitica. As with all diseases
caused by soil-borne pathogens, use pathogen-free pots,
potting media and plant material.
3) Powdery mildew (Oidium
sp.)
- Symptoms -
- Lesions appear on flowers, petioles and leaves. A powdery
white coating can form up to 1/2 inch circular areas as
single lesions or can coalesce to cover the entire leaf.
- Control -
- The disease apparently does not cause serious losses in
Florida since many growers do not apply fungicides during
an outbreak.
NEMATODE PROBLEM
Reference Pest Control Guides Here
1) Foliar nematode - (Aphelenchoides ritzemabosi)
- Symptoms -
- Small, tan, interveinal sunken areas appear on lower leaf
surfaces. These lesions eventually are visible on the
upper leaf surface as well. Lower leaf surfaces become
shiny, brown and slightly cupped. Severe reduction of
leaf size as well as distortion also are common.
INSECT AND RELATED PROBLEMS
Reference Pest Control Guides Here
The major arthropod pests of this plant species
include aphids, moths (worms), fungus gnats, mealybugs,
mites, scales, and thrips. Mealybug, mite, and scale
infestations are typically the result of bringing
infested plant material into the greenhouse. Aphids,
moths, fungus gnats and thrips have the ability to fly
and thus invade the greenhouse from weeds and other
infested plants outside. In the control section for each
pest, a few of the many registered and effective
pesticides will be listed. For a complete listing please
consult the references at the end of this report.
1) Aphids
- Symptoms -
- Aphids are pear-shaped, soft-bodied insects which vary in
color from light green to dark brown. Infestations may go
undetected until honeydew or sooty mold is observed.
Aphids can cause distortion of new growth or, in extreme
cases, infested plants can be stunted.
- Control -
- Aphids are relatively easy to control with many
registered materials.
2) Caterpillars (worms)
- Symptoms -
- Infestations are easy to detect because worms, their
excrement and the damage they cause, are usually quite
visible to the unaided eye. Damage appears as holes in
the center or along the edges of leaves. Damage by worms
is often confused with slug or snail damage. The only way
to determine which pest is involved is to find a
specimen. Old damage can be distinguished from new by the
calloused appearance of the older damaged areas (worms
are usually gone by this time).
3) Fungus Gnats
- Symptoms -
- Fungus gnats are small black flies (1/8 inch long) and
are frequently observed running around the soil surface
or on leaves and often confused for Shore flies (see
later section). The adults have long bead-like antennae
and their legs hang down as they fly. These insects are
very weak fliers and appear to "flit" around
randomly. The larvae are small legless "worms"
with black heads and clear bodies that inhabit the soil.
The larvae spin webs on the soil surface which resemble
spider webs. Damage is caused by larvae feeding on roots,
root hairs, leaves in contact with the soil and lower
stem tissues. Feeding damage may predispose plants to
disease and they are often found in close association
with diseased plants or cuttings (See Shore flies).
Adults do not cause any direct damage, but are
responsible for many consumer complaints to growers.
Adults emerge and fly around in retail shops, homes, or
offices and are therefore a nuisance. For further
information please consult Extension Entomology Report#74
(Management of fungus gnats in greenhouse ornamentals).
- Control -
- Reduce the amount of water applied to each pot where
possible. Avoid algae growth on walkways, benches, and
cooling pads. Nematodes that seek out insects in the soil
are sold commercially and have been shown to control
these pests without causing any negative effects to the
host plants. Adults are very sensitive to most chemicals.
4) Mealybugs
- Symptoms -
- Mealybugs appear as white, cottony masses in leaf axils,
on the lower surfaces of leaves and on the roots.
Honeydew and sooty mold are often present and infested
plants become stunted, and with severe infestations,
plant parts begin to die.
- Control -
- Control of root mealybugs is accomplished with soil
drenches with an insecticide, but can cause some
phytotoxicity. When pesticides are applied to the soil,
care must be taken to assure that the pots have good
drainage and that no saucers are attached, or
phytotoxicity may result.
5) Mites (Broad mite and
false spider mites)
- Symptoms -
- Mites are very small and go unnoticed until plants become
severely damaged. Broad mites cause foliar necrosis of
the vegetative shoot apex. Initial symptoms of injury
show new leaves cupped downward, puckered, stunted and
have serrated margins. Broad mite eggs are covered with
many tubercles which give them the appearance of being
jeweled. False spider mites (Brevipalpus spp.) are
red in color and sedentary. Eggs are bright red and
oval-shaped and are laid on both surfaces of leaves.
Initial infestations are indicated by faint brown,
scruffy flecks, later becoming bronze or reddish in
color. Basal leaf areas are affected, vegetative shoot
apexes may be killed, and severe leaf drop may occur.
- Control -
- The critical point in any control program is thorough
coverage with a pesticide. The best control program is to
minimize the possibility of introducing mites into the
growing area on infested plant material.
6) Scales
- Symptoms -
- Infested plants become weakened or stunted and begin to
die. Scales can be found feeding on leaves, petioles, or
stems. They are usually distinct from the plant material
on which they are feeding. Their shape (round to oval),
size (pinpoint to 2 mm long), and color (light to dark
brown) are quite variable and many scales are hard to
distinguish from the plant material on which they are
feeding.
- Control -
- See Mealybugs
7) Shore Flies
- Symptoms -
- Shore flies are small black flies (1/8 inch long) and are
frequently observed sitting on the tips of leaves or on
the soil surface feeding on algae. The adults have very
short antennae. These insects are very strong fliers and
exhibit very directed flight (straight between 2 points).
The larvae inhabit the soil and are small legless
"worms" with clear bodies and no obvious heads.
No known damage is caused by larvae. This insect is
believed to feed only on algae. Adults do not cause any
direct damage, but are responsible spreading disease
organisms, reducing value by defecating on the leaves
(small black to green spots) and for many consumer
complaints to growers. Adults emerge and fly around in
retail shops, homes, or offices and are therefore a
nuisance.
- Control -
- Reduce the amount of water applied to each pot where
possible. Avoid algae growth on walkways, benches, and
cooling pads on which they feed. Chemicals are not
believed to be very effective in the control of this
pest.
8) Slugs
- Symptoms -
- Slug and caterpillar damage are similar and determining
which pest is present can be difficult. Snails and slugs
are voracious feeders, with small stages feeding on
surface tissue and larger ones eating irregular holes in
foliage. Generally, the culprit can be found on close
examination of the plant. Slugs often live under benches
or in dark, moist protected places close to the damage.
These pests are nocturnal and can be found feeding at
night.
- Control -
- Sprays or baits applied to moistened soil around plants
are effective. Repetitive applications are necessary.
Good sanitation with removal of extraneous plant material
and debris which might shelter these pests aids in
control.
9) Thrips (Western flower thrips and Banded
greenhouse thrips)
- Symptoms -
- Thrips are small (less than 1/20 inch long), thin
insects. Adult thrips can be identified by a long fringe
of hair around the margins of both pairs of wings. Color
varies between species with western and other flower
thrips being yellow to light brown and banded greenhouse
thrips and a few other thrips that feed mainly on leaves
being dark brown to black. Feeding takes place with
rasping type mouth parts. Infested leaves become curled
or distorted, with silver-gray scars or calloused areas
where feeding has occurred. Thrips can transmit the
tomato spotted wilt virus to this plant. Any unusual
symptoms should be investigated.
- Control -
- Many materials are registered and effective at
controlling thrips.
This plant is sensitive to most insecticides depending on
environmental conditions. Avoid spraying plants that are stressed
or spraying when hot, sunny conditions exist. Use tepid water in
your spray tank.
Reference Pest Control Guides Here
Pesticides should be applied according to label
directions.
Regardless of the pesticide or mixture of
pesticides used, it is
strongly recommended that the effects be evaluated on a few
plants, under your particular conditions before treating all
plants.
Mention of a commercial or proprietary product
in this paper
does not constitute a recommendation by the authors,
nor does it imply registration under FIFRA as amended.
REFERENCES
1. Chase, A.R. 1990. Phytotoxicity of bactericides and
fungicides on some ornamentals. Nursery Digest 24(5):11.
2. Chase, A.R., T.J. Armstrong and L.S. Osborne. 1981. Why
should you test pesticides on your plants? ARC-Apopka Research
Report RH-81-6.
3. Conover, C.A. and R.T. Poole. 1990. Light and fertilizer
recommendations for production of acclimatized potted foliage
plants. CFREC-Apopka Research Report RH-90-1.
4. Gislerod, H.R., A.R. Selmer-Olsen and L.M. Mortensen. 1987.
The effect of humidity on nutrient uptake of some greenhouse
plants. Plant and Soil 102(2):193-196.
5. Mortensen, L.M. 1986. Effect of relative humidity on growth
and flowering of some greenhouse plants. Scientia Horticulturae
29:301-307.
6. Papenhagen, A. 1986. High humidity has a marginal effect on
plants. Gb + Gw 86(36):1343-1346.
7. Poole, R.T. and C.A. Conover. Response of foliage plants to
commercial interior paints. CFREC-Apopka Research Report
RH-86-15.
8. Poole, R.T., C.A. Conover and Y. Ozeri. 1986. Response of
African violets to fertilizer source and rate. HortScience
21(3):454-455.
9. Poole, R.T., C.A. Conover and K.G. Steinkamp. 1990. Effect
of fertilizer formulation on blooming potential of 21 cultivars
of African violets under interiorscape and greenhouse conditions.
CFREC-Apopka Research Report RH-90-8.
10. Price, J., D.E. Short and L.S. Osborne. 1989. Management
of fungus gnats in greenhouse ornamentals. Extension Entomology
Report #74.
11. Short, D.E., L.S. Osborne and R.W. Henley. 1984.
Phytotoxicity of insecticides and miticides to foliage and woody
ornamental plants. Extension Entomology Report #57.
12. Short, D.E., L.S. Osborne and R.W. Henley. 1989. 1989-90
Insect and related arthropod management guide for commercial
foliage plants in Florida. Extension Entomology Report #53.
13. Simone, G.W. and A.R. Chase. 1989. Disease control
pesticides for foliage production (Revision #4). Plant Protection
Pointer. Extension Plant Pathology Report #30. [also in Foliage
Digest 12(9):1-8]
14. Son, K.H. and D.Y. Yeam. 1987. Effect of light intensities
and temperature in various indoor situations on growth of some
foliage plants. J. Korean Soc. Hort. Sci. 28(2):173-184.
15. Vogelezang, J.V.M. 1988. Effect of root-zone heating on
growth, flowering and keeping quality of Saintpaulia.
Scientia Horticulturae 34(1/2):101-113.