African Violet Nematode Control: Treating Root Knot Nematodes In African Violet

By: Teo Spengler

Africanviolets may have come from South Africa, but since they arrived in thiscountry in the 1930s, they have become one of the most popular household plants.They are generally easy-care and long blooming, but look out for nematodes.

Nematodes of African violet are tiny worms that infest theroots. For information about African violetroot knot nematodes, read on.

African Violet with Root Knot Nematodes

You’re not likely to ever lay eyes on African violet rootknot nematodes even if your plant is crawling with them. That’s becausenematodes are so tiny that they are not visible to the naked eye. What’s more,nematodes of African violets dwell in the soil. They feed inside the roots,leaves and stems of the plants, places a gardener is not likely to look.

In addition, an African violet with root knot nematodesdoesn’t show symptoms right away, just a gradual slowing in growth. By the timeyou notice the problem, your houseplants can be severely infested.

The long-term symptoms of nematodes of African violetsdepend on the type of nematode involved. Two types are common. Foliar nematodeslive inside the leaves and cause browning on the foliage. However, theroot-knot nematodes in African violets is more destructive and also morecommon. These pests thrive and grow in moist, porous soil. Females penetratethe roots of the plant, feed on the cells and lay eggs there.

As the eggs hatch, the young nematodes that stay in theroots cause them to form gall-like swellings. The roots stop functioning andthe plant’s health declines. Yellowing leaves turning down at the edge aresure-fire symptoms of root knot nematodes in African violets.

African Violet Nematode Control

When you see your plant’s beautiful velvety leaves becomingdull yellow, your first thought will be to save it. But there is no cure for anAfrican violet with root knot nematodes. You cannot get rid of the nematodeswithout killing the plant. But you can exercise some African violet nematodecontrol by preventing the problem, keeping nematodes out of your soil.

First, realize that African violet root knot nematodes caneasily move from soil to plant and from plant to plant. So you’ll want to isolateany new plants for a month or so until you are certain they are free of thepest. Destroy infected plants immediately, taking care with the infected soiland all water draining from it.

You can also kill nematodes in soil by using of VC-13 orNemagon. Repeat this procedure frequently, but realize it only works on soiland will not cure an African violet with root knot nematodes.

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Nematodes are a breed of unsegmented roundworms which frequently cause problems in vegetable gardens. While many types of nematodes are beneficial to the soil, plant-parasite nematodes will attack and destroy plant roots, effectively killing the whole plant. [1] X Trustworthy Source EDIS Electronic database of the University of Florida Institute of Food and Agricultural Sciences's peer-reviewed articles Go to source The pests cannot be killed by most pesticides. So, gardeners will need to use gardening methods to make their soil as inhospitable as possible to the nematodes. Practices include solarizing the soil and rotating crops to discourage nematodes.

Texas Plant Disease Handbook

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.

African Violet Root Knot Nematodes – What To Do About Nematodes Of African Violet - garden

African Violet Plant Care Instructions: Part 3
African Violet Care

Many successful growers of African Violets recommend repotting with fresh potting soil, twice a year or more. At the very least, an African Violet should be repotted whenever the plant becomes rootbound, i.e., the Violet has outgrown its current pot to the extent that its roots are growing out and around the rootball. This process of repotting an African Violet into a larger pot is called potting up, and if you know what you are doing, it is very easy to do and takes very little time.

One of the most commonly used methods of potting up is called mold potting. While the method is very simple, it also minimizes the potential of shock caused by repotting. Your first step is to select an appropriate pot and a good potting soil (see below). After you have done this, take your new pot and put enough potting soil at the bottom to compensate for the difference in height. For instance, if your current pot is 2-1/2 inches in height, and your new pot is 3 inches in height, then the difference in height is 1/2 inch. You will, therefore, need to put 1/2 inch of potting soil at the bottom of your new pot. (Note: As you prepare your new pot, keep in mind that the final soil level should be about 1/2 to 3/4 inch below the rim of the pot.)

After you have put soil at the bottom of your new pot, remove your African Violet from its current pot. To do this, simply place your hand over the top of the pot so that the crown of the plant is between your fingers. When doing so, be careful not to damage any of the leaves or stems. Next, turn the pot upside-down. If the pot is plastic, you will only need to push on the bottom of it to loosen the rootball. If the pot is clay, gently tap on the bottom of the pot to loosen the rootball. If this does not work, try inserting a pencil or some other device into one of the drain holes in order to ease the rootball away from the pot. If the rootball still does not budge, do not continue to push. By forcing the pencil into the rootball, you may damage the roots or even penetrate the crown. Instead, try sliding a butter knife between the pot and the rootball. However, only do this as a last resort, since the knife can easily damage your African Violet.

In preparation for repotting, some growers suggest watering your African Violet. They say that doing so makes it easier to remove the rootball from the old pot. However, other growers suggest waiting until the Violet has already been repotted in order to minimize the amount of turgidity in the leaves and stems. This will reduce the likelihood of damaging your African Violet during repotting. Whichever you choose depends on your particular circumstances. If you are trying to remove a Violet from a clay pot, you may find that watering the Violet is essential. In this case, any consideration of the Violet's turgidity becomes secondary in importance. On the other hand, if you are removing a Violet from a plastic pot, you will probably find that watering is not necessary. In this case, you should probably delay watering in order to allow for as much flexibility, in the leaves and stems, as you can.

After you have removed your Violet from its old pot, set the Violet aside and place the old pot into the new one. Make sure the old pot is centered. Now, put potting soil around it until the soil is level with the height of where the rootball will be. The potting soil, which you are adding, should be packed tight enough so that it remains in place once you have removed the old pot. When you have done this, place the Violet (and its rootball) into the hole which you have just made. Finally, place your Violet and its new pot into a saucer of water. Allow the Violet to absorb whatever water it needs and, then, let any excess drain away.

Once you have finished repotting, you many want to bag it. Many growers recommend this, asserting that the increased humidity helps African Violets recover from any transplant shock. To do this, place the African Violet into a clear, plastic bag which is large enough to accommodate the plant without damaging the leaves or stems. Seal the bag with a wire twist. Keep your Violet in the bag for one week. After you have removed the Violet from the bag, it will be safe to resume your normal watering and fertilizer schedule.

Aside from potting up, you may sometimes have to pot down. Potting down is required when it is determined that an African Violet is too small for its pot. Though rare, such instances become apparent when a Violet is unable to form a cohesive rootball or when the soil remains chronically soggy, even though the pot provides adequate drainage. When potting down, use the next smallest pot size available. After removing any excess soil from around the roots, gently shape the soil and roots until you are able to squeeze them into your new pot. Because of the amount of handling required for potting down, you should employ the bagging method to minimize the effects of shock (see above).

Another repotting procedure is called potting down a neck. Though it sounds similar, this procedure has nothing to do with potting down, as described above. In fact, when potting down a neck, you do not use a smaller pot. Instead, you use the same pot. The time to use this procedure becomes apparent when the neck of an African Violet becomes elongated. This happens, most often, when an African Violet is subjected to a disease or nutrient imbalance which predominantly affects the oldest leaves. These are the bottom-most leaves of an African Violet. As these leaves die off, the neck (sometimes called the stalk or main stem) of an African Violet becomes more and more exposed until it appears abnormally elongated, i.e., more than 1/2 inch long. Since all new growth originates from the center of the crown, the only way to correct this is to pot down the neck.

The procedure for potting down a neck is simple and relatively safe to do. First, remove the Violet and its rootball from the pot. Starting from the bottom, you must cut away a section of the rootball equal to the length of the neck. Next, return the Violet to its pot. If it is seated properly, the bottom leaves of the African Violet will be resting on the rim. Now, add fresh potting soil up to the top of the neck, i.e., where the leaf stems issue from the main stem. Make sure that the new potting soil is pressed down firmly. Finally, give your African Violet water and let any excess drain. Because of the likelihood of shock, you should employ the bagging method (see above).

The pot that best suits an African Violet is called an Azalea pot. Compared to a standard pot, an Azalea pot is relatively shallow. Whereas the height of a standard pot is roughly equal to its diameter, as measured at the top, the height of an Azalea pot measures only about three-quarters its diameter. It is important to use an Azalea pot, because the roots of African Violets tend to grow out more than they grow down. When planted in a standard pot, this means that an African Violet's roots will not grow to the bottom of the pot. As a result, the unused potting soil will remain soggy, thereby reducing the amount of aeration that the roots receive and increasing the potential for Root Rot or other deadly fungi.

There are two ways to determine the correct pot size for your African Violet. When potting up, you should simply use the next largest pot size available. Pots for African Violets are available in increments of roughly one inch. Therefore, if you have an African Violet which is currently in a 2-inch pot, you will want to repot it in a 3-inch pot. Another way to determine proper pot size is to measure the diameter formed by the outer edge of an African Violet's leaves. Generally, if an African Violet is planted in the correct size pot, the diameter of its leaves will be about three times the diameter of the pot. Therefore, if the diameter of your African Violet's leaves measure 12 inches, then it should be planted in a 4-inch pot.

Always make sure that your pot has adequate drainage. This is essential when watering from the top. When using a bottom-watering method, drainage becomes less important, since a good potting soil will only absorb the amount of water that an African Violet needs. However, whether watering from the top or the bottom, there will inevitably be times when it is necessary to thoroughly rinse the soil, e.g., when leaching the soil of excess fertilizer salts. Therefore, good drainage should always be taken into account when selecting a pot for your African Violet. If you have a pot which either provides no drainage or insufficient drainage, then holes should be added. On plastic pots, this can be done by using a soldering iron or by simply heating up the metal shaft of a screwdriver and pushing it through the bottom. On clay pots, use a drill. When doing so, do not press too hard. Go slowly and let the drill do the work. The size and number of holes depends on the size of the pot. On 4-inch pots, make as many as four holes, 1/4 inch in diameter. On 2-inch pots, make two holes, 1/8 inch in diameter. On 1-inch pots, make one 1/8-inch hole.

The choice between clay pot and plastic pots is one of preference. While African Violets can successfully be grown in either one, each offers different benefits and drawbacks. An unglazed, clay pot is porous. This allows a greater amount of aeration to the soil and increases the amount of humidity around your Violets as water soaks through the clay and evaporates into the air. For many, a clay pot also offers greater aesthetic value, because it has a more traditional and/or natural look. However, clay pots also have their disadvantages. They can be difficult to clean and sterilize. The porosity of them encourages the growth of algae and the accumulation of fertilizer salts, while increasing the rate of water loss. Moreover, they are heavy and easy to break. Plastic pots, on the other hand, are lightweight and virtually unbreakable. They are also much less expensive than clay pots. And because plastic pots are not porous, they are very easy to clean and sterilize, they conserve water by minimizing evaporation, they are not prone to the accumulation of fertilizer salts, and they discourage the growth of algae. However, plastic pots, too, have their disadvantages. They, of course, do not offer the same aesthetic appeal as clay pots. But more importantly, because they are not porous, plastic pots contribute less to the air moisture around the plants, and aeration of the soil becomes a greater concern.

When weighing the different advantages associated with clay pots and plastic pots, keep in mind that some of their respective drawbacks can be offset. For instance, the effects of accumulated fertilizer salts on clay pots can be minimized by placing aluminum foil or a coating of wax around the rim. When using plastic pots, you can compensate for the decreased humidity around the plants by misting, grouping your plants together or using a self-watering device, such as the Watermaid, which employs capillary matting.Aeration of the soil, in plastic pots, can be increased by using a recommended potting mix which is comprised of light, porous materials, such as block-harvested peat moss and perlite. And, of course, the aesthetic appeal of plastic pots can be enhanced with a decorative, self-watering device or a ceramic, outer container.

One final consideration, in regard to clay versus plastic pots, is the use of a self-watering device.
If you are planning on using a self-watering device, you should know that many of them are specifically designed to accommodate plastic pots. However, there is at least one type of self-watering device which is versatile enough to handle both clay pots and plastic pots. An example of this type of watering device is the Watermaid. The Watermaid can accommodate clay pots, plastic pots or any kind of pot up to 5-1/2 inches, as long as it has drainage holes at the bottom. This and other self-watering devices are available online at the Selective Gardener, a mail order supplier that specializes in plant care products made specifically for African Violets.

Once you have chosen the correct pot for your African Violet, you will need to disinfect it. Disinfecting African Violet pots is vital, especially if you have one that has already been used. But even for new pots, disinfection is highly recommended. If you do not disinfect your pots, you run the risk of exposing your African Violets to Nematodes and other deadly micro organisms. The process is easy. Simply soak them in a 10 percent bleach solution, i.e., one part bleach to nine parts water. After soaking, rinse them with plain water.

African Violet Potting Soil

At first glance, the subject of potting soil may sound less important than it really is. This may be due to the fact that many people believe that "potting soil" is simply another name for "dirt." To be sure, there are products which claim to be potting soil for African Violets when, in fact, they are nothing more than dirt. These are heavy mixes which would easily crush the roots of African Violets. In addition, because heavy potting mixes hold so much water, they tend to leave African Violets vulnerable to such deadly pathogens as Crown Rot, Root Rot and Pythium. Moreover, many of these "dirty" potting soils do not even have the correct pH. This, in addition to their heavy quality, would further stifle an African Violet's ability to absorb the nutrients it needs.

A good potting soil for African Violets actually contains no soil (or dirt) at all. A good potting soil will be very light and porous, a quality which enhances aeration, while keeping the soil moist, but not soggy. Such a potting soil will be made primarily of block-harvested, sphagnum peat moss. Perlite or expanded polystyrene will be added to maintain optimal porosity. This contributes to the proper aeration of the potting soil, while keeping it light and porous. In addition, since peat moss by itself is very acidic, small amounts of calcium carbonate, or some type of lime, will be added to correct the pH. For African Violets, the pH should be between 5.8 and 6.2. This is still slightly acidic, but very close to neutral. The pH of a potting soil is important, because if it is too high or too low, African Violets can not properly absorb nutrients.

While it is unlikely that potting soil from a reputable manufacturer will harbor unfriendly micro organisms, it may nevertheless be prudent to treat the soil before exposing it to your African Violets. The process for treating potting soil is called pasteurization. To pasteurize your potting soil, it must be heated to 180 degrees F for 30 minutes. This can be done by simply sealing the potting soil into heavy aluminum foil (minus the bag, of course) and placing it into your oven. By inserting a meat thermometer through the aluminum foil, you can monitor the temperature of the soil. Once the temperature reaches 180 degrees F, continue to heat it for 30 minutes. When the process is complete, remove the potting soil from the oven and let it cool. Once it has sufficiently cooled, you should seal it in a plastic bag or some other air-tight container in order to prevent contamination.

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Megan Meyers* and Brian Hudelson, UW-Madison Plant Pathology

What are foliar nematodes? Foliar nematodes are microscopic worm-like organisms in the genus Aphelenchoides. They live in and on the leaves (and other above-ground plants parts) of over 450 plant species in more than 75 plant families. They are commonly found on hostas, but can affect other herbaceous ornamentals (e.g., African violet, anemone, begonia, chrysanthemum, fern, orchid, veronica) and woody ornamentals (e.g., azalea, elm, privet), as well as fruit crops (e.g., sour cherry, strawberry) and vegetable crops (e.g., broccoli, celery, lettuce, onion, pinto bean, potato, squash, tomato). Damage from foliar nematode is usually cosmetic and non-lethal making ornamental plants less attractive and less saleable. In severe cases and on particularly susceptible hosts (e.g., strawberry), foliar nematodes can cause extensive leaf injury and defoliation, and can interfere with and limit flowering.

What does foliar nematode damage look like? Unlike most other nematodes which cause root damage, foliar

Angular dead areas on Brunnera leaves typical of infections by foliar nematodes. (Photo courtesy of Monica Lewandowski, The Ohio State University Plant Pathology)

nematodes cause damage to above-ground plant parts, especially leaves. In young plants, foliar nematodes can cause new growth to curl, twist, and stunt. In more mature plants, foliar nematodes cause small, discolored, angular (i.e., straight-edged) blotches on leaves. The blotchy areas are typically bordered by veins. Blotches eventually turn brown and dry, and may fall away, giving the leaf a “shot-holed” appearance. Angular blotches often are not apparent until late in the growing season (e.g., August).

How do I save a plant with foliar nematodes? Eliminating foliar nematodes is virtually impossible. No chemical products are available for foliar nematode control in home gardens. Hot water treatments have been developed to treat high-value plants, but are not recommended for home gardeners. Exact temperatures/timings for these treatments vary depending on the type of plant being treated, and missteps in timing/temperature can either kill plants or can lead to less than 100% control of the nematodes. If you have plants infected with foliar nematodes, the best course of action is to dig them up, bag them and remove them from your garden as soon as you notice symptoms to reduce the risk of the nematodes spreading to healthy plants. After working with infected plants, wash your hands with soap and water and decontaminate anything that has come into contact with the plants (e.g., tools, pots, bench surfaces, etc.) for 30 seconds with either 70% alcohol (e.g., rubbing alcohol) or 10% bleach. Spray disinfectants that contain approximately 70% alcohol can also be used. Because soil is virtually impossible to decontaminate, avoid planting susceptible hosts in an area where foliar nematodes have been a problem.

How do I avoid foliar nematode problems in the future? The easiest way to avoid problems with foliar nematodes is to not bring them into your garden. Carefully inspect plants for nematode symptoms before purchase, but keep in mind that plants may not show symptoms early in the growing season. Avoid using overhead sprinklers as watering in this manner can splash foliar nematodes from plant to plant and promote spread. Instead use a soaker or drip hose that applies water directly to the soil, rather than onto leaves. Space plants far enough apart so that potential spread via water splash during natural rains is minimized, and avoid working with plants when they are wet. DO NOT use foliar nematode-infected plants or even healthy-looking plants suspected to be infested with foliar nematodes when taking cuttings to propagate plants.

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