Nancy Robitaille
Nancy Robitaille
Meet the Soil Mealy Bug and the Foliar Mealy Bug families.
Soil Mealy bugs, or what we once learned was called Pritchard’s Mealy Bugs, are from the Rhizoecus family. Rhizoecus americanes or Rhizoecus dianthi. It is no longer called Pritchard except in old reference material.
Foliar mealy bugs are from an entirely different family, the Coccoidea family. This family includes scale insects and coccids as well as foliar mealy bugs.
Common names have a way of confusing growers in the same way as seeing three or four different episcias using the same name of E. ‘Chocolate Soldier’.
While I am not suggesting the violet world learn the Latin names for the bugs that haunt us, I would say that we should learn the differences and the treatments of each.
Foliar Mealy Bug
Foliar mealy bug is easy to differentiate because it lives most of its life on the foliage of plants. These bugs appear to us as what looks like white foam on plants and will melt when touched with alcohol dabbed with a Q-tip. This white mass is actually the nest of babies and not the adult bug.
Mealy bug on Agave
Foliar mealy bugs are fairly easy to spot and can be found on the upper and lower sides of leaves and the trunk of our plants.
What do they look like?
Photo: Lance Osborne
Males are tiny gnat-like insects and are not often seen. These have wings and are very small, about one-thirty-second of an inch long.
Photo: Lance Osborne
Females are usually oval, flattened. Females have no wings but are coated with bright white waxy hairs around the body.
Adults may be found on all parts of the foliage and stem of the plant. The female is three thirty-seconds of an inch long. She has a fringe of filaments surrounding her and has short antennae.
Adult female and immatures
The female mealy bug lays eggs up to six hundred at a time in a loose cottony waxy “house” on foliage.
Mealy Bugs, ant
Eggs hatch into a first instar nymph. These look similar to the adult and are less than one thirty-seconds of an inch long. Nymphs are not at first covered in the wax. The hatchlings are able to crawl and can be carried to neighboring plants by air currents.
Juveniles go through a second and third nymph stage, molting at each stage.
Mealy bug nest on violet leaf
Young mealy bugs feed, and then begin to exude or excrete a white waxy material that will soon form a cover for the whole body.
Some species of mealy bug can produce live young.
Populations can build up rapidly under good breeding conditions with three to four generations occurring each year. In cooler weather, the insects begin to slow down.
Foliar Mealy bug eggs and nymphs are not visible and tend to shelter in leaf axils and hide under leaves.
Foliar Mealy Bug with nest
The insect itself is often yellow or grey and may have a darker stripe running down the middle of the back. Other species have two stripes on the back. When squeezed the body becomes red.
Damage or Symptoms:
Foliar mealy bugs have piercing and sucking mouth parts which injure the plant by sucking sap. A heavy infestation can weaken plants.
Plant Symptoms:
1. Growth stops.
2. Foliage yellows.
3. Foliage becomes twisted and distorted.
4. Leaves are disfigured.
Foliar Mealy bugs can extract large amounts of plant sap in order to obtain proteins. Some of the excess sap is excreted as honeydew, and left as a sticky deposit on plant leaves. Sooty mold may eventually grow on this honeydew.
TAKING CARE OF THE PROBLEM
Natural Control:
The waxy coating on foliar mealy bugs protects them from good control. For slight infestations, the white patches may be brushed with alcohol. It is advisable to rinse the plant with warm water afterwards since alcohol is drying.
The most effective control options for killing more than just a few foliar mealy bugs are the use of oil sprays or natural predators or parasite insects.
Oil sprays such as Neem Oil used with a good wetting agent (dish soap—a few drops) will make the spray adhere and the oil will suffocate the insects.
Neem oil applied on a regular basis—every three days should control the infestation. Neem oil breaks down in sunlight and should be applied every three days in order to break the life cycle. Neem oil disrupts the molting and feeding of the insects. Apply every three days during the period of one month.
Biological Control
These predators will rid you of your infestation.
Lady Bugs (Crytolaemus)
Hypoaspis mites
Lace Wing
With patience, persistence and predators, your plant room should soon be free of this pest.
Chemical Control
It is recommended to use the above controls since they are fast and effective. These chemicals are also effective on large outbreaks of foliar mealy bug: Acephate (orthene), Diazonion, and Malathion, others.
AND NOW, THE BUG-A-BOO!
Soil mealy bug
Photo: By permission NC State University
Soil Mealy bug is known by many names, Rhizoecus americanue, root mealy bug, soil mealy bug, Pritchard’s mealy bug and Rhizoecus Pritchard. Do not confuse soil mealy bug with foliar mealy bug.
What do they look like?
Soil Mealy bugs are small, oval-elongated insects that live most of their lives among the roots of plants. They may also be seen on the trunk of African violets near the soil line.
Soil mealy bugs are from one-sixteenth inch to one-eighth inch in length and can be seen under a magnifying glass or jeweler’s loupe.
Photo by permission NC State University
The insect has six legs on a slim body. It looks like a particle of perlite or rice. The insects are completely covered with a powdery wax which is secreted from glands into each mealy bug’s body. This waxy material makes them appear snow-white.
Soil mealy bugs on roots of hydroponically grown African violet. Note color of plant. Photo: Korina
Soil Mealy Bugs in tinted water of reservoir
The waxy powder may be found throughout the root ball, on pots or even floating in water reservoirs. Infestations can easily be seen as white patches in the soil and at the pots sides or bottom.
SMB leaves a powdery residue on the insides of pots.
SMB are closely related to scale (Coccoidea family) but in place of the scales’ hard shell, SMB have the protective waxy powdery coating. This coating protects them from most pesticides. SMB crawl about a great deal and this is the method they have for infecting your entire collection.
The working part of the SMB is the mouthparts which act like a hypodermic needle which pierces the root then sucks up the plant juices. The action of sucking out the plants juices naturally causes stress to the plant because of loss of moisture and nutrients.
As they pierce the plant the insects also inject chemicals into the plant which may act as anticoagulant which allows the juices to be removed more readily. These chemical toxins may also destroy plant cell walls and at the same time allow the pests to feed. Certain species of these pests also transmit viral diseases. They may also destroy chlorophyll or plant tissue.
SMB on rootball
SMB thrives in dry and loose soils and are especially attracted to peat moss. This is certainly one main reason for pasteurizing peat moss before it is added to the soil less mix.
The life cycle of soil mealy bug is completed in two to four months. All stages of life may be found on the plant at any given moment thus the reason for at least three consecutive sprayings (drenching) of a chemical so that eggs hatching may also receive treatment.
Plant appears in need of water But soil is wet.
Damage or symptoms
1. Leaves become pale, yellowish or grayish.
2. Wilted leaves are translucent brown, with soft jelly-like consistency.
3. Plant does not flower. (This is a symptom, but I have seen beautifully flowering show plants which were later diagnosed with SMB.)
4. Reduced plant growth and vigor.
5. Roots and basal stem rot.
6. Infested plants may become small in the center.
7. Buds cease to form as the infestation continues.
If these symptoms are left untreated, the plant will likely die.
Often Soil mealy bug is hard to control because symptoms are not noticed until internal damage is too widespread.
Natural control
None available.
Biological control
There are few if any natural predators for soil mealy bugs; however some mention of tests with parasitic nematodes have been carried out but no satisfying results have been produced.
Chemical Control
Since we are unable to control soil mealy bug with either natural or biological control we must use chemicals in order to control these insects.
Remove and discard infected soil.
The rootball may be completely cut away from the plant and the plant may be rerooted in fresh soil. Leaves, if not touching the soil may be used for propagation.
You wish to keep the rootball. A soil drench is called for where the whole plant plus the root ball is drenched. A mere foliar spraying will not affect the bugs in the soil.
Soil mealy bugs have been known to seek safer places in the foliage of the plants when the plant is drenched from below.
Drench the foliage first so bugs will not seek safety there when the root ball is drenched.
Chemicals:
Acephate
Malathion
Diazinon
Dimethoate
Imidacloprid
Other chemicals are developed and formulae are changed often.
Diatomaceous Earth is fully inert, non volatile and has been proven effective as a treatment against SMB. DE is the skeletal remains of diatoms, which are a microscopic form of algae. When processed into DE, these skeletal remains form razor-sharp particles which cut into the bodies of soft-bodied insects in the soil but no harm is done to African violets. Use one tablespoon of DE to a liter of dry soil.
I would not rely on Diatomaceous earth by itself. Although DE can help, it can not control a large outbreak.
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