I have a dieffenbachia plant that has bumps growing all over its stalk. I have searched the internet but can't find any mention of this problem. Does anyone have any idea what this could be? I'm not sure if it is some kind of disease and don't know if i should just throw the plant away. It is otherwise healthy and is growing well, already reaching the ceiling of our living-room.
I have attached a few pictures to help in the diagnosis.

Thanks.

What you have is a insect called SCALE.

Adult scales are black and to the left in the picture, immature scales are beige and to the right. Actual size approx 5 mm.

Several species of scale insects commonly infest plants in the home or greenhouse. These sap-feeding insects have a tan to brown shell-like covering or scale that protects the insect's body. Scales may be from 1/16 to 1/4 inch in diameter and are usually found on the stems and/or leaves. Some scales are hemispherical in shape, while others are oval and flat. Scale insects feed by sucking plant sap and may cause poor, stunted growth. Death of infested plants is possible in severe cases. A large quantity of a sweet sticky liquid called honeydew is excreted by scale insects. Honeydew can make a sticky, shiny mess on the plant and nearby furniture and floors. A black fungus called sooty mold may grow on the honeydew.

Scale insects are difficult to control. There are several well-known remedies that can be tried in an attempt to eliminate scales from a houseplant. However, there is no easy, simple cure for a scale infestation. One possibility is to pick off individual scales or gently scrub (or rub) the scales loose from the leaves and stems. This is a laborious task that works only on small, large-leafed plants. Dabbing each scale with an alcohol-soaked cotton swab is another possibility on lightly infested plants.

Scale insects are difficult to control. There are several well-known remedies that can be tried in an attempt to eliminate scales from a houseplant. However, there is no easy, simple cure for a scale infestation. One possibility is to pick off individual scales or gently scrub (or rub) the scales loose from the leaves and stems. This is a laborious task that works only on small, large-leafed plants. Dabbing each scale with an alcohol-soaked cotton swab is another possibility on lightly infested plants.

Sprays can be used for scale control. Success will depend upon thoroughness and persistence. Insecticide sprays (aerosols or hand pump sprayers) made just for houseplants are available at garden centers. You can use a mild dish washing detergent in place of the commercial insecticide soaps. Use a dilute solution of 1 Tbs of detergent per quart of water. Soap sprays can be applied with a sprayer or used with a soft cloth while washing infested leaves and stems. Insecticides must be applied thoroughly, repeatedly and persistently (weekly for a month or more) to get good control.

Granular insecticides that you add to the soil of infested houseplants seem to have some effectiveness. On those plants that regrow after pruning, removing the heavily infested stems and treating the remainder is a possibility. Finally, unless the plant is particularly valuable, many people find it best to throw away infested plants before the pests spread to other houseplants.

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Operational Manager at
Earl May Nursery and Garden Center in Ames, Iowa

I wish I had found this sooner. Dieffenbachia is one of my favorite evergreen, tufted perennials and I'm a cultivator of D.maculata 'Exotica'
What was seen here in the pictures was not an infestation but what is called root knot or "nodes". The cells on the innermost walls have become deprived of light in the red and green spectrum and mutated to form thin-cell Masses.
In the natural low lands of the tropics Dieffenbachia stems rarely become more than 3" thick and the weight aided by its height forces the cane to bend or lean over often to the ground or against an other plant were these "nodes" become deprived of all light and receive more moisture allowing more thin cells to grow and produce tap roots that transform to take on nutrients. Do to phototropism (the plant grows towards the light)the stalks usually fall into better light were the "nodes" now on top are radiated in the full spectrum and photosynthetic responses produce vegetative growth.

Had this person air layered the top half of this plant to manage its size and reduce the shock of being removed from its support system. They would have been left with a treasure trove of stem cuttings.
The remaining cane could have been cut in to 3" to 6" pieces with root knots("nodes") and laid flat or placed vertically nearly covered in a moist peat mix were they would have reproduced Exact vegetative copies of the parent plant. Also if the remaining root ball was left undisturbed new growth would have been produced.