Trees, shrubs and ornamental plants are susceptible to a variety of diseases. Some infections may create a common shape -- witches' broom -- that gets its name from the shape the plant comes to resemble. A plant with witches' broom occurring within its structure will look unattractive and it may not thrive. Prune witches' broom to improve a plant's shape and growth pattern and to remove the disease.
Examine the witches' broom formation in the plant's structure. You will find a knobby cluster of branches or stems exploding out from the bulbous point. Look beneath the originating point of the disease to the portions of the stems or branches where the tissue appears healthy and normal. This is the point where you must prune.
Cut off the diseased portion of the plant about 6 inches below the knob of the witches' broom. Use the pruning shears for thin stems or the lopper pruner for thicker branches.
Examine the cut stem to notice disease inside the stem. If you notice unhealthy discolouration instead on the healthy light-coloured interior stem, cut the stem back farther. Continue cutting back the stem until you see only healthy stem interior.
Collect the diseased witches' broom in the bucket or basket. Dispose of the removed plant or tree portions in the trash.
Witches broom may result from powdery mildew, fungal infections, insects and herbicides, according to the University of California.