Control of Woody Perennials

A common problem in desert landscapes is the germination and growth of unwanted woody perennials. For example, desert broom is problematic in many areas because it is widely distributed and wind effectively disperses desert broom seed long distances. Woody shrubs and trees rapidly establish a deep taproot system that makes all but the smallest seedlings difficult to pull out of the ground by hand. In addition, cutting or breaking the shoot results in resprouting rather than death of the plant. Woody desert shrubs and trees are also tolerant to most herbicides partly because of their limited leaf area in relation to the size of their shoot and root systems leading to excessive dilution of the herbicide in the plant. However, these woody species can be killed and stump sprouting stopped using cut stump herbicide treatments of 2,4-D amine, glyphosate, or triclopyr.

Cut stump herbicide treatments work on most woody perennials including trees such as mesquites, palo verdes, salt cedar, ornamentals such as mulberry trees, and desert shrubs such as desert broom. The cut stump treatment is initiated by cutting the stem or trunk of the weedy woody perennial so that the cut surface is relatively horizontal and smooth. The cut must be made rapidly. A sharp saw or pair of pruning shears can be used on shrubs and seedling or small trees but a chain saw should be used on large trees. Saturate the cut surface with herbicide as soon as possible after cutting. On large tree trunks, the cambium area next to the bark is the most vital area to wet. Do not wait more than several minutes to paint the stump. Woody plants have a wound response that quickly seals the cut surface and restricts the movement of herbicide into the roots. The best results are achieve by treating woody perennials that are not water stressed and are growing actively. The herbicides used for cut stump treatments, 2,4-D amine, glyphosate, and triclopyr, are commercially available in several different concentrations. Only the most concentrated herbicide formulations should be used for cut surface treatments; 2,4-D amine (46% solution), glyphosate (41% solution), and triclopyr (44% solution). The herbicide used can be applied using a paint brush or a small hand-held spray bottle. For homeowners, the easiest herbicide to obtain and to use on cut surfaces is glyphosate. These three herbicides are not active in soil and can be used safely around desirable ornamentals.

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