Tom's Blog

Wednesday, May 15, 2013

Selective spraying of leafed-out invasive shrubs

This is the time of year when weed plants are above ground and can be sprayed with herbicide. Unfortunately, shrubs that did not get top-killed by a burn are also leafing out. At Pleasant Valley Conservancy most of these shrubs are scattered, single, short stems, with four or five leafy buds. Although these stems should be sensitive to foliar spray, it is difficult to spray them without getting herbicide on nearby "good" plants.

Here is a technique that works well under these conditions, provided you are using glyphosate (2% glyphosate; 41% active ingredient). If I see an isolated buckthorn stem leafing out I step on it and press it to the bare soil. Then I spray each leafed out bud. I don't worry if I get some herbicide on the soil, since it will cause no harm.

The rationale here is that glyphosate that reaches the soil is inactivated by soil particles. (Here is what the label says: "Glyphosate does not have herbicidal properties once it contacts soil. It is not absorbed from the soil by plant roots.")

The only limitation here is that there must be bare ground surrounding the shrub. In a few weeks the whole soil surface will be green. Once that condition is reached, the only way to selectively kill isolated stems is by basal bark, using a sponge on a stick. That technique is described in this link.


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