The last half of September is the time to kill woody invasive perennials, most notably those rogues of the Rockbridge countryside: autumn olive, multiflora rose, ailanthus (paradise) tree, and callery (“Bradford”) pear. These species we humans unfortunately loosed on the countryside either through a desperate effort to halt soil erosion (the first two) or through a desire to establish quick and easy landscape shade (the second two) without careful consideration of the long run consequences of introducing nonnative, rapidly growing, highly prolific perennials into our landscape.
The book of Ecclesiastes, chapter 3, verses 1 – 8 is among the most often cited passages from the Bible and it begins “For everything there is a season and a time for every matter under heaven ...” with verse 3 being “ a time to kill and a time to heal; a time to break down and a time to build up” (New Revised Standard Version).
And it is this particular verse that is the basis of the deliberately weighty title of this week’s column. For it is in killing these unwanted invasive species we can contribute to healing and building-up our Rockbridge landscape.
The last half of September and early October, before the leaves of these plants begin to turn, is a good time to kill them because, like all woody perennials, they are photoperiod sensitive. This means the plant can detect when the number of daylight hours is declining and it responds by translocating sugars from the photosynthetic leaves into its root system.
Judicious and targeted application of the correct herbicides during this period is highly likely to be translocated to the root system and effectively kill the entire plant. Springtime applications of the same herbicides may give the appearance of effectiveness, only to see secondary and tertiary shoots emerge later in the season.
In reality, it is unlikely a single early autumn campaign against these invasives will address the problem. Stewardship has never been a “one-anddone” task. However, early fall applications are most likely to be most effective and achieve the most efficient use of time and material. This period can also be a good time to kill the biennials thistle and poison hemlock when their small rosettes are just emerging. The same herbicides so effective on the woody perennials also kill these problematic weeds. Biennials, different from perennials, are best controlled in the vegetative rosette stage before they “bolt” in their second year to produce seed.
The active ingredients of choice are triclopyr; 2,4-D; and dicamba ,but there are others that are effective. There are a number of retail products available at farm supply stores that contain these active ingredients and do not require an applicator license. Glyphosate (a.k.a. ‘Round Up™’) can be effective on the weeds mentioned in this column but it is not the best choice. Glyphosate is a broader spectrum herbicide that kills grasses as well as broad leafed plants so there is much more likely to be “collateral damage” if glyphosate is used.
Important to remember is to include a non-ionic surfactant in the herbicide mix. The surfactant breaks the natural surface tension of the droplets of spray and allows the water and herbicide mix to adhere to the leaves. Some herbicide pre-mixes already have the surfactant included. “Readyto- Spray” pre-mixed herbicide products are generally much more expensive per unit of effective product. Regardless of what product is used, the label is the law and the directions for use on the label must be followed.
A detailed guide of weeds common to open fields of the Rockbridge region with color photos and detailed herbicide recommendations is available at the Rockbridge Extension office on the second floor of the Rockbridge County Administrative Building, 150 S. Main St., Lexington. You can contact the Rockbridge Extension office at (540) 463-4734.
