Timely Topics
There is a rogues’ gallery of weeds many farmers and landowners in Rockbridge know all too well. Late summer through early fall provides an opportunity to suppress and perhaps nearly control many of these problematic weeds. The combination of mowing management, weather conditions and shortening day length all impact the susceptibility of these weeds to herbicides and late summer affords us an opportunity to treat them effectively.
For those who do not wish to use herbicides, cutting, digging and other means of mechanical removal are (for most weeds) their only option. I have read of a number of “homemade herbicides” that typically involve ingredients such as mild acids like vinegar, dish detergents and baking soda. Combinations of these products typically achieve foliar burn and will have no impact on the root systems. For some annual weeds, severe foliar burn is sufficient to achieve some degree of suppression but these products will have no lasting impact on perennial plants. For those prepared to use herbicides and want to minimize the amount we release to the environment, then read on.
Woody perennials like autumn olive, Callery (Bradford) pear, paradise tree (ailanthus), and multiflora rose have extensive root systems in which the plant stores carbohydrate to feed new growth the following spring. Timing herbicide applications with when the plant is moving carbohydrates from the leaves into the roots is an optimal time for the herbicide to be most effective.
Johnsongrass, pokeweed and horsenettle (sand briar) are herbaceous perennial weeds that make their presence known in mid to late summer. Poison hemlock and most thistle species are biennials meaning the miniscule rosette stage of their two-year life cycle is prevalent in September and highly susceptible to herbicides.
All of the aforementioned “rogues,” if left undisturbed, would have slightly different flowering and seed production patterns across the season. They each present their own unique windows of opportunity during the growing season when they are especially susceptible to the correct herbicide. But making time to target particular weed species at their own unique period of susceptibility can be quite time consuming.
If a land steward happened to have mowed these weeds in late July or August, there is a good chance these herbaceous weeds have had their natural pattern late summer senescence delayed and they are still capable of absorbing and translocating herbicide.
Important to effective use of herbicides is weather conditions. Hot dry weather can cause plants to shut down resulting in poor herbicide uptake. At this writing, it appears we have sufficient soil moisture and the moderate temperatures to create a good opportunity to apply herbicides effectively now through early October.
For more detailed guidance on product options and strategies for weed control in pastures or hayfields, contact Tom Stanley at the Rockbridge County Extension Office (540) 463-4734 or by email to stanleyt@ vt.edu.
Notice the column began with a description of how a land steward could “suppress or nearly control” weeds in September. Weed control strategies are never truly complete; it is a part of regular stewardship. If our rogue weeds could express a thought following an effective September weed control effort, I’m guessing they would choose the words of a famous movie antihero: “I’ll be back.”
