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There is a rogues’ gallery of weeds many farmers and landowners in Rockbridge know all too well. Late summer through early fall provide 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. For those prepared to use herbicides and want to minimize the amount we release to the environment and achieve the most efficient use of limited time, then read on.
Woody perennials like autumn olive, Callery (“Bradford”) pear, paradise tree (ailanthus), and multiflora rose have extensive root systems that over-winter. 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.
Depending on the timing and frequency of mowing, many of these weeds can be tricked into producing vigorous tender vegetative growth in September just as the days are getting shorter, sending a message to the plant that it is time to move carbohydrates in to the root system ahead of the short cold days of winter.
If you have the rogues’ gallery of weeds around the farmstead, in the fields, or in the fencerows, consider some late July or early August cutting to set these weeds up for a September herbicide application. Important to effective use of herbicides is weather conditions. Hot, dry weather can cause plants to shut down resulting in poor herbicide uptake. Timely rains and moderate temperatures in September create a good opportunity to apply herbicides effectively.
For more detailed guidance on product options and strategies for weed control in pastures or hayfields, call Tom Stanley at the Rockbridge County Extension office at (540) 463-4734 or send email to [email protected].
Notice the column began with a description of how some forward planning could allow you to “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.”
