In pastures, glyphosate can only be applied as a directed application, such as a wiper application or as a spot application to prevent injury to desired grasses and legumes. Glyphosate requires weeds to be actively growing and translocating photosynthates efficiently for increased herbicide efficacy on perennial weeds. The authors attributed low control to rainfall and the poor growing conditions during those years. In a study by Peters and Lowance (1979) ironweed control was reported to range from 2% to 88% depending on year (6). However, control with glyphosate may provide variable results depending on environmental conditions. Glyphosate applications have been reported to result in good to excellent levels of ironweed control (5,6). In contrast, Western ironweed that was mowed early (May 20 th) then mowed repeatedly whenever the regrowth reached 6 to 8 inches resulted in 19 to 87% stand reduction compared to the nontreated plots (4). In a study conducted in Missouri investigating mowing regimes of western ironweed, single mowing events often resulted in higher stands (4). Tall ironweed was reported to produce between 1460 to as much as 14,550 seeds per plant (3).Ĭontrol by mowing may be affected by mowing date, number of mowing events, and environmental conditions.
The ironweeds can produce a large amount of seed, but seed production appears to be variable.
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