Useful Herbicides: Chemical Controls: Knapweed is relatively easy to kill with herbicides, but it takes many repeat treatments to get any plants
that were missed the first time through, plus all the new plants that germinate from seeds left in the soil. By itself, 2,4-D is
effective only if applied in the early spring as the flower stem begins to elongate. Dicamba combined with 2,4-D is
also effective, if applied to the rosettes prior to bolting. Clopyralid by itself or combined with 2,4-D is also effective. Picloram is probably the most favored selective herbicide to control knapweed because it is persistant in the soil, so it costs less over the long run.Among non-selective herbicides, glufonsinate-ammonium is more effective than glyphosate. However, the knapweeds are spindly plants, and it is difficult to spray them without hitting surrounding vegetation. Caution is advised, since non-selective herbicides will kill everything and open up more habitat for the weeds to spread. But it is possible to use non-selective herbicides effectively during dry years when the knapweeds are still green, but the grasses are completely
dormant and yellow.
Herbicide Brand How to Apply When to Apply Comments 2-4D Broadcast Activily growing or fall growth 2pts per acre Tordon " " 1pint per acre Tordon & 2-4D " " 1pint Tordon & 1qt 2-4D per acre Curtail " " 2-3 qts per acre Transline " " 1-1/3 pts Redeem " " 1.5-2 pts per acre 2,4-D Amine 3 Gal. Backpack Activley growing or fall growth 4.5 OZ/3-Gal. Water 2,4-D & Tordon " " 1.5OZ Tor +2.25 2,4-D Tordon " " 1.5 OZ Curtail " " 4-4.5 OZ Tranline " Rosette to bloom 1.5 OZ Redeem " " 1.5 OZ
Further Information about these herbicides:
Herbicide Brand Active Ingredient Mode of Action Comments Transline - - - 2,-4D,Amine 2,-4D amine,2,-4DLV ester Systematic Abnormal growth (twisted stems, Cupped leaves) in 2-10 days. Tordon Picloram acid Systematic " Redeem triclopyr acid " " Curtail cloyraild, MCPA ester " "
By Jennifer Berna 5/2002.
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