Prickly sida or tea weed has increasingly become more of an issue in soybeans. There are two reasons for this. First, the Group 15 herbicides (Dual Mag, Warrant, Zidua) are the most common PRE-applied herbicides utilized. Though that group of herbicides provides good residual control of pigweed and grasses, it provides no help on sida. Second, is that glyphosate nor dicamba has ever been very effective on this weed. The only POST option that can give some control is Liberty. However, even Liberty is limited to controlling only very small (<3”) prickly sida.
The best PRE option to control prickly sida is Command. That herbicide has good activity on members of the mallow plant family like prickly sida, arrowleaf sida and wild cotton.
Other options that are close but not quite as robust for PRE control of sida is flumetsulam (Python) or any premix with chloransulam (FirstRate). There are several premixes that contain chloransulam and they include Sonic, Surveil and Tendovo. Also premixes that contain Authority, Classic or Valor have pretty good activity on prickly sida as well as hophornbeam copperleaf. Some of those premixes contain metribuzin and others do not. If the premix does not include metribuzin adding some will aid prickly sida residual control.
POST emergence prickly sida options other than Liberty come down primarily to Python. Regardless of herbicide, applying to small sida is critical for consistent control. Python will provide good sida control at rates as low as 0.23 ozs/A on prickly sida up to 2” tall. Increase the rate to 0.46 oz/A for 3” tall sida and to 0.69 oz/A for prickly sida up to 6” tall. The best tankmix partner with Python for sida is glyphosate. Limited research last spring would suggest that adding dicamba does not increase sida control and may be antagonistic. If Python is used PRE and followed with a POST, the season total use rate is 1.4 oz/A. The draw back to using Python is the plant back to cotton is 18 months for rates above 0.25 oz/A. The plant back to cotton for rates 0.25 oz/A or less is 9 months.
If the recrop to cotton is a deal breaker, then the next two best options are Basagran or FirstRate. Basagran can be very effective on prickly sida. However, this herbicide has three draw backs. First Basagran is typically not in great supply at most retailers. Second is that it can be quite costly. Third is that it provides no residual sida control. FirstRate, though not as efficacious as Python on sida, can provide some control at higher rates (0.5 to 0.6 oz/A). If chloransulam premix was applied PRE and one plans to follow up with FirstRate POST then remember that the season total use rate on soybean is 0.055 lb ai/A or 1.05 oz/A of FirstRate. The recrop to cotton after a FirstRate application is 9 months.