Perennial sow thistle is now growing very well in many corn and soybean fields
The good moisture the last two years helped this weed to grow and produce a great root system. This root system must be destroyed to get rid of it.
You need repeated control measures over at least three years to control it.
There are a number of ways to control it in soys. The best way in non Roundup Ready soys is with Classic. The addition of Sure Mix seems to increase control. Ask your dealer about rates. In Roundup Ready soys spraying with glyphosate is a good option.
In corn, Peak Plus or glyphosate in Roundup Ready corn are the two best options. Talk to your dealer about what stage of corn you can safely spray with Peak Plus.
Perennial sow thistle in winter wheat can be controlled with a pre-harvest treatment of glyphosate. This should be followed up with a second application in September when the plant is putting out new rosettes.
Perennial sow thistle can be eradicated from a field. To do this you must control this weed for three years. By doing this you deplete the root reserves. It mainly spreads by under ground roots. Plants that start from seed are fairly easy to control with many herbicides, such as those containing atrazine or metribuzin. BF