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Biennial Wormwood
Biennial wormwood, contrary to its name, may emerge in the fall or spring. Biennial wormwood is difficult to control because of extended emergence period, tolerance to many PPI, PRE and POST herbicides used in row crops, detected late after most POST herbicides are applied, AND is often confused with common ragweed. It thrives in low areas where soil may remain wet for extended periods of time. It also is a problem in no-till or minimum-till fields in the absence of tillage.
Biennial wormwood is tolerant to most PPI and PRE herbicides including, trifluralin, Sonanlan, Prowl, Lasso, Dual, Frontier, Harness, Surpass. Biennial wormwood is tolerant to many POST herbicides used in row crops including Basagran, Blazer, Pinnacle, Raptor, and Pursuit.
Biennial wormwood is susceptible to phenoxy or growth regulator herbicides, such as 2,4-D, Banvel SGF, Stinger and Curtail, Liberty, and glyphosate.
Limited research and experience has shown some options in control, including, Authority/Spartan applied PRE, Basagran on wormwood less than 3 inches tall, Cobra at 6 fl oz/A + PO at 1 pt/A on wormwood less than 3 inches tall, possibly Flexstar on small wormwood, Liberty in Liberty resistant crops, and glyphosate on Roundup Ready crops.
A common situation occurs when biennial wormwood survives soil and POST herbicides then is detected and misidentified later after most other weeds have been killed. Rescue treatments are applied with little effect. Biennial wormwood is easily misidentified with common ragweed. Many herbicides that control ragweed, such as Basagran, Blazer, and especially FirstRate do not control wormwood. Though research has not been conducted to support this but small wormwood, 1 to 3 inches tall, may be controlled with some herbicides now thought to be ineffective. Wormwood quickly becomes tolerant to herbicides as size increases.
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