Note pre-emergence label restrictions when controlling winter annuals

With planting underway or just around the corner, be sure to check herbicide label restrictions for preplant intervals if you're still trying to get a handle on this year's crop of winter annuals.

Rapid growth of winter annuals -- species that germinate in the fall, overwinter and then continue growing in early spring -- starts as soon as the soil temperatures reach 50-55°F. Winter annuals consume large amounts of moisture, which will have a negative impact on seed germination and early growth. Common winter annuals, such as field pennycress, shepherds purse, henbit, blue mustard and treacle mustard (bushy wallflower), appear as green patches in October-November and March-April. In addition, dandelion and curly dock, which are not winter annuals, can be seen in early spring and at planting.

In no-till fields, winter annuals can be effectively controlled with various herbicides. In corn and soybean they can be controlled 0-45 days before crop planting, depending on the herbicide, or after crop planting but before crop emergence. The same is true for the fields that are planted with herbicide-tolerant crops (e.g. Roundup-Ready or Liberty-Link). The use of pre-plant or pre-emergence herbicides with residual activity in Roundup Ready crops also would provide a longer comfort zone in which to apply glyphosate-based products. Winter annuals not controlled in the fall are best controlled in early April before they become too large for herbicide efficacy. Control will be reduced the closer the plant is to flowering.

Examples of burndown herbicides that can be used in corn and grain sorghum include: Aim (0.3 oz/ac), 2-4-D Ester (1.0 pt/ac); 2,4-D Ester + Banvel (0.5 pt+0.5 pt); Banvel (Atrazine (2 qt); Atrazine + Banvel (2 qt+0.5 pt), Atrazine + 2,4-D (2.0 qt+1.0 pt); Field Master (4 qts), Gramoxone Extra (1.5 pt); Gramoxone Extra + Atrazine (1.5 pt + 2.0 qt); Roundup Ultra Max (18-26 oz), Touchdown (24-32 oz/acre) and one of many generic glyphosate products (24-32 oz). The list of pre-emergence herbicides in corn includes: atrazine, Axiom, Balance, Bladex and Prowl.

Examples of burndown herbicides in soybean that can be used from 0-30 days before crop planting include: Aim (0.3 oz/ac), Canopy (5-7 oz/ac), Command 3E (1.5 pt/ac); Gramoxone Extra (1.5 pt/ac); Extreme (3 pt/ac), Gauntlet (co-pack, 5.33+0.6 oz), Pursuit (4 oz), Pursuit Plus (2.5 pt), Sencor/Lexone DF (16/13 oz), Roundup Ultra Max (18-26 oz), Touchdown (24-32 oz/ac) and one of many generic glyphosates (24-32 oz). The list of pre-emergence herbicides in soybean includes: Axiom, Pursuit, Prowl and Sencor/Lexone Also note that the glyphosate-based products (eg. Roundup or various generic glyphosates) used alone may not provide good control of winter annuals if spring is cool. Weeds need to grow actively in order to move systemic product such as glyphosate throughout the plant to get a good plant kill. During cool spring temperatures, performance of glyphosate-based products is reduced. Mixtures with atrazine, 2,4-D or other modes of action can improve weed control.

Herbicide costs

Also be sure to review how much you’re paying for glyphosate-based products. Studies we conducted over three years and six Nebraska locations clearly showed that generic glyphosates provided an equal level of weed control as that provided by more expensive Roundup products.