Control of Winter Annuals Helps Conserve Moisture

Control of Winter Annuals Helps Conserve Moisture

May 11, 2007

Winter annuals are species that germinate in the fall, overwinter and then continue growing in early spring. Rapid growth of winter annuals starts as soon as soil temperatures reach 50-55°F. They consume large amounts of moisture, which has negative effects on crop seed germination and early growth.

The list of the most common winter annuals that you may want to scout for includes: field pennycress, shepherds purse, henbit, blue mustard and treacle mustard (bushy wallflower). You may want to watch for those species. They make the "green patches" commonly seen in the fall (October, November) and early spring (March-April). In addition, dandelion and curly dock, which are not winter annuals, often are visible at planting.

Treatment Options

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 fields planted with herbicide tolerant crops (e.g. Roundup-Ready or Liberty-Link crops). 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 are usually controlled in the first two weeks of May, before they become too large for herbicide efficacy.

Examples of burndown herbicides that can be used in corn and grain sorghum include: Aim (0.3 oz/acre), 2-4-D Ester (1.0 pt/acre); 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 that can be used in soybean from 0-30 days before crop planting include: Aim (0.3 oz/acre), Canopy (5-7 oz/acre), Command 3E (1.5 pt/acre); Gramoxone Extra (1.5 pt/acre); Extreme (3 pts/acre), Gauntlet (co-pack, 5.33 + 0.6oz), Pursuit (4 oz), Pursuit Plus (2.5 pt), Sencor/Lexone DF (16/13 oz), Roundup Ultra Max (18-26 oz), Touchdown (24-32 oz/acre) and one of many generic glyphosates (24-32 oz). The list of pre-emergence herbicides in soybean includes: Axiom, Pursuit, Prowl and Sencor/Lexone.

Glyphosate-based products (eg. Roundup or generic glyphosates) used alone may not provide good control of winter annuals if spring is cool. Weeds need to grow actively to move systemic product such as glyphosate throughout the plant to get a good plant kill. Therefore, during cool spring temperatures, avoid using Roundup. Mixtures with atrazine, 2,4-D or other modes of action can improve weed control.

Generics a Good Buy

Another thing to watch for is the price you are paying for your glyphosate-based products. UNL studies conducted over three years and six locations across Nebraska clearly showed that generic glyphosates provided equal level of weed control when compared to a much more expensive Roundup products. So why spending more money than what is needed to get the job done.

With all these products, consult the label directions for additives and pre-plant and post-plant intervals. For example, corn should not be planted five days before or after application of 2,4-D. Also, 2,4-D can be used for burndown in soybean if used at least seven days before planting.

For more information on herbicides and use rates, check UNL's Guide for Weed Management, which is updated annually. It is available online or from your local Extension office.

Stevan Knezevic
Extension Weeds Specialist

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