May 9, 2008

Winter annuals are species that germinate in the fall, overwinter and then continue growing in early spring. Once soil temperatures reach 50-55°F, they grow rapidly. They also consume large amounts of moisture, which can affect crop seed germination and early growth. The most common winter annuals include: field pennycress, shepherds purse, henbit, blue mustard and treacle mustard (bushy wallflower). You may want to watch for these species. They often make the green patches that appear in fields in October-November and March-April. In addition, dandelion and curly dock, which are not winter annuals, appear in early spring.

Burn-down Treatments

In no-till fields, winter annuals can be effectively controlled with herbicides. In corn and soybean they can be controlled 0-45 days before crop planting, depending on the herbicide, or after planting but before emergence. The same is true for fields planted with the 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 would provide a longer period for applying glyphosate-based products. Winter annuals usually are 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/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/ac) and one of many generic Glyphosate type 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.

Cool Spring Alert

Glyphosate products (Roundup or generic products) 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. During cool spring temperatures avoid using Roundup. Mixtures with atrazine, 2,4-D or other modes of action can improve weed control.

Glyphosate Prices

Also pay attention to the glyphosate price. A multi-site, multi-year UNL study showed that generic glyphosates provided equal weed control when compared to a much more expensive Roundup-named products.

Consult 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 but at least seven days prior to crop planting. More details on these herbicides and their use rates is available in the UNL Guide for Weed Management.

Stevan Knezevic
Extension Weeds Specialist
Haskell Ag Lab, Concord, Northeast REC