Burndown herbicide applications are an essential part of weed management in cotton.
An early burndown can help fields dry out quicker from winter and spring moisture.
Early burndowns can help conserve soil moisture in drought-prone areas.
Prior to planting cotton, fields should be free of live weed growth unless the cultural weed control practice of planting into green cover is being utilized. This can be accomplished with tillage or burndown herbicides. Ideally, existing weeds should be controlled at least a couple of weeks prior to planting to allow for decomposition of the plant material. Planting into existing weeds, or heavy, non-decayed weed residue can interfere with seed placement and reduce emergence due to poor seed-to-soil contact.
If herbicides are used as a burndown, the herbicide labels MUST be reviewed for timing intervals between application and cotton planting date. The full recommended herbicide rate and proper application timing should be used for the toughest-to-control weed species in the field.
The emergence profiles of weeds can significantly affect the performance of weed management programs and should be a major consideration for planning. In addition to starting with a clean field, controlling weeds after planting when weeds are less than 4 inches tall is necessary to help preserve yield potential. Integrated pest management principles should be used to help determine the appropriate herbicide program for each field. Sequential herbicide applications combining different sites of action, and foliar and residual activity provide the most effective weed management plans.
Controlling weeds early can help fields dry from winter and spring moisture. In drought-prone areas, early weed control prevents weeds from using precious moisture that can be used later by cotton plants. Weed management tactics for tough-to-control weeds, such as marestail, giant ragweed, kochia, lambsquarters, Amaranthus species, and others, can be found at https://www.roundupreadyxtend.com/products/Pages/xtendimax.aspx.
Environmental conditions affect the rate of weed growth, crop development, crop tolerance to herbicides, and herbicide performance. Fluctuating day and night temperatures are typical in the spring. The effectiveness of a burndown herbicide application can be reduced by cold temperatures. It is recommended to wait on applying herbicides until nighttime temperatures are above 40°F and daytime temperatures are in the high 50s to low 60s.1 Weed control may be increased with several days of warmer weather prior to herbicide application rather than applying on the first warm day of the season.
XtendiMax® herbicide with VaporGrip® Technology, a Restricted Use Pesticide (RUP), is labeled for burndown applications in some geographical areas. The XtendiMax herbicide label and individual state notifications MUST be read and followed and XtendiMax herbicide MUST be used with VaporGrip® Xtra Agent or an equivalent volatility reduction adjuvant (VRA). For additional information, please see https://www.roundupreadyxtend.com/stewardship/Pages/default.aspx.
XtendiMax with VaporGrip Technology applications may only be made by dicamba-trained certified applicators.
Geographical pre-emergence herbicide recommendations for XtendFlex® Cotton appear in Table 1.
1 Loux, M. 2007. Burndown herbicide activity – Can we kill anything when it’s this cold? C.O.R.N. Newsletter. Agronomic Crops Network. Ohio State University Extension. The Ohio State University. https://agcrops.osu.edu/newsletters/2007/08.
Hartzler, R. 2003. Is your weed management program reducing your economic return? Iowa State University Weed Science. http://extension.agron.iastate.edu/.
Hartzler, B., Boerboom, C., Nice, G., and Sikkema, P. 2006. Understanding glyphosate to increase performance. The Glyphosate, Weeds, and Crops Series. GWC-2. https://www.extension.purdue.edu/.
Nalewaja, J.D. and Matysiak, R. 1991. Salt antagonism of glyphosate. Weed Science 39: 622-629.
Web sources verified 12/8/2020.