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Since weed species do not compete equally, the timing and intensity of each weed’s emergence determines its competitiveness with a soybean crop. Weed emergence may vary from year to year depending upon environmental conditions, crop planting dates, and other management practices. The unique emergence profile for each weed species is defined by its initial emergence date, the duration of emergence, and the distribution of emergence within this time period. Because of each weed’s profile, a successful herbicidal weed control program may include a burndown, a pre-plant or at planting residual(s), and in-crop applications.
Prior to planting, existing weeds should be controlled with a burndown herbicide application or tillage early enough to promote residue decomposition. Planting into existing weeds or heavy weed residue can interfere with seed placement and can reduce emergence from poor seed-to-soil contact. A residual during burndown should also be considered to help reduce the potential for emergence of new growth. However, applying soil-applied residuals too early can result in a shorter residual period for weed control and later weed escapes may occur. Residuals have planting interval or crop rotation restrictions and precautions that need consideration if conditions warrant a change in planting intentions. Consult individual product labels for precise instructions.
Emerged weeds should be removed after planting when weeds are less than 4 inches tall to help preserve soybean yield potential. University research noted a 2 to 3% yield loss for every inch of weed height greater than 4 inches.1
Weed management recommendations for herbicide resistant or tough-to-control weeds such as marestail, giant ragweed, kochia, lambsquarters, Amaranthus species, and others can be found at http://www.roundupreadyPLUS.com.
Farmers using Roundup Ready 2 Xtend® soybeans have the ability to use XtendiMax® herbicide with VaporGrip® Technology. XtendiMax® herbicide with VaporGrip® Technology can be applied to Roundup Ready 2 Xtend® soybeans from before planting up to and including beginning bloom (R1 stage). The wide application window allows for the control of weeds when they are small (less than 4 inches) and more vulnerable, such as marestail at early burndown. The ability to use this product through the planting window can allow Roundup Ready 2 Xtend soybeans to get a head start towards their high yield potential with minimal competition from weeds.
Cleaning the tank is critical to help minimize crop injury when switching herbicides in different herbicide-tolerant trait systems. Consult individual product labels for detailed instructions.
Specialized and Mandatory Dicamba Training
A herbicide containing dicamba is a consideration for in-crop herbicide use in soybean fields containing plants with glyphosate and dicamba resistance. Indiana is among several states that requires applicators to attend mandatory training in order to apply dicamba. If you are applying XtendiMax® herbicide with VaporGrip® Technology (Monsanto), FeXapan® Herbicide plus VaporGrip® (DuPont), Engenia® Herbicide (BASF), you must attend a mandatory training session. To receive certification, attendance is required for the entirety of the approximate 90 minute training session. Training dates for Indiana can be found at: Indiana https://ppp.purdue.edu/private-applicators/recertification-parp/parp-events/. Growers and applicators are encouraged to access www.roundupreadyxtend.com for additional information on mandatory dicamba training.
Source: 1 Kamienski, C. 2003. Masters thesis: Effect of postemergence glyphosate application timing on weed control and grain yield in glyphosate-resistant soybean. University of Illinois. Source verified 2/6/18. 180206112443