Every producer knows the menace of weeds in the field. The cornerstone of weed control in recent years has been glyphosate application with excellent results. However, the ease and low cost of glyphosate based control is threatened by glyphosate-resistant weeds, which have gained a foothold in South Dakota production systems. These weeds include common ragweed, kochia, common waterhemp, and horseweed. In addition, weeds with resistance to herbicides with other modes of action (ALS, ACCase) are also reported in South Dakota (Heap, 2014). Therefore, it is imperative that information about weed control and management is updated so that producers and consultants continue to make wise and informed decisions.
Dicamba resistant (Xtend) and 2,4-D resistant (Enlist) soybean are fairly new to SD and in the past few years we have conducted trials at three or four locations with three planting dates. 2019 was challenging year for planting. The earliest planting at NE farm, May 15, had the greatest yield for Enlist when rhizobia were applied at V5 (60 bu/a) the other two planting dates (May 30 and June 14) had 3 to 6% lower yields. Xtend soybean similar yields at May 15 and May 30 planting but had reduced yield at June 14. Weeds were well controlled with either 2,4-D (with or without glufosinate) and dicamba, but acifluorfen had had some weeds but this did not impact yield. At Beresford, the May 5 planting of Enlist soybean had poor weed control compared to June 5 or June 19. June 5 and June 19 had the highest average yields (~50 bu/a). Xtend soybean seed was untreated and had uneven stands for the May 5 planting. June 5 planting averaged the highest yield at about 60 bu/a. Delaying planting until June 19 resulted in an average yield of about 50 bu/a. Weed biomass in the May 5 plots was higher than the other dates due to poor stand establishment. We are currently evaluating data from the Aurora location.

1. Establish demonstration plots in three areas of SD that highlight today’s best herbicide options and application timings for resistant weed control in soybean
2. Assess alternative herbicide treatments on glyphosate resistant waterhemp with more modes of Action.
3. Continue assessment of agronomic traits of Xtend and Enlist soybean varieties.
4. Establish simulated drift on non dicamba soybeans and determine effects on yield.

The first objective is to continue herbicide demonstration plots at three eastern South Dakota experiment station farms. These studies are needed to allow producers to observed products in action in the locale and under local environmental conditions. These studies allow informed decisions about products without company bias and help demonstrate how different methods, timings, spray solution additives, carrier amounts, combinations, and sequential applications enhance or deter herbicidal weed control efforts.
The second objective is to assess alternative herbicide treatments on glyphosate resistant waterhemp. These trials will be conducted at two locations in South Dakota. Field days at these sites will allow local producers to observe multiple tactics to control these problems.
The third objective is to continue the assessment of Xtend and add Enlist-type soybean at several locations and planting dates to help growers evaluate the strengths and weaknesses of these varieties. Bradyrhizobia applications are also being applied at about V5 of soybean to determine if this foliar application changes yield potential, protein content, or nodulation.
The fourth objective is to examine drift on non dicamba resistant soybean after injury with other products and determine effects on yield.

A series of herbicide program demonstration plots including herbicide (glyphosate) resistance options in soybeans will be established at three locations; Southeast SD Research Farm (Beresford), Northeast SD Research Farm (South Shore) and the SDSU Volga Research Farm. The primary objective of this portion of the project is to increase grower knowledge of herbicide resistance in soybean weed control programs (primarily common waterhemp and kochia) and help growers to fine-tune their weed management strategies. The strategies will include treatments of preemergence, pre-post combinations, post emergence, and new technology herbicide options such as Liberty, Xtend, 2,4-D and Balance.

The demonstration plots will be utilized for grower and professional agronomist tours and training events. Data taken from the plots will include weed efficacy, crop injury ratings, and yield. Cost of treatment will also be calculated. Results will be printed in the annual SDSU Extension WEED Project Data book and will also be used in updating the weed control section of the SDSU Pest Management Guide-Soybeans and IGrow Soybean Production manual. Pictures of the plots and plot data will be used at winter meetings around the state. Examples of meetings that data will be used at include Commercial Applicator Training, Private Applicator Training, Row Crop Clinics, IPM Consultant Training and Winter IPM Short Course.

The glyphosate resistant plots will be utilized for grower and professional agronomist tours and training events. Data taken from the plots will include weed efficacy, crop injury ratings, and yield. Cost of treatment will also be calculated. Results will be printed in the annual SDSU Extension WEED Project Data book and will also be used in updating the weed control section of the SDSU Crop Protection Guide-Soybeans and IGrow Soybean Production manual. Pictures of the plots and plot data will be used at winter meetings around the state. Examples of meetings that data will be used at include Commercial Applicator Training, Private Applicator Training, Row Crop Clinics, IPM Consultant Training and Winter IPM Short Course.

Updated December 2, 2020:
See attached report

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Updated February 26, 2021:
See attached report

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Updated July 30, 2021:
I. Statement of the project objective(s):
Examine weed management and herbicide efficacy in soybean.
II. Statement of quantifiable progress toward project objective(s) achieved during this reporting period:
Copy of the 2020 WEED Project report is enclosed
A short written narrative is uploaded for the 3rd quater report
III. Activities planned between now and the next reporting period:
Finish graduate student thesis. Extension activities are expected with field days at Southeast and Northeast farm
IV. Problems and/or obstacles that may impact the completion date, cost or scope of the project:
Covid travel restrictions limited inperson meetings, although Soy 100 occured and recorded extension talks were conducted in January.

View uploaded report

Herbicide resistant and difficult to control weeds cause yield loss and significant management costs to soybean farmers. The information gained on herbicide resistance, and Xtend and Enlist soybean project has been, and will continued to be, presented through outreach and education materials to soybean farmers through information at applicator training, Soy 100, field days, and written materials.