An online survey was distributed to South Dakota stakeholders to understand how noxious weeds are currently being managed. The response rate was 26%; 129 stakeholders completed the survey of the 491 stakeholders who opened the survey. Eighty percent of respondents stated noxious weeds were a problem. Canada thistle [Cirsium arvense (L.) Scop.], leafy spurge (Euphorbia esula L.), and absinth wormwood (Artemisia absinthium L.) were the most common and troublesome, but all statewide noxious weeds were reported. The most common singular response to manage noxious weeds was herbicides alone (25%), but respondents utilized two (27%) to three (24%) other tactics as well. Most respondents (47%) were somewhat satisfied with management tactics, while others were completely satisfied (9%), neither satisfied nor dissatisfied (20%), somewhat unsatisfied (11%), or very unsatisfied (15%). A covariate analysis showed that the more management tactics individual stakeholders utilized, the less satisfied they were with control (P < 0.0001). The most common barrier of adopting new tactics was effectiveness (26%) followed by a combination of effectiveness + current production practices + cost + labor (13%). An additional covariate analysis showed that the increase in management tactics increased the barriers of adoption (P = 0.04) and increasing the number of barriers of adoption resulted in stakeholders being dissatisfied with control (P = 0.0003). Overall, the results of the survey suggest that statewide noxious weeds remain a problem, and multiple tactics are used to manage these weeds. However, Cooperative extension efforts need to address how to use current management and implement new management strategies to increase effectiveness.

Outdoor studies were conducted to determine the extent of leafy spurge biomass reduction resulting from broadcast application of 2,4-D (2,244 g ae ha−1) with and without wiper-applied glyphosate. Glyphosate (575 g ae L−1) was applied at 0%, 33%, 50%, and 75% diluted concentrate with a wiper 24 h after 2,4-D was broadcast-applied. Injury estimates and shoot biomass did not differ between plants treated with 2,4-D only or when glyphosate was wiper-applied 21 d after treatment. Shoot regrowth biomass of plants treated with 2,4-D only was approximately 560% greater than nontreated plants 3 mo after treatment. Plants treated with wiper-applied glyphosate exhibited shoot regrowth biomass of less than 10% compared with nontreated plants 3 mo after treatment. Root biomass of plants treated with 2,4-D only (160% of nontreated plants) exhibited a similar pattern of shoot regrowth biomass. Root biomass of plants treated with wiper-applied glyphosate exhibited approximately 50% reductions compared with nontreated plants. All vegetative metrics were equally reduced with all tested concentrations of glyphosate; therefore, all labeled concentrations should be effective. The results of the experiment indicate that broadcast-applied 2,4-D is more effective at reducing leafy spurge biomass with the addition of wiper-applied glyphosate.

The widespread adoption of glyphosate-resistant corn and soybean in croppingrotations often results in volunteer plants from the previous seasonbecoming problem weeds that require alternative herbicides for control. Cornyield losses due to season-long volunteer soybean competition at severaldensities in two growing seasons were used to define a hyperbolic yield lossfunction. The maximum corn yield loss observed at high volunteer soybeandensities was about 56%, whereas, the incremental yield loss (I) at low densities was 3.2%. Corn yield loss at lowvolunteer soybean densities was similar to losses reported for low densitiesof velvetleaf and redroot pigweed, with 10% yield loss estimated to occur at3 to 4 volunteer soybean plants m−2. Several herbicides,including dicamba with or without diflufenzopyr applied at the V2 growthstage of volunteer soybean, provided > 90% control, demonstrating severaleconomical options to control volunteer glyphosate-resistant soybean inglyphosate-resistant corn. Reevaluation of control recommendations may beneeded with commercialization of other genetically modifiedherbicide-resistant soybean varieties.

Volunteer corn is often overlooked as a weed in soybean. To aid in management decisions, this study determined soybean yield loss attributed to volunteer corn and efficacy of various herbicides at several rates and timings. A hyperbolic equation estimated (R 2 = 0.88) incremental yield loss (I) of 39.7% at low density when maximum yield loss (A) was constrained to 71%, the highest yield loss observed in these trials, revealing a more competitive plant than many common midwestern weedy species. Clethodim applied at 51 g ai ha−1 at V4 soybean resulted in > 90% volunteer corn control with < 5% soybean yield loss, whereas if applied at 12.7 g ai ha−1 volunteer corn control was 15%, but soybean yield was 50% greater than the nontreated control. On the basis of these data, the partial volunteer corn control improved soybean yield. Timing of glufosinate application influenced volunteer corn control. Glufosinate applied to 15-cm-tall corn resulted in 33% control, whereas applications to 36- to 91-cm corn resulted in > 70% control. Glufosinate combined with grass herbicides improved control to > 85%, with concomitant yield increases. Results demonstrated that volunteer corn substantially reduced soybean yield at low densities and yield increased when volunteer corn was controlled with various herbicides. On the basis of these results, and current soybean grain and herbicide prices, soybean yield gains from volunteer corn control could increase net return by > $150 ha−1.