Arkansas Research Evaluates New Soybean Weed Control Technologies
Evaluating new weed control technologies that are becoming available in soybean varieties is necessary to determine how they will supplement or complement already available technologies. Although the “new” herbicide tolerant technology is currently centered on 2,4-D and dicamba (auxinic Group 4 herbicides), two other new technologies will soon be available.
According to Dr. Bob Scott in the Oct. 8, 2014 issue of Delta Farm Press, HPPD-inhibiting herbicide-tolerant soybean is close to a reality for producers. This technology will soon be available in Syngenta’s MGI soybean [tolerant to mesotrione (Callisto), glufosinate (Liberty), and isoxaflutole (Balance)] and Bayer’s Balance GT soybean [tolerant to glyphosate and isoxaflutole]. Currently this chemistry is available in the corn herbicides Callisto, Zemax (S-metolachlor + mesotrione), Halex GT (S-metolachlor + glyphosate + mesotrione), and Balance Pro (isoxaflutole). Both mesotrione and isoxaflutole are Group 27 HPPD-inhibiting herbicides. Currently available soybean herbicides do not have this site of action (SOA).
According to a press release from MS Technologies on July 22, 2016, the European Union has approved the importation of Balance GT soybean for food and feed uses. This follows approvals already received from the US, Canada, and Brazil for its cultivation. The first launch of this new technology in the US is planned for 2017 pending final key approvals.
The current (dicamba and 2,4-D tolerance) and forthcoming (HPPD-inhibiting herbicide tolerance) availability of these new technologies in soybean prompted scientists at the Univ. of Arkansas to conduct experiments in 2013 and 2014 at Keiser, Arkansas to evaluate current and future herbicide programs that contain multiple sites of action. Results from this research are reported in an article entitled “Herbicide programs for managing troublesome weeds using new soybean technologies” that was published Apr. 29, 2016 in PMN’s Crop, Forage, and Turfgrass Management online journal.
In their studies, they evaluated weed control programs that used preemergence (PRE) herbicides only and combinations of PRE followed by early (EPOST–3-4 weeks after PRE) and late (LPOST–6-7 weeks after PRE) applications of POST herbicides for control of barnyard grass [BYG], ivyleaf morningglory [IMG], and prickly sida [PS]. These three weeds are common in Midsouth soybean production systems.
Because several of the new herbicide-resistant traits are still regulated, the treatments were applied to plots that simulated a soybean production system but that was devoid of soybean so that the new technologies could be evaluated for efficacy against the targeted weeds. A total of 16 herbicide products representing 7 SOA’s were used in the studies.
As might be expected, individual points of results from this extensive study are numerous. Therefore, I will summarize what I consider the major results from this study that pertain to the new technologies.
● Auxinic and HPPD-inhibiting herbicide technologies were not different in their control of IMG and BYG.
● The two new technologies did not outperform current technologies for control of BYG and PS, but they did outperform current technologies for control of IMG. Thus, adding the new technologies into a weed control program will improve control of IMG.
● n the PRE-only treatments, control of the weed species in these studies was greater for the tank-mixes that contained HPPD-inhibitors than for tank mixes containing auxinic herbicides. Thus, HPPD-inhibitors may be the more valuable of the two new technologies when applied PRE.
● Using auxinic herbicides with another PRE product provides additive benefit and increases the SOA diversity in PRE applications of current soybean herbicides.
● Even though the new technologies may not improve control of all problem weeds in soybean, they will increase the number of herbicides and SOA’s that are available for both PRE and POST herbicide applications to soybean. This will reduce the selection pressure on herbicides currently used in soybean weed control programs, and will be a valuable tool in managing the spread of herbicide resistance.
I encourage you to access this article to assess the many treatments that were used. If you do not have a subscription to the journal, I suggest you contact the senior author at cjmeyer@uark.edu to obtain a copy.
Composed by Larry G. Heatherly, July 2016, larryheatherly@bellsouth.net