By Jeremy Ross, Extension Soybean Agronomist
With the recommendation from the Arkansas State Plant Board on an application ban on all dicamba products from April 16 through October 31 in the row crop production areas of Arkansas, selecting soybean varieties and what herbicide technology to plant in 2018 has become more complicated. To make matters worse, soybean producers being offered strong incentives by seed companies to decide on which varieties to plant next spring with 50% of this year’s soybean crop still to be harvested.
Soybean yields that I have seen or heard about so far this year are several bushels better than what was reported at this time last year. I’m hearing very good yields from soybean varieties across all herbicide technologies. Overall, weather conditions and rainfall have been somewhat better than those seen in 2016, which could be the main reason for better than expected yields so far in 2017. Many of the April planted soybean fields did have poor seed quality, but this seems to be getting better as we move into later planted fields.
Even though we have a large majority of the soybean crop in Arkansas to harvest, I’ve already had several calls about what soybean varieties to plant next spring. Some of our early planted OVT locations have been harvested, and we are waiting for preliminary yields and for the later planted tests to mature so we can harvest these tests. Without any harvest data yet for 2017, I’m referring producers who need to make decisions now to the 2016 Soybean Update and the 2016 Arkansas Soybean Performance Tests.
With the proposed ban on dicamba products, a majority of soybean producers in Arkansas will not be able to apply any postemerge applications of labeled dicamba formulations to Xtend soybean fields next year. Survey data from the USDA-NASS shows that the 5-year average of emerged soybean on April 15 in Arkansas is only 2% of the soybean acreage. Without the use of in-season dicamba, especially in areas of the State where producers are facing glyphosate-PPO resistant Palmer amaranth, managing these weeds in fields planted to Xtend soybean varieties will be extremely difficult. If Xtend varieties are planted into these fields, the only effective modes of action in these fields will be the Group 15 (Dual/Zidua) and Group 5 (metribuzin) herbicides. Postemerge herbicide options in these Xtend fields will be the same as if a RoundUp Ready soybean variety were planted, practically no POST herbicide options. The best alternative for fields where glyphosate-PPO resistant Palmer is a problem is the LibertyLink (LL) system. Many have said that the LL soybean varieties do not have the yield potential that the RoundUp Ready 2 Yield (RR2Y) and Xtend soybean varieties have. Data generated from 21 trials comparing LL and RR2Y varieties for both MG4 and MG5 soybean varieties show no yield differences between the two herbicide technologies when yields are averaged across each technology. To compare varieties in all of the herbicide technologies currently available (Conventional, RoundUp Ready, RoundUp Ready 2 Yield, Xtend, and LibertyLink), soybean yield data from the 2016 official variety trials (OVT’s) from the University of Arkansas System Division of Agriculture (UASDA), LSU AgCenter, and Mississippi State University (MSU) MAFES were evaluated this past spring.
To compare between each herbicide technology and across locations, relative grain yields were calculated for each variety at each location. Average relative yields were calculated for each herbicide technology. Soybean varieties for the five herbicide technologies were tested together in the UASDA and LSU OVT’s. The MSU trials separately tested the conventional and LL soybean varieties from the RR, RR2Y, and Xtend varieties. Only the RR, RR2Y, and Xtend results from the MSU OVT will be presented. Soybean varieties examined ranged from mid-MG 4 to early-MG 5 in the UASDA and LSU trials, and late-MG4 and early-MG 5 from the MSU trials. The number of varieties in each herbicide technology and test are shown in Table 1.
Mid-MG4 Soybean Varieties (2016)
Average relative yields for the RR, RR2Y, and Xtend technologies were not statistically different from the Mid-MG4 UASDA OVT’s (Figure 1). Both the LL and Conventional technologies had average relative yields significantly less that the other three technologies.
Data from the LSU Mid-MG4 OVT’s showed RR, RR2Y, and LL technologies with statistically the same average relative yield (Figure 2). The Xtend technology had a numerically lower average relative yield compared to these three technologies, but was not statistically different than the RR2Y, LL, or Conventional technologies.
Late-MG4 Soybean Varieties (2016)
This Late-MG4 OVT’s contained the largest number of soybean varieties tested in each of the University’s test. When the data from the UASDA Late-MG 4 OVT was analyzed, there was a significant technology by location interaction. All five technologies had statistically the same average relative yield for the Kibler Irrigated, Keiser Non-irrigated, and Marianna Irrigated locations (Figure 3). The RR, LL and Conventional technologies had statically identical relative yields at the Rohwer Irrigated, Keiser Irrigated, and Stuttgart Irrigated locations, with the RR2Y technology at the Rohwer Irrigated locations not statically different than these three technologies. The RR2Y and Xtend technologies had significantly lower relative yields at the Keiser Irrigated and Stuttgart Irrigated locations, and the Xtend technology had a significantly lower relative yield at the Rohwer Irrigated location compared to the other four technologies.
When the data for both the LSU and MSU Late-MG4 OVT trials were analyzed, all five technologies (RR, RR2Y, Xtend, LL, and Conventional) in the LSU trials and the RR, RR2Y, and Xtend technologies in the MSU trials had average relative yields that were not statistically different from one another (Figure 4 and 5).
Early-MG5 Soybean Varieties (2016)
From the UASDA Early-MG5 OVT, all five technologies had average relative yields that were not significantly different. The Conventional technology from the LSU Early-MG5 OVT had statistically higher average relative yield compared to the other four technologies (Figure 6), and the RR2Y technology from the MSU Early-MG5 OVT had a significantly higher relative yield compared to the RR and Xtend technologies.
Based on the data obtained from the 2016 OVT’s from three different universities in the mid-south, the current herbicide technologies available for use by soybean producers had comparable relative yields in maturity groups from mid-MG4’s to early-MG5’s. Similar results were seen when yield data from the University of Wisconsin, Madison (here) and University of Minnesota (here) OVT’s were analyzed to compare RR2Y and Xtend soybean varieties. Even though the maturity groups evaluated at these two universities were different from the ones grown in the mid-south, like maturity groups were examined to compare the technologies. Keep in mind that herbicide traits are not yield traits and do not enhance yield, but protect yield by having the ability to apply a specific herbicide to eliminate weeds and reducing competition from these weeds. This doesn’t mean that every variety within a technology will perform and yield the same. Care should be taken when determining what technology and variety within that technology will be planted next year. Evaluate yield data from several sources (University OVT, company data, on-farm trials, etc.), consider agronomic characteristics (plant height, chloride sensitivity, etc.), disease and nematode resistances, and herbicide tolerances (metribuzin, STS, etc.) when selecting soybean varieties.