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Information from the University of Arkansas

Two articles published by Univ. of Arkansas Division of Agriculture/Cooperative Extension Service staff provide information that may be of interest to Midsouth soybean producers.

Growers who are growing non-dicamba tolerant soybean for seed production want to be sure those seed are vigorous and free of dicamba exposure symptoms. An Oct. 6, 2017 article by Mary Hightower provides information about a service the university is offering to screen those seed to ensure they are free from the effects of possible off-target dicamba exposure. Growers desiring this service will need to download and fill out a form [link provided in above article], specifying the type of seed [RR, LL, Enlist, Conventional, or variety name] and an estimate of the level of exposure to dicamba that might have occurred. Preferred sample size is approximately 1,000 seeds. Data provided from the test will include percentage germination and percentage of seedlings that show auxin-type exposure symptoms 14 days after emergence. The cost per sample is $100. For more information about this service, see the above-linked article.

In an article posted on the Arkansas Row Crops blog site, Dr. Jeremy Ross, Extension Soybean Agronomist, provides a summary to provide guidance in selecting soybean varieties with varying herbicide-resistant [HR] technology traits. He composed this summary because of the recommendation by the Arkansas State Plant Board to ban the application of all dicamba products from April 16 through Oct. 31, 2018 in the row crop production areas of Arkansas [see article here]. This recommendation and potential implementation will essentially mean that producers will not be able to make any postemergence [PE] applications of dicamba formulations to Xtend soybean varieties in 2018 since little of the planted soybean acres will be emerged by the proposed April 15 deadline.

The potential loss of dicamba for PE application to Xtend soybeans means that these varieties will have the same PE options that are allowed for Roundup Ready [RR] varieties since Xtend soybean varieties are also resistant to glyphosate. This means that the best PE option for fields with glyphosate- and PPO-resistant Palmer amaranth is the Liberty Link [LL] system. However, according to Dr. Ross there is the perception that LL soybean varieties do not have the same yield potential as the Roundup Ready 2 Yield [RR2Y] and Xtend soybean varieties. Thus, he used data generated from the 2016 official variety trials [OVT’s] conducted in Arkansas[UASDA], Louisiana [LSU], and Mississippi [MSU] to compare yields of varieties from the currently available HR technology groups [Conv., LL, RR, RR2Y, and Xtend].

Soybean varieties for the five HR technologies were tested together in the UASDA and LSU OVT’s, while the MSU OVT trials had the Conv. and LL varieties tested separately from the RR, RR2Y, and Xtend varieties. Thus, results from only the latter three sets of varieties in the MSU tests are presented. Soybean varieties used in the calculations from the UASDA and LSU tests ranged from mid-MG 4 to early-MG 5 in maturity, and from late-MG 4 to early-MG 5 in the MSU trials. A summary of the calculations follows.

Mid-MG 4 [4.6-4.7] Varieties

In the UASDA 2016 trials, RR, RR2Y, and Xtend varieties had average relative yields that were not different, but were greater than average yields from LL and Conv. varieties. In the LSU tests, RR, RR2Y, and LL varieties had the same average relative yields. Xtend varieties had average yield that was lower than average yields of varieties with the above three technologies, but similar to average yield from the Conv. varieties.

Late-MG 4 [4.8-4.9] Varieties

In the 2016 UASDA trials, average yields of varieties in the RR, LL, and Conv. groups were similar at all test locations. At 3 of 6 test locations, average yields from Xtend varieties were lower than average yields of varieties from the above three technologies, whereas average yields from RR2Y varieties were lower than average yields from the above three technologies at 2 of the 6 test locations. In the 2016 LSU trials, average yields from varieties in all 5 technology groups were statistically equal. In the 2016 MSU trials, varieties in the RR, RR2Y, and Xtend techology groups had statistically equal yields.

Early MG 5 [5.0-5.3] Varieties

In the 2016 UASDA trials, average yields from varieties of all HR technology groups were statistically equal. In the 2016 LSU trials, average yield of varieties in the Conv. group was greater than average yields of varieties in the other 4 groups, which had statistically equal yields. In the MSU trials, average yield of varieties in the RR2Y group was greater than average yields of varieties in the Xtend and RR groups, which had statistically equal yields.

Conclusions

The above summary of data from the 2016 UASDA, LSU, and MSU OVT’s do not indicate a trend for varieties of any one of the 5 HR technology groups being superior in yield to varieties of any other group. This indicates that mid-MG 4 through early-MG 5 soybean varieties within the above 5 HR technologies will likely have comparable yields when grown in Midsouth locations. Dr. Ross reminds producers that HR traits are not yield traits, but merely indicate which specific herbicide can be applied to eliminate weeds in those varieties. And of course, the above summary of data does not mean that every variety within a particular HR technology group will perform and yield the same.

As always, producers are encouraged to evaluate yield and performance data from multiple sources–e.g. university OVT’s, company data– to ensure that chosen varieties from a particular HR technology group have the required/necessary agronomic traits, herbicide tolerances, and disease and nematode resistance traits for the intended planting site.

Composed by Larry G. Heatherly, Oct. 2017, larryheatherly@bellsouth.net