Is There a Place for "Public" Soybean Varieties?

There is no doubt that glyphosate-resistant [GR] soybean varieties used with POST-only glyphosate for weed management in soybeans was a boon for Midsouth producers. In fact, results from research conducted during the early 2000's near Stoneville, Miss. [Agron. J., Vol. 96:742-749 and Agron. J., Vol. 97:568-577] showed that growing GR soybean and applying only glyphosate for weed control effectively managed weeds, was the least expensive system, and provided the most profit to producers. However, the selection for GR weeds has rendered this production system ineffective and/or not sustainable. In fact, this occurrence has left soybean producers scrambling for alternative management options to control now-GR problematic weeds such as Palmer amaranth.

Prior to glyphosate-resistant [GR] soybean and sole use of POST glyphosate herbicide, and glufosinate-resistant [GLR] soybean and use of glufosinate herbicide, numerous “conventional” [CONV] herbicides were applied both PRE and POST to control weeds that infested soybeans. These herbicides were generally effective at managing the myriad broadleaf and grass weeds that are common in the Midsouthern US, and they were from more than one SOA group [see below table footnote].

An online article [June 1, 2017] in Crop, Forage, and Turfgrass Management journal [published by PMN] authored by Oliveira et al. reports results from a Nebraska study titled “Weed control in soybean with preemergence- and postemergence-applied herbicides”. These results are rather unique in the current weed control arena because they report weed control in soybeans by herbicides that were available and used before HR [herbicide-resistant] soybean varieties were available. In other words, this is a report of results from a herbicide weed control study where only CONV herbicides were applied [e.g., no herbicides (glyphosate, glufosinate, dicamba) that are applied to current HR soybean varieties were used].

The herbicide treatments [9 PRE-only and 5 POST-only] used in the study are shown in the below table. A nontreated control treatment was included for comparison. Two GR soybean varieties were used even though glyphosate herbicide was not applied. Eleven non-GR weed species [7 broadleaf (no Palmer amaranth) and 4 grass] were seeded in the plots. Weed control was visually estimated at 40 and 60 days after PRE treatment and 10 and 30 days after POST treatment using a scale of 0 for no control to 100 for complete control or death of weeds.
 

Pertinent results from this study follow.

•   In general, PRE-applied herbicide premixes controlled both broadleaf and grass weeds better than POST-applied herbicides, with the best PRE treatments providing ≥90% weed control at both 40 and 60 days after treatment.

•   POST-applied herbicides did not provide acceptable control [<50%] of barnyardgrass and fall panicum.

•   Greater soybean yields were obtained from plots with PRE-applied herbicides, and this was likely due to the lack of adequate control of grass weed species by POST-applied herbicides.

•   Although not tested in this study, the application of PRE herbicides would provide flexibility for timely and effective POST herbicide applications targeted to weeds that escaped PRE herbicide control, as well as providing additional SOA’s for controlling GR weeds in soybean production systems. Thus, PRE-applied herbicide mixtures with different SOA’s can be the base for controlling weeds and protecting soybean yields.

The above cited results lead to the following important point.

If future weed control in soybeans is to include herbicides that were available before HR soybean varieties were developed (e.g., RR, LL, etc.), then why not consider planting public soybean varieties that have desirable yield and agronomic traits to avoid the expense of purchasing seed with HR/GM traits from private companies while still incurring the costs associated with CONV weed control?

Consider the following points.

•   According to MSU budgets, growing GR soybean varieties and applying both PRE and POST non-glyphosate and glyphosate herbicides results in a weed control cost of about $65/acre. This does not include the estimated cost of about $50/acre for preplant herbicide applications [likely the same for any soybean production system in the Midsouth] and $65/acre for seed of a private GR variety [based on 50 lb. planted seed/acre].

•   Seed of a non-GR public soybean variety will cost $26-$30/acre.

•   Seed of a GR public soybean variety will cost $32-$38/acre.

•   Seed of the above-priced public soybean varieties is available, but in limited quantities. However, if there is demand, the amount of seed of a popular public variety can/will be increased by the Foundation Seed programs of the various states or a non-profit entity such as UniSouth Genetics; this can likely be done in 1-2 years. Also, seed of public varieties can be saved by the producer for future plantings.

•   Public soybean breeders work diligently to select for and incorporate current pest resistance traits [i.e., HG types of SCN, other nematodes, stem canker, SDS, frogeye leaf spot, etc.] into newly-released public varieties. They also ensure that these newly-released public varieties yield as well as commercial varieties.

So if a producer chooses to plant a public GR-resistant soybean variety that is shown to yield as well as a commercial GR variety, the cost for seed will be significantly less and the cost for herbicides used for weed control will be about the same as that for commercial GR varieties [see above-cited budget figures]. Thus, the overall expense when using such a public variety will be less because of the significantly lower seed cost.

If a producer chooses to plant a non-GR or non-GMO public soybean variety that is shown to yield as well as a commercial HR variety, the seed cost savings is even greater, but the option to apply glyphosate will be lost. This could be an important consideration since the POST application of glyphosate is a valuable tool for managing grass weeds in any soybean production system. However, there is a separate market for non-GMO soybean that may bring a premium for harvested seed.

The above presentation is not intended to encourage or discourage the use of one soybean production system vs. another. Rather, it is an attempt to provide insight into options that can be considered in the current environment of GR-resistant problematic weeds, the likely development of HR weeds in general, and the myriad problems that are associated with application of auxin herbicides to the new auxin herbicide-resistant varieties.

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