Proper variety selection is one of the first steps in producing a high-yielding crop. Choosing an appropriate variety is one of the most important decisions a soybean producer will make and one of the hardest because there are so many varieties available. Each variety has specific strengths and weaknesses that make it more- or less-suited to a given environment. Maturity group, yield potential, disease tolerance, and herbicide technology are all important to consider when selecting a variety.

One of the first steps in variety selection is to choose the relative maturity. This can be a complicated decision in North Carolina, where MGs from 2 to 8 can be produced successfully. Understanding and selecting the appropriate maturity for a given production situation are critical to maximizing soybean yield and seed quality. Soybean MGs are latitudinal zones developed to define where a soybean genetic package best fits, based on photoperiod and temperature. More background information about MGs can be found in Chapter 1.

The NC State Extension Soybean Program has invested effort over the years to determine the optimal soybean MG for use in diverse production scenarios across North Carolina. The following highlights from that work can help inform MG selection for your production situation.

• In optimal production situations where limited stress is encountered, MG3 and MG4 soybean varieties optimize yield in North Carolina. Using an earlier-maturing variety (MG<5) was one of the strongest predictors of high soybean yield in the North Carolina Soybean Yield Contest. Earlier-maturing varieties have shown superior genetic gain each year and have been bred to thrive under high-yield scenarios. In addition, considerable premiums have been available for August and September delivery of soybeans in North Carolina over the past few years, and use of these earlier-maturing varieties at full-season planting dates facilitates delivering on these timelines.

• While the yield potential of earlier-maturing varieties (MG<5) is often superior in full-season production situations on productive land, growing earlier-maturing varieties in North Carolina generally creates the need for more aggressive management to be successful and protect seed quality.

• In average production scenarios across the state, we have generally found that MG5 and MG6 varieties optimize yield, even in full-season planting situations.

• Producers have a lot of flexibility in MG selection in soybean planting situations in mid-June and mid-July. We have consistently seen similar yields of MG4 to MG7 varieties planted in mid-June and MG5 to MG7 varieties planted in mid-July, so the old rule of thumb that the later you plant, the later-maturing variety you need to use is no longer true in our environment.

• BeanPACK, a tool developed by the NC State Extension Soybean Program, should be used to make data-driven decisions on the optimal MG to be used across the diverse planting dates and regions of North Carolina.

The next step in choosing a variety is to select the herbicide-tolerance trait(s) you want. The majority of soybeans grown in the United States contain at least one genetically engineered herbicide-tolerance trait. Herbicide-tolerant classes include Roundup Ready (RR), Roundup Ready 2 Yield (RR2), Liberty Link (LL), sulfonylurea-tolerant soybeans (STS), Roundup Ready Xtend, XtendFlex, and Enlist E3 (2,4-D) (Table 2-1). The RR, RR2, LL, Xtend, and Enlist traits are genetically modified, whereas the STS trait was developed using conventional methods and is not considered a genetic modification. In addition, many of the herbicide-tolerance traits are now being stacked to allow for multiple modes of action for weed control (XtendFlex and LibertyLink GT27).

The herbicide-tolerance technology used should be based on the most problematic weeds present in a field and, more important, on what kind of resistance those weeds possess. In fields with glyphosate-resistant weeds, switching to the LibertyLink, dicamba, or 2,4-D technology may help combat those weeds.

Tolerance or resistance to disease is another important factor to consider when selecting a soybean variety. Using varieties with genetic resistance is likely the most cost-effective way to manage disease. A wide range of environmental conditions occurs across North Carolina during the growing season, and these conditions often influence the occurrence and severity of soybean diseases. While no single soybean variety can provide complete protection against all the diseases that may occur, knowing the history of disease in a particular field will help you select a variety with the most appropriate disease resistance package. Fields with a history of disease are likely to have those diseases again; therefore, resistant soybean varieties should be chosen for those fields.

Common diseases occurring in North Carolina for which genetic-resistant varieties are available include frogeye leaf spot (FLS), sudden death syndrome (SDS), and stem canker (SC). Information on the disease resistance package of a variety is available from your seed dealer.

Nematodes are pests that can also cause significant yield losses for North Carolina soybean growers. Soybean cyst nematode (SCN) is possibly the most serious soybean pest problem in North Carolina and is found in fields across the state. Other common nematodes, such as root-knot nematode (RKN), can also significantly reduce yields. Many varieties possess resistance to some nematodes, and that information is available from your seed dealer.

Finally, once you have narrowed down the list of varieties, yield can be considered. Yield potential is probably the most important factor when selecting soybean varieties. Selecting a variety that is high yielding is important, but yield stability across multiple locations and years is an even more important consideration.

Yield potential is highly sensitive to environmental conditions, so multiyear, multilocation data will provide the most accurate indications of a given variety’s “true” performance. It is a natural tendency to want relative yield data from situations close to home, on similar soils, and with similar weather. Since there’s no way to forecast next year’s weather, the more environments the data encompass, the better. Next year’s yield in county X is better predicted by the statewide averages from the previous year than by the county X results from the previous year. Where possible, plant the majority of your acreage in varieties for which multiple-year and multiple-location data are available. To take advantage of the newest genetics, with greatest yield potential and/or pest resistance, you may have to choose varieties based on a limited set of performance data. In such situations, plant those varieties on limited acreage to test yield performance in your environment.

To provide unbiased, sound estimates of soybean variety yield, NC State Extension conducts official variety testing (OVT) each year and compiles this information on both the NC State Extension OVT website and the Variety Selection Tool. These resources provide valuable multi-environment data that can be used to aid in variety selection. Using the Variety Selection Tool, you can filter and search for soybean variety characteristics that are important for your specific operation and that will maximize your yield potential. A video overview of how to use this tool can be found online. In addition, the OVT program hosts a webinar each year after soybean data are released to discuss the results of tests and to highlight the highest-performing varieties by multiple and single-year views. Recordings from those webinars are hosted on the NC OVT YouTube channel. Data reports from the tool are also provided on the NC State Extension OVT website.

After reviewing the previously discussed characteristics, if you still have more varieties on your list of possibilities than you will realistically buy, consider price. Seed is a significant expense, but there is a limited range of prices among varieties. If two varieties differ enough in yield potential that the value of the additional yield is greater than the difference in the seed cost, then that additional seed cost would pay for itself. Yield probably contributes more to profits than seed cost does.

Some varieties shatter more readily than others, but such damage is not nearly as big a problem as it used to be. Propensity for shattering might still be worth considering if you anticipate that harvest may be very late (for example, after Thanksgiving) or if you are planting an earlier-maturing variety.

Some varieties lodge (fall down) more readily than others, especially at higher populations. If you plant varieties that are susceptible to lodging, reducing the seeding rate is one way to lower the risk of lodging. Growth habit can also influence lodging. Varieties that tend to grow taller could pose more risk for lodging. Some varieties grow taller than others, but unless the soybeans are being grown for forage, this trait is of little consequence. It seems logical that relative height would be a useful characteristic for double-crop situations, but examining which varieties yield relatively higher with late planting dates is probably a more useful consideration.

Soybean seed size can vary widely but generally does not affect yield potential. Seed size is influenced more by environmental conditions at the seed production site the previous year. Under typical planting conditions, seed size would also not influence emergence or seedling vigor.

Flower color (purple or white), pubescence color (gray or brown [“tawny”]), hilum color (black, brown, buff, or variable), and pod-wall color (tan, brown, or black) appear to be of no consequence in how a variety performs.

Availability of seed for the varieties you selected may be a final consideration. Select multiple varieties that meet your expectations so that you have some backup options if your preferred varieties are not available that year.

Seed Treatments

Fungicide seed treatments: Soybeans in North Carolina are susceptible to several early-season pathogens (see Soybean Seedling Diseases). These pathogens are most effectively managed using diverse strategies, including varietal resistance, cultural tactics, and chemical control options. Active ingredients in fungicide seed treatments have different activity on seedling diseases encountered in North Carolina soybean production. Information on fungicide efficacy on soybean seedling diseases can be found in the Crop Protection Network publication Fungicide Efficacy for Control of Soybean Seedling Diseases. As you prepare to plant soybeans, you may wonder whether fungicidal seed treatments are needed to protect soybean stand and ultimate yield. Research from 2014 to 2018 across 15 North Carolina environments showed that fungicidal seed treatment had no impact on soybean yield when soybeans were planted after mid-May. (See the NC State Extension publication AG-860, Nonfoliar Yield Enhancement Products in North Carolina Soybeans). However, more recent small-plot and strip-plot research conducted in North Carolina indicates that a fungicidal seed treatment can have value for protecting stand and yield at planting dates earlier than mid-May in environments where disease pressure and varieties used are conducive for disease development (see “What is the Value of a Fungicide Seed Treatment in NC Soybean Production?”). We encourage scouting and subsequent diagnosis of soybean seedling diseases using the Plant Disease and Insect Clinic, which can aid in the future selection of effective seed treatments for the various seedling diseases in that field and inform selection of varieties with resistance to the identified seedling diseases.

Insecticide seed treatments: Soybean insecticide seed treatments do not provide a yield benefit in North Carolina and most of the areas where soybean is grown. Out of 26 replicated Extension tests across North Carolina, we have never measured a yield advantage to using insecticide seed treatments (see “Neonicotinoid Soybean Seed Treatments Provide Negligible Benefits to US Farmers”). While insecticide treatments kill soybean pests, such as thrips, the pests have not been observed at levels that are high enough to cause yield loss (see “Impact of Neonicotinoid Seed Treatments on Thrips (Thysanoptera: Thripidae) and Soybean Yield in Virginia and North Carolina”). Bean leaf beetle is another common pest attributed to impacting soybean yield due to their foliar feeding. However, when soybeans are seedlings, numbers of bean leaf beetles are too low to cause enough defoliation to lead to yield loss. Not only are soybean insecticide seed treatments an unnecessary expense, their overuse can drive resistance in other crops and can kill predatory ground beetles, which prey on slugs that clip plants and reduce yields (see “Insecticide Resistance Signals Negative Consequences of Widespread Neonicotinoid Use on Multiple Field Crops in the U.S. Cotton Belt” and “Neonicotinoid Insecticide Travels Through a Soil Food Chain, Disrupting Biological Control of Non-Target Pests and Decreasing Soya Bean Yield”). Unfortunately, there is no remedial management method to kill slugs; therefore, avoid using insecticide on soybean seed when possible.

Nematicide seed treatments: Plant-parasitic nematodes are microscopic roundworms that feed on the roots of the crop plant, causing damage and reduced growth. Management of nematodes requires a multipronged plan. This plan should include monitoring of nematode populations; use of soybean varieties with genetic resistance to the nematodes of concern, where available; and chemical options, including nematicide seed treatments, where appropriate. Nematicide seed treatments are chemical or biological compounds with nematode-killing properties applied to the seed before planting. These seed treatments are designed to provide early-season protection, guarding young plants during early growth. Nematicide seed treatments are most beneficial under low to moderate nematode pressure. Fields with high or heavy levels of nematode pressure are unlikely to be successfully managed through seed treatment alone. Several seed-treatment products are available, including biologically based and conventional chemistry-based (Table 2-2). Additional information on seed treatments for soybean and other crops is also available in the North Carolina Agricultural Chemicals Manual. Please refer to the current chemical labels in all cases for directions on safe use and information on application rates, timing, and harvest intervals.

Table 2-2. Nematicide Formulation and Trade Name, Rate, and Nematodes Targeted with Various Nematicide Seed Treatments

Symbiotic inoculant seed treatments: Soybeans form symbiotic relationships with bacteria living in the soil and the rhizosphere. These bacteria, known generally as rhizobia, receive signals from the soybean to form root nodules. Inside the nodules, rhizobia “fix” atmospheric nitrogren (N₂), providing the plant with readily available nitrogen in exchange for carbon, which the microbes use as an energy source. Rhizobial inoculants are available as seed treatments (applied directly to the seed) or as in-furrow treatments (applied to the soil during planting). Bradyrhizobium and Rhizobium species are the most common inoculants. A common recommendation, in both the South and the Midwest, is to inoculate any field that has not been planted in soybeans in the previous four to five years. Research from decades ago found that inoculants in North Carolina fields that had been out of soybean production for at least 8 years resulted in a positive yield response in only 2 of the 23 locations evaluated. The yield response from the two positively affected sites, however, generated value in yield three times greater than the cost to treat all 23 sites. Of the two sites that produced a positive yield response, one was in the sandhills (Moore County) and one was in the blacklands (Tyrrell County). Interestingly, the 17 inoculants used ranked similarly in yield order at both sites; all soil-applied inoculants outperformed all seed-applied inoculants.

More recent research from across the United States indicated that neither seed-applied nor soil-applied inoculants increased yield in fields with a history of soybeans or in fields that were not under severe stress. In the North Carolina Soybean Yield Contest analysis, inoculating soybeans was not a strong predictor of high soybean yield, even in high-yielding environments (see Key Management Strategies to Increase North Carolina Soybean Yield: What We Have Learned From 877 Soybean Yield Contest Entries and “Soybean Yield, Biological N₂ Fixation and Seed Composition Responses to Additional Inoculation in the United States”). For fields that have been out of soybean production, inoculants may not be necessary, but farmers cannot afford to risk omitting inoculants in these scenarios.

Biostimulant seed treatments: Besides rhizobia inoculants, there is a large and diverse commercial market of other biological seed treatments referred to as “biostimulants.” Biostimulants are defined by the U.S. Department of Agriculture (USDA) in the 2018 Farm Bill and the Plant Biostimulant Act of 2023 as “a substance or micro-organism that, when applied to seeds, plants, or the rhizosphere, stimulates natural processes to enhance or benefit nutrient uptake, nutrient efficiency, tolerance to abiotic stress, or crop quality and yield.” In the United States, biostimulants are not federally regulated but are typically registered at the state level similar to fertilizers. Biostimulants for soybean include microbes (bacteria or fungi and either single-species or multiple-species consortia) advertised as carrying out a range of beneficial activities, including enhanced germination or increased tolerance to environmental stress (for example, drought or salinity). The term “biofertilizer” is sometimes used interchangeably with “biostimulant” and refers to microbes that improve plant nutrient acquisition. Biostimulants also include natural products derived from living organisms, including substances like seaweed extracts or organic acids (for example, humic and fulvic acids). While promising, biostimulant efficacy is highly variable. Field performance may vary between soybean varieties and across soil types and production environments. You can find local, unbiased field performance data of soybean biostimulants in North Carolina through the Soybean On-Farm Trialing (OFT) Program and the NC State Extension Soil Health and Management website.

The key to determining the best variety for a field depends upon individual production systems. Before selecting a variety, you must understand the type of variety needed to maximize yield. Recording information about each field allows you to understand its history related to pests and pathogens and what specific needs it has. This will allow you to select the best variety for each environment.

Data can be obtained at the NC State Extension OVT website and via the Variety Selection Tool. The Variety Selection Tool also contains links to technical sheets on specific varieties. Spending time and effort reviewing these resources to select the right variety is a good investment. For more on how to use the Variety Selection Tool, including information on upcoming training opportunities, contact Ryan Heiniger.