Its been an interesting couple of weeks in South Dakota. Many row crop producers have gone from worrying about drought to wondering when it will be dry enough to get back in the field. A couple common concerns now include the effectiveness of late pre-emergence herbicides and soybean emergence issues/late planted beans.
Between wind and rain, many row crop fields have gone without their initial preemergence herbicide pass shortly after planting. The list of PRE or early postemergence herbicides for corn is fairly extensive and does allow for a decent window of opportunity. In many cases, late postemergence applications can be quite effective on corn as well. If weather permits in the next week or two, an early postemergence application will likely take care of weeds creeping into corn fields.
Many soybean preemergent herbicides, however, are not recommended to be applied more than three days after planting and cannot be applied to a crop that is already up due to potential soybean injury or death (less than ideal); examples include the active ingredients in Valor, Mauler, and Spartan. However, herbicides that belong to Group 15, like Warrant, Dual Magnum, Zidua, or Outlook can safely be sprayed on emerged soybeans. Keep in mind these products do not have activity on weeds that have emerged, so a tank mix with a foliar product may be necessary.
Before spraying the general premix that the neighborhood is using, be sure to go out and scout fields, identify if soybeans and weeds are emerging, and adjust your plan accordingly. Always take the time to read herbicide labels (keep temperature in mind as well) before applying pesticides. For more information on herbicide options and characteristics visit extension.sdstate.edu and search pest guide for the 2025 Pest Management Guides.
For those worrying about soybeans that have endured some cold rains or those looking at fields waiting to be planted, here are a few considerations.
Soybeans tend to like soil temps a bit warmer than corn; with a required three-day average soil temperature of 55 F for emergence, the ideal soil temp is actually 77F. If you have concerns about soybeans that havent come up, consider that it may not be warm enough for even germination yet.
In addition to soil temps, we have to consider the possibility of chilling injury. Corn and soybeans both go through an imbibition period, which occurs when moisture hits the seed right after planting. Seeds tend to be quite susceptible to cold, wet soils during this time. If that initial water is colder than 50 degrees Fahrenheit, seeds may become swollen and non-viable due to cell rupture, and roots and shoots may also be aborted. This risk is heightened when seeds are planted into dry, cool soils, and a cold rain occurs afterward.
Corn that was seeded into wet soils with temperatures above 50 degrees Fahrenheit within the first 48 hours following planting should germinate just fine. Soybeans have a shorter imbibition period, and soil temps above 50 degrees Fahrenheit for 24 hours are usually long enough for acceptable germination.
If crops are planted early and germinate as expected, of course, there are still a few temperature-related risks to consider. If the air temperature drops into the 40s for several days, emergence will likely be significantly slowed, meaning crops may take two weeks or longer to emerge depending upon accumulated growing degree days. This being said, crops planted but not yet emerged may just be waiting for warmer temps, but other, not so great, issues that Ive listed are possible.
For those waiting for soils to dry up to get back to planting, you arent alone! As of 5/27, 79% of the intended soybean crop was planted, this is ahead of the five year average of 64% average, but we have a ways to go (NASS, 2025). If you purchased a very long maturity originally, you may want to consider switching maturities. However, conventionally its said that maturity does not need to be changed prior to a 6/10 planting. Those planting early maturing beans should be alright through June. Much of these findings are due to soybeans being photoperiod sensitive, therefore they can catch up to some degree; so, switching to inferior genetics for an earlier maturing soybean may not be worth it.
Some agronomists will recommend increasing planting rates, but regional studies observed max yields at a planting population of 154,000 seeds/acre, just slightly higher than the recommended rate of 140,000 (the yield difference was just 0.7 bu/acre) . With a small margin of yield advantage, seed cost should be heavily weighted when making decisions regarding increasing seed population.
Despite planting later than intended, the weather during the growing season often has a larger impact on yield than planting timing. In South Dakota, a study consisting of four locations over two years, June planted beans out-yielded May planted soybeans half of the time. Higher soybean yields are seen most commonly in early planted beans, but a well-timed rain can have a much bigger impact later in the growing season.
Summer Field Day schedule
Find details for all field days here.
- West River Research Farm Field Day June 11; 3-8 p.m. at 13370 Alkali Road, Sturgis. Dinner provided.
- Dakota Lakes Research Farm Field Day June 26; 3 p.m.-dusk at 21310 308th Ave., Pierre. Dinner provided.
- Southeast Research Farm Summer Field Day and Family Evening July 8; 1:30-4:30 p.m. at 29974 University Road, Beresford. Dinner included. (New additions include food trucks, kids activities, SDSU ice cream, and informational booths.) Please register at extension.sdstate.edu/events.
- Northeast Research Farm Field Day July 10; 4 p.m.-dusk at 15710 455th Ave., South Shore. Dinner provided.
- Oak Lake Field Station Field Day July 10; 9 a.m.-4 p.m. at 19862 483rd Ave., Astoria. Lunch provided.
- Cottonwood Field Station Field Day Aug. 13; 9 a.m.-noon at 23738 Fairview Road, Philip.
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