If soil moisture is sufficient for germination and emergence, August alfalfa seedings offer several advantages over spring seedings, say Rory Lewandowski and Mark Sulc, Ohio State University Extension educator and forage specialist, respectively.
In late summer, alfalfa seedlings have less weed competition, and soil-borne disease organisms that thrive in cool, wet soils aren’t an issue. Also, time spent on field preparation and planting doesn’t compete with corn and soybean field work.
However, late-summer seedings come with risks that must be managed, the two specialists warn. Ideally, seedings should be completed by mid-August in northern Ohio and by Aug. 31 in the southern part of the state. Those timelines are based on average frost dates and the time needed for alfalfa plants to develop root systems capable of overwintering. Later planting dates will work if the fall is warmer than normal, but the risk of failure is higher.
No-tilling alfalfa into a small-grain stubble often works well, Lewandowski and Sulc point out. However, Sclerotinia crown and stem rot is a concern with no-till seedings, especially where clover has been present in the past. The disease, which causes white mold on alfalfa seedlings, infects them during cool, rainy spells in late October and November. Early August plantings dramatically improve the crop's ability to resist the infection. Late-August seedings are very susceptible, with mid-August seedings being intermediate.
In no-till situations, the two experts recommend a preplant glyphosate application to minimize competition from existing weeds. After the alfalfa is up and growing, late-emerging winter-annual broadleaf weeds must be controlled, and butyrac, Pursuit and Raptor are the primary herbicide options. Fall applications are much more effective than spring applications for controlling those weeds, especially if wild radish or wild turnip is in the weed mix.
If tillage is used to prepare the soil for planting, a firm seedbed is needed to ensure good seed-to-soil contact. A preplant herbicide isn’t required, but the risk of establishing a tilled seedbed for a late-summer planting, especially this year, is moisture loss. Don’t plant seeds into a dry seedbed, Lewandowski and Sulc emphasize.
Finally, they say to keep the following factors in mind anytime alfalfa is planted:
● Soil fertility and pH – The recommended soil pH for alfalfa is 6.8. The minimum or critical soil phosphorus level is 25 ppm and the critical soil potassium level is between 100 and 125 ppm for many Ohio soils.
● Seed selection – Be sure to use high-quality seed of adapted, tested varieties and use fresh inoculum of the proper Rhizobium bacteria.
● Planter calibration – If coated alfalfa seed is used, be aware that coatings can account for up to one-third of the weight of the seed. That can affect the number of seeds planted if the planter is set to plant seed on a weight basis. Seed coatings can also dramatically alter how the seed flows through the drill, so be sure to calibrate the drill or planter with the seed being planted.
● Seed placement – The recommended seeding depth for alfalfa is ¼-½”. It’s better to err on the side of planting shallow rather than too deep.
For more late-season alfalfa seeding recommendations, read Seed Alfalfa In Early Fall, California Research Indicates.