August gives growers another window of opportunity to establish an alfalfa stand, provided there is sufficient soil moisture for seed germination and plant emergence. There are some advantages to a late summer alfalfa planting as compared to a spring planting. One big plus is that planting time and field preparation is not competing with corn and soybean field work. No-till planting following a small grain crop often works well. Late summer planting means alfalfa plants are not competing with the flush of annual spring and summer weed emergence/growth. The soil borne root rot and damping off disease organisms that thrive in cool, wet soils are not an issue. However, late summer alfalfa planting has some other risks that must be managed.
Ideally, planting would be completed by mid-August in Northern Ohio and by the end of August in Southern Ohio. These timelines are based on average frost dates and the time needed for an alfalfa plant to develop a root system capable of overwintering. If the fall is warm and extended, alfalfa could be successfully established with later planting dates, but the risk of a planting failure is higher. How lucky do you feel?
Sclerotinia crown and stem rot is a concern with no-till seedings of alfalfa and especially where clover has been present in the past. This is a pathogen that causes white mold on alfalfa seedlings. They become infected during cooler rainy spells in late October and November, the disease develops during the winter, and seedlings literally “melt away” in winter and early spring. It can be devastating where the pathogen is present. No-till is especially risky where clover has been present because the sclerotia germinate from a shallow depth. Early August plantings dramatically improve the alfalfa’s ability to resist the infection. Late August seedings are very susceptible, with mid-August being intermediate.
In a no till situation, minimize competition from existing weeds by applying a burndown application of glyphosate before planting. After the alfalfa is up and growing, late summer and fall emerging winter annual broadleaf weeds must be controlled. A mid to late fall application of butyrac, Pursuit or Raptor are the primary herbicide options. Fall application is much more effective than a spring application for control of these weeds especially if wild radish/wild turnip are in the weed mix. Pursuit and Raptor can control winter annual grasses in the fall but should not be used with a mixed alfalfa/grass planting.
If tillage is used to prepare the soil for planting, a firm seedbed is needed to ensure good seed-to-soil contact. Follow the “footprint guide” that soil should be firm enough for a footprint to sink no deeper than one-half inch. A pre-plant herbicide is not needed for a tilled seed bed, but the risk of establishing a tilled seed bed for a late summer planting, especially this year, is the loss of moisture. Do not plant seeds into a dry seedbed because this increases the likelihood of a seeding failure.
Finally, keep in mind that any time alfalfa is planted the following factors must be managed:
* 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 somewhere between 100 and 125 ppm for many of our 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 a coated alfalfa seed is used, be aware that coatings can account for up to one-third of the weight of the seed. This 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 one-quarter to one-half inch deep. It is better to err on the side of planting shallow rather than too deep.