Rory Lewandowski, OSU Extension Educator, Wayne County and Mark Sulc, OSU Extension Forage Specialist

Seeding alfalfa requires a firm seedbed

Ohio growers experienced another wet spring and compressed 2018 spring planting season.  On some farms, this caused postponement of plans for spring seeding of alfalfa and other perennial forages.  In some areas, the prolonged wet weather affected forage harvest schedules, resulting in harvest equipment running on wet forage fields leaving ruts, compacted soils and damage to alfalfa crowns.  Some of these forage acres need to be re-seeded.

Late summer, and especially the month of August, provides growers with another window of opportunity to establish a perennial forage stand. Typically, the main risk with a late summer August planting is having sufficient moisture for seed germination and plant growth. There are some advantages to late summer forage planting as compared to a spring planting. Late summer planting means forage seedlings 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, growers need to be aware of planting dates and the potential for late summer diseases in some situations.

According to the recently revised, 15th edition of the Ohio Agronomy guide, planting of alfalfa and other legumes should be completed by mid-August in Northern Ohio and by the end of August in Southern Ohio.  These timelines take into consideration average frost dates and the time needed for forage plants to develop a root system capable of overwintering.  For example, at about 8 to 10 weeks after emergence alfalfa plants pull the growing point below the soil surface, a process termed ‘contractile growth’.  Alfalfa is only a true perennial plant once contractile growth occurs, and the plant needs to reach this growth stage to overwinter.  Clover plants need to have a crown formed, and grasses should be at least in the tillering stage of development before the onset of winter.

If the fall is warm and extended, similar to what we have experienced the past few years, successful establishment is possible with later planting dates.  How much later is really a question of risk management.  Late summer and early fall planting dates of forages were tested in Pennsylvania in the mid-1990’s at two locations that historically are a little milder than most of Ohio’s winters.  For each day planting was delayed after August 1, total forage dry matter yields the next year were reduced by an average of 158, 105, and 76 lbs./acre for alfalfa, red clover, and birdsfoot trefoil.  Later planting dates usually affected grasses to a lesser degree.  For example, orchardgrass yields only decreased significantly when planting was delayed past late-August and perennial ryegrass yields were actually greater in late-August than in early August plantings.  However, for each day planting was delayed after August 30, yields declined 100 lb. /acre for orchardgrass and 153 lb. /acre for perennial ryegrass. Reed canarygrass, a slow establisher, was more sensitive to planting dates. Reed canarygrass yields the year after seeding declined 120 lbs. /acre for each day planting was delayed after August 1.   The best policy is usually to plant most perennial forages as soon in August as possible, when soils conditions allow and when soil moisture is present.

Sclerotinia crown and stem rot is a concern with no-till seedings of alfalfa in late summer and especially where clover has been present in the past. This pathogen 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 plantings being intermediate.

In a no-till situation, minimize competition from existing weeds by applying a burndown application of glyphosate before planting. Using no-till when herbicide-resistant weeds are present, such as marestail in a previous wheat field, creates a very difficult situation with no effective control options, so tillage is probably a better choice in those situations.  Post-emergence herbicide options exist for alfalfa. After the alfalfa is up and growing, control late summer and fall emerging winter annual broadleaf weeds. A mid- to late fall application of Butyrac, Buctril 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 in pure legume stands but not with a mixed alfalfa/grass planting.  Consult the 2018 Ohio and Indiana Weed Control Guide and always read the specific product label for guidelines on timing and rates before applying any product.

For conventional tillage seeding prepare a firm seedbed to ensure good seed-to-soil contact. Be aware that too much tillage depletes soil moisture and increases the risk of soil crusting. Follow the “footprint guide” that soil should be firm enough for a footprint to sink no deeper than one-half inch.  Tilled seedbeds do not need a pre-plant herbicide.  Finally, keep in mind the following factors to increase establishment success.

  • Soil fertility and pH: The recommended soil pH for alfalfa is 6.8. Forage grasses and clovers should have a pH of 6.0 or above. The minimum or critical soil phosphorus level for forage legumes is 25 ppm (Bray P1) 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. “Common” seed (variety not stated) is usually lower yielding and not as persistent, and from our trials the savings in seed cost is lost within the first year or two by lower forage yields.
  • Planter calibration: If coated seed is used, be aware that coatings can account for up to one-third of the weight of the seed. This affects the number of seeds planted in planters set to plant seed on a weight basis. Seed coatings can also dramatically alter how the seed flows through the drill, so calibrate the drill or planter with the seed going into the field.
  • Seed placement: The recommended seeding depth for forages is one-quarter to one-half inch deep. It is better to err on the side of planting shallow rather than too deep.

Do not harvest a new perennial forage stand this fall. The ONLY exception to this rule is perennial and Italian ryegrass plantings.  Mow or harvest these grasses to a two and a half to three-inch stubble in late November to improve winter survival.  Do not cut any other species, especially legumes.

Source: Ohio Beef Cattle Letter