Rain and wet soil conditions condensed the spring planting season this year and some planned alfalfa plantings got moved to the back burner. August provides another window of opportunity to establish a perennial forage stand and it fits nicely into rotations after wheat grain harvest. Typically the main risk with an 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. 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 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, late summer forage planting has some other risks that must be managed.
Ideally, planting should 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 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 is called ‘contractile growth’. Once contractile growth occurs the alfalfa plant is considered a true perennial. The alfalfa plant needs to reach this growth stage to overwinter. Clover plants also 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 it might be possible to get successful establishment with later planting dates. How much risk are you willing to take? How good are you at predicting the weather? 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. The year after seeding legumes, forage yield declined as planting dates were delayed after early August in the previous year. 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. Grasses were usually less affected by later planting dates. 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. So 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 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 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 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, late summer and fall emerging winter annual broadleaf weeds must be controlled. A mid- to late fall application of Butyrac, Pursuit or Raptor and Buctril 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. Consult the 2014 Ohio and Indiana Weed Control Guide and always read the specific product label for guidelines on timing and rates before applying any product.
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. Generally, the risk associated with establishing a tilled seed bed for a late summer planting is the loss of moisture. Finally, keep in mind that any time forages are planted the following factors must be managed:
· 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 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 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 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, which should be mowed or harvested to a two and a half to three-inch stubble in late November to improve winter survival. All other species, especially legumes, should not be cut.