Issue No. 18, Article 5/August 6, 2010
Late-Summer Forage Seeding Reminders
The time for late-summer seeding of perennial legumes is fast approaching. Remember, this is late-summer seeding, not fall seeding. Let's review steps that help improve the chances of successful stand establishment.
Since alfalfa needs 6 to 8 weeks of growth or 6 to 8 inches of height before a killing frost, the preferred seeding period differs across Illinois. August 10 to 15 is preferred for the northern quarter, August 30 to September 4 for the central half, and September 5 to 10 for the southern quarter. Cool-season perennial grasses can be seeded 1 to 2 weeks later. Warm-season perennial grasses should not be seeded until spring.
Planning ahead is critical for alfalfa and grass seedings. Be sure there is no herbicide carryover from a previous application. Perennial weeds should have been controlled, soil tests taken, and any corrective limestone already applied. Fertilizer can be applied during seedbed preparation.
If there is not adequate soil moisture to establish the stand, seed should not be planted. It is very risky planting seeds into dry soil.
A firm seedbed is needed to ensure good seed-to-soil contact. With a prepared seedbed, follow the "footprint guide"--soil should be firm enough for a footprint to sink no deeper than 1/2 inch. A rule of thumb is that seeds should not be planted deeper than five times their diameter. For most forage crops, the seeding depth should not exceed 1/2 inch on medium- and heavy-textured soils and 1 inch on sandy soils.
Tilling the seedbed may not be necessary. No-till forage seedings can be successful, such as seeding into small grain stubble once the straw is removed.
Do not seed alfalfa following an older established stand. Autotoxic compounds released by the older alfalfa inhibit the growth, development, and production of new alfalfa seedlings. If the alfalfa is more than one year old, it is best to rotate to another crop before going back to alfalfa. If less than a year, alfalfa can be replanted.
Be sure to use certified seed (look for the blue seed tag) of adapted, tested varieties, and use fresh inoculum of the proper Rhizobium bacteria on the legume seed. Late-summer seeding rates are the same as spring seeding, but a companion crop is not recommended. Since weeds are slow to germinate in late summer, a preplant herbicide is typically not required. A postemergence herbicide can be used if weed problems develop and become competitive.
Lastly, late-summer seeded alfalfa and cool-season grass fields should not be harvested in the fall of the establishment year.
More details are available in the new Illinois Agronomy Handbook (24th edition), available at the University of Illinois Pubs Plus web site (800-345-6087).--Jim Morrison