Establishing Alfalfa During Late Summer
UWEX Crops and Soils Agent
Fond du Lac County
Seeding perennial forage species such as alfalfa during the late summer in Wisconsin can result in vigorous and productive stands when proper establishment practices are followed. Late summer alfalfa seeding does not replace traditional spring-seeding recommendations, but rather provides growers with an establishment alternative when crop rotation allows. Like most crop production practices, success is achieved with management and attention to details. This Focus on Forage will discuss the opportunities, advantages, risks and management practices needed for successful late summer alfalfa establishment.
What are the Opportunities?
opportunities exist in Wisconsin crop rotations where growers can seed
alfalfa during the late summer.
when a small grain or vegetable crop is grown and harvest occurs before or
during early August, growers may consider seeding alfalfa immediately
after harvest. It is important to make sure that herbicide carryover from
the previous crop will not prevent alfalfa seedling establishment. This
may especially be a problem where alfalfa seedings follow a sweet corn
A second circumstance where growers may consider late summer alfalfa establishment is when a spring seeding has failed. Disease buildup or allelopathic effects are generally not of concern in this situation because alfalfa plants did not have time to become fully established. There have been confirmed reports of fields that were successfully established during the late summer of the year when a spring-seeded alfalfa stand failed due to Pythium, Aphanomyces, or Phytophthora root rots.
Often forage producers can determine in early spring that an established stand will no longer be productive, and alternative acres for additional spring seedings are limited by such factors as previous herbicide use. In these situations, the fastest and least risky alternative to get a nonproductive field back into alfalfa would be to plow and seed the field to a small grain crop for silage or grain harvest and then establish alfalfa later in the summer. This option minimizes the risk of allelopathy or disease problems.
What are the advantages of seeding alfalfa in late summer?
summer alfalfa establishment offers several advantages over traditional
spring seedings. Weed and insect pests seldom limit stand establishment
success. Using a pre-plant incorporated herbicide or a companion crop is
not recommended. Companion crops will compete too strongly with the
developing alfalfa seedlings for moisture. Also, the first hard freeze
will kill any annual weeds that may have germinated. Remember that soil
temperatures are much higher in the late summer than they are in the early
spring. With adequate moisture, alfalfa seedlings will germinate, grow and
develop a crop canopy at a much faster rate.
yields of late summer seedings during the first production year are
generally higher than yields of spring seedings during the establishment
year. In fact, yields are often comparable to 2- and 3-year-old stands. By
seeding alfalfa during the late summer, forage producers can have the
equivalent of an established stand the following spring. Additionally,
springtime workload is reduced.
What are the risks of seeding alfalfa in late summer?
are also risks associated with late summer alfalfa establishment. The
primary concern is the possibility of moisture stress during germination
and seedling establishment. Timely seeding will reduce this risk
significantly. Itís always advisable to make late summer seeding
decisions based upon current soil moisture conditions and short-term
weather forecasts. Near normal August and September rainfall should be
more than adequate to establish vigorous and productive stands.
Another risk is the threat of an early killing frost and/or severe winter. Again, timely seeding is important to minimize these risks.
What are the recommended seeding and establishment practices for late summer seedings?
that throughout this text reference has been made to seeding date as late
summer, NOT FALL!
weather and soil conditions vary each year, it is recommended that late
summer seedings be made between August 1 and August 15 in Wisconsin. If
you are in the northern half of the state, plant alfalfa in the early part
of August. If soil moisture and temperature conditions allow, seeding
slightly earlier or later than these dates will also result in successful
a rule of thumb, seed alfalfa 6-8 weeks before the average first killing
frost in your area. Seeding too early increases the risk for hot, dry
conditions to occur during germination and seedling development. Seeding
too late will not give the plants enough time to develop adequate root and
top growth before winter.
September 1, your chances of successfully establishing alfalfa are very
low. Researchers at Purdue University (at a location much farther south
than Wisconsin) reported that September 6 and 20 seeding dates in 1984 and
1985 resulted in significant winterkill and/or a high influx of weeds into
alfalfa stands the following spring. In northern Pennsylvania, alfalfa
yield in the first production year were reduced by 158 lbs/acre for each
day seeding was delayed after August 1.
fertility requirements for late summer-seeded alfalfa are the same as
spring seedings. Take a soil test during the fall prior to the
establishment year and follow recommendations for correcting soil pH,
phosphorus, and potassium deficiencies. The UW-Extension bulletin A2809
(Soil Test Recommendations for Field, Vegetable, and Fruit Crops) provides
specific soil fertility recommendations for growing alfalfa.
Tillage and Seedbed Preparation
the amount of tillage immediately before late summer seedings to avoid
unnecessary soil moisture loss. Perform secondary tillage operations that
provide a good seedbed for the type of seeding equipment being used.
enough credit is given to the importance of firm seedbeds in successful
alfalfa establishment. This is especially true for late summer seedings. A
loose, fluffy seedbed in August can severely reduce germination success. A
firm seedbed improves seed-soil contact and maintains more favorable soil
many situations, one pass with a roller seeder may not be sufficient. A
second trip at an angle to seeding with an empty seeder, pulvi-mulcher
(tines up), or cultipacker will often make the difference between stand
success and failure. On coarse, sandy soils, a firming operation may be
needed prior to seeding.
late summer forage establishment can be successful if proper seeding
equipment is used and seedling competition from weeds is eliminated using
an approved herbicide.
3-year study in Manitowoc County, showed that moldboard plowing was more
effective than disking as a primary tillage operation for eliminating
volunteer cereal competition in late summer seedings following winter
Seeding Rate and Depth
no adjustment is needed from recommended spring seeding rates. A seeding
rate of 12-15 pounds per acre at a depth of ľ to Ĺ inch is recommended.
weeds is generally not a concern with late summer-seeded alfalfa. Annual
broadleaf weeds such as velvetleaf or pigweed usually do not grow very
tall and will be killed by the first frost. Occasionally, winter annual
broadleaves like shepherd's purse or field pennycress can be severe. If
this is the situation, a post-emergence herbicide application of Pursuit
or Buctril will control these weeds. Severe infestations of grassy weeds
can be a concern in late summer-seeded alfalfa because of the over winter
smothering effect they have on young alfalfa seedlings. In these
situations, an application of Poast Plus or Select herbicide (with the
appropriate additives) is an effective control measure. Make applications
to volunteer winter wheat when the wheat plants are 4 to 6 inches tall and
actively growing. Don't wait until spring to treat winter cereals because
control will be much less effective.
no-till or conventional till, perennials such as quackgrass need to be
controlled before seeding alfalfa. A glyphosate product can be applied
when quackgrass is 6 to 8 inches tall and actively growing.
When should late summer seeded alfalfa be harvested?
Fall of Seeding Year
plant root systems are not well developed, it is never recommended to
harvest late summer-seeded alfalfa in the fall of the establishment year.
Even with a large amount of top growth, alfalfa will not smother itself
out during winter.
Spring After Seeding Year
of late summer seeded alfalfa can be treated similar to an established
stand during the first production year. Research at Iowa State University
has shown that total-season forage yield in the first production year is
slightly lower for late summer seeded alfalfa as compared to spring seeded
alfalfa when cut at the same stage of maturity and frequency. Stand
persistence was good when late summer seeded alfalfa stands were cut at
the mid-vegetative to early bud stage during first cut and subsequent
harvests are were delayed until early flower.