Crabgrass

Turfgrass Update
By Zac Reicher, Department of Agronomy and Horticulture, UNL

Record drought and heat during the summer of 2012 took a
toll on the cool-season turf across the northern Great Plains. Adding
insult to injury was continuation of the drought into the fall,
limiting seeding during the prime establishment period, and thus
turf remained thin going into winter. However, a relatively snowy
and mild winter limited damage from desiccation or direct cold
temperature, so at least the turf damage did not worsen over the
winter. Many cool-season turf areas will require some intervention
early this spring to improve density and aesthetics.
As of writing this article in mid-March, consistent warming
temperatures are not yet in the extended forecast, but it is still important
to seed Kentucky bluegrass or tall fescue as soon as possible.
Seeding from Thanksgiving through usually mid-March is considered
dormant seeding because germination would not be expected
for weeks to months when soil temperatures warm. The earliest
references to dormant seeding in turf that I found was a 1923 version
of the United States Golf Association's Green Section Record, though
it was likely used much before that in agriculture. The benefit of
dormant seeding is that the seed is in the ground, likely has absorbed
water, and is ready to begin the germination process as soon as
temperatures warm. Waiting to seed after temperatures warm up in
spring may lead to delays due to wet soils, wind, busy schedules, etc.,
thus costing the seedlings valuable time to mature. Seeding coolseason
grasses in the spring is hampered by weed competition from
crabgrass and other weeds, increased water requirements because of
shallow rooting, and poor tolerance of immature plants to summer's
heat. Dormant seeding should maximize the time for seedlings to
mature prior to summer stresses. The downsides of dormant seeding
could include some seed loss from predation or erosion, or seedling
death from extended warm periods in winter followed by cold
temperatures. The latter becomes less of an issue as we move later
into winter. We currently compensate potential seed loss of winter
by increasing seeding rates by 10-20%; we are currently conducting
research to try to understand potential changes in seed viability or
seed loss during the winter.
Regardless of whether turf areas were dormant-seeded or yet
to be seeded this spring, weed management is critical. All herbicides
labeled for turf have restrictions for use over seedlings.
However, minor herbicide injury to seedlings is quickly compensated
by reduced weed pressure, so much of our recent research
focuses on identifying herbicides that can be used safely and effectively
over newly-seeded cool-season grasses. Recently released
herbicides have increased the flexibility in weed control in new
seedlings. A summary of our research results follows:
• Mesotrione (Tenacity®) is probably the most flexible
product to use over cool-season seedlings and can be used
in the seedbed as a preemergence (PRE) herbicide and as
early as 28 days after emergence (DAE) according to the
label. Our research indicates it could be applied earlier with
little risk to seedlings and it will control crabgrass as well as
many broadleaf weeds PRE and POST

• Quinclorac (Drive® and many trade names) is labeled for
use at 28 days after emergence (DAE), but our work shows
it could also be applied earlier with little risk of damage.
Do not use the methylated seed oil additive when using
over seedlings. It will control crabgrass as well as many
broadleaf weeds POST.
• Carfentrazone (QuickSilver®) is a contact broadleaf herbicide
and has almost no restrictions on use over seedling
turf. However, multiple applications will be required since
it is a contact herbicide.
• Quinclorac+carfentrazone (SquareOne®). Can be used
as early as 7 DAE and control crabgrass as well as many
broadleaf weeds POST.
• Dithiopyr (Dimension® and others) (primarily preemergence
plus early postemergence on annual grasses) is the
safest of the typical PRE herbicides and can be used usually
after the second mowing. This herbicide is often recommended
after an application or two of quinclorac (Drive) or
mesotrione (Tenacity) for long-term PRE control.
• Siduron (Tupersan®) is an older PRE herbicide that can be
used in the seed bed to provide crabgrass control while allowing
the cool-season grasses to germinate. Siduron has a
short residual and therefore will require repeat applications
about every 3 to 4 weeks for extended control; or one or
two applications can be used shortly after seeding followed
by traditional PRE's with better residual.
The drought has spurred tremendous interest in converting
lawns to buffalograss. Our buffalograss breeder/geneticist Keenan
Amundsen has been extremely busy spearheading the last details
for releasing our newest seeded cultivar, "Sundancer," as well as collaborating
on research to further refine establishment and management
of buffalograss. One frequent complaint on buffalograss is its
slow establishment. However, in side-by-side research plots seeded
in spring, buffalograss that is maintained properly will establish
almost as fast as tall fescue and faster than Kentucky bluegrass.
We believe the complaint on slow establishment is usually a result
of consumers perceiving buffalograss as a low maintenance grass
that needs "little or no inputs." However, buffalograss requires
similar irrigation, fertilization and mowing as Kentucky bluegrass
or tall fescue during the first year of establishment to maximize
cover, and only then can maintenance be dramatically reduced. We
are also in the process of evaluating a number of new herbicides
with apparent safety on seedling buffalograss. In the past, quinclorac
was the standard herbicide, and though it is still effective,
a number of new products like Tenacity (mesotrione), Dismiss®
(sulfentrazone) Solitaire® (sulfentrazone+quinclorac), or Echelon®
(sulfentrazone+prodiamine) can be applied at seeding with little
risk of buffalograss injury. Different herbicide options should improve
buffalograss establishment and thus reduce long-term inputs.
Much more information on dormant seeding as well as establishing
and maintaining buffalograss can be found at http://turf.unl.edu.

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