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Number 1, 1999
Annual bluegrass Seedhead Control
Annual bluegrass (AB) is probably the most prevalent weed problem
in cool season golf course turf. While great strides have been
made in managing annual bluegrass to overcome some of its disease
and stress tolerance shortcomings, perhaps the biggest complaint
from golf course superintendents is the abundant seedhead production
of annual bluegrass in the spring.
Many superintendents could better tolerate AB if seedheads could
be controlled. What choices do superintendents have if they wish
to reduce or eliminate AB seedhead production? In our view, two
options exist. First and most widely used are plant growth regulators
to either eliminate (Embark) or compact (Scott's TGR, Cutless,
Primo) annual bluegrass seedheads. Second, some superintendents
and turf researchers have reported success using wetting agents
to reduce AB seedhead formation. Both topics will be covered in
this Turf tip.
We have had the most experience using Embark for AB seedhead control.
Embark is a growth regulator that actually stops turfgrass growth
and so will eliminate seedhead production if applied at the proper
rate and timing. However, the growth stoppage that occurs with
Embark can cause some initial turfgrass phytotoxicity. Usually,
this discoloration will last for 7-10 days following application.
After, this period of initial discoloration the turf become dark
green in color, displaying the normal greening response observed
with most PGR applications.
Most turf managers apply an iron source tank-mixed with the Embark
to help mask some of the phytotoxicity inevitably observed with
Embark. Our research has shown that many iron sources will antagonize
the action of Embark if tank-mixed with Embark. Most iron sources
sold today have some portion of non-chelate iron in the product
and many are simply inorganic iron salts, most commonly iron sulfate.
The inorganic forms of iron apparently react with Embark in the
spray tank causing a reduction in the actual rate of Embark applied.
Our research indicates that using a fully chelated iron source
will not antagonize the Embark application allowing the superintendent
to achieve the full activity of the Embark application. If you
have used a non-chelated iron source in the past and have been
pleased with the results, this would indicate that if you switch
to a fully chelated iron source, the Embark rate should probably
be lowered by 15-30% to account for the increased activity. Otherwise,
increased phytotoxicity may result.
What rate of Embark should you use? Good question. Higher rates
in the spring can cause more turf injury. In our experience, the
highest rate that should be used on mixed AB/creeping bentgrass
fairways is 5 pVA (1/8 lb ai/A or 1.8 oz/M). This will give excellent
seedhead suppression but may cause too much turf discoloration.
In our experience, rates of 2.5 pVA or less do not give reliable
seedhead control. Therefore, if injury is a real concern, try
rates of between 3 - pts/A (1.1 to 1.5 oz/M). Embark has been
widely used by superintendents on golf course fairways; however,
use on greens has generally given unsatisfactory results, i.e.
too much turf injury.
Embark applications have been timed using growing degree day models;
however, equally effective results can be achieved using a scouting
approach. Applications should be delayed until full turf greenup,
otherwise the greenup process will be delayed and turf quality
will suffer. Production of seedheads follows a normal bell curve,
that is, some individual plants will be early compared to the
bulk of the population. Scout for the first occurrence of these
early flowering types and then spray as soon as they are observed.
This should occur in mid-to-late April in central and northem
Illinois.
PGRs such as Primo, Scott's TGR, or Cutless do not stop growth,
but are true regulators that reduce the growth of each turfgrass
plant. Thus, seedheads are still produced, but the plants are
more compact, and the seedheads do not elongate as much as if
they were unregulated. Also, it is our observation that using
this class of PGRs may reduce the large of flush of seedheads
seen in the early spring. This gives the impression of some seedhead
control; however the price that is paid is that the seedhead production
window may be extended compared to untreated turf. So while less
seedheads appeared initially, the production window is stretched
by the PGR application.
Many superintendents have reported satisfactory results with Scott's
TGR for seedhead suppression. These applications have generally
been on greens and fairways. The reduction in seedhead elongation
results in a putting surface that is less bumpy even though seedheads
are present. Mike Sauls at Butler National has been using Scotts
TGR for 2 years on his greens with good results. His program starts
with an application of 7 oz/A in mid to late April (15-21) followed
up 2 weeks later with an application of 6 oz/A. Maintenance applications
are applied every 14-18 days at a rate of 4-5 oz/A, the lowered
rate used if AB population is greater than 25%.
Wetting agents have been used in the past for AB seedhead control.
Petrovic at Cornell published some research in the 1980s showing
that AquaGro, a commonly used wetting agent, would give reasonable,
70-80%, AB seedhead suppression. However, AquaGro is no longer
on the market, having been replaced by a new generation of wetting
agents. Two of the those wetting agents have been reported by
superintendents in the Midwest to achieve partial AB seedhead
control. Those products are Cascade and LescoFlo. We will be examining
the use of these products for seedhead suppression this spring,
but their use at this time would have to be considered experimental.
(Bruce Branham and Tom Voigt)
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