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Number 3, 1998
Stemmy Turf and Postemergence Annual Grassy Weed
Control
Stemminess in cool season turfgrasses appears to be a concern
this spring. Flower bud initiation in cool season turfgrasses
occurs during fall's shortening days and cooler temperatures;
when conditions in the following spring are appropriate, these
grasses become reproductive and begin flowering.
Mowing, of course, leaves only the remnants of the flowering stem
(culm) and its associated blades. After flowering, the reproductive
shoots (stems and attached leaves) die and begin to decompose.
In turf, the dying shoots intermingled in the non-flowering grasses
produce an uneven, mottled appearance. Often, appearance is made
worse when the tough stems are shredded or ripped rather than
cleanly cut. In fact, flowering stems may lodge and not be cut
at all in turf mowed with reel mowers.
What to do? First, understanding the natural growing cycles of
these grasses won't reduce stemminess, but does allow you to explain
the situation. Second, nitrogen fertilization can reduce flowering.
Evaluate your fertilization program; if you're supplying only
1 or 2 pounds of N per 1,000 square feet per year in sunny areas,
increasing to 3 or 4 pounds may improve overall turf quality.
Nitrogen fertilization, however, can be a double-edged sword.
Be careful not to apply excessive nitrogen as root growth may
be impacted and the severity of some diseases enhanced. Finally,
be sure to mow frequently and maintain sharp mower blades. Frequent
mowing will keep culms from being pushed over rather than cut,
and sharp blades may reduce ragged, ripped stems and improve overall
turf appearance.
Postemergence Annual Grass Control
As soils warm, summer annual grassy weeds can become a problem.
These weeds, including smooth and large (hairy) crabgrasses, goosegrass,
foxtails (green and yellow), barnyardgrass, fall panicum, and
sandbur are likely to be found in settings where the turf is thin
or open. Spring-seeded sites, heavily trafficked areas, sites
not treated (or improperly treated) with preemergence controls,
or areas that are poorly managed or poorly adapted to turf development
are likely areas of annual grassy weed invasion.
While preemergence controls are usually more effective, postemergence
annual grass herbicides, when handled properly, can also provide
acceptable control. Several controls are commonly used and include
dithiopyr (Dimension), fenoxaprop-ethyl (Acclaim Extra), and the
organic arsenicals (DSMA and MSMA, both of which are available
under several trade names). For best results, apply these controls
to young, actively growing weeds. Remember to always read, understand,
and follow label directions for the safest, most effective control
when using any pesticide.
Dithiopyr - Dimension should be used as a postemergence
control soon after emergence of crabgrass. It can be used on unstressed,
well-established creeping bentgrasses, Kentucky bluegrasses, fine
fescues, tall fescues, and perennial ryegrasses with well-developed
root systems. Check the label for use restrictions on fine fescue
varieties and creeping bentgrass putting greens. Dithiopyr should
be applied between 0.25 and 0.30 lbs. ai per acre with an organosilicone
wetting agent for best postemergence results.
Fenoxaprop-ethyl - Acclaim Extra is labeled to control
smooth and large (hairy) crabgrasses, goosegrass, foxtails species,
barnyardgrass, fall panicum, and sandbur. It can be applied to
Kentucky bluegrass, perennial ryegrass, tall and fine fescues,
perennial ryegrass, and creeping bentgrasses mowed above 0.25
inch. Be aware that creeping bentgrass can be very sensitive to
applications of fenoxaprop-ethyl. See the label for compatible
postemergence broadleaf herbicides.
Organic Arsenicals - DSMA and MSMA are labeled to control
smooth and large (hairy) crabgrasses, goosegrass, foxtails (green
and yellow), barnyardgrass, fall panicum, and sandbur and can
be applied to Kentucky bluegrass; injury may result from applications
to fescues and bentgrasses. When using organic arsenicals, the
turf should be well-established, actively growing, and mowed at
1 - 1.5". Reapplication may be needed every 14 days and phytotoxicity
may occur when the desirable turfgrasses are stressed or not actively
growing. Quadmec or Trimec Plus combines 2,4-D; MCPP; and dicamba
with MSMA for broad-spectrum postemergence control.
In recent years, turf researchers at the U. of I. have evaluated
two other potentially useful postemergence annual grass controls.
The first combines fenoxaprop-ethyl and pendimethalin and has
been tested under the trade name, "Preclaim." While
still unlabeled, this product has effectively controlled crabgrass
both pre and postemergently. The second, quinclorac, has shown
good postemergence control of crabgrass, as well as several broadleaf
weeds. This product is also currently labeled and was tested most
recently under the proposed trade name, "Drive." Watch
for announcements of the commercial availability of these two
herbicides.
(Tom Voigt, Bruce Branham, and Bruce Spangenberg)
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