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White Margin Sedge ID and Control
By: Tommy Butts, Extension Weed Scientist
Harvest is rapidly approaching, and the majority of folks have put weed control thoughts
behind them. However, identifying and assessing late season weed escapes is a necessity
to develop an effective weed control strategy for the next year. Sedges have really
exploded over the past couple of seasons and identifying specific sedge species escapes
in the fall can lead to much improved control the next growing season. Specifically,
a relatively new problematic sedge, white margin or white-edge sedge (Cyperus flavicomus), has really burst onto the scene in several areas of the state. It has become extremely
problematic in areas where it may have been misidentified early and improper herbicide
selection led to a lack of control, and in severe cases, complete fields of rice being
taken down (Figure 1). Several on-farm and greenhouse research trials were conducted
in 2020 to find key identification characteristics and effective control methods of
white margin sedge.
White margin sedge is an annual sedge species with no rhizomes or nutlets. It is difficult
to distinguish apart from rice flatsedge early after emergence. However, when crushed,
white margin sedge does not have the characteristic pine needle smell that rice flatsedge
has. White margin sedge also appears to be a slightly later emerging species, commonly
beginning emergence in mid to late May. Young white margin sedge plants have a light-yellow
appearance, and the roots are typically a deep red color (Figure 2). Once bigger (>
6 inches), the undersides of leaves begin turning extremely white while keeping a
green midvein (Figure 3); the tops of some leaves may also turn a silver-white color.
The base of the sedge plant has an extremely waterlogged, fleshy feeling. Finally,
the seedhead appears almost as if a yellow nutsedge and rice flatsedge seedhead were
crossed (Figure 4).
The first on-farm demonstration study conducted near Light, AR evaluated burndown
herbicide options to control white margin sedge (Figure 5). Sedge plants were sprayed
at 2 inches tall. Roundup (32 fl oz/acre) and paraquat (64 fl oz/acre) were the best
burndown treatments to control white margin sedge providing >95% control. Sharpen
(3 fl oz/acre) and 2,4-D (2 pt/acre) were the next best treatments and controlled
white margin sedge 80% and 65%, respectively.
An on-farm preemergence (PRE) study was conducted near Light, AR evaluating nine common
rice residual herbicides (Figure 6). At the start of the trial, the site was completely
weed-free, and herbicides were sprayed the last week of April. Bolero (4 pt/acre)
and Sharpen (3 fl oz/acre) treatments each provided the best and most consistent white
margin sedge control (>85%). Permit Plus (0.75 oz/acre) was the only other PRE treatment
to provide 80% control or greater; however, control was less consistent with Permit
Plus compared to Bolero or Sharpen.
A greenhouse study was conducted in Lonoke, AR to evaluate postemergence (POST) rice
herbicide options to control white margin sedge (Figure 7). Sedge plants were sprayed
when 6 inches tall. Basagran (2 pt/acre) and Loyant were by far the best options to
effectively control white margin sedge (>90% control). If white margin sedge is less
than 6 inches tall at the time of application and the density is low, the rate of
Loyant can be reduced to 8 fl oz/acre and effective control can still be achieved
(90%). If sedges are greater than 6 inches and/or the population is dense, the rate
of Loyant should be increased to the 16 fl oz/acre rate. Propanil (4 qt/acre) and
Sharpen (1 fl oz/acre) were the next best POST treatments but did not provide adequate
control alone (56% and 45%, respectively). However, they may be viable tank-mixture
options with Basagran to provide multiple effective modes-of-action and heat up the
herbicide solution for greater levels of control if populations are large or dense.
Overall, Roundup or paraquat as a burndown, Bolero or Sharpen as a PRE, and Basagran
or Loyant as a POST are the best herbicide options for effectively controlling white
margin sedge. RiceBeaux may also be a viable option if densities are low and plants
are small as propanil was effective at suppressing emerged plants and the thiobencarb
(Bolero) component would add residual to mitigate another flush. As with other weeds,
successful management of white margin sedge requires the use of multiple effective
herbicide options and applying POST herbicides when plants are small.
Make sure to double-check weed escapes prior to harvest this year and determine whether
any sedges may be white margin sedge. Hopefully, these results and recommendations
will help to provide a plan for next year to combat this problem weed.
This research was made possible through the support of Rice Checkoff funds allocated
by the Rice Research and Promotion Board. More research will be conducted next year
to validate these results across years and environments. If you think you may have
white margin sedge in your field, please let your county Extension agent or myself
know as we are beginning to map its distribution.
Please let me know if I can help, and good luck with the upcoming harvest!
Tommy Butts | Extension Weed Scientist | (501) 804-7314