The Alkali (Scirpus Maritimus L.) and Saltmarsh (S. Robustus Pursh) Bulrushes: A Literature Review
Control Methods
Chemical Control
This section is a review of information on attempts to kill Scirpus maritimus and S. robustus or to control their growth with herbicides.
Scirpus maritimus or closely-related species are difficult to control because of apical bud dormancy and ability to produce numerous corms (Ampong-Nyarko and De Datta 1991). Herbicides can be used in rice fields but may not be readily available or may be too costly for widespread use (Vergara et al. 1977). Additionally, rice planted from seedlings requires different herbicides than sown rice. The most common herbicides used to treat S. maritimus and other weeds in rice fields in Italy, France, and the Phillipines are the phenoxypropionics (e.g., fenoprop, mecoprop, and dichlorprop), oxadiazon, bentazon, bensulfuron-methyl, 2,4-D, 2,4,5-T, MCPA, and propanil mixed with phenoxyics (Zanini 1974, cited in Podlejski 1981; Vergara et al. 1977; Bernasor and De Datta 1986). An effective but expensive method to control S. maritimus is to stimulate corm sprouting with benzyladenine and then kill topgrowth with selective herbicides (Kim and De Datta 1974). Field drains where S. maritimus impedes water flow may be opened with a mixture of paraquat (gramoxone) and dalapon (2,2-Dichloropropionic acid; Batten 1967). Paraquat can control this bulrush, but dalapon kills topgrowth only (Axell 1982; Thomas 1982). In England, openings for waterfowl in dense stands of S. maritimus can be made with 1 kg a.i./ha glyphosate sprayed in July (Hanley 1981). Ampong-Nyarko and De Datta (1991) provided additional information on the use of herbicides to control this species. Scirpus maritumus and putative S. glaucus × maritimus hybrids are pests in California rice fields (Browning et al. 1995), but I found no information on chemical control methods.
Physical and Biological Controls
Reviews of the physical and biological methods used to control Scirpus maritimus or closely-related species in rice fields include Vergara et al. (1977) and Ampong-Nyarko and De Datta (1991). Thorough weeding by hand gives good control of the plant but is arduous because of the difficulty of extracting the corms. Also, repeated treatment is necessary. Mechanical plowing and multiple harrowings may be effective, but timing is crucial. Corms quickly resprout and delayed harrowing may separate sprouted corms, break their dormancy, and result in increased rather than decreased populations. Growers find that plowing of rice fields within 20 days after harvest reduces sexual reproduction, buries regenerated shoots, and exposes some corms to the atmosphere. If fields are drained and dried after plowing to dessicate exposed corms and lower germinability, populations of bulrush can be reduced, but this practice may be impractical if another rice crop is to be planted immediately or if rainy conditions develop. Rotations of rice with 3 consecutive years of dry-land crops can eliminate S. maritimus.
Cultural methods to control S. maritimus include the use of taller and longer duration rice cultivars and the closer spacing of plants to take advantage of the sensitivity of this bulrush to shade. For control of this species in northern European wetlands to improve livestock forage, A. Koridon (personal communication in Brehm 1979) suggested a November underwater mowing followed by one or two cuttings in the following year. I found no information on physical or biological control of S. robustus.
Previous Section -- Propagation and Management
Return to Contents
Next Section -- Research Needs
