McGregor and Gourlay (2002) report that, "The main, current control methods for this species include the application of herbicide (usually Diquat), mechanical and suction dredging and weed matting, but all these have substantial disadvantages; particularly their cost, their failure to give long-term control and, for some, the question of adverse environmental effects, whether actual or perceived."
Chemical: Hofstra and Clayton (2001) report that, "The aquatic herbicide diquat is the only product registered in New Zealand for controlling the submerged weeds, including lagarosiphon (L. major." The authors claim that, "However, diquat can be ineffective under some environmental conditions and it does not control certain submerged weeds." The authors studied three other herbicides (endothall, triclopyr, and dichlobenil), and found that, "Endothall killed coontail, lagarosiphon and hydrilla and some species of Myriophyllum and Potamogeton but not egeria or species of Chara or Nitella. Only transient growth effects were observed in target plants treated with triclopyr and dichlobenil."
Davies et al. (2003) investigated the use of Sulfosulfuron, which is a selective, post-emergence, sulfonylurea herbicide intended for use in winter wheat. The authors found though that, "Treatment with sulfosulfuron at any concentration stimulated biomass accumulation." This product should not be used as a treatment method.
Biological: Lake et al. (2002) state that, "Selective feeding by rudd may also be significant in lakes that have been invaded by exotic oxygen weeds in New Zealand (e.g. Egeria densa, Elodea canadensis, and Lagarosiphon major) by facilitating their monospecific habit through suppression or exclusion of more desirable species."
McGregor and Gourlay (2002) report that, "The nematode Aphelenchoides fragariae has been recorded attacking the apical tips of L. major causing shoot dwarfing. Nymphula nitens feeds on many aquatic weeds and might be a potential biological control agent, but it also feeds upon native aquatics. Biological control offers the prospect of re-establishing native macrophyte communities in infected waters, however biological control and the removal of L. major may only result in the replacements of one exotic species for another."Chapman and Coffey (1971) review the introduction and spread of L. major in New Zealand. The possibility of the use of grass carp was investigated for control so a few fish were imported from Malaysia.Trials showed that carp would eat the problem weeds.