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Journal of Aquatic Plant Management 40: 6-10.

Angela G. Poovey and Kurt D. Getsinger

ABSTRACT

In clear water, diquat [6,7-dihydrodipyrido (1,2-1a:2',1'-c) pyrazinediium dibromide] provides excellent submersed plant control at low concentrations, such as <0.5 mg active ingredient (ai) L^-1; however, turbid water conditions can interfere with the activity and effectiveness of this herbicide. Little work has been done to examine what ranges of turbidity caused by different suspended sediment types affect diquat efficacy against a target species. A growth chamber study was conducted using diquat against the submersed macrophyte egeria (Egeria densa Planch.) under a range of turbid conditions. Two materials were used to create turbid water conditions: 100% bentonite clay for a "worst-case" scenario and a natural partial-clay (20% clay). Results indicated that a high rate of diquat (2 mg ai L-1) controlled egeria under relatively low levels of turbidity (5-10 NTU) using bentonite clay; however, higher levels (25 to 50 NTU) of turbidity essentially blocked effectiveness of diquat when applied at all rates tested (0.5, 1, 2 mg ai L-1). When using a natural partial-clay sediment, rates of 1 to 2 mg ai L^-1 diquat provided good control of egeria in moderately turbid water (15 NTU). Additional evaluations using different clay types would be useful to determine the effect of inorganic turbidity on diquat efficacy.

For more information:

Poovey, Angela
USAERDC Vicksburg
CEERD-EP-P
3909 Halls Ferry Road
Vicksburg, MS 39180-6199
Email: pooveya@wes.army.mil