Effect of Aquathol K on Hydrilla verticillata (L.F.) Royle

A recently synthesized herbicide Aquathol K was tested on the water weed Hydrilla verticil/ata. Results from the laboraoty tests indicated that Aquathol K with concentrations ranging from 1.0 mg/l to 2.0 mg/l can kill this weed. EVidently, 100% injury was achieved within 10 days for the plants treated with the highest concentration., 2. 0 mg/l of Aquathol K. The rate of 100% injury was recorded much slower with 1.0 mg/l. With lower concentration O.Smg/1 and 0.1 mg/l, 100% injury was never achieved within 25 days. Therefore, the herbicide was not very effective at lower concentrations. INTRODUCTION Hydrilla is a submerged aquatic weed and according to Hiller (I978) it originated from Central Africa. Currently, this weed has spread widely to most countries in the tropics and is known to cause severe problems in waterways. Accordings to Mahler (I 979), hydrilla is considered to be the number one problem in Floridian waterways. In Peninsular Malaysia, it is a menace to irrigation and drainage canals particularly in rice growing areas (Mansor, 1985). Evidently, works on the problems caused by hydrilla to the aquatic ecosystem are well documented, particularly from several Southern States of the United States of America (Steward and Van, 1987). Aquathol K is an aquatic herbicide manufactured by Penwalt Corporation, Philadelphia, USA. This herbicide is approved for use in water systems by the United States Environmental Protection Agency (Registration no. 4581-204). It constitutes active gradient dipotassium salt of endonthall 40.3% and inert ingredients 59.7%. According to Reiner and Rogers (1986), the potassium salt exhibits lower organism toxicity and is much preferred to other herbicides in controlling the aquatic weeds, particularly at the localities where fish population density is relatively high. Some important properties of this herbicide are shown in Table 1. Evidently, there are also no apparent effects on any genera of cladeocera or sub orders of MASHHOR MANSOR, JOSEPH JOYCE AND DAN THYER TABLE 1 Aquathol K properties based on Anon. (1984).