Previous PageTable Of ContentsNext Page

Broad-leaved weed control in annual medic pastures

J.A. Dickinson1, R.J. Saunders2, M.L. Evans2 and A.J. Fatchen2

South Australian Department of Primary Industries
PO Box 1783, Port Lincoln, SA. 5606; 2P0 Box 31 Minnipa. 5654

In low rainfall areas with high pH soils, grass-free annual medic pastures provide high quality feed, improve soil properties, and break cereal disease cycles. Effective broad-leaved weed control is essential for successful annual medic pastures, but herbicides used for broad-leaved weed control can also damage annual medics and need to be evaluated carefully before use.


A trial was conducted in 1992 on upper Eyre Peninsula at Minnipa Research Centre (ay. ann. rainfall 320 mm) on a light sandy clay loam soil with a surface pH of 8.5-9.5. Dominant weeds were Indian hedge mustard (Sinapsis orieniale (L.)) and rough poppy (Papaver hybridum L.). Nineteen herbicide treatments were applied over three annual medic varieties.

The European Weeds Research Council (EWRC) rating system was used to assess efficacy of weed control ( I: complete (100%) kill; 2: 98% kill; 3: 95% kill; 4: 90% kill - sufficient in practice, but plants affected could recover; 5: 82% kill; 6: 70% kill: 7: 55% kill; 8: 30% kill; 9: no (0%) kill, as untreated) and phytotoxicity effects on annual medic plants (I: no effect (as untreated); 2: very light symptoms; 3: light symptoms; 4: symptoms not reflected in yield; 5: medium (yield depression likely); 9: complete kill). Dry matter was measured using a capacitance meter, and pods were collected using a vacuum harvester prior to thrashing and aspirating to obtain clean seed.

Results and discussion

Results for treatments with an EWRC efficacy rating of greater than 5 are not presented, as they are unlikely to be of commercial value. The remaining treatments had efficacy and phytotoxicity ratings plus seed yields that would make them suitable for further evaluation (Table I). Dry matter production (1.4-1.9 t/ha) did not vary significantly between treatments. Flumetsulam was the best treatment, with good weed control, low phytotoxicity ratings and high seed yields, and the dillufenican+bromoxynil was worst, with high phytotoxicity ratings and low seed yields (Table 1).

Table 1. Chemical treatment effects on broad-leaved weed control, phytotoxicity, and yield in three annual medic varieties sown at Minnipa on upper Eyre Peninsula in 1992.

Previous PageTop Of PageNext Page