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Seed-applied herbicides and antidotes for the establishment of lucerne and phalaris

J.M. Scott and G.J. Blair

Department of Agronomy and Soil Science,
University of New England, Armidale, N.S.W. 2351.

The establishment of both lucerne and phalaris on the Northern Tablelands of N.S.W. can be severely reduced by annual grassy weeds such as rat's tail fescue (Vulpia myuros) which germinates during autumn, the preferred time for sowing temperate species in this region. Populations of rat's tail fescue as high as 40,000 seedlings m-2 have been observed in the field. Direct drilling of pastures precludes the use of pre-planting soil-incorporated herbicides and, thus, the possibility of incorporating herbicides in a seed coating applied to the sown species is attractive (1). A range of candidate herbicides was evaluated when applied as coatings to lucerne seed and the possibility of applying a herbicide antidote to the phalaris seed was also investigated.


A series of glasshouse trials was conducted to investigate: (i) the effect of a range of populations of rat's tail fescue (0,5,10,20,40, and 80 x 103 seeds m-2) on the early growth of lucerne and phalaris; (ii) 9 herbicides (each at 4 rates) applied to lucerne seed to control rat's tail fescue (which was sown at 40,000 seeds m-2); and (iii) 6 herbicide antidotes (each at 3 rates) applied to phalaris seed to protect the phalaris from herbicide damage (EPTC) whilst not protecting the rat's tail fescue (again sown at 40,000 m-2).

Results and Discussion

In the first trial, the yields of both lucerne and phalaris were dramatically reduced by rat's tail fescue populations as low as 3900 m-2 under both high and low fertility conditions. Of the nine seed-applied herbicides tested in the second trial, only EPTC was effective in both reducing the yield of rat's tail fescue and in increasing the yield of lucerne (Fig. 1).

Fig. 1 Grassy wood control with seed-applied EPTC

Fig. 2 Effect of anfldote on EPIC damage to phalaris

Of the antidotes tested, naphthalic anhydride (N.A.) (applied to phalaris seed at 8% w/w) was the most effective in protecting the phalaris from EPTC damage (Fig. 2). This protection permitted a phalaris yield seven times that of the control at a herbicide application of 0.4 kg EPTC ha-1 but the protection at 1.2 kg EPTC ha-1 was negligible. Field studies are needed to confirm the efficacy of seed-applied herbicides and antidotes and to examine any effects of sowing method on their efficacy.

1. Dawson, J.H. 1978. Proc. of Western Soc. of Weed Sci. 31,71.

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