Spraytopping reduces seed production in Chilean needle grass (Nassella neesiana (Trin. & Rupr.) Barkworth)

Shiv GaurA, David McLarenA,C and Kym ButlerB

A Department of Primary Industries Frankston, PO Box 48, Frankston, Victoria 3199, Australia.

B Department of Primary Industries, 621 Sneydes Road, Werribee, Victoria 3030, Australia.

C CRC for Australian Weed Management.


Summary

Two field trials and one glasshouse trial were used to evaluate the effect of sub-lethal rates of glyphosate and 2,2-DPA on panicle and cleistogene seed production of Chilean needle grass (Nassella neesiana (Trin. & Rupr.) Barkworth). One field trial was conducted in each of the springs of 2003 and 2004 on established tussocks, while a glasshouse trial was done in spring 2004 using young tussocks raised from seedlings. Results in the first field experiment indicated that application of glyphosate at 510 g a.i. ha-1 from 3 September (vegetative) to 13 October (flag-leaf swelling) reduced panicle seed development and produced the minimum number of filled and germinable panicle seeds. 2,2-DPA proved to be ineffective. The second field experiment showed that application of glyphosate at ≥135 g a.i. ha-1 on 18 October (flag-leaf swelling) and 28 October (panicle emergence) prevented production of filled panicle seeds. However, this level of control could be achieved at 1 October (vegetative) only with glyphosate at ≥270 g a.i. ha-1. The glasshouse trial showed that glyphosate at 216 and 270 g a.i. ha-1 applied in October prevented the production of filled panicle seeds. Increasing glyphosate rates decreased stem and panicle seed germination but did not influence basal seed germination. Glyphosate at ≥135 g a.i. ha-1 during November proved to be most effective in controlling stem seeds. We conclude that glyphosate spraytopping at rates of 250 g a.i. ha-1 between August and October may be a useful contribution to Chilean needle grass management, but timing is critical.

 

Plant Protection Quarterly (2007) 22 (1) 35-39.