Effect of time of application of flupropanate in reducing seedhead production of serrated tussock

Effect of time of application of flupropanate in reducing seedhead production of serrated tussock

M. H. Campbell and R. Van de Ven
56 Green Lane, Orange and NSW Agriculture, Orange Agricultural Institute, Orange, 2800
February 2003

аFlupropanate (Taskforceт, 74.5% a.i.) was applied to mature serrated tussock (Nassella trichotoma) growing on slate derived soil, at three rates, from 14.9 to 4.0 weeks before flowering began, to examine the effect of different intervals between spraying and the beginning of flowering on seedhead production (Table 1). The beginning of flowering is defined as the appearance of the first tips of the awns of the seeds at the top of the flowering tillers containing them. There were three replications of each treatment arranged in randomised blocks in an experiment near Tuena in the southern tablelands of NSW.а

Table 1.Reduction (%) in fertile seedheads produced after applying flupropanate at three rates on six occasions before flowering began; measured on 20 November 2001

Time of spraying in 2001		L/ha of flupropanate			Rainfall after spraying
Date	Weeks before flowering began	ааа 1.0 аааааааааааааааааа (%)	1.5 ааааааааа (%)	2.0 аааааааааааа (%)	Ten daysааа аа (mm)а
13 July	ааааа 14.9	а 93 a	а 96 a	а 99 a	ааа 30
31 July	ааааа 12.3	а 85 a	а 92 a	а 99 a	ааа 10
12 August	ааааа 10.3	а 71 b	а 85 a	а 99 a	ааа 35
24 August	ааааааа 8.9	а 30 c	а 56 b	а 82 b	ааа 58
11 September	ааааааа 6.3	ааа 5 d	а 23 c	а 41 c	ааа 22
27 September	ааааааа 4.0	ааа 0 d	ааа 1 d	ааа 4 d	ааа 27

аValues in columns not followed by a common letter differ significantly at P>0.05.

Results

The time needed to reduce seedhead production by >90% was 14.9, 12.3 and 10.3 weeks respectively for the 1.0, 1.5 and 2.0 L/ha rates of flupropanate.

In this experiment sufficient rain fell in the ten days after each spraying (Table 1) for the flupropanate to be washed into the soil and taken up by the serrated tussock before the next spraying; thus each spraying was an independent event.

Because flupropanate is a slow acting herbicide (due to the need to be washed into the soil and taken up by the roots of the weed, and/or because of slow chemical processes within the plant), it has to be applied quite a long time before flowering to stop seedhead production. This experiment determined the minimum time necessary for the three rates of flupropanate used to substantially reduce seedhead production because sufficient rainfall was received soon after each spraying to ensure the flupropanate entered the weed soon after spraying.

By adding a low rate of glyphosate to the flupropanate, the time between spraying and the beginning of flowering necessary to substantially reduce seedhead production, can be reduced to two to four weeks (Campbell et al. 1998). However glyphosate has detrimental effects on useful plants growing with the serrated tussock and can cause massive seedling reinfestation of serrated tussock if the useful plants are killed.

Conclusion

As serrated tussock generally begins to flower in late October at Tuena, it would be necessary to apply 1.0, 1.5 or 2.0 L/ha flupropanate in, respectively, early July, late July or early August to reduce seedhead production by >90%.аааа

Reference

Campbell, M. H., Miller, L. G. and Nicol, H. I. (1998). Effect of herbicides on seedhead production and control of serrated tussock. Plant Protection Quarterly. 13, 106-110.