Herbicide resistance in annual ryegrass and wild oats
| Date: 14 Feb 2008
Herbicide resistance in annual ryegrass and wild oats – current situation and what to do about it, and everything old is new again – trifluralin + triallate
Andrew Storrie, Weeds Agronomist, NSW Department of Primary Industries
• Annual ryegrass - widespread Group A resistance, scattered Group B resistance and some glyphosate resistance in the Coonamble area
• Wild oats - widespread resistance to Group A, with some Mataven® (Group K) resistance and Group B resistance is developing. A number of populations are resistant to more than one MOA.
• The focus on weed control must include seed bank management (stopping seed set), as well as making a profit, and keeping weed numbers low
• Weed control MUST be continued through the season to prevent weeds seed setting seed - more than one weed control operation will be necessary each crop season.
• Using tank mixes of trifluralin + Avadex® Xtra improves control of both wild oats and annual ryegrass compared to when they are used alone
• Trifluralin + Avadex® Xtra, and other soil active herbicides can be successfully used in no-till if their characteristics are fully understood.
Herbicide Resistance
Herbicide group
|
Years of application
|
Herbicide resistance risk
|
A
|
6–8
|
High
|
B
|
4
|
High
|
C
|
10–15
|
Medium
|
D
|
10–15
|
Medium
|
F
|
10
|
Medium
|
I
|
Not known
|
Low
|
L
|
>15
|
Low
|
M
|
15
|
Low
|
- Initial frequency of the resistant gene in the population.
- MOA group being applied
- What percentage of the weeds sprayed are killed (herbicide efficacy) – this will depend on how well it is applied and environmental stress.
- Size of the weed population being treated.
Resistance to more than one MOA in the same weed population
- multiple resistance – where a range of different MOAs have been used on the weed population and weeds containing resistant genes to 2 or more MOA’s are selected
- cross resistance – where use of one MOA gives resistance to that group of herbicides plus at least one other MOA group. This second MOA group has not been used on that population before. WARNING: because a herbicide MOA has never been used before, doesn’t mean that it will be effective. Therefore herbicide testing is essential.
Annual ryegrass (ARG)
|
2004
|
2005
|
2006
|
2007
|
A (fops)
|
77
|
90
|
97
|
91
|
A (dims)
|
10
|
27
|
16
|
41
|
B
|
48
|
88
|
87
|
81
|
C
|
0
|
0
|
0
|
0
|
D
|
13
|
9
|
5
|
7
|
Wild oats
|
2003
|
2004
|
2005
|
2006
|
2007
|
|
% (no.)
|
% (no.)
|
% (no.)
|
% (no.)
|
% (no.)
|
‘fops’
|
88 (24)
|
96 (29)
|
93 (51)
|
77 (51)
|
100 (22)
|
‘dims’
|
5 (20)
|
4 (26)
|
7 (50)
|
5 (42)
|
15 (33)
|
K
|
0 (18)
|
9 (23)
|
14 (28)
|
9 (22)
|
12 (15)
|
Testing – know what you are dealing with!
Economic impact of not controlling resistant ARG and wild oats
Managing herbicide resistance
- Keep weed numbers low – this greatly reduces the risk of resistance developing.
- Monitor weed control – if you don’t know weeds have survived, how can management be adjusted to control them. Once the header is in the paddock it is generally too late.
- Stop the seed set of all weeds – one pre-emergent or early post emergent herbicide in a crop will not do it!! The survivors could be resistant so they must be controlled.
Soil residual herbicides in no-till
Avadex® Xtra and trifluralin in no-till
Herbicide Treatment
|
Wild oats m-2
|
Nil
|
76
|
Trifluralin 0.8 L/ha Incorporated
|
18
|
Avadex 2 L/ha Incorporated
|
13
|
Trifluralin 2 L/ha IBS
|
12
|
Trifluralin 1.2 L/ha Incorporated
|
8
|
Trifluralin 2 L/ha + Avadex 2 L/ha IBS
|
7
|
Avadex 1.6 L/ha Incorporated
|
6
|
Trifluralin 1.5 L/ha + Avadex 1.6 L/ha IBS
|
5
|
Trifluralin 1.5 L/ha IBS
|
3
|
Trifluralin 0.8 L/ha + Avadex 1.6 L/ha + Glean 20 g/ha Incorporated
|
3
|
Trifluralin 1.5 L/ha + Avadex 1.6 L/ha + Glean 20 g/ha IBS
|
2
|
Trifluralin 0.8 L/ha + Avadex 1.6 L/ha Incorporated
|
2
|
lsd (pr.= 0.05)
|
20
|
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