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How does paraquat kill
Three populations of paraquat-resistant annual ryegrass (Lolium rigidum) have been confirmed in south eastern South Australia in 2010 by glasshouse experiments. One population is also resistant to glyphosate. Glyphosate resistance evolved on an irrigation channel and subsequently moved into the paddock, where it was then selected with paraquat.
In 2013 a population of ryegrass from a Western Australian vineyard was found to be strongly resistant to both paraquat and glyphosate and can be seen in the image below.
Other species have previously developed resistance to Group L herbicides in Australia. The first case being northern barley grass in 1983 (Table 1). Small square weed (Mitracarpus hirtus) was the first case of resistance to paraquat in Australia that developed outside of broadacre agriculture. This has been followed by the confirmation of paraquat resistance in crowsfoot grass (Eleusine indica), cudweed (Gamochaeta pensylvanica) and blackberry nightshade (Solanum nigrum) in mixed cropping in the Bundaberg area of Queensland in late 2015.
Flaxleaf fleabane (Conyza bonariensis) is the latest species confirmed resistant to paraquat and developed in a vineyard in southern New South Wales. This fleabane population has been sprayed multiple times per year with top label rates of paraquat. Paraquat resistant fleabane is also a significant problem in South African vineyards.
All cases of resistance to paraquat are in situations with long histories of use (>15 years).
Australia currently has 10 species with populations resistant to paraquat (Table 1).
Table 1. Species that have developed resistance to paraquat in Australia
The poster of Australian paraquat resistant weeds can be downloaded here.
Outside of Australia there are 24 species with confirmed populations resistant to paraquat. These include 6 grass and 18 broadleaf species. Paraquat is widely used in tree crops and plantations around the world. The use of paraquat in no-till farming has increased markedly in recent years due to the development weeds with resistance to glyphosate in these systems.
Table 2. Species that have developed resistance to paraquat in other countries
Source: International Survey of Herbicide Resistance 2018
some examples of trade names of herbicides containing paraquat on
the Australian market at time of writing.
Risk assessment and management of paraquat resistance in the
pasture seed industry
Understanding and Management of Resistance to Group M, Group L and
Group I Herbicides
Busi, R., Powles, S.B. (2011) Reduced sensitivity to paraquat evolves under selection with low glyphosate doses in Lolium rigidum. Agronomy for Sustainable Development, 31, 525-531.
Yu, Q., Huang, S., Powles, S.B. (2010) Direct measurement of paraquat in leaf protoplasts indicates vacuolar paraquat sequestration as a resistance mechanism in Lolium rigidum. Pesticide Biochemistry and Physiology, 98, 104-109.
Yu, Q., Han, H., Nguyen L., Forster, J.W., Powles, S.B. (2009) Paraquat resistance in a Lolium rigidum population is governed by one major nuclear gene. Theoretical & Applied Genetics, 118, 1601-1608.
Preston, C., Soar, C.J., Hidayat, I., Greenfield, K. M., Powles, S.B. (2005) Differential translocation of paraquat in paraquat-resistant populations of Hordeum leporinum. Weed Research, 45, 289-295.
Soar, C.J., Karotam, J., Preston, C., Powles, S.B. (2004) Polyamines can inhibit paraquat toxicity and translocation in the broadleaf weed Arctotheca calendula. Pesticide Biochemistry and Physiology, 80: 94-105.
Yu, Q., Cairns, A., Powles, S.B. (2004) Paraquat resistance in a population of Lolium rigidum. Functional Plant Biology. 31: 247-254.
Soar, C.J., Karotam, J., Preston, C., Powles, S.B. (2003) Reduced
paraquat translocation in paraquat resistant Arctotheca calendula
(L.) Levyns is a consequence of the primary resistance mechanism not the
cause. Pesticide Biochemistry & Physiology, 76, 91-98.
Alizadeh, H.M, Preston, C., Powles, S.B. (1998) Paraquat resistant biotypes of Hordeum glaucum from zero tillage wheat. Weed Research. 38, 139-142.
Purba, E., Preston, C., Powles, S.B. (1996) Growth and competitiveness of paraquat-resistant and susceptible biotypes of Hordeum leporinum Link. Weed Research. 36: 311-317.
Purba, E., Preston, C., Powles, S. B. (1995) The mechanism of resistance to paraquat is strongly temperature dependent in resistant Hordeum leporinum and Hordeum glaucum. Planta. 196: 464-468.
Preston. C., Balachandran, S., Powles, S. B. (1994) Investigations of mechanisms of resistance to bipyridyl herbicides in Arctotheca calendula (L) Levyns. Plant Cell & Env. 17: 1113-1123.
Purba, E., Preston, C., Powles, S.B. (1993) Paraquat resistance in a biotype of Vulpia bromoides (L) S.F. Gray. Weed Research. 33, 409-413.
Purba, E., Preston, C., Powles, S.B. (1993) Inheritance of bipyridyl herbicide resistance in Arctotheca calendula and Hordeum leporinum. Theoretical & Applied Genetics.87, 598-602
Preston, C., Holtum, J.A.M., Powles, S.B. (1992) On the mechanism of resistance to paraquat in Hordeum glaucum and H. leporinum. Delayed inhibition of photosynthetic O2 evolution after paraquat application. Plant Physiol. 100, 630-636.
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