Combating waterhemp’s metabolic resistance requires new strategies

07 July 2020 | Muriel Cozier

‘It’s just another example of how we need a more integrated system, rather than relying on chemistry only.’

Herbicide resistant weeds are a threat to food supply as they can out-compete the crops being grown for human and animal consumption.

In the US’s Midwestern states where corn and soybean production are prevalent, waterhemp is a problem as it has become resistant to almost every commercially available herbicide. Scientists at the University of Illinois, US, have spent several years studying how waterhemp adapts and have found that the weed can increase production of detoxifying enzymes that neutralise certain herbicides before they can disrupt essential cellular processes.

Publishing their work in the journal Pest Management Science, the researchers say ‘Metabolic resistance, as this strategy is known, is just one process by which waterhemp evades herbicides. Unfortunately, because there may be hundreds of detoxifying enzymes involved, metabolic resistance is hard to identify and even harder to combat.’

The researchers have studied waterhemp’s metabolic resistance to three commonly used herbicides, and important genetic cues are beginning to emerge.

‘These waterhemp populations are adapting and evolving incredible abilities to metabolise everything. It’s bad news, but at least we understand the mechanisms better. Ultimately that understanding could potentially be exploited to use waterhemp’s metabolic arsenal against itself.  That’s one interesting way our research could be directly applied to controlling the weed,’ said Dean Riechers, professor in the Department of Crop Sciences at University of Illinois and study co-author.

The researchers found that waterhemp is resistant to Group 15 herbicides, which target very-long-chain fatty acid production in sensitive plants.  The Group 15 herbicides include S-metolachlor and the study indicates this compound is neutralised by two classes of detoxifying enzymes known as GSTs and P450s. Group 15 herbicides can be safely used in corn because the crop uses GSTs to naturally detoxify the chemicals; in other words corn has a natural tolerance to these chemicals.

Aaron Hager, associate professor in the Department of Crop Sciences at University of Illinois and co-author of the study added ‘With metabolic resistance our predictability is virtually zero. We have no idea what these populations are resistant to until we get them under controlled conditions. It’s just another example of how we need a more integrated system, rather than relying on chemistry only. We can still use chemistry, but we have to do something in addition. We have to rethink how we manage waterhemp long-term.’

Discussing the issues around herbicide resistant weed, Dr Todd Gaines, associate professor in the Department of Agricultural Biology at Colorado State University, US, will be speaking at the SCI webinar Herbicide resistant weeds: call to action. Organised by SCI Agrisciences Group and Pest Management Science, Dr Gaines will be discussing the pressing need to come up with effective solutions as well as the latest developments in crop protection.

To find out more, register to our free webinar here:

Herbicide resistant weeds: call to action 

23 July 2020: 15.00 – 16.00 BST




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