Farming and horticulture relies on a varied toolbox

Paraquat has been used in New Zealand agriculture for around fifty years and is widely used throughout the world. It has some unique characteristics which make it necessary to control weeds in many crops of significant value to our economy. Its use is limited to agriculture and can only be purchased by a WorkSafe certified handler. In these circumstances, it is a safe and effective herbicide when used as directed on the label.

It is used for a variety of crops including green leafy vegetables like lettuce, silverbeet and spinach as well as stone fruit, strawberries, brassica, celery, kumara, onions, potatoes and seed crops. Paraquat is not sprayed onto food crops – Instead it is only applied to weeds between plants before fruit or vegetables appear.

Weeds are a massive cost to primary producers. Not only due to the loss of production caused by a select group of prominent weeds, but also in costs associated with weed control itself. The herbicide keeps kumara crops commercially viable. Without it, kumara paddocks would need to be hand weeded as no mechanical weeding machines exist. This is also because kumara is particularly vulnerable to competition from weeds. Alternative products would need to be used at higher rates to be efficacious. As this damages the kumara crop, yields would decrease.

Clover seed and lucerne also use benefit from the herbicide.

Clover seed is essential to the New Zealand pasture based economy. The use of paraquat in its production reduces competition and contamination with weed seeds and aids harvest.

Lucerne is an important forage crop and is growing in popularity due to its high feed value. Paraquat can be used to remove weeds from lucerne crops, even at low temperatures, unlike alternative contact sprays.

Its specific advantage over other herbicides is that it kills the plant tissue it makes contact with. Other products, like glyphosate, are systemic and could kill the whole plant.

The product is rapidly absorbed into green plant tissue and is rainfast within 15-30 minutes of application. This is particularly useful for weed control in winter and spring in New Zealand, as application windows are often very narrow. Paraquat also works rapidly in the presence of light to desiccate green plant tissue. This reduces weed competition for water and nutrients more quickly than alternatives. It is also rapidly absorbed in the soil. This minimises the risk of it leaching from the soil to contaminate waterways, and also allows for rapid replanting without adverse herbicidal effects on following crops.

Where total vegetation control is required, it is used to control multiple grasses and broadleaf weeds in a site. This reduces the need for multiple selective herbicides. It’s mainly applied by tractor mounted or boom spray. In fact, more than half of the paraquat sold in NZ is applied by professional spray contractors.

As part of their chemical review programme, the Australian Pesticides and Veterinary Medicines Authority reviewed the herbicide. The Authority concluded that the continued approval of paraquat is unlikely to be harmful to people.

It is important that farmers have access to a wide range of crop protection tools to ensure they are able to sustainably manage pest resistance. Paraquat is an important tool in dealing with the threat posed by weed resistance to selective herbicides.

Growers rotate between herbicides with different modes of action wherever possible to prevent the development of resistance in a weed population. The threat posed by resistance means it is important to retain approval of a broad range of herbicides, both so that the development of herbicide resistance can be delayed, and so that there are control options available that can be readily deployed, if resistance does develop in a weed population.

For these reasons, it’s important that New Zealand keeps a good toolbox of products including paraquat to manage pesky weeds. That way, the best suited product can be chosen depending on the situation. This is vital for the sustainability of arable and horticultural production in New Zealand.