Speed of paraquat captured on video

Paraquat’s fast action allows earlier plantingParaquat’s famous fast speed of action has been captured by a time-lapse video produced by Ohio State University, USA. No herbicide acts faster than paraquat and across such a broad spectrum of weed species too. Fast action gives farmers important benefits including opportunities for higher yields and better prices through earlier planting; rainfastness within 15-30 minutes; and ease of seeing where weeds have been treated after a break in spraying operations. Ohio State University chose giant ragweed (Ambrosia trifida) as the target for paraquat in this video1. Despite being one of the tougher weeds for paraquat to control, the ragweed in the video is desiccated over the course of a day with effects clearly visible after only a few hours. You can watch the video here Mixing paraquat with 2,4-D or a photosynthesis inhibitor herbicide such as metribuzin will give the best control of giant ragweed. A similar video showing the time course of glyphosate effects on common ragweed (Ambrosia artemisiifolia) is also available. Glyphosate takes around one week to desiccate the weed. You can watch the video here

Why ragweeds?

Ragweeds are native to North America and classed as summer annual broadleaved weeds


The leaves are "broad" as opposed to the "narrow" leaves of grasses. Also called 'dicots' having two seed leaves, while grasses are 'monocots' having one seed leaf.

Authoritative On-line References and Resources

http://www.iwss.info The International Weed Science Society.
. They are amongst the earliest weeds to emerge in fields to be prepared for spring crops. This makes them suitable for control by burndown herbicides to give a clean start before planting2,3. If uncontrolled, they are powerful competitors to young crops. Giant ragweed, in particular, can grow over 3 metres tall, severely shading crops and reducing yields by up to 50%2.
Ragweeds have become an increasingly serious problem in US crops of corn and soybeans. This has been exacerbated by the popularity of glyphosate tolerant crops, and the increasingly heavy use of glyphosate for weed control. Populations of ragweed resistant to glyphosate have been recorded in crops of corn and soybeans in North America since 20044. Several of these are also resistant to ALS inhibitor herbicides too. Maintaining a range of options for farmers to use herbicides with different modes of action is vital to ensure that these and other weeds currently succumbing to resistance can continue to be controlled. Paraquat has a unique mode of action not shared by any other class of herbicide.

Benefits of fast action

The benefits of paraquat’s fast action are appreciated on farms around the world and have been illustrated in earlier articles posted on the Paraquat Information Center. For example:
  • In the US, rapid desiccation of cover crops


    Cover crops are primarily planted not to be harvested for food but to reduce soil erosion, control weeds and improve soil quality. They are usually plowed or tilled under before the next food crop is planted, in which cases the "cover crop" is used as a soil amendment and is synonymous with "green manure crop."

    Authoritative On-line References and Resources

    http://attra.ncat.org/attra-pub/covercrop.html ATTRA is the US National Centre for Appropriate Technology's Sustainable Agriculture Information Centre.
    allows earlier planting of corn.
  • In the mountains of Vietnam, corn can be planted only two days after clearing fields of weeds with paraquat, while it is necessary to wait 10 to 15 days after spraying glyphosate. Earlier planting generally means higher yields and can mean better prices at harvest by being sooner to market.
  • In the tidal rice growing areas of Indonesia, paraquat is the only herbicide that can be absorbed by weeds fast enough before the next tide washes over the fields. Tidal rice farmers using paraquat can triple their income.
You can read about the other benefits of paraquat on the farm, for the environment and in rural communities here.


Ohio State University Purdue University/Ohio State University factsheet: Management of giant ragweed in Roundup Ready soybean fields with a history of poor control. Purdue University factsheet: Burndown herbicides in no-till International Survey of Herbicide Resistant Weeds


The brand name of the leading paraquat product is Gramoxone.