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Paraquat 101: Everything Farmers Need to Know About Paraquat
This guide includes the following sections:
What Is Paraquat?
Paraquat dichloride is a non-selective, contact herbicide commonly used in burndown applications to control grass and broadleaf weeds in a variety of row and specialty crops. It may also be used as a harvest aid, particularly in legume crops and as a desiccant or defoliant in cotton and soybeans. Paraquat is also commonly used to terminate cover crops. It has no soil residual activity, making it a helpful option for rotational cropping systems.
Paraquat was first commercialized in the 1960s. It is a restricted-use pesticide that may only be applied by certified applicators with specialized training. Products that contain paraquat dichloride as an active ingredient include the branded herbicides Gramoxone®*, Firestorm®*, Helmquat® 3 SL*, and Parazone®*.
How Does Paraquat Work?
Paraquat is a Group 22 site-of-action herbicide (photosystem I electron diverter) in the bipyridylium chemical family, which also includes diquat. It works by creating peroxides and free electrons that destroy the plant’s cell membranes, resulting in rapid death. Group 22 and Group 14 herbicides are collectively referred to as cell membrane disruptors and also include PPO inhibitor herbicides like fomesafen and sulfentrazone.
How Long Does Paraquat Take to Work?
Paraquat is a relatively fast-working herbicide. Severe plant injury may become apparent hours after application, starting as water-soaked areas that later turn yellow or brown. Complete weed kill may be achieved within a week or even less.
Paraquat is a contact herbicide; incomplete spray coverage will result in partial shoot kill, and surviving plants will display normal new growth. Consider adding appropriate, labeled adjuvants, like a non-ionic surfactant, to improve spray coverage and weed control.
Paraquat Application Best Practices
Paraquat is commonly used as a burndown herbicide in a variety of row and specialty crops. It is very effective and relatively affordable, making it an excellent option for managing a broad spectrum of grass and broadleaf weeds with limited risk of carryover to subsequent crops.
Typical burndown rates for Willowood Paraquat 3SL* in various cropping systems are shown below.
Paraquat application rates will vary depending on the:
Product
Application timing
Crop
Targeted weed species
Weed pressure
Consult the herbicide label for specific application requirements and suitable tank-mix partners.
Paraquat is a non-selective herbicide, and virtually all plants are susceptible to it. It will cause significant damage to non-target foliage, so it’s important to follow all label instructions and best application practices to avoid crop injury.
Paraquat is a restricted-use pesticide and requires extra safety precautions for handling and application. See the human and environmental safety section below for more details.
Learn how a pre-plant burndown application can deliver season-long benefits.
How to Tank Mix with Paraquat
Paraquat can be tank mixed with compatible herbicides to improve residual activity for longer-lasting broad-spectrum grass and broadleaf weed control.
The addition of photosynthetic inhibitor (PSI) herbicides (site of action Groups 5 and 6) can slow the activity of paraquat to thoroughly distribute the active ingredient through the treated leaf. PSI herbicide tank-mix partners help improve weed control compared to applying paraquat alone.
Common PSI herbicide tank-mix partner active ingredients suitable for use with paraquat include, but are not limited to:
Tank mixing paraquat with a labeled low-volatile 2,4-D ester will help improve control when perennial broadleaf weeds such as bindweed, Canada thistle, or dandelion, or hard-to-control annual broadleaf weeds like morning glory or giant ragweed are present.
Tank-Mixing Order
Follow these general guidelines for tank-mixing paraquat with other approved crop protection formulations. For more information, refer to specific product label instructions.
Fill the spray tank half full with clean water, clear liquid fertilizer, or another approved carrier.
Start tank agitation and carry on throughout mixing and spraying.
Put in the spray tank dry formulations (DF, WP, etc.).
Put in the spray tank liquid formulations (EC, L, SC, etc.).
Put in the spray tank paraquat herbicide.
Put in the spray tank nonionic surfactant.
Fill the balance of the tank.
The pesticide user is liable for ensuring all tank-mix products are registered for the intended usage. Follow all relevant directions, limitations, and restrictions on every product label involved in tank mixing. Applicators are obligated to adhere to the most restrictive directions for use as well as the precautionary disclosures of every product in the tank mix.
Should you use a premix herbicide or custom tank mix? Review the pros and cons of each option in this FBN blog.
Paraquat Resistance Management
Paraquat has been widely used in row and specialty crop production since the 1960s. In the mid-1980s, a paraquat-resistant American black nightshade weed population was identified in Florida. Since then, several other U.S. weeds, including hairy fleabane, horseweed, goosegrass, dotted duckweed, and Italian ryegrass, have developed resistance to paraquat.
7 Tips to Slow the Development of Paraquat-Resistant Weed Populations
Make timely herbicide applications when weeds are 4” or smaller
Use multiple sites and modes of action
Employ crop rotation to diversify herbicides
Use full herbicide rates and layered residuals to extend the window of weed control
Add effective adjuvants to improve spray performance and plant uptake
Scout fields after applications to verify the application was effective
Add cultural or mechanical weed control practices, including tillage, where appropriate
Learn how to manage 5,000 pests through the FBN Pest Solutions pages.
Paraquat Human and Environmental Safety Guidelines
Paraquat Human Safety Guidelines
Paraquat is a restricted use herbicide and should only be handled by certified applicators. Unlike most other restricted-use products, paraquat cannot be used by persons working under the supervision of a certified applicator.
Paraquat is toxic to humans in even very small doses. To avoid unintended consequences, it’s critical to review all label instructions and follow safety guidelines. Over the past decade, the EPA has implemented more stringent packaging guidelines and risk mitigation measures for registered paraquat herbicides.
Do not enter treated areas during the restricted entry interval (REI). The REI for most use cases is 48 hours, although cotton desiccation requires a REI of seven days.
When handling paraquat, wear appropriate personal protective equipment (PPE), including coveralls, waterproof and chemical-resistant gloves, socks, closed-toed shoes, and protective eyewear.
Wash your hands after handling the herbicide and remove clothing and PPE immediately if the product gets on them.
Follow all label instructions to ensure the safe use of paraquat.
Paraquat Environmental Safety Guidelines
Generally, paraquat is moderately toxic to freshwater fish but less toxic to estuarine and marine fish. Paraquat is moderately toxic to mammals on an acute oral exposure basis. According to the U.S. EPA, it also has low toxicity to honeybees.
Paraquat typically has limited soil activity and doesn’t travel through the soil. Therefore, the risk of water contamination is low when using paraquat.
Virtually all plant species are sensitive to paraquat exposure. To avoid off-target movement, follow all label instructions when spraying paraquat and use these best application practices:
Avoid applications when weather conditions favor drift from treated areas. Even a small amount of herbicide moving off-target from treated fields may injure crops.
Use the label recommended spray nozzles, boom heights, and spray volumes.
Add required and/or recommended adjuvants to reduce the risk of off-target movement.
Carefully clean equipment following a paraquat application. Be mindful of residual chemicals that could injure non-tolerant crops.
Buy Paraquat from FBN
Paraquat is a useful burndown herbicide, crop desiccant, and harvest aid. Whatever your intended use, FBN can provide a paraquat herbicide like Willowood Paraquat 3 SL* and suitable tank-mix partners at a competitive price.
With a convenient online platform, transparent pricing, and direct-to-farm delivery available on your schedule, FBN puts Farmers First®.
Related Resources
Herbicides 101: Everything Growers Need to Know About Herbicides
Crop Nutrition 101: Everything Growers Need to Know About Crop Nutrition
Clethodim 101: Everything Growers Need to Know About Clethodim
Glufosinate 101: Everything Farmers Need to Know About Glufosinate
Glyphosate 101: Everything Farmers Need to Know About Glyphosate
Fungicides 101: Everything Farmers Need to Know About Fungicides
Insecticides 101: Everything Farmers Need to Know About Insecticides
Inoculants 101: Everything Farmers Need to Know About Inoculants
Biostimulants 101: Everything Growers Need to Know About Biostimulants
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