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Department of Agronomy

Kansas State University

1712 Claflin Rd.

2004 Throckmorton PSC

Manhatan, KS 66506

785-532-6101

agronomy@ksu.edu

Extension Agronomy

Paraquat: What you need to know for use in 2022

Paraquat is a restricted use herbicide that was first commercialized in the 1960s and it is found in herbicides such Gramoxone, Helmquat, and Parazone. It is a non-selective, contact herbicide and desiccant that belongs in group 22 site of action(photosystem I electron diverter). Paraquat is one of the most widely applied herbicides in the United States where it is heavily used in corn, cotton, and soybeans and some specialty crops like grapes, peanuts, and pistachios for weed management and crop desiccation.  Paraquat has a low oral LD50 and the signal word “Danger” is used on product labels to signify this risk.

The 15-year EPA herbicide registration review for paraquat began in December 2011.  In 2016, there were several new safety measures implemented in order to mitigate the of human illness and injury caused by accidental paraquat toxicity. These include:

  • Label changes to emphasize toxicity
  • Paraquat can only be applied and handled by certified applicators
  • Required all handlers to have a paraquat-specific training, found at https://npsec.us/paraquat
  • Closed system packaging for non-bulk end use containers (< 120 gallons)

In August of 2021, the EPA released the final Interim Decision (ID) for paraquat. These EPA determined that these additional label parameters are necessary to mitigate the risk of human illness and injury. The parameters are as follows:

  • Increased label clarity (already included on label for Gramoxone SL 3.0)
    • The maximum number of applications, maximum annual rates, maximum single application rate, minimum retreatment interval, Pre-Harvest Interval (PHI) can be found in Tables 1, 2, and 3.
  • Limited aerial applications
    • Permitted for all labeled crops and is restricted to 350 acres/24 hours/individual applicator, but there is no acreage limit when sprayed as cotton desiccate
  • Required residential buffers
    • Rate dependent
      • 50-foot buffer when applying < 1.6 pints/acre
      • 75-foot buffer when applying > 1.6 pints/acre
    • Existing label restricts the use of paraquat in residential or public areas or if there is a high likelihood of drift onto sensitive areas
  • Prohibited pressurized handgun and backpack sprayer applications
    • Manually pressurized hand wands are permitted
  • Required enclosed cabs or respirators for ground boom applications
    • If applying, >80 acres/24 hours an enclosed cab is required
    • If applying, < 80 acres/24 hours an enclosed cab is preferred, but a N95 respirator is the minimum requirement
  • Increased the Restricted Entry Interval (REI) for several labeled crops
    • The REI is 48 hours for all labeled crops, except when paraquat us used as a harvest aid in cotton, when the REI is 7 days
  • Transport requirements
    • Truck drivers who are not certified applicators must have no contact with or access to paraquat, but they may transport previously opened containers of paraquat if specific requirements are met
      • Containers must be securely closed to prevent accidental release of paraquat
      • All openings on portable containers must have a tamper-evident device applied by a certified applicator, a one-way valve, or both for portable/refillable containers
    • If containers are not permanently attached to the motor vehicle they must be secured to prevent shifting and motion between packages
    • Truck drivers who are not certified applicators must not transfer or have any access to paraquat or any formulation containing paraquat 
    • Full and emptied portable containers must be transferred to a certified applicator, a secured and locked storage facility that is controlled by a certified applicator, or a licensed disposal facility
    • Certified applicators are required to ensure that truck drivers understand the risks associated with paraquat and the consequences of misuse

 

Table 1. The maximum number of applications, annual rates, and single rate application, the minimum retreatment interval, and Pre-Harvest Interval (PHI) for paraquat use in alfalfa, fallow, and wheat (Sourced from the Gramoxone SL 3.0 label).

Crop

Application Timing

Max # of application/yr

Maximum annual rates

Maximum single application rate

Minimum retreatment interval

Pre-Harvest Interval

Alfalfa

PRE, PP, Broadcast, or Banded over row in no-till or conventional planting

2

2.7 pts/ac (do not exceed 1.0 lbs ai/ac/year for all paraquat containing products)

2.7 pts/ac

7 days

Harvest at normal maturity

New seedling (do not use on alfalfa grown for seed)

1

1.3 pt/ac (do not exceed 1. 0 lbs ai/ac/year for all paraquat containing products)

1.3 pts/ac

NA

70 days

Between cuttings in established stand

3

2 pts/ac (do not exceed 0.75 lbs ai in between cuttings applications; do not exceed 1.0 lbs ai/ac/year for all paraquat containing products)

0.7 pts/ac

1 application/cutting interval

30 days for cutting, harvesting, and grazing

Dormant

1

2 pts/ac (do not exceed 0.75 lbs ai for dormant applications; do not exceed 1.0 lbs ai/ac/year for all paraquat containing products)

2.0 pts/ac

NA

42 days in KS, NE, MO, CO for established stands and  60 days in OK for established stands and newly established stands in KS, NE, MO, CO, and OK

Fallow

 

2

5.4 pts/ac (do not exceed 2.0  lbs ai/ac/year for chemical fallow  applications)

2.7 pts/ac

7 days

NA

Wheat

PRE and PP

3

8.0 pts/ac (do not exceed 3.0 lbs ai/ac/year for PRE and PP applications)

2.7 pts/ac

7 days

Harvest grain, straw, forage, and hay at normal maturity



Table 2. The maximum number of applications, annual rates, and single rate application, the minimum retreatment interval, and Pre-Harvest Interval (PHI) for paraquat use in corn, soybeans, and sorghum (Sourced from the Gramoxone SL 3.0 label).

Crop

Application Timing

Max # of application/yr

Maximum annual rates

Maximum single application rate

Minimum retreatment interval

Pre-Harvest Interval

Corn

PRE and PP

3

8.0 pts/ac (do not exceed 3.0 lbs ai/ac/year for PRE and PP applications; do not exceed 5.0 lbs ai/ac/year for all paraquat containing products)

2.7 pts/ac

7 days

Harvest at normal maturity

POST directed

3

4.0 pts/ac (do not exceed 1.5 lbs ai/ac/year for POST directed applications; do not exceed 5.0 lbs ai/ac/year for all paraquat containing products)

1.3 pts/ac

7 days

Harvest at normal maturity

Harvest aid

1

1.3 pts/ac (do not exceed 0.5 lbs ai/ac/year for Harvest aid applications; do not exceed 5.0 lbs ai/ac/year for all paraquat containing products)

1.3 pts/ac

NA

7 days for grain and stover

Soybeans

PRE and PP

3

4.0 pts/ac (do not exceed 1.5 lbs ai/ac/year for PRE and PP applications; do not exceed 2.9  lbs ai/ac/year for all paraquat containing products)

2.7 pts/ac

7 days

Forage/hay: Not before R3                   Seed: Harvest at normal maturity

POST directed

2

1.3 pts/ac (do not exceed 1.0 lbs ai/ac/year for POST applications; do not exceed 2.75 lbs ai/ac/year for all paraquat containing products)

1.3 pts/ac

14 days

Forage/hay: 46 days

Harvest aid

1

0.7 pts/ac (do not exceed

0.25  lbs ai/ac/year for harvest aid  applications; do not exceed 2.75 lbs ai/ac/year for all paraquat containing products)

10.7 fl/oz

14 days

Grain only: 15 days                           Soybeans grown for research, field trials, and seed production only: 3 days

Sorghum

PRE and PP

3

8.0 pts/ac (do not exceed 3.0 lbs ai/ac/year for PRE and PP applications; do not exceed 4.0 lbs ai/ac/year for all paraquat containing products)

2.7 pts/ac

7 days

Forage: 20 days                                      Grain: 48 days

POST directed

2

2.7 pts/ac (do not exceed 1.0 lbs ai/ac/year for POST applications; do not exceed 4.0 lbs ai/ac/year for all paraquat containing products)

2.7 pts/ac

7 days

Forage: 20 days                                      Grain: 48 days

 

Table 3. The maximum number of applications, annual rates, and single rate application, the minimum retreatment interval, and Pre-Harvest Interval (PHI)  for paraquat use in cotton and sunflower (Sourced from the Gramoxone SL 3.0 label).

Crop

Application Timing

Max # of application/year

Maximum annual rates

Maximum single application rate

Minimum retreatment interval

Pre-Harvest Interval

Cotton

PRE and PP

3

8.0 pts/ac (do not exceed 3.0 lbs ai/ac/year for PRE and PP applications; do not exceed 3.0 lbs ai/ac/year for all paraquat containing products)

2.7 pts/ac

7 days

Harvest at normal maturity

POST directed

3

4.0 pts/ac (do not exceed 1.5 lbs ai/ac/year for POST directed applications; do not exceed 3.0 lbs ai/ac/year for all paraquat containing products)

1.3 pts/ac

14 days

Harvest at normal maturity

Harvest aid

4

1.3 pts/ac (do not exceed 0.5 lbs ai/ac/year for Harvest aid applications; do not exceed 3.0 lbs ai/ac/year for all paraquat containing products)

1.3 pts/ac

7 days

7 days for western cotton and 3 days for all other cotton

Sunflower

PRE and PP

3

8.0 pts/ac (do not exceed 3.0 lbs ai/ac/year for all paraquat containing products)

2.7 pts/ac

7 days

Harvest at normal maturity

Desiccation

2

1.3 pts/ac (do not exceed 1.0 lbs ai/ac/year for paraquat-containing desiccation products; do not exceed 3.0 lbs ai/ac/year for all paraquat containing products)

1.3 pts/ac

7 days

7 days

 

Although the ID is finalized, the paraquat herbicide registration is not complete and will not be completed unto the environmental risk assessment completed. The final ID can be found at https://www.regulations.gov/document/EPA-HQ-OPP-2011-0855-0307.

Links to the aforementioned paraquat products can be found below:

Gramoxone SL 3.0 label – https://www.syngenta-us.com/herbicides/gramoxone-sl-3.0

Parazone 3 SL – https://www.amvac.com/products/parazone-3-sl

Helmquat label – https://us.helmcrop.com/crop-protection/herbicides/helmquat-3sl

 

The use of trade names is for clarity to readers and does not imply endorsement of a particular product, nor does exclusion imply non-approval. Always consult the herbicide label for the most current use requirements.

 

 

Tyler Meyeres, Weed Science Graduate Student
tpmeyeres@ksu.edu

Sarah Lancaster, Weed Management Specialist
slancaster@ksu.edu

Frannie Miller, Pesticide Safety and IPM Coordinator
fmiller@ksu.edu