KnockDown Defense®

Algae and Aquatic Weed Control

Cannot be shipped to AK, CA, CT, DC, HI, MA, ME, NJ, NY, PR, RI, VT, WA, or Canada

Please select an option.

  • 16 Ounce
  • Item: 530268
  • $124.99


KnockDown Defense provides fast control of tough invasive weeds such as duckweed, watermeal, fanwort, hydrilla, as well as algae. KnockDown is an EPA registered liquid herbicide which contains 42% of the active ingredient Flumioxazin. Ideal for controlling algae and submerged aquatic weeds in ponds and lakes. Effective in slow-moving or quiescent waters such as bayous, canals, drainage ditches, reservoirs, and marshes. KnockDown is very versatile and breaks down quickly in water without accumulating in the sediment or clogging application sprayers. Best results when mixed with water and Treatment Booster® Plus in a tank sprayer.



Algae & Weed Control
Product Label - 16 Ounce

Weeds Treated

String Algae
American Pondweed

Curly Leaf Pondweed
Eurasian Watermilfoil

Sago Pondweed


How to Use

KnockDown Defense
16 Ounce
Application Liquid
Temperature Restriction None
Square Footage Per Container Up to 10,000 Square Feet
Shelf Life 2-Year

Dosage Rates

KnockDown Surface
KnockDown Subsurface Application
3' Avg. Depth
Booster Plus
1/8 Acre (5,445 Sq Ft) 0.75-1.5 Ounces 6.6-13.2 Ounces 1 Gallon 2 Ounces
1/4 Acre (10,890 Sq Ft) 1.5-3 Ounces 13.2 - 26.4 Ounces 2 Gallons 4 Ounces
1/2 Acre (21,780 Sq Ft) 3-6 Ounces 26.4 - 52.8 Ounces 4 Gallons 8 Ounces
1 Acre (43,560 Sq Ft) 6-12 Ounces 52.8 - 105.6 Ounces 8 Gallons 16 Ounces

Please note: Above are recommendations. Always read the product label. Treat at proper rates to prevent plants from building chemical resistance. Early morning treatments are most effective.


KnockDown Defense has no temperature restriction. Apply when weeds are actively growing. In areas with dense weed vegetation, only treat 1/2 of the water body at one time and wait 10-14 days before treating the remaining area. Do not re-treat the same section of water within 28 days of application.


Dilute with clean tap water. When treating submerged weeds and algae, submerge the spray nozzle several inches into the water. When treating floating plants and algae, evenly spray rain-size droplets over the treatment area. For best results, use Treatment Booster Plus.

  • SURFACE APPLICATION: Mix 0.75-1.5 oz of KnockDown, 2 fl oz Treatment Booster Plus and 1 gal of water for every 1/8 acre (5,456 sq ft).
  • SUBSURFACE APPLICATION: Mix 2.2-4.4 oz of KnockDown, 2 fl oz Treatment Booster Plus and 1 gal of water for every 1/8 acre (5,456 sq ft) per 1' average depth. Example: 1/8 acre with 3' average depth would require 12 oz ( 4 fl oz x 3).


Wait 5 days before using treated water for irrigation. Do not use in water utilized for crawfish farming. Do not re-treat the same section of water within 28 days of application.


KnockDown Defense can not be shipped to Alaska, California, Connecticut, Deleware, District of Columbia, Hawaii, Massachusetts, Maine, New Jersey, New York, Puerto Rico, Rhode Island, Vermont, Washington, or Canada.


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Item Numbers and UPC

Item Number
UPC Code
530268 810089840295 16 Ounce

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