Tackling Aquatic Weeds: A Guide to Effective Herbicide Use and Long-Term Prevention
Q. A service for keeping a lagoon (about 80cm by 15m up to max 2.5m deep) clear of surface and underwater weeds.
ANSWER
Aquatic weeds can quickly transform a healthy pond, dam, or lagoon into an unsightly mess. Not only do these weeds detract from the beauty of the water body, they can also impede recreational activities, disrupt irrigation, and even harm aquatic life. While manual removal can be effective to some degree, sometimes a targeted herbicide application is necessary, especially for larger infestations. However, it’s important to understand that treating different types of aquatic weeds requires different approaches. This guide will explain how to properly use AQ200 herbicide for both floating and submerged weeds, as well as provide long-term solutions for preventing future infestations.
1. Treating Floating Weeds
Floating weeds like duckweed and azolla, which sit on the water’s surface, require a specific approach. For these, you will need:
5L of AQ200 Herbicide: Fast Acting.
2L of Wetting Agent: This helps the herbicide adhere to the plant leaves for better absorption.
This combination should be sufficient to treat between 1250 and 2500 square meters, depending on the density of the weed cover.
Application:
Mix: In a 100L container, combine 400ml of AQ200 with 150ml of wetting agent. Fill the rest of the container with clean town or tank water.
Drench: Use a sprayer with a heavy setting (not a mist). Thoroughly drench the floating weeds, ensuring complete coverage. You should use most of the 5L solution in this initial application.
Spot Spray: Save a small amount for any spot treatments that may be required 14 days after.
Important Note: AQ200 has a 10-day withholding period. During this time, the water should not be used for drinking, irrigation, livestock, recreation, or any other purpose. After the 10 days have passed, the water can be used again.
2. Treating Submerged Weeds
Submerged weeds require a different approach to treatment.
Assess Water Clarity: If the water is particularly turbid or muddy, you will need to apply a flocculant first. The active ingredient in AQ200 can be neutralized by sediment.
Flocculant Application (If Necessary): If your water is muddy, apply a flocculant according to the product instructions. Wait three days prior to applying herbicide.
Herbicide Application: 6L of AQ200 (no wetting agent needed) is required to treat 1.2 megaliters (1.2 million liters) of water. Dilute 6L of AQ200 with 60L of clean water and spray this solution evenly across the entire surface of the lagoon.
Important Note: For the most effective treatment, apply the submerged weed herbicide after you have removed the majority of the floating weeds. You should see the submerged plants begin to decay after about two weeks.
3. Prevention and Reduction Plans for Long-Term Control
Killing the weeds is just one part of the process. Preventing future infestations is equally important. Here are several steps you can take:
Muck Breaker: Decaying plant matter can contribute to nutrient build-up, which fuels further weed growth and algal blooms. Introduce “Muck Breaker” tablets into the water body to help break down decaying weeds and introduce beneficial bacteria. Toss 5 tablets evenly spaced within the lagoon when you first apply the herbicide, and then apply once a fortnight for 6-8 weeks, followed by monthly applications to maintain a healthy environment.
Aquatic Blue: To combat seasonal submerged weed infestations, consider applying “Aquatic Blue” every six months (at the start of winter and spring). This product restricts UV light penetration, slowing down photosynthesis in submerged weeds and algae.
Surface Clear: To help prevent floating weeds from re-establishing, applying “Surface Clear” will change the surface tension of the water and cause surface weeds such as duckweed and azolla to sink.
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