A Farm Pond Used for Irrigation and Trout

Nothing goes in this pond until three things are settled:

1. Permits. Treating a pond with an aquatic pesticide in New York requires the appropriate NYSDEC authorization, and the applicator must hold the aquatic category. Stocking grass carp is a separate authorization (triploid fish stocking) and is not a way to avoid the pesticide permitting process.
2. The complete use picture. This is not just a fish pond: it irrigates lettuce and tomatoes and waters 20 horses, and it discharges to a marsh and then a stream where people swim. Each of those is a separate exposure route with its own label restriction - an irrigation restriction that the vegetable schedule cannot tolerate rules the product out regardless of how well it kills duckweed.
3. The trout. Brook trout are cold-water, high-oxygen fish and are far more sensitive to copper than warm-water species, particularly in soft, low-alkalinity water where copper stays biologically available.

Diagnosis first: confirm the algae/duckweed identification and the nutrient source (runoff from the horse operation is likely feeding it). A treatment that ignores the nutrient loading regrows within weeks and repeats the exposure.

Copper sulfate: no, not in this pond, not in a July heat wave. Chelated and unchelated copper products are toxic to trout at low concentrations, especially in soft water; the label rates that control algae are uncomfortably close to trout-toxicity levels. Killing a heavy algae/duckweed mat in hot, still weather also strips oxygen from the water as the plants decay - a classic summer fish kill on top of the copper. And a pond feeding lettuce and tomatoes has label irrigation restrictions that must be checked against the harvest schedule.

Grass carp: not a solution to this problem. Triploid carp are permitted for specific vegetation, mainly submerged and some floating plants, and they do not control filamentous algae mats well. They require authorization, are difficult to remove, and are a long-term commitment.

A defensible plan:

• Identify and control the nutrient input first (manure runoff, field drainage).
• If treatment is warranted, choose a product whose label permits both the irrigation use and the livestock use after the stated waiting period, and check trout toxicity and the irrigation interval against the lettuce schedule.
• Treat in sections or strips rather than the whole pond, leaving untreated refuge areas, so oxygen is not driven down by one large kill.
• Treat on a cooler, overcast day with wind, and monitor dissolved oxygen; be prepared to aerate.
• Post the pond, notify the owner and downstream users per label and permit conditions, and set a setback at the outflow so product does not leave the pond.

The label and the permit govern, not the owner's schedule. If the full-pond, high-temperature application is outside label directions (rate, water temperature limits, irrigation intervals, fish precautions) or outside the permit conditions, I decline it and say so in writing.

Handling it in practice:

1. Restate the specific constraint - e.g., "the label prohibits irrigation of food crops for X days after treatment" - not a general "I'm not comfortable." Owners comply with reasons tied to the label.
2. Offer the compliant alternative with a calendar: split treatment over a longer window, treat the duckweed before the algae, wait for cooler weather, or start with source control this season and treat after the harvest schedule allows.
3. Confirm the permit conditions allow the timing and the treated area; if the permit requires pre-notification of downstream users, do it.
4. Document the refusal and the reason in the file, and inform my supervisor and the farm's decision-maker.

If the owner proceeds on his own or hires someone else, my obligation to explain the restriction and to document it stands - and the applicator who signs the record is the one who answers for it.