Aquatic Herbicides

1. Aquatic Herbicides • An overview of the herbicides permitted for use in Region 8 aquatic applications

2. Aquatic Vegetation Emergents - rooted in soil – leaves extend into air Floaters - either lacking roots or roots not growing in soil Immersed Plants completely submerged - not rooted Submergents - rooted in soil - leaves do not extend out of water

3. Acre Foot A measure of WATER 1 surface acre in area X 1 foot deep = 43,560 square feet X 1 foot = 43,560 cubic feet

4. Chelation From “Chela” – a lobsterlike claw When an ion is held to two other non-metal ions in a ring compound by coordinate bonds

5. Chelation More simply – though less accurately An ion held to - but not part of - another chemical compound

6. Copper Compounds Skip details

7. Copper compound formulations

8. Copper compounds summary COMMON NAME Copper compounds (all below are chelated compounds) BRAND NAMES Cutrine-Plus (0.909 lbs elemental copper/gal) – labeled for use in AQUATIC SITES to control algae Cutrine-Plus Granular (0.0366 lb elemental copper per lb. formulated weight) - labeled for use in AQUATIC SITES to control algae K-Tea (0.8 lb metallic copper/gal) - labeled for use in AQUATIC SITES to control algae

9. Copper compounds summary MODE OF ACTION Copper ion released after application is toxic to vegetation Unfortunately, the copper ion concentration needed to kill algae is only slightly lower than that which kills fish Relatively slow release of the copper ion from these formulations makes them slightly less risky than copper sulfate that was used in the past

10. Copper compounds summary SELECTIVITY Selective; kills algae but not other aquatic vegetation

11. Copper compounds summary SOIL ACTIVITY AND MOBILITY Not soil active Copper is strongly adsorbed to clay and organic matter

12. Copper compounds summary PERSISTENCE AND BREAKDOWN Remains in soil indefinitely; however, at application rates used it is essentially chemically inactive a short time after application

13. Copper compounds summary TOXICITY TO HUMANS AND WILDLIFE Generally low in toxicity; rat oral LD50 is listed as 1,312 mg/kg for K=Tea and 1,930 mg/kg for Cutrine Plus Due to the relatively slow release of copper ions by these products, fish toxicity is fairly low; LC50 for bluegill is 1.2 ppm for Cutrine Plus Irritating to eyes and skin; Cutrine-Plus carries the signal word DANGER due to the potential for it to cause irreversible eye and skin damage

14. Copper compounds summary APPLICATION TIMING During the active growing season for algae copper compounds should be applied early in the day on sunny days when the water is relatively warm (at least 60o F)

15. Copper compounds summary WEAKNESSES OR LIMITATIONS Wear goggles or a face shield and rubber gloves when handling Cutrine-Plus Hard water interferes with the action of the released copper ions and makes dose calculation difficult Copper triethanolamine complex (K-Tea) should not be used where water pH is below 6

16. Copper compounds summary WEAKNESSES OR LIMITATIONS Some states require permits for application of copper herbicide to water Despite the eye and skin damage potential of the concentrated formulations, there is no waiting period after application for use as drinking water or for swimming; both activities may begin immediately after application

17. 2,4-D Skip details

18. 2,4-D formulations

19. 2,4-D summary COMMON NAMES 2,4-D BRAND NAMES Aqua-Kleen (0.19 lb a.i./lb) – labeled for AQUATIC use

20. 2,4-D summary NOTE Many other 2,4-D products are available, with or without other a.i.s in the formulation Terrestrial application of 2,4-D may be made only with prior approval of the Regional Forester, and often products in this compendium are equally or more effective without the toxicological concern raised by 2,4-D Labels for products to be applied to terrestrial sites are not included in this discussion

21. 2,4-D summary MODE OF ACTION Growth regulator; causes plant tissues to outgrow their ability to feed themselves Absorbed by both leaves and roots, and translocated to actively growing areas Aqua-Kleen is a granular formulation which sinks to the bottom of treated water areas It is absorbed primarily through the roots

22. 2,4-D summary SELECTIVITY Selective; see label for susceptible aquatic plants In terrestrial applications, grasses are tolerant while trees and broadleaf weeds tend to be susceptible

23. 2,4-D summary SOIL ACTIVITY AND MOBILITY Soil active Amine formulations are readily mobile in soil if percolating water is present Ester formulations are less mobile

24. 2,4-D summary PERSISTENCE AND BREAKDOWN Short half-life, generally 1-4 weeks; breakdown is by microbial action

25. 2,4-D summary TOXICITY TO HUMANS AND WILDLIFE Moderately toxic; rat oral LD50 is 639 mg/kg; formulated Aqua-Kleen’s oral LD50 4,050 mg/kg for male rats Ester formulations can be highly toxic to fish Animal studies have indicated possible carcinogenicity

26. 2,4-D summary PRIMARY FORESTRY USES Aquatic use is primarily to control water milfoil or water stargrass in ponds Little current use in Region 8; past use has been primarily in combination with other herbicides May be useful for broadleaf weed control in wildlife openings or rangelands Any terrestrial use of 2,4-D requires Regional Forester approval

27. 2,4-D summary APPLICATION TIMING Should be applied during periods of active growth Do not treat an entire pond or lake at one time; treat strips or quadrats and wait at least two weeks before follow-up treatments are made so as to avoid oxygen depletion resulting from decomposition of dead plant material and subsequent fish kill

28. 2,4-D summary WEAKNESSES OR LIMITATIONS In general, other products are available which pose less risk and are more effective Fish kill can result from treating too large an area of aquatic vegetation at one time Some states have additional restrictions on the use of 2,4-D Terrestrial application may be made only with Regional Forester approval

29. Diquat Skip details

30. Diquat formulations

31. Diquat summary COMMON NAME Diquat BRAND NAMES Reward (2 lbs a.i./gal) – labeled for AQUATIC use

32. Diquat summary MODE OF ACTION Contact herbicide; rapidly absorbed by vegetation, but not readily translocated

33. Diquat summary SELECTIVITY Nonselective Effective in controlling most submerged aquatic plants

34. Diquat summary SOIL ACTIVITY AND MOBILITY Not soil active Strongly adsorbed to clay particles Rapidly deactivated by muddy water Also, degraded by water with low pH

35. Diquat summary PERSISTENCE AND BREAKDOWN Breakdown is primarily by photolysis, although persistence is generally limited by adsorption rather than chemical breakdown When bound to soil diquat is very persistent – but is biologically unavailable Microbial degrade is limited and almost completely stops once diquat adsorbs to vegetation

36. Diquat summary TOXICITY TO HUMANS AND WILDLIFE Moderately toxic; rat oral LD50 is 230 mg/kg; for Reward it is 810 mg/kg Relatively low toxicity to fish However, dermal toxicity to mammals is generally higher than oral toxicity, and care must be taken to avoid dermal exposure

37. Diquat summary APPLICATION TIMING Should be applied when target plants are actively growing

38. Diquat summary WEAKNESSES OR LIMITATIONS Due to risk associated with dermal toxicity, this product is a poor choice if lower-risk products are effective on the target species Rapid plant kill can result in oxygen depletion in ponds, which can cause fish kill Diquat is rapidly inactivated when applied in muddy water Do not allow swimming in treated areas for 24 hours following treatment

39. Endothall Skip details

40. Endothall formulations

41. Endothall summary COMMON NAME Endothall BRAND NAMES Aquathol (0.101 lb a.i./lb of formulation product) – labeled for aquatic weed control in LAKES and PONDS Aquathol K (3.0 lbs a.e./gal) - labeled for aquatic weed control in LAKES, PONDS, and DRAINAGE DITCHES Hydrothol 191 (2 lbs a.i./gal) - labeled for algae and aquatic weed control in LAKES, PONDS, and DRAINAGE DITCHES Hydrothol 191 (granular) (0.112 lb a.i./lb of formulation weight) - labeled for algae and aquatic weed control in LAKES, PONDS, and DRAINAGE DITCHES

42. Endothall summary MODE OF ACTION Interferes with RNA synthesis Acts as a contact herbicide, with little translocation

43. Endothall summary SELECTIVITY Nonselective Generally used against submerged aquatic plants

44. Endothall summary SOIL ACTIVITY AND MOBILITY Some soil activity, although absorption is primarily through leaf surfaces in aquatic applications Mobile in water

45. Endothall summary PERSISTENCE AND BREAKDOWN Broken down in both soil and water by microbial action at rates which are dependent on temperature and nutrient availability

46. Endothall summary TOXICITY TO HUMANS AND WILDLIFE Highly to moderately toxic, depending on formulation Rat oral LD50 for technical endothall acid is 38 mg/kg; for sodium salt, 182 mg/kg; for amine salt, 206 mg/kg Formulated products have lower toxicities: rat oral LD50 for Hydrothal 191 granular is 1,540 mg/kg and for the liquid it is 233 mg/kg Dermal toxicity is higher than oral toxicity, so precautions must be taken to avoid dermal exposure

47. Endothall summary TOXICITY TO HUMANS AND WILDLIFE Endothall is also an eye irritant, and inhalation of vapors or dusts can cause irritation and injury Generally nontoxic to fish at concentrations of 500 ppm or less Hydrothol formulations are more toxic to fish than Aquathol formulations

48. Endothall summary APPLICATION TIMING Apply when water temperature is 65 degrees or above, and plants are actively growing

49. Endothall summary WEAKNESSES OR LIMITATIONS Due to its toxicity, endothall should not be used if other products are available which will effectively control the target species Granular formulations are preferred to liquids due to reduced risk of dermal absorption

50. Fluridone Skip details