VIII. CONTROL OF AQUATIC WEEDS 



FLOATING WEEDS 



For control of water -hyacinth and waterlettuce : Amine salts or low- 

 volatile esters of Z,4-D at 1 to 4 pounds in 2 to 150 gallons of water per 

 acre. The higher volumes of spray often give better results. Spray at low 

 pressure with large nozzles to reduce spray drift. Use oil, or an oil-water 

 emulsion in spraying waterlettuce to insure proper wetting of the leaves. 

 A mixture of amitrole and ammonium thiocyanate (known as amitrole-T) 

 at 2 to 4 pounds per acre has proved more effective than 2,4 -D on both 

 water -hyacinth and waterlettuce in Florida experiments. 



SUBMERSED WEEDS 



In Irrigation and Drainage Canals 



(1) For control of rooted submersed species (such as pondweeds and 

 waterweed in Western and Great Plains irrigated areas): (a) Emulsifiable 

 aromatic solvents (methylated benzenes such as xylene) applied in canal 

 at 400 to 740 p. p.m., which is 5.4 to 10 gallons per c.f.s. (cubic feet per 

 second) of water flow, during a 30-minute period. More than one treatment 

 may be necessary in regions with long grow^ing seasons. For detailed 

 recommendations on use of this method, see USDA Circular No. 971, "The 

 Use of Aromatic Solvents for Control of Submersed Aquatic Weeds in 

 Irrigation Channels." This circular is not now stocked for distribution but 

 should be available in many libraries, (b) Acrolein at 1 to 3 gallons per 

 c.f.s. has proved even more effective than aromatic solvents in numerous 

 experiments and limited commercial use. Due to severe irritation of respira- 

 tory passages and eyes, it must be applied by licensed skilled operators with 

 specialized equipment. Each application gives control for 4 to 8 weeks. 

 Follow instructions of manufacturers relative to use of water by livestock. 



(2) For control of rooted submersed species (such as southern naiad, 

 coontail, and bladderwort in Southeastern States): Use emulsifiable aromatic 

 solvents at 20 to 200 p. p.m. during a continuous treatment period of 24 to 

 48 hours. Gasoline mixtures with polychlorobenzenes at similar concentra- 

 tions and exposure times have given good control in drainage canals in 

 Florida. Water temperature and movement influence the rate of treatment 

 and exposure time. The w^armer water and quasi-static water conditions 

 prevalent in water control canals of Southeastern States permit much longer 

 treatment exposure times and make possible control of waterweeds with 

 much lower concentrations of herbicides than are necessary in colder and 

 rapidly flow^ing water conditions in canals of Western and Great Plains 

 States. 



(3) For control of filamentous green and red algae (in water flowing at a 

 velocity of 0.5 foot or more per second): For green algae, apply copper 

 sulfate at 1/5 to 2 pounds per c.f.s. every 2 to 4 weeks during the growing 

 season. For red algae, apply copper sulfate at 10 to 12 p.p.m. during a 

 continuous treatment period of 30 minutes. The treatments usually must be 

 repeated at intervals of 2 to 6 weeks to maintain adequate control of algae. 



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