44 WATERCHESTNUT 



MARYLAND: Large beds of waterchestnut have recently (1954) been 

 found in the Chesapeake Bay area, near the mouth of the Gun- 

 powder River. Extensive cutting and spraying operations were 

 conducted here in 1955, but only limited reduction was evident in 

 1956. Full control will probably not be obtained for a good many 

 years, and meanwhile nearby areas valuable to waterfowl are 

 endangered. 



CONTROL 



Since the plant is an annual, the main aim in control operations 

 is to prevent maturing of new crops of seeds. It is these which 

 maintain and spread infestations. All feasible means of control 

 should be used. For extensive, dense beds, herbicidal spraying is 

 likely to be practical. Underwater mowers are valuable, both for 

 extensive cutting of beds and to clear paths for spraying equip- 

 ment. Hand pulling and disposal of plants on land is advisable 

 where growths are sparse or beds are small. 



Timing of operations appears important. Cutting and pulling 

 should begin early in the season, about the time small rosettes 

 have reached the surface and before flowering and seed-setting 

 have commenced. The best time for spraying is about midsummer 

 when many of the leaves are forced above the water by the pres- 

 sure of rosettes on each other. These conditions favor direct con- 

 tact with the herbicide. Spraying after seeds are developed is 

 likely to be too late. 



After infestations have been suppressed, regular patrolling 

 must be maintained for an indefinite number of years to prevent 

 reestablishment. The maximum longevity of waterchestnut seeds 

 is not known, but it is evident they can survive under silt for at 

 least 10 years. 



HERBICIDES 



Tests by the New York State Department of Conservation in 

 1950 showed that though treatments with 2,4-D at rates of 2 or 

 4 pounds of acid equivalent per acre can be fairly effective, better 

 or more uniform results were obtained at 8 pounds per acre. 

 Amine and ester formulations of 2,4-D were found nearly equiva- 

 lent in effectiveness. New York State has limited its control 

 operations largely to amine-salt formulations to avoid danger of 

 damage to crops and has made applications at the rate of 8 pounds 

 acid equivalent in about 50 gallons of water or #2 fuel oil per 

 acre. The Massachusetts Department of Conservation has used 

 a low-volatile ester of 2,4-D at about 4 pounds acid equivalent in 



