METHODS 



CONTROL BY WATER-LEVEL AAANAGEMENT 



Suppressing weeds by water-level management has been prac- 

 ticed in many places because of its practical advantages in econ- 

 omy and simplicity. The method requires sufficient water supply 

 and a suitable type of dam to maintain desired levels at different 

 seasons. 



Various kinds of marsh weeds can be eliminated by drowning, 

 either as seedlings or in more mature stages of growth. Flowering 

 beds of lotus have been killed by a 30- to 36-inch increase in depth 

 lasting for 12 days. Mowed needlerush was destroyed by an 8-inch 

 rise in water level held for 3 weeks. Mowed cattails can be con- 

 trolled more effectively when water covers the cut bases. Most tree 

 and brush stumps lose their ability to sprout if covered by water 

 during one growing season. Many other species that are some- 

 what tolerant of flooding can be drowned if depth and duration are 

 sufficient. 



An especially important water-level measure for improving vege- 

 tation is the seasonal drawdown. In certain instances, however, 

 the drawdown can be a liability rather than an asset since more 

 weeds or worse weeds can become established while water levels 

 are down. Potentialities of the drawdown for good or harm depend 

 upon local conditions — particularly upon plants, soils, and weather 

 of the area. 



In places where dark-stained water, excessive acidity, turbidity, 

 troublesome weeds, carp, or similar factors limit production of 

 good duck foods, it is often advantageous to drain or partially 

 drain the pond basin during summer and raise wild or cultivated 

 seed-producing annuals. Gradual restoration of water levels in 

 the fall makes abundant food supplies readily available for ducks 

 and geese. If weedy perennials survive inundation through win- 

 ter and spring and become a nuisance, it may be advisable to omit 

 the drawdown in some years so the undesirable plants can be 

 drowned during continuous high water. 



At the Patuxent Refuge, a system of alternating drawdowns on 

 two adjacent ponds, one pond being lowered one year and the other 

 the next, has worked particularly well. The plan has not only pre- 



