During four years of investigation on the use of herbicides to control pest plants in waterfowl habitat in western Kentucky and Tennessee, it was found that: (1) Ammate at 3/4 pound to a gallon of water and 2,4-D at 6% strength can, under selected conditions, be used effectively on many plants, including important pest species such as lotus, giant cutgrass and several woody species. For the greatest degree of success, application must be at certain stages of plant growth and certain environmental conditions. (2) For non-hormone types of chemicals, such as Ammate, best results are likely to be obtained at the period when treatment causes maximum shock to the plant. Generally this is somewhat later than the optimum time for 2,4-D and, in many plants, occurs when the plant is fruiting. (3) Best results with the hormone-type of herbicide, such as 2,4-D, were obtained during active vegetative growth and when foliage development is nearly maximum. Correlated with this optimum stage of the plant's development, the environment should be wet and the average temperature should be 70?F. or higher. (4) Successive treatments of 2,4-D and Ammate made at periods when hormone and non-hormone herbicides are each most effective, were used on hard-to-kill woody sucker growth and on spatterdock. This procedure was more effective than double treatment with either 2,4-D or Ammate, and may show promise for controlling resistant vegetation. (5) Effective application of herbicides in waterfowl areas requires procedures that will result in economical replacement of objectionable vegetation by more desirable plants.