ZTrain - There are granular aquatic herbicide brands including 2-4D formulations that can be used for spot treatments by just spreading the correct amount of product in a specified area. I and others here have also used liquid diquat brands such as Reward and Harvester that are likely what are used by the 'professional' applicators that are hired by the HOA. These liquid formulations can be used as spot treatments by injecting the mixed solutions underwater into areas with curly leaf for good results in sections of a pond. Good injection methods and even coverage into treatment areas are important for best results.

If the curly leaf in your pond seems to returning as abundant or more of growths each successive year then IMO the professionals are not applying the herbicide early enough in the life cycle of curly leaf. Chem-kills for curly leaf should be applied before the plants form turions and seeds. Turions and seeds are how the plants repopulate the pond each year. Good effective efforts of annual kills each year should gradually over time reduce the amount of redevelopment of curly leaf that appear each year.