Boatman: There are a number of aquatic plants that qualify as XYZ "pond weed", such as
Baby Pond Weed. Fortunately, most of members of the Potamogeton genus similarly respond to the various treatment-options; BUT in virtually every instance, the performance of ANY treatment is dependent upon achieving an adequate concentration and "contact-time" - which varies from one product-type to another.
That said, the success of "spot treatments" (a relative term) are inherently less successful - and sometimes complete failures - when the targeted area is too small to resist rapid diffusion/dispersion of the selected product, thereby failing to achieve and maintain the necessary concentration and contact-time.
The contact-time required by some products might be measured in hours, days OR weeks; so product-selection is especially critical when conducting "spot-treatments" OR when targeting areas that will or might experience undercurrents produced by wind or an assortment of other natural or mechanical influences.
Keep in mind that granular herbicides are rarely a solution for avoiding the effects of diffusion and dispersion. The granule is simply a "carrier" of the active-ingredient, and in that respect the granule replaces water as the "carrier" when conducting liquid-applied applications. Once the herbicide granule contacts the pond's water, it takes only a matter of seconds or minutes before the coated or integrated active-ingredient is released into the water-column where it is free to migrate with any existing currents.
Detrimental currents may not be visible to the naked eye, especially if they're only moving a foot or two per minute, yet their impact on a treatment's performance could prove significant. As a result, the smaller the "spot treatment", the greatly the chances that transient and virtually undetectable currents will diffuse and disperse the active-ingredient, yielding sub-lethal concentrations within the targeted treatment-area.
