Q: What do you know about the new organic weed kilers that contain chelated iron as the active ingredient?
A: Several products use chelated iron (iron in plant-available form) to kill weeds. I’m familiar with Ortho Elementals Lawn Weed Killer and Natria Lawn Weed Control.
Another product is Fiesta. The manufacturer says:
“The active ingredient of Fiesta is 4.43% iron in the form of FeHEDTA. Fiesta is iron chelated with hydroxyethylenediaminetriaceticacid (HEDTA) to form FeHEDTA.
“Fiesta’s mode of action is through iron toxicity (oxidative damage) at the cellular level. The excessive uptake of FeHEDTA by many broadleaf weeds leads to the contacted area to turn black and brown (tissue necrosis) and ultimately plant death. Broadleaf weeds (dicots) absorb and uptake iron differently than turfgrass (monocots) which provides the mechanism of selectivity. This allows the turfgrass to NOT be affected by the application and only the weed is controlled.”
In my experience, the iron products do just what they say: selective control of broadleaf weeds in a lawn.