Atrazine is a common but controversial pre- and post-emergent herbicide used to control broadleaf and grass-like weeds in commercial farming fields. It is also a component of granular weed and feed lawn products designed for the home and landscape gardener. The use of atrazine is banned in Europe due to concerns over groundwater contamination, the birth defects it imparts to animals and the medical complications that it can manifest in humans. Atrazine is considered moderately effective in killing grasses in the fescue family.
Disruption of Photosynthesis
Atrazine, when sprayed onto the leaves and stems of weeds and undesirable grasses, disrupts the plant's ability to conduct photosynthesis. This halts the plant's ability to manufacture nutrients for itself and it withers from malnutrition and dies. Warm season grasses, like fescue, are particularly acclimated to high levels of sunlight to power their root and blade growth. The choke that atrazine puts on the light absorption process in fescue makes it effective when applied under optimal conditions. Applying when rain is not anticipated and refraining from irrigation for several days after application increases the efficacy of atrazine on fescue and all warm season grasses.
Atrazine that does not land on the top green growth of weeds falls to the soil and to be washed onto the soil surface and into the roots of the weeds. Atrazine commonly stays in the top 6 inches of soil where it will continue to be absorbed over time by any roots in the vicinity. The roots of more newly established and mature weed plants will soak up the atrazine from the moist soil and metabolize it. This spreads the compound up into the green fescue tops, disrupting nutritional processes which typically result in death or damage to the plant.
Germination and Seedling Kill
When atrazine is sprayed onto the fescue grass, much of the product coats the blades. The balance of the applied product falls onto soil surface and is leached into the top 6 inches of soil over time with irrigation or natural rainfall. When atrazine hits the thatch or soil surface, it will kill fescue seedlings near the time of germination. As with its action on mature plants, atrazine blocks a young seedling's ability to conduct photosynthesis. This provides the broader prevention against new weed growth. Seedling kill fills the gap between spraying the mature green weed tops and killing those mature weed roots.