Experts urge layered strategy for weed control when converting lawns to water-wise landscaping

At a Utah Division of Water Resources webinar, extension specialists advised homeowners converting lawns to water-wise landscapes to use layered strategies — exclusion, competition, mechanical control and targeted herbicides — and to follow herbicide labels and program rules.

Weeds commonly surge when lawns are removed because turf acts as a living mulch; the panel warned that seeds in the soil can remain dormant for decades and will germinate after soil disturbance and watering.

Katie Wagner, an educator with Utah State University Extension, said it is “really important to formulate both short term and long term weed management plans,” and urged homeowners to choose maintenance approaches that match their time, budget and values. She and other presenters walked through options ranging from mechanical removal and solarization to pre-emergent and post-emergent herbicides.

The presenters stressed preventative measures for new projects: minimize unnecessary soil disturbance, keep the soil covered with mulch or dense plantings, and use drip irrigation so water is focused on intended plants rather than bare soil. “Some of the seeds can remain dormant and viable in the soil for decades,” Candace Scheible, water conservation coordinator with the Division of Water Resources, warned, noting that a single square foot of soil can hold thousands of dormant seeds.

On chemical choices, speakers distinguished pre-emergent products (applied before germination) and post-emergent products (applied to visible plants). Scheible described combination products that include both pre- and post-emergent ingredients and said granular pre-emergents generally require watering to activate. The presenters reiterated the importance of reading and following the product label, including restrictions on temperature, protective equipment, mixing and application rates.

The panel also warned about herbicide drift: selective broadleaf herbicides such as 2,4-D can volatilize under high temperatures and damage unintended plants. Katie Wagner said practitioners have seen rising drift injury this season and noted possible changes in formulations of commonly used products: “I think part of what’s going on is actually not just my opinion... Roundup, the formulation has changed.” Speakers advised avoiding broadcast applications during hot conditions and following label temperature windows.

Longer-term site-preparation options discussed included soil solarization (clear plastic heat treatment for several weeks), stale-seedbed preparation (encouraging weeds to germinate and removing them before planting), and heavy mulching or green-mulch groundcovers to maintain competition against weeds. The panel recommended ongoing monitoring for winter and summer annuals, and addressing weeds while seedlings are small.

The webinar concluded with references to USU Extension field guides and local county extension offices for plant identification and pest diagnostics. Scheible reminded participants in the landscape incentive program not to remove living lawn material before their project is approved because program rules require verification of living turf in the project area.

Resources: USU Extension weed and turf fact sheets and local county extension offices. The webinar recording and follow-up links will be shared by the Division of Water Resources.