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Open Space Weed Management

Spring is here and along with warmer temperatures and longer days weeds are starting to appear in lawns, parks and open space areas. As part of an integrated management approach, herbicide applications and mowing are used to combat weed infestations in the open space. This year’s herbicide applications will be conducted from approximately April to July depending on weather and growing conditions. Mowing operations are usually performed in late summer to prevent seed production. Some follow-up spraying in fall may occur if there is re-growth after the summer mowing operations.

Bare-ground areas like picnic pads, hard-surface trails and kiosk pads are treated first with a pre-emergent herbicide. Applications can be conducted before weeds emerge, and these herbicides prevent weeds from germinating in the area throughout the growing season.

The next weeds managed are the biennial weed species like Musk thistle and Mullein. Mullein and Musk thistle are on the Colorado noxious weed list, which mandates that landowners make attempts to control and stop the spread of these weed species. The first year and early spring growth forms for these weeds is a rosette of basal leaves lying close to the ground. At this stage they are most vulnerable to chemical application because of their increased uptake of water and nutrients. Even though mullein and musk thistle can be effectively treated all the way up to the budding stages, we have found that spring and fall spraying in the rosette stage is most effective.

As spring turns into summer, management efforts shift to deeply rooted perennial weeds like Canada thistle. Spraying Canada thistle and other deeply rooted perennials is more effective when the plants have bolted and grown to approximately 10 inches in height. At this point, they are still transporting nutrients to the root system, which will allow for more herbicide uptake. Mowing is also an effective way to make the perennials use more energy as they attempt to recover from the mowing. Mowed perennials are also more susceptible to fall herbicide applications.

The weeds being managed this season are very aggressive invaders that have the potential to take over native plant communities. Priority was given to areas where infestations pose the worst threat to native plant communities and where they are bordering home lots. A contract herbicide applicator and the in-house open space crew will be performing the herbicide applications.

Contact KCRMA Park Ranger Gary Norton with any questions about noxious weed management or specific weed management areas at 720-599-3265 or garyn@kcranch.org. See Map of the Weed Management Areas.

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