Gardening: May have to resort to conventional chemicals to get rid of noxious weeds

A friend recently bought a house with a yard that had seen better days. She was up for the challenge and began cleaning it before leaving for a trip to Italy. She came back to a lovely crop of rush skeletonweed she thought she’d pulled. “What do I do now?” she lamented.

Noxious weeds like skeletonweed are legally defined by the Washington Noxious Weed Control Board as “non-native plants that, once established, are highly destructive, competitive or difficult to control using common cultural or chemical practices and can negatively impact agriculture, ecosystems, recreation, and overall land values.” Succinctly, they are thugs.

Why are they such a problem? Noxious weeds are not native to our region. Many of them are native to the eastern Mediterranean region where they were kept in check by other plants and insects that we don’t have here. Without those controls, the weeds have aggressively crowded out native species by disrupting nutrient cycles and hogging water resources.

Skeletonweed’s name is derived from its leafless flowering stems that are blooming right now with a tiny yellow flower. Controlling it isn’t a one -and -done process. It involves several principles that are bundled into what’s called integrated pest management. IPM follows a series of cultural, mechanical, biological and chemical control practices that over time will reduce the weed populations and promote desirable plants.

In my friend’s case, her infestation is manageable, but she will have to use several IPM practices to get it under control. First, she needs to cut the flowering stalks to reduce seed production and throw the cuttings in the trash. Then she needs to water her lawn regularly and apply fertilizer in early September to encourage grass growth. Digging the weeds out or tilling the area only allows the severed roots to resprout. For biological control, there is a gall mite that creates swollen stems on infested plants. These plants can be cut and placed among other skeletonweed so the mite can migrate to them. This is a very slow process however, and may take longer than you have patience for. Lastly, if after all these methods fail, it might be necessary to apply chemicals.

Unfortunately, organic chemicals like horticultural vinegar will kill the tops of the weeds but they won’t kill the roots, which will resprout.

That leaves conventional chemicals like 2,4-D found in products like Weed B Gon. Bringing out conventional chemicals is the last method because skeletonweed and other noxious weeds are thugs that don’t play by anybody’s rules but their own. The best time to apply the chemicals is in the spring when the skeletonweed rosettes appear. They look like a large dandelion rosette but with deeply toothed leaves. In this stage, there is enough leaf area to absorb the chemical into the roots. The tall stems we see now don’t have enough leaf area. The weed has a waxy leaf, so add a teaspoon of dish soap to your spray. Multiple yearly spring applications are needed to eliminate it.