Meadow and Spotted Varieties of Knapweed
These perennials are our most pervasive invasive weeds on both public and private land in the Illinois Valley. Knapweed has a long tap root and often develops many side roots. Both have attractive purple or pinkish (depending on the type) multi-petaled dandelion type flowers. Knapweed varies from single-stemmed to bushy, and ranges from about 6 inches to several feet tall. We have not found any conditions these plants cannot adapt to, from hot, dry and disturbed to fully shaded undisturbed soils. Perhaps its ability to adapt comes from the fact that it is a hybrid between black and brown knapweeds.
The soils in the Illinois Valley are often thin and rocky. Knapweed roots can go down several feet winding through the soil and rocks. Small pieces of taproot left even deep in the ground have an unfortunate ability to regrow the full plant. On the plus side, knapweed seeds do not travel far from the mother plant. So if you tackle one area at a time, with little monitoring you can keep the treated areas weed-free as you expand your treated areas. With experience, you can learn to recognize small new knapweed plants and pull them while they are easy and simple to pull.
Meadow knapweed makes a nutritious mulch. The seedlings, when tiny, are easy to recognize and remove to avoid the danger of spreading the population.
Following are the two basic non-chemical methods FAC has developed for Meadow and Spotted Knapweed control.
- Black Plastic: Properly utilized, 6 mil black plastic will kill meadow knapweed in one season. Apparently it also kills the seeds because we have never had new plants grow in the years following the plastic treatment. The plastic needs to be 6 mil. Anything thinner gets too many tears and holes in it. The plastic needs to be black. Light colored materials let in too much light and turn the situation into a greenhouse. Old truck tarps can be used provided they are dark in color. You need to use a weed eater on the area to be treated so the tarp can lay right down to the ground. And the tarp needs to be firmly anchored with rocks, wood, tin can lids nailed in, whatever works. Lay the plastic in the spring, remove it in the fall. The plastic can be re-used one or two times before it disintegrates too much.
- Digging: Because of the ability of small amounts of root to regrow plants, we have found out the hard way that it is worth another five or ten minutes per plant to get absolutely all the root you can. And after getting out all the root you can, fill up the hole you dug and pack the earth down good so the root will have to use maximum energy to reach the surface again. If the plant surfaces again, dig it up again before the root has the chance to revitalize. We have two basic digging tools:
- 1. Dandelion Tool - These tools are about one foot long with a forked tip and can be useful for digging smaller plants. They usually cost under $20 for a long tool, and under $10 for a shorter version. They can be found at many retail stores that have a gardening center.
- 2. Miner's Pick - This is by far the best tool to go after mature knapweeds whose roots have gone down into the rocks. We have found cheaper picks to be a waste of money because the metal tip blunts rapidly with use and becomes useless. Some miner’s picks are made of a quality to hack at rock and endure. We buy the Estwing pick at Armadillo Mining Shop in Grants Pass. It costs $69.95 and the tip remains the same after years of hard use. The handle is slightly shorter than an ordinary full-sized pick and is nicely weighted for maximum ease of aim control. This is the only tool we have found that goes right into the cracks in and between the rocks and enables you to get enough of the root to be effective.
More information about Spotted Knapweed
More information about Meadow Knapweed
