From the Lassen county Farm Advisor's Update newsletter (Aug. 2020)

 

Highlighting Two Uncommon Noxious Weeds
Let's keep them uncommon!

There are two species of noxious weeds I want to bring to your attention, as they are not that common in our area: rush skeleton weed (Chondrilla juncea) and sulfur cinquefoil (Potentilla recta). Both of these perennial species have relatively small populations in the Intermountain area. If possible, we want to keep them from becoming the next widespread noxious perennial species like Canada thistle or perennial pepperweed.

I'll start with rush skeleton weed. It is relatively difficult to identify when it is young. The leaves and rosettes look fairly similar to a dandelions. As the growing season progresses, it sends up long spindly shoots as it bolts in early summer. After it bolts it looks quite a bit like chicory, but it is much more invasive. (Chicory has larger blue or white flowers.) Eventually it develops a yellow flower and seeds like a dandelion that can blow in the wind.

This plant is not widespread in California and is considered an A-list noxious weed on the old noxious weed list. The map from Cal Flora shows where is has been officially documented within the state. There have been sightings in Plumas county, a couple in Shasta, and there is an established population on the west shore of Honey Lake. I wouldn't be surprised if there are other populations around our region which do not show up on the map!

Chicory in flower. Before flowering, the growth and leaves can look similar to skeleton weed. Chicory is much more widespread and is common along roadsides and pastures of the Intermountain area. (Photo courtesy of sanbi.org)

Skeleton weed has the potential to expand in the Intermountain region, overtaking rangeland and dryland pastures. In conversations I have had with weed scientist Tim Prather, skeleton weed has completely escaped control in his state of Idaho. It has established on over 3 million acres in the mountains of Idaho, and in many parts of eastern Washington. Skeleton weed is not just problematic here in the western US, but is also a problematic plant in dryland wheat production in Western Australia and parts of Argentina. Keep your eye out for it, so we can prevent it from overtaking our landscapes!

Unlike “showy” weeds, such as pepperweed or Scotch thistle, it is easy to glance over skeleton weed as its spindly stems do not catch the eye. Before it flowers it can blend in with grasses and forbs alike. The best time to see skeleton weed is right now as it is flowering. Keep your eyes out for yellow flowers on a plant that looks like chicory to find it.

Skeleton weed is not desirable forage for livestock or wildlife, and grazing tends to promote skeleton weed over other species that are more desirable. Generally, mechanical control is not effective for established plants because of the deep root system. However, there are multiple biocontrol agents established in the state. A rust, a gall forming midge, and a gall forming mite can all help reduce spread, but not eliminate populations.

Like many deep-rooted perennial weeds, herbicides are often relied upon to control established skeleton weed patches. The best time to make applications is in the rosette stage. If you do find a population on your property, mark the area out now while you can find the plants and see the flowers. The next year, finding the rosette will be easier. Feel free to give me a call to discuss what control options might be best utilized for your situation.

 

The second species I want to bring to your attention is sulfur cinquefoil. Sulfur cinquefoil (Potentilla recta) is relatively common in the western US, but has limited populations here in California (at least documented populations). It is a deep perennial plant with a woody crown that looks very similar to some of our native cinquefoils, and is easy to confuse with a native plant. Cinquefoils can be found in a wide variety of ecotypes from forested areas to native meadows or pastures. It is not a desirable forage as is has a high tannin content which is unpalatable to livestock and wildlife. Under grazing pressure, it will often be ignored and can eventually dominate a pasture.

Sulfur cinquefoil has palmately compound leaves and a light yellow flower. There are at least nineteen other native cinquefoils that grow in the area, so if you suspect you have sulfur cinquefoil, make sure to get it identified.

Previously, sulfur cinquefoil was considered an A-list noxious weed, but its status is under evaluation, as many noxious designations are. Regardless of the category it is listed under, it is still a noxious weed, and not one we want to let take over our landscapes. It has the ability to spread by seed, as well as by root, and established plants can live up to 20 years forming a woody crown.

One key characteristic of sulfur cinquefoil compared to other cinquefoils is the stiff hairs that stick straight out from the stem. Many other native cinquefoils have hairs that lay flat on the stem. This can be key to help identify the noxious weed before it goes to flower.

 

Notice the stiff hairs sticking out directly from the stem on sulfur cinquefoil.

Often invasive weeds are associated with large patches, and this is typically true of sulfur cinquefoil. However, since I learned to identify sulfur cinquefoil, I have found numerous large patches of native cinquefoils along roadways and in pastures (Highways 36, 44, and 139 to name a few). If you have questions about how to identify what cinquefoil you have, you can always drop off a sample at the Cooperative Extension office, or send a sample down to Davis.

Controlling weeds while patches are small can pay large dividends on efforts needed in the future. If you suspect you may have either of these species, let's eliminate them before their populations really get started in our region.

 

Original source: Lassen county Farm Advisor's Update newsletter (Aug. 2020)