By: Amy Grant
Skeletonweed (Chondrilla juncea) may be known by many names – rush skeletonweed, devil’s grass, nakedweed, gum succory – but whatever you call it, this non-native plant is listed as invasive or a noxious weed in a number of states. This makes managing skeletonweed a primary concern.
Killing rush skeletonweed isn’t easy. It is extremely resilient and resistant to mechanical and cultural methods of control. Since it is so persistent, the question is how to control skeletonweed?
Rush skeletonweed is thought to have been introduced to eastern North America via contaminated seed or animal bedding around 1872. Today, this nearly 3 foot (just under a meter) herbaceous perennial has spread across the country.
It reproduces by seed as well as lateral roots that, even when broken, determinately produce a new plant. This dogged determination to reproduce makes managing skeletonweed a challenge. Since it can re-sprout from root fragments, mechanical control by pulling, digging, or disking is ineffective unless consistent (6-10 years) mechanical controls are applied.
Also, burning is ineffective in managing skeletonweed as is livestock grazing, which seems to just disperse rootstock that results in additional plants. Mowing is inadequate skeletonweed control as well.
The only successful non-chemical method of killing rush skeletonweed is the introduction of the rust fungus (Puccinia chondrillina). First introduced in Australia, it has since been used as a bio-control in the western United States, though with less stellar results. Since this sole bio-control was not effective in killing the invasive weed, two additional bio-controls have been added to the mix: skeletonweed gall midge and skeletonweed gall mite, which appear to be reducing the incidence of the plant in states like California.
Otherwise, the only other option for killing rush skeletonweed is with chemical controls. Herbicides are often inadequate because of the extensive root system and lack of leaf area on the plant. However, for large-scale infestations, it is the only option.
Always read and follow the manufacturer’s safety and application instructions. Successful skeletonweed control will rely on several applications. The herbicides that give the best results are fall applications of picloram alone or picloram combined with 2, 4-D. Clopyralid, aminopyralid, and dicamba also affect the root system and can be of assistance in managing skeletonweed.
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State Asks For Idahoan’s Help In Battling Rush Skeletonweed Noxious Weed Infestations
Read the News Release here
The Enemy: Rush Skeletonweed (Chondrilla juncea L.) is a perennial plant that has infested several million acres in Idaho. Originally found in the early 80’s as a five acre patch near Horseshoe Bend, it has grown to over 1 million acres in only 20 years. Noticeable, leaves are found as rosettes which are sharply toothed like others in the Asteraceae family. Stem leaves are very small, inconspicuous and narrow, thus giving the plant the look of no leaves or skeletal in appearance. Flowering heads are found scattered on the branches, approximately ¾ inch in diameter. This plant resembles an alfalfa plant after a migration of grasshoppers has stripped all the leaves off. To tell the difference look at the base of the stems. If the stem has small red hairs on the lower 3 to 4 inches, where other plants do not, it will be this noxious weed. One can also look for the milky latex that is produced if the stem is broken.
The Strategy: The dandelion-like seeds float in the air for miles and miles. The plant is not foraged upon and invades very rapidly, which, like in the Boise National Forest, adds to its ability to destroy an ecosystem.
The Defense: Mechanical control is very difficult on this plant. Deep roots that may or may have rhizomes make it so that the growing parts of the roots are not destroyed. Herbicides such as Milestone®, Opensight®, Transline® or Tordon 22K are most effective when used in the fall or early spring. Once the plant has bolted, the basal rosettes recede, thus giving very little leaf surface to allow the pesticide to get into the plant. Hand harvesting the plants (if there are just a few of them) in the late summer will keep the seeds from spreading, then in early fall, treating the plants with herbicide is the most effective method of control.
ERADICATING RUSH SKELETONWEED
Bayer CropScience™ recommends their Perspective® herbicide.
Dow ™ recommends their herbicides such as Milestone® and Tordon 22K.
PLEASE NOTE - The proper use and application of herbicides can be an effective way to control and eradicate noxious and invasive plants. Before using herbicides, always carefully follow the label and safety instructions on the label. While we recommend the use of herbicides as one of the effective tools for integrated pest management, the Idaho Weed Awareness Campaign assumes no liability for herbicide applications.
For more information, click on the link below to download the Idaho's Noxious Weeds Control Guidelines publication produced by the University of Idaho Extension.
Bradyrrhoa gilveolella, or the skeletonweed root moth, was recently approved for release. Adults emerge from exit tubes extending from the plant’s root in May and June. Females are capable of producing up to 300 eggs, laying them in the rosette crown or in the soil.
The eggs hatch in six to 10 days and the caterpillars penetrate the soil and begin to feed externally on the roots. The larvae feed both internally and externally on the root tissue, producing elongated tubes attached to the roots. These tubes are composed of frass, root fragments, sand grains, and latex from the plant. Larvae complete their development in 45 to 60 days in the tubes. Final instar larvae extend the exit tubes to the surface and pupate inside. Following their pupal stage, which lasts from seven to 10 days, adult moths force their way out of the capped exit tubes.
This insect is destructive in only the larval stage, when it destroys the cortical and vascular tissues of rush skeletonweed roots. The root feeding also exposes the plants to soilborne plant pathogens. Although establishment of this agent has not yet been confirmed, its preferred habitat (foreign collections) is sandy, granitic, or loose-textured soil.
Approved Biological Control Agents for release in Idaho:
Rush Skeletonweed starts as a rosette in the fall, with leaves that resemble a dandelion and grows from 1 to 4 feet tall during the summer with 1 to 6 branching flowering stems.
Its slender, taproot can reach down 8 feet or more.
Stem bases have coarse, downward pointing brown hairs and very few leaves.
Leaves are narrow and linear in shape. The dandelion-like rosette leaves die off during flowering, leaving a skeleton-like appearance to the plant.
Flowers are bright yellow about 3/4 inch in diameter growing at the branch tips, or along the stem in the leaf axil. They are found individually, or in clusters of 2 to 5. The ridged petals have small teeth across their blunt ends.
Seeds are pale brown to black, with a ribbed surface and white bristles on one end which makes them easily distributed by wind.
This species is a threat to irrigated lands, wheat areas, rangelands. Infestations impact the cattle industry because it displaces native or beneficial forage species grazed by livestock and wildlife. The plants extensive root system makes it highly competitive to crop plants for moisture and nutrients, especially nitrogen.
It is found in pastures, rangeland, crop-fields, roadsides and open areas.
A mature plant can produce 1,500 flower heads, with up to 20,000 seeds, 90% of which will germinate. Each seed has a pappus which is capable of carrying seeds up to 20 miles away. It can reduce crop yields by as much as 70 percent.
Hand pulling or digging is not an effective means of control for this species because of its extensive root system and its ability to produce new shoots from root fragments.
Three biological control organisms, Rust Fungus, Gall Midge, and Gall Mite, have been released across Washington State where there are large populations of this plant. For information about the biological control of this or any other noxious weed, see the WSU Extension Integrated Weed Control Project.
Download our Flyer or visit Washington State Noxious Weed Control Board Here. Photo by Leo Michels
Habitat & Distribution
Reproduction & Spread
Integrated Pest Management
Early Detection and Prevention
Manual, Mechanical, & Cultural Control
Biological control is the deliberate introduction of insects, mammals, or other organisms which adversely affect the target weed species. Biological control is most effective when used in conjunction with other control techniques.
* For more information on biocontrol agents, contact your local weed authority.
Specific Herbicide Information
Herbicides are described here by the active ingredient. Many commercial formulations are available containing specific active ingredients. References to product names are for example only. Directions for use may vary between brands.
This BMP does not constitute a formal recommendation. When using herbicides, always consult the label. Please refer to the Pacific Northwest Weed Management Handbook or contact your local weed authority.
Time Apply to rosettes in the spring immediately before or during bolting.
Remarks 2,4-D inhibits further aboveground growth but will not prevent new plant development from root buds.
Caution Re-treatment is important.
Site of action (both) Group 4: synthetic auxin
Chemical family (both) phenoxy acetic acid
aminocyclopyrachlor + chlorsulfuron (Perspective)
Rate 1.8 to 3.2 oz/a aminocyclopyrachlor + 0.7 to 1.3 oz/a chlorsulfuron (4.5 to 8 oz/a of product)
Time Apply to actively growing plants in spring.
Remarks Adjuvants can be used these include methylated seed oils 0.5 to 1% v/v, nonionic surfactants at 0.25 to 1% v/v, and crop oil concentrates at 1% v/v. Can be applied using an invert emulsion rather than water.
Caution Even low rates can kill nontarget tree and shrub species, so avoid application within a distance equal to the tree height of the sensitive species. Do not allow spray to drift off target. Can injure several grass species including bromes, as well as basin wildrye.
Site of action (aminocyclopyrachlor) Group 4: Synthetic auxin (chlorsulfuron) Group 2: ALS inhibitor
Chemical family (aminocyclopyrachlor) Pyrimidine carboxylic acid (chlorsulfuron) Sulfonylurea
Rate 1.75 oz ae/a (7 fl oz/a Milestone)
Time Spring or fall when rosettes are present.
Remarks A nonionic surfactant at 1 to 2 quarts per 100 gal of spray enhances control under adverse environmental conditions.
Caution Do not allow drift to desirable vegetation. Many forbs (desirable broadleaf plants) can be seriously injured or killed. Do not exceed 7 fl oz/a Milestone per year.
Site of action Group 4: synthetic auxin
clopyralid (Transline or Stinger)
Rate 0.25 to 0.375 lb ae/a (0.66 to 1 pint/a)
Time Apply to rosette in fall or up to early bolting in spring.
Remarks Consult labels for specific site registrations.
Caution Product will injure or kill sensitive broadleaf forages. Consult label for crop rotation restrictions before using. Several crops may be injured several years after application.
Site of action Group 4: synthetic auxin
Time Apply from late fall to early spring. For best results, apply just before or during bolting.
Remarks Rush skeletonweed can reduce crop yields by as much as 70%, so it is important to treat small infestations. Picloram is the most effective treatment available. Re-treatment is necessary.
Caution Most formulations are restricted-use herbicides . Do not contaminate water. Potatoes, beans, and many other broadleaf crops are sensitive to picloram do not use in diversified crop areas.