After cardboard is laid, much of the roots will die. When one of the roots does not die and manages to punch through, your choices are restricted. You can not dig it up without ruining the seal, and if you pull it, there will be more coming from that spot. It is the downside of the very organic method of cardboard+mulch. Yes, touching up with a paint brush is not organic. I also still have more than half of the smallest bottle of Round up you can buy. I bought it in 1998, and I never sprayed it, only applied with a paint brush. With ivy and poison ivy it is a must-have backup. In the case of poison ivy (my #1 enemy) you can not even dig the thing out without risking an ER visit, and the local largest PI vines are (or rather, were) thicker than my forearm and 100 ft long, and a root system to match. After you cut one such thing, no matter how much cardboard and mulch you put down, there will be dozens of shoots punching through within a 20 ft radius for a couple of years.

Ken, you don't like fruit trees ==>> i have a half dozen or so fruit ... i just dont spray .. dont care.. and suggest to dreamers.. that their crop will never look like store stuff w/o proactive IPM ... scale.. i was wondering if that was an exoskeleton ... more along he line of a mollusk .. which arent bugs.. per se ... and too lazy to look it up ... in the case above.. this scale has been building for quite a few years.. that infestation did NOT occur this year.... and if i.. with 30 years of experience.. can NOT time out precise repeated sprayings of oil... then one might suggest the OP.. as a novice.. isnt going to be able to either ... and when it comes down to doing ANYTHING.. repeatedly ... i usually just get rid of it ... ergo.. no more privet for me.. too many teenage nightmare trimming the family ones... is OP is up for the challenge... go for it.. but the easy answer is.. get rid of it .. ken ps: actually personally ... if this were a $100 exotic specimen.. i would go systemic hardcore bayer tree and shrub.. one application.. done forever.. but OP doesnt want chems .... but this plant is NOT exotic .... nor worth the cost of cure ...

Try this one- got it from a website that I can't go back to for some reason: Lesser celandine Ranunculus ficaria L. Buttercup family (Ranunculaceae) Download PDF version formatted for print (174 KB) -------------------------------------------------------------------------------- NATIVE RANGE Europe DESCRIPTION Lesser celandine, also known as fig buttercup, is an herbaceous, perennial plant. Plants have a basal rosette of dark green, shiny, stalked leaves that are kidney- to heart-shaped. The flowers open in March and April, have eight glossy, butter-yellow petals, and are borne singly on delicate stalks that rise above the leaves. Pale-colored bulblets are produced along the stems of the above-ground portions of the plant, but are not apparent until late in the flowering period. When in bloom, large infestations of lesser celandine appear as a green carpet with yellow dots, spreading across the forest floor. There are many varieties of lesser celandine including a double-flowered form with many crowded petals and dark green leaves mottled with silvery markings. NOTE: Lesser celandine closely resembles marsh marigold (Caltha palustris), a native wetland plant that occurs in the eastern United States. Marsh marigold is a robust plant with glossy, rounded or kidney-shaped leaves and flowers on stalks that are 8 in (20.3 cm) or more in height and consist of five to nine deep yellow "petals" (actually sepals). Marsh marigold does not produce tubers or bulblets, nor does it form a continuous carpet of growth. Extreme care should be taken to correctly identify lesser celandine before undertaking any control measures to avoid impacts to this plant. ECOLOGICAL THREAT Lesser celandine is an exotic spring ephemeral and a vigorous growing groundcover that forms large, dense patches on the forest floor, displacing and preventing native plants from co-occurring. The ecological impact of lesser celandine is primarily on the native spring-flowering plant community and the various wildlife species associated with them. Spring ephemerals complete the reproductive part of their life cycle and most of their above-ground development before woody plants leaf out and shade the forest floor. Native spring ephemerals include bloodroot, common and cut-leaved toothwort, Dutchman's breeches, harbinger-of-spring, squirrel-corn, trout lily, Virginia bluebells, and many others. Because lesser celandine emerges well in advance of the native species, it can establish and overtake areas rapidly. DISTRIBUTION IN THE UNITED STATES Lesser celandine is currently found in nineteen states in the Northeast and Pacific Northwest (USDA PLANTS map). It is reported to be invasive in nine states (Connecticut, Delaware, Maryland, New Jersey, Oregon, Pennsylvania, Virginia, Wisconsin, West Virginia), and the District of Columbia (WeedUS Database). HABITAT IN THE UNITED STATES Lesser celandine occurs in moist forested floodplains and in some drier upland areas, and seems to prefer sandy soils. BACKGROUND Lesser celandine was introduced to the United States as an ornamental plant. It is still available commercially in the U.S., along with many colorful varieties. All varieties of lesser celandine should be assumed to be invasive. BIOLOGY & SPREAD Lesser celandine is an exotic perennial plant and spring ephemeral that spends much of the year (summer through early winter) underground as thickened, fingerlike tubers or underground stems. During the winter, leaves begin to emerge and photosynthesize in preparation for flowering. Flowering usually occurs from late winter through mid-spring (March through May), depending on conditions. Afterwards, the above-ground portions die back. Lesser celandine spreads primarily by vegetative means through abundant tubers and bulblets, each of which is ready to become a new plant once separated from the parent plant. The tubers of lesser celandine are prolific and may be unearthed and scattered by the digging activities of some animals, including well-meaning weed pullers, and transported during flood events. MANAGEMENT OPTIONS Lesser celandine is very difficult to control but it can be managed with persistence over time using methods that are site appropriate. While manual methods are possible for some (small) infestations, the use of systemic herbicide kills the entire plant tip to root and minimizes soil disturbance. Biological No biological control agents are currently available for lesser celandine. Chemical The window of opportunity for controlling lesser celandine is very short, due to its life cycle. In order to have the greatest negative impact to celandine and the least impact to desirable native wildflower species, herbicide should be applied in late winter-early spring (March through May). Apply a 1.5% rate of a 39 to 41% glyphosate isopropylamine salt (e.g., Rodeo for wetland areas) mixed with water and a non-ionic surfactant to foliage, avoiding application to anything but the celandine. Glyphosate is systemic; that is, the active ingredient is absorbed by the plant and translocated to the roots, eventually killing the entire plant. The full effect on the plant may take 1-2 weeks. Applications can be made during the winter season as long as the temperature is above about 50 degrees Fahrenheit, and no rain is anticipated within 12 hours. Because glyphosate is non-specific, spray should be controlled such that it touches only lesser celandine and does not drift onto desirable plants. To minimize impacts to sensitive-skinned frogs and salamanders, some experts recommend applying herbicide in March and then switching to manual methods.

This plant is a pain and the window of time in which to address it during any given year is limited. See the attached link. You would probably have to go chemical to knock it back significantly. Here is a link that might be useful: PCA fact sheet