Invasive Plants of California's Wildland

Foxglove (Digitalis purpurea) is an erect, knee-high to head-high herbaceous perennial with a basal rosette of leaves. In its second growing season it produces a leafy stock bearing a column of long, bell-shaped, nodding flowers on one side. Flowers are generally pinkish purple or white, with spots on the inside lower portion.

Foxglove is found along the California coast northward from Santa Barbara County, infesting moist meadows and roadsides. It is also reported from the northern Sierra Nevada foothills. A cultivated ornamental, it is often found escaping. It grows in full sun to part shade, in any well drained, fertile, acid soil in open woodland, pastures, roadsides, and disturbed places at less than 3,000 feet (1000 m) elevation. It thrives throughout the United States except in southern Florida and along the Gulf Coast, where it is suppressed by high humidity.

Native to Europe (especially western Europe), the Mediterranean, and northwest Africa, foxglove has been introduced to many areas as an ornamental and medicinal plant. By 1940 it was established in Humboldt and Mendocino counties (Robbins 1940). It escapes cultivation, and seeds are dispersed by wind and water.

A source of the cardiac glycoside digitalis, a medically important heart stimulant, all parts of the plant are toxic. Foxglove is lethal to animals consuming small amounts of fresh or dried material (Scott 1997). It readily colonizes areas of soil disturbance, forming dense patches that displace natural vegetation.

Sites will need to be monitored for five to ten years. Control efforts are required for at least five years.

Manual methods: Hand pulling of stalks is effective. In spring, while soils are moist, stalks and root masses are easily pulled from the ground. Pulled material must be removed from the site and destroyed (flower stalks left on site will continue to mature and release thousands of seeds). It is easy to strip flowers from the stalks, and little additional effort is needed to pull up the entire plant. If flower stalks are cut back before seeds ripen, the plant can bloom again in mid- to late summer. Therefore, above-ground treatments such as clipping and mowing may be counter-productive unless repeated before resprouts have time to produce seed. Workers must protect themselves from extended contact with the poisonous leaves.

Prescribed burning: Fire associated with other management programs is problematic, since stands of foxglove are not a good fuel source. Also, habitat in which foxglove typically becomes established does not contain enough fuel to sustain a fire long enough to kill the plant. Smoke from burning leaves is toxic and has caused injury to workers on control projects (Scott 1997).

Foxglove is valuable commercially in horticulture, so biological control has not been pursued.

Herbicide trials were conducted in late summer and early spring by Scott (1997) on infestations of Digitalis lanata in Wilson county, Kansas. Metsulfuron methyl (as Escort®) at label strength and triclopyr (Garlon®) at 2 pts/acre showed some effect on the plants but did not kill all of them. Herbicides may work, but hand pulling is more efficient and effective with fewer effects on non-target plants.