Source: California Invasive Plant Council


URL of this page: http://www.cal-ipc.org/ip/management/ipcw/pages/detailreport.cfm@usernumber=42&surveynumber=182.php

Invasive Plants of California's Wildland

Digitalis purpurea
Scientific name   Digitalis purpurea
Additional name information: L.
Common name foxglove, purple foxglove
Synonymous scientific names none known
Closely related California natives 0
Closely related California non-natives: 0
Listed CalEPPC Need more information,CDFA nl
Distribution
digitalis-map

HOW DO I RECOGNIZE IT?
Distinctive features:

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.

 

Description:
Scrophulariaceae. Biennial or perennial herb. Stems: 1-5 ft (0.3-1.8 m) from taprooted caudex, branched above. Leaves: lanceolate to ovate, 4-12 in (10-30 cm) long, evenly spaced but reduced upward 2-8+ in (5-20+ cm), ovate, margins deeply dissected, upper surface green and soft-hairy, lower surface gray-tomentose, lower leaves soon deciduous. Inflorescence: pedicel 0.5-1 in (6-25 mm), spike 1-4 ft (30-130 cm), tomentose. Flowers: calyx lobes <0.7 in (<1.8 cm), lanceolate to ovate; corolla 1.6-2.4 in (4-6 cm), white to pinkish purple with darker spots on lower inside surface, lobes ciliate, sparsely hairy inside. Fruits: approximately 0.5 in (1.2 cm), ovoid with many 0.02 in (0.5 mm) seeds (Hickman 1993).
digitalis-illus

WHERE WOULD I FIND IT?

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.

 

WHERE DID IT COME FROM AND HOW IS IT SPREAD?

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.

 

WHAT PROBLEMS DOES IT CAUSE?

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.

 

HOW DOES IT GROW AND REPRODUCE?

Foxglove reproduces only by seed. In the spring of the second year of growth, it rapidly produces stalks two to five feet (1-2 m) tall, lined with blossoms. Flowers mature in early summer, producing abundant seeds. Seeds are dispersed throughout the summer and remain viable in the soil at least five years (Scott 1997). Sprouts of the small seeds are not able to penetrate turf to any depth. Soil disturbance greatly increases establishment of seedlings. Stalks die back in winter.

digitalis-small2

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digitalis-large2

HOW CAN I GET RID OF IT?

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

 

Physical control:

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).

 

Biological control:

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

 

Chemical control:

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.