Source: California Invasive Plant Council
URL of this page: http://www.cal-ipc.org/ip/management/ipcw/pages/detailreport.cfm@usernumber=23&surveynumber=182.php
Invasive Plants of California's Wildland
|Scientific name||Cardaria draba|
|Additional name information:||(L). Desv.|
|Common name||white top, perennial pepper-grass, heart-podded hoary cress, pepperwort, white-top, pepperweed whitetop, hoary cress, whitetop, white weed|
|Synonymous scientific names||Cochlearia draba, Lepidium draba, Nasturtium draba|
|Closely related California natives||0|
|Closely related California non-natives:||Cardaria pubescens|
|Listed||CalEPPC List A-2,CDFA B|
|By:||Carla Bossard,David Chipping|
HOW DO I RECOGNIZE IT?
Three species of hoary cress are found in
These three Cardaria species are differentiated mainly by the shape of their fruit pods. The pods of heart-podded hoary cress are heart-shaped at the base. The pods of the lens-podded hoary cress are circular. The pods of both heart-podded and lens-podded are flattened in cross-section and have no hairs. The pods of globe-podded hoary cress are globular or spherical and are covered with fine hairs (Hickman 1993, Robbins et al. 1974).
|WHERE WOULD I FIND IT?||
Cardaria draba and C. chalepensis grow in many habitats and
areas of the state, except in the Mojave and
Cardaria chalepensis concentrations exist in grainfields and hayfields and
along roadsides in
|WHERE DID IT COME FROM AND HOW IS IT SPREAD?||
Hoary cress is native to central
Cardaria species occur as crop weeds throughout the
Hoary cress appeared in
Seed is commonly spread in hay and forage such as cut alfalfa, in soil attached to livestock and farm equipment, and by flowing water. Seed may be spread by wind along highways (South Australia Dept. of Agriculture 1973; Chipping 1992). Despite prolific seed production, spread by seed is likely not the most important means of spread. Many infestations remain virtually the same size year after year in spite of annual seed production (Parsons 1992).
Plants also spread by means of extremely persistent root systems, which consist of extensive rhizomes from which shoots emerge (Mulligan and Findley 1974). Another method of dispersal is through movement of root fragments in mud carried by livestock and vehicles, spread by highway maintenance, carried in streams, and spread by tillage (Cook 1987, Robbins et al. 1974). Even very small pieces of root are capable of growth. Infestations in areas with frequent disturbance, such as cultivation, regularly increase in size and density (Parsons 1992).
|WHAT PROBLEMS DOES IT CAUSE?||
Cardaria draba establishes monospecific mats that exclude most or
all other herbaceous vegetation. C. chalepensis forms dense infestations
that crowd out forage plants in meadows and fields. By displacing native
vegetation used by wildlife, both species negatively affect native fauna as
well. These Cardaria species are strong competitors for nutrients and
|HOW DOES IT GROW AND REPRODUCE?||
Growth and reproduction are better understood for Cardaria draba
than for C. chalepensis, although the two may be quite similar. C. draba
reproduces by seed and expands by creeping roots. Flowering is generally from
March to June, but may occur as early as December in mild coastal climates. In
large stands that are close to the water table a few flowering plants may be
encountered year round. In early spring, infestations may resemble carpets of
snow (Cook 1987, Robbins et al. 1974, Mulligan and Findlay 1974). Under
stressful conditions flowers may develop on stems just four to six inches (10-15
cm) high with just one branch, but in well watered conditions flowering may
start when the plant is as small, but continue until many flowering branches
have developed and plant height approaches twenty inches (50 cm). The plant is
self-incompatible, is pollinated by insects, and can produce 1,000 to 5,000
seeds per stem, with seed viability of about 80 percent. Seeds are small, with
550,000 seeds per kilogram. Plants appear to produce few seeds in dry years and
are prolific seeders in wet years. Seedbanks are generally depleted in three
years under both irrigated and non-irrigated conditions. Seed survives in
uncomposted cattle dung.
|HOW CAN I GET RID OF IT?|
Manual/mechanical methods: Tillage may control infestations if started at flower bud time and continued every ten days throughout the growing season. Slightly longer intervals may be possible at different times of year, but it is essential that no green leaves be allowed to form. This deprives rootstock fragments of energy, but the process may have to be continued for at least three growing seasons to deplete the seedbank. Care should be taken not to spread fragments of the plant out of the infested area on tillage equipment.
Prescribed burning: Cardaria species apparently are favored by fire through removal of competition.
Flooding: For control of Cardaria draba, flooding to a depth of six to ten inches (15-25 cm) for about three months can produce 90 percent control of the plant (Cook 1987, Fryor and Makepeace 1978, Pryor 1959, Robbins et al. 1974). However, short-term submergence lasting a week has no effect on the plant (Chipping, pers. observation).
Insects and fungi: No USDA recommended biological control agents exist, and potential introductions from the native range are complicated by the large numbers of cruciferous crops. Although the mite Acerea draba is effective in sterilizing plants of Cardaria draba, it is also found on commercial crops, as is the aphid, Aphis armoracea (Cook 1987).
Grazing: Grazing is not effective on Cardaria draba, as it survives and resprouts using energy stored in its rhizome-like rootstock. In C. chalepensis young plants may be grazed to the ground by cattle and sheep, which also ingest seed heads.
Although C. chalepensis contains glucosinolates and can be mildly toxic, nutritional levels are adequate to meet the requirements of most livestock, especially in early growth stages. Problems arise as the foliage becomes coarse and bitter as it matures, when plants have low nutritive value compared to other forages (Cook 1987, Robbins et al. 1974).
These plants actually are spread by grazing, as cattle ingest seed heads and may become vectors for plant fragments.
Most research on chemical control of Cardaria
species has focused on cropland, usually alfalfa, clover, or wheat fields.
Experiments commonly include combinations of herbicides and other non-chemical
methods in association with the herbicide treatment. Check with your county
agricultural agent to determine which of the possible chemical means of control
are currently registered for use in wildlands in
Different forms of 2,4-D have been tried with limited
success in northern
Mixes of 2,4-D ester and dicamba have been applied by aircraft, and mixes of 0.50 2,4-D and 0.25 each dicamba and R-11 surfactant have worked in roadside applications of one gallon of the mix in 100 gallons of water. Airplane application inevitably affects non-target plants and carries with it the danger of drift of the herbicide to non-target areas and surface water.
which is selective for broadleaf plants, has been used on