||Long-lived, rhizomatous perennial
||May-June (Second flowering
can occur in late summer.)
||June-July (Second seed set can
occur in late summer.)
are three different white tops that have been introduced in to the
United States. The white top that has a heart-shaped pod, also known
as hoary cress, is native to western Mediterranean countries and
the Middle East (Turkey, Israel, Syria, Iraq and Iran). Hoary cress
probably entered North America in contaminated alfalfa seed. It
was first found at Long Island, New York, in 1862. This weed is
now introduced on every continent.
is a member of the mustard family. New plants can grow from both
seed and root fragments. Leaves grow very rapidly after seedling
emergence, and lateral roots develop within three weeks. Seedlings
over-winter as rosettes,
and usually bloom in May. After producing seed the plant continues
to grow until heavy frost.
cress is highly competitive once it is established, and can quickly
dominate an area. Each flowering stem can produce 850 seeds annually.
With the possibility of producing seed twice a year, the surrounding
area can become saturated with seeds. Seeds are spread by wind,
irrigation/waterways, and vehicles. Buried seeds remain viable for
up to three years.
cress doesn't rely on seedling establishment alone. A single plant
can send out rhizomes that
will spread out over 12 feet in the first year. This spread can
continue to grow at a rate of 2-5 feet per year. These rhizomes
send up shoots that act as a new plant. An average of 50 new shoots
are produced every year. In addition to these creeping rhizomes,
an extensive root system can grow up to 30 feet in 2-3 growing seasons.
Lateral roots branch off a main tap root and spread though the surrounding
area. Each root has adventitious
buds that can develop into additional rhizomes and new shoots.
can form a dense monoculture,
similar to leafy spurge (Euphorbia esula), that displaces
native plants, degrades wildlife habitat, and decreases species
diversity. The loss of available forages is a serious threat to
the cattle industry. In addition to this, hoary cress contains a
toxin (glucosinolates) which can affect some cattle. This weed can
also invade cultivated fields and reduce harvest yields.
provide nectar for honeybees, and the seeds can be used as a substitute
plant grows in open, unshaded areas, and is usually found with other
exotics such as smooth bromegrass (Bromus inermus) and Russian
knapweed (Centaurea repens). Hoary cress requires moderately
wet sites (12-16 inches). Invasion of dry rangeland is unlikely.
It prefers alkaline soils that are wet during late spring, but will
grow in other soils. Lands most likely to be invaded are sub-irrigated
pastures/croplands, rangelands, ditch banks, roadsides, and waste
This is a
very difficult weed to control. Eradication is only an option with
very small patches. Control requires an integrated plan with constant
monitoring and work.
• Containment is the best option when dealing with this weed. Create
a perimeter and attack any plants that get out.
• Digging can be successful on small new sites. New shoots must
be dug up within 10 days after emergence. Sites must be rechecked
throughout the growing season, for four years.
• Herbicides are effective, but are best used on small sites or
around a perimeter (example
herbicides: 2,4-D (4 and 6EC), Telar 75 (DF), Ally (60 DF), and
at herbicide label: free search]).
• No biocontrol available.
• Tilling or other mechanical means of control are not recommended
(mowing with herbicide application can be effective).