Master Gardeners gardening and blogging in the mountains of Colorado. For more information contact your local extension office, wwwhttp://extension.colostate.edu/staff-directory.
Sunday, June 26, 2016
Managing Whitetop by Todd Hagenbuch
noticed that the hillsides in Routt County have turned white again? No, Old Man
Winter has not returned. What you’re seeing is the bloom of hoary cress, or
‘whitetop,’ one of Routt County’s most aggressive noxious weeds.
ago I wrote an article about this nasty actor, but given the unbelievable
amount of it I continue to see, it seems necessary to remind everyone why it’s
so important to control this plant.
a deep-rooted perennial that grows as much as 2 feet tall and reproduces from
root segments and seed. The leaves are a blue-green or dull, gray-green color
and are lance-shaped.
blooming, the plants have white flowers with four petals arranged in an umbel
shape, giving the plant a white, flat-topped appearance. Plants emerge in very
early spring and bloom and set seed quickly, as evidenced this year.
weed, whitetop is common on alkaline, disturbed soils and is highly competitive
with other species once it becomes established. It often is confused with field
pennycress, or fanweed, which is an annual and has a strong odor. Whitetop has
little to no smell.
whitetop plant can produce as many as 850 seeds per stem and 4,800 seeds per
plant. Seeds can remain viable in the soil for as long as three years, meaning
that once you start to control, you’ll have to keep up with it for a few years
in order to get total control.
property in good shape is the best way to keep whitetop from getting a foothold
on your property. If whitetop does become established, it should be contained
as soon as possible. This can be achieved by managing the outside perimeter to
prevent the spread of whitetop.
whitetop in the early spring is effective only on seedling plants. If the
plants are established, mechanical means are not effective. In fact, many
people unwittingly cause more harm than good by tilling or mowing whitetop.
These activities actually stimulate the rhizomes and cause more plants to grow.
controls are limited because of whitetop’s competitive nature. Also, there are
no biological controls available at this time. This means that, while sometimes
difficult, spraying is really the only option when it comes to controlling
recommended to control whitetop in rangeland situations include 2, 4-D,
chlorsulfuron, and metsulfuron methyl. Make sure that you carefully read the
label for any of these products to figure out if it interferes with any seeding
application you may make in the area and to see how long you need to wait to
harvest any hay in the area. Also pay close attention to the application rates.
Remember, the label is the law.
situations, such as lawns, make sure to use a herbicide that is labeled
specifically for turf. In a garden situation, the safest spray to use would be
one containing glyphosate. Make sure when using glyphosate in these situations
that you are targeting individual plants of whitetop because glyphosate will
kill anything it is sprayed on. Make sure to spray on a day that is free of any
breeze, and if you’re worried about overspray hitting desirable plants, place a
paper towel or toilet paper roll over the whitetop plant and spray the
herbicide into it.
whitetop season came on so quickly this year, we are nearly to the point where even
chemical control will provide unsatisfactory results.That being the case, go out NOWand cut and gather the
tops off the plant to stop seed production and spread.Make note of the area that has the whitetop by
taking photos, marking a map, or by taking GPS points so you can spray the
young plants next year, even before they bloom, increasing your chances of
getting good control. Controlling whitetop is mandatory, by law. The longer we
wait to get this weed under control, the more difficult control will be because
of the aggressive nature of the plant.
printed in in the Community Agricultural Alliance column dated June 5, 2014)