Good morning everyone!
This is the first email on the Nursery Weeds List. Subsequent emails
will be sent approximately every 2 weeks (or sooner if I get inspired to
This week's email will focus on two weeds currently prominent in our nurseries
and landscapes, mayweed-chamomile and pineapple weed. These are two
of the most problematic weeds for nursery growers in Oregon, and right now
both are in full bloom. When in flower, it is easy to distinguish the
two species from each other. However, during the late winter months
of January through March, when not in flower, they are quite similar in appearance
and difficult to distinguish. In this email, I will provide some background
information on each species. Visit my website to see more vivid color
images of each plant (I tried to insert images in this email, but could not
get it to work!).
Mayweed chamomile (Anthemis cotula)
Mayweed chamomile (MC) is an annual common throughout many parts of the U.S.
It will germinate and grow year-round (albeit very slowly over the winter).
MC is in the family Asteraceae (used to be called Compositae). It will
grow in any site with exposed soil, preferably in full sun.
MC has deeply dissected foliage, which if crushed gives off a not-so-pleasant
odor. Plants can grow up to 18 inches tall and wide, though they are
usually smaller. MC has daisy like flower heads with 12 to 15 white,
petal-like ray flowers, and yellow disk flowers.
MC is an annual that spreads by seed. Use properly timed preemergence
herbicides for control. My experience has been that postemergence control
with herbicides is difficult and often unsuccessful. Goal typically
provides excellent postemergence control of small weeds (less than 4 inches
tall); however, in one of our trials Goal merely turned the plant a deep
shade of purple, after which it continued to grow and flourish. Our
research also shows that Goal will provide excellent preemergence control
of this weed, provided applications are made prior to weed seed germination.
Pineapple weed (Matricaria matricarioidies)
Pineapple weed is an annual common throughout much of the U.S, though it
is native to the Pacific Northwest. It germinates very early spring
(early March) and is flowering by April. I have seen a few plants struggle
through the winter and survive, but it's rare, and those that do barely cling
to life. Pineapple weed grows in the poorest and most compact of soils.
Pineapple weed also has deeply dissected foliage. But the foliage and
stems emit a sweet smell when crushed. In large patches, you can smell
the weed by merely walking on it. Flower heads are comprised of disk
flowers only, with none of the petal-like ray flowers.
Pineapple weed is reportedly resistant to triazine herbicides. For
nurserymen, that means Princep (simazine) won't work very well to control
this plant. According to work done in orchard crops, Surflan provides
poor control while Devrinol provides good control (preemergence). Roundup
or cultivation provides good postemergence control, but mowing will not adversely
affect this plant.