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 write!).  

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!).

http://oregonstate.edu/dept/nursery-weeds/email_pubs/mayweed_pineapple/anthemis_cotula_vs_matricaria_matricarioidies.html

http://oregonstate.edu/dept/nursery-weeds/

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.