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By Jane Gilbertsen 

Inside the Deer Fence

Dear Methow Gardener,

I really appreciate the feedback I have been receiving so if you have  any thoughts or comments please let me know.  With that in mind, I decided to write on the subject of another weed - MUSTARD.

It seems mustard, ours is mostly Sisymbrium altissimum, or tumble  mustard or Jim Hill mustard, is on everyone's mind.  It is ubiquitious.  Our most common mustard is named after the Northern  Pacific railroad tycoon James J. Hill.  He is reviled by some for  bringing thousands out to settle land unfit for farming along the  rails.  So the mustard bears his name.  I guess it is a clue to how  people feel about this weed.

Why so much this particular year?  Well, it seems there might be a  couple factors at play.

First, the local view...

The mustards are cool season broadleaf annuals.  They start with a  rosette (like the first year Barnaby thistle) and then bolt - shoot up  a flowering stalk.  They germinate between 32 and 68 degrees,  preferably about 50 degrees.  They like some water and a little space  between rocks, sand or a niche in the soil to hold the seed and  water.  Each plant can easily produce 12,500 siliques (elongated seed  pods) which release a total of 1.5 million seeds.  With that  production level, only a few need reach favorable conditions to  germinate into a mess.  We had a wet cool late spring, perfect for  mustard germination.  Our valley soil continues to be disturbed by  road construction, grazing animals both wild and domestic and so on.   Mustard is also known for its "morphological plasticity".  That means  it can take the shape and size the space allows.  It can deal with  poor nutrients, competition, mowing, traffic, whatever and still grow,  flower and set seed.  Most grazers avoid it allowing it to grow and  set seed amidst grazed down neighbors.  It can be killed by herbicides  that work for dandelions but those chemicals also kill native  wildflowers and shrubs in the nonlawn areas.  Handpulling is about  it.  No biological agents work.

Now, the global view...

Mustard is a C3 weed, as opposed to a C4 or a CAM plant.  This  designation refers to the 3 carbon-atom molecules of the  photosynthetic pathway.  C3 plants are considered nonefficient or rather, moving at half-speed literally.  What makes them more  efficient?  More CO2.  What do we have these days in our atmosphere?   More CO2, actually 25% more following the industrial revolution  (fossil fuel use).   If you double the CO2 you get about 50% more  growth - above ground, below ground and pollen production.

What other weeds are C3?  Starthistle (a dreaded new invader),  cheatgrass (major invader and huge fire starter), quackgrass (our  irrigation water is loaded with seeds), lambquarters (at least it is  nutritious), knapweed, canada thistle (demonstrating a resurgence from  mid 20th Century), narrowleaf plaintain (taking over our irrigated  pastures), and bindweed.  Studies on the efficacy of Roundup on these  weeds under enhanced CO2 shows a dramatic decrease.

I suppose not too surprisingly, this issue is a major hot button of  the global climate change deny-ers and the chemical industry.  The  crux of the issue is the impact on crops v. weeds of increased  atmospheric CO2.  Most crops are C3 (42 is the US).  Most weeds are C4  (410 for ag in the US) but there are a lot more weeds.  The deny-ers  argue that if our crops do better with pollution than why worry about  it, maybe it is a good thing?  Of course, this is pretty simplistic  considering the chemical control issues, changes in temperature and  rainfall on established and widespread ag crops not to mention our  wildlands, and the problems presented by erratic weather, etc.  The  chemical industry thinks we should just use more chemicals.  No  problem there either.

Sorry for the serious diatribe.  On a positive note, the Fulton Ditch  Directors will spray the ditch banks after the irrigation season for  the poison hemlock.  It definitely does not pull out when nestled in  the canary reed grass (another weed issue)!  My neighbor that allows  her horses to graze the ditch banks cut off the flower heads as a  partial and temporary solution.  It is a start.  Every journey starts  with a single step.

Aug 3, 2010