Do all grains produce an herbicide?

Carol Deppe says the barley she grew produced a natural herbicide that affected the plants that followed it in the garden.  Is this true for all grains?

Cereal crops including rice, sorghum, wheat, rye, maize, and barley, show strong allelopathic activities.   I'm guessing some of those chemicals remain in the soil after the cover crop is mulched.

It's a miracle so lets put a patent on it.  Ag companies are working to amplify that gene....yeah another GMO.  

I'm not denying the fact that she had that affect on her garden, but I have planted barley in some unused areas of my garden as a cover crop and to help smother out chickweed.  I experienced no adverse affects on the next crop I planted in that part of the garden the next spring.  

My first question would have to be which variety of Barley did she grow?  There are already modified 6 row barley varieties that were modified for their allopathic tendencies if it were one of these varieties then perhaps her observations are dead on.

Most barley, while being slightly allopathic in nature does not produce allopathy that persists over time.
I've never found any grass or vegetable type plant that has a persistent allopathy, unlike trees, which do have persisting allopathic compounds they exude, one of the most famous of these is the Black Walnut.

Redhawk

Bryant RedHawk wrote:My first question would have to be which variety of Barley did she grow?  There are already modified 6 row barley varieties that were modified for their allopathic tendencies if it were one of these varieties then perhaps her observations are dead on.

Most barley, while being slightly allopathic in nature does not produce allopathy that persists over time.
I've never found any grass or vegetable type plant that has a persistent allopathy, unlike trees, which do have persisting allopathic compounds they exude, one of the most famous of these is the Black Walnut.

Redhawk

I'm going to find out just how allopathic next year in my garden.  I just put down a pretty large amount of chips that came from a black walnut tree, complete with chopped up walnuts in them.  I'm hoping by spring they will be okay to plant in, but I grow lots of extra everything in different areas anyway.  It will be an interesting experiment no matter how it turns out.