[APWG] Fw: [Aliens-L] Garlic mustard and Seed Bank

[Marc Imlay]

Here are developments on how to respond to the seed bank 
problem with garlic mustard removal including the importance of, 

1) immediately catching new populations which may not have 
a seed bank and 

2) research into reducing the seed bank to more efficacious control, 

as well as removal of the green reproductive stage in autumn 
and winter. Thanks!

Marc Imlay, PhD

Chair of the Biodiversity and Habitat Stewardship Committee
for the Maryland Chapter of the Sierra Club.
Board member of the Mid-Atlantic Exotic Pest Plant Council,
Hui o Laka at Kokee State Park, Hawaii
Vice president of the Maryland Native Plant Society,
Conservation biologist, Anacostia Watershed
Society (301-699-6204, 301-283-0808)

----- Original Message ----- 
From: John Ambler 
To: Marc Imlay 
Sent: Monday, February 28, 2005 10:50 AM
Subject: Re: Garlic mustard


Marc:

Thanks for the reply.  If you want to post this on a listserve, feel 
free to do so, but let me know where you sent it.

I am a plant physiologist and have some understanding of the 
causes of seed dormancy.  I even did some class experiments 
on factors that will break dormancy in garlic mustard seeds.  
Abrasion (light sanding) of the seed coat and gibberellin (a 
plant growth hormone) increased the number of seeds that 
would germinate in a Petri dish.  

In the case of dark-colored seeds like garlic mustard has, 
there is a thickened impermeable seed coat that must be 
degraded by microorganisms before oxygen and water can 
readily enter and cause germination.  (I should check and 
see that this really occurs in garlic mustard by weighing 
soaked seeds that have the seed coat abraded and ones 
that have not been abraded.)

There are always inhibitor chemicals involved in preventing 
immediate sprouting on the plant.  Inhibitors sometimes 
need to be leached over time or broken down in some way.  
This is basically what happens with seeds that require 
prolonged cold treatment (stratification) before they will 
germinate.  In this case there may be growth hormones that 
accumulate in the cold and help break dormancy.

Many small seeds will not germinate unless they are exposed 
to some light.  If they germinated when buried in the soil, 
they would not be able to emerge.  And related to this, there 
are effects of day length with these seeds.

Early formed seeds of garlic mustard are most likely to 
have time to develop the impermeable seed coat (and 
possibly inhibitor accumulation) needed for prolonged 
dormancy.  Heat and water stress in June when the seeds 
are maturing may reduce dormancy - that's my guess.  June 
is often quite hot.  If this is true, then seeds of garlic 
mustard growing in moist soil should have greatest dormancy.

Seeds formed during water stress will not be as dense, 
and they are the ones most likely to float and be carried 
in a flood.

John Ambler
----- Original Message ----- 
From: Marc Imlay 
To: John Ambler 
Sent: Monday, February 28, 2005 6:22 AM
Subject: Re: Stiltgrass, garlic mustard


John, I am wondering if all the flood seeds came up now  because 
of some dormancy release factor had not had time to be set. Marc

----- Original Message ----- 
From: John Ambler 
To: (nvp) Mark Imlay 
Sent: Saturday, February 26, 2005 9:10 AM
Subject: Garlic mustard


Marc:  

I am making good progress on eradicating garlic mustard 
where I pull it.  Really the best time to pull it is in late fall 
and early spring because then you can find every single plant, 
but this can be hard on the back.  I pull the rosette-stage 
plants by grasping the top of the root.  If it breaks off, I 
brush away the leaves to find and pull the white root.  I 
repeatedly check the same spots during the spring.  The 
rechecks take very little time.

I made an interesting observation about garlic mustard 
plants from seeds carried onto floodplains by flooding.  
A big crop came up along river banks and on a low island.  
I pulled these plants and there were none in the following 
years!  This means that the seeds carried in the flood did 
not have long-term dormancy and they were lighter than 
the dormant seeds.  This makes sense because seeds that 
do not fill out well (late-forming seeds) probably do not 
have time to form as much dark seed coat.

John Ambler