Re: Roundup - Can I use it now?

Duncan,
Round-Up gets absorbed and translocated.  That's why you get the root-kill
when you spray the top of the plant.  The movement of the herbicide in the
plant is going to be a function of photosynthesis.  If it's warm and sunny,
the perennial grasses are probably going to be photosynthesizing, and
therefore, the glyphosate will be moving (and killing).  

Remember, the rate of photosynthesis (and most all biological processes) is
going to slow down at reduced temperatures.  The "kill" will probably be
even slower than usual for Round-Up.

The other concern should be that the decomposition of the herbicide is also
probably going to slow down.  If you are not going to be planting
immediately, you are probably OK.  Even a relatively gentle herbicide like 
Round-Up has a recommended waiting period between application and planting.
 With cold air and cold soils, this period should be extended.

In my single experience at violating the waiting period, I used Round-Up to
kill a piece of turf where I intended to put in a new garden bed.  As soon
as the grass began to turn yellow (about 7 days), I tilled it under and
planted onion sets immediately.  It was early April in PA --- soil temps
were probably in the 50's at best.  The onion sets seemed to go to sleep. 
Emergence was spotty, and slow.  Some eventually rotted.  Some emerged
late, and then grew slowly.  Some normally.  Was this due to the Round-Up? 
Or to something in the grasses that I turned under?  Or to the source of
the onion sets?  I really don't know.

But it does make me hesitate to plant too soon after a Round-Up
application.  Especially in cold soils.

Rick Grazzini
rickg@centrelab.com
5b/6a central PA
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