We were recently asked the following question.

I am looking to do a final gorse spray before I plant pine seedlings this winter. Which should I use, MSF or Grassmate to ensure that the pine seedlings are not affected? And how long should the gap be before the last use of MSF/Grassmate and planting pine seedlings? 

Our reply was:

Both MSF600 and GrassMate have some residual effect that might impact on young seedlings. 

MSF600 (metsulfuron methyl 600g/kg) is not tolerated at all by young pines which sort of makes sense given it will kill gorse so the minimum time to plant back after application is at least 2 months and I would be inclined to err on the side of caution and wait at least 3-4 months.  MSF600 has a half-life in the soil of between 5 and 63 days so worst case it might still be at half strength 2 months later.  Bear in mind though that MSF600 is a slow kill so if you are waiting the 4-6 months until you get a complete kill then you are probably good to go.

The picloram content of GrassMate also has residual effect.  This is not quite as bad as MSF600 but the recommendation is not to plant for 1-2 months.  Especially clovers, although this is not relevant to you.  

A couple of other alternatives are:

• Triclo (600g/L triclopyr).  While this still has some residual activity it is lower than both MSF600 and GrassMate and is still effective on gorse.  

• Granny  or Glyphosate 540 – while not used on gorse so much these day glyphosate has no soil residual effect at all and you could safely plant back in as little as 7-days.