Safe sprays for BlackBerry and gorse
Thank you for submitting your questions about blackberry to Ask an Expert. Whatever the source, it’s possible to get rid of those weedy vines as long as you are consistent and persistent in your actions. You have several options to remove the blackberries. All will need to be repeated as needed which, depending upon how well established the vines were when you started, may take 2 to 4 years. If you skip a season, you'll be back to square one. Your options: 1. Dig out the vines then, when new shoots appear, pull or dig them immediately. 2. Use translocated herbicide in summer or early fall, then follow-up by removing new green growth as it appears. The most effective time to apply translocated herbicides is when sugars within the plant area moving to the roots. Cut the main stem several inches above the soil surface then immediately paint with full-strength weed killer such as glyphosate (as in Roundup) or triclopyr (as in Blackberry & Brush Killer; Cut Vine & Stump Killer; or Brush-B-Gone); follow label directions. Remove new shoots as they appear. Timing for translocated herbicides: a. If only first-year canes are present, apply late summer. b. If a combination of 1st year and 2nd year (fruiting) canes, or mostly fruiting canes, apply late fall after fruiting is complete but before the plants go dormant. Recall that persistence wins!
Jean Master Gardener Diagnostician (Washington, Multnomah and Clackamas Counties) Oregon State University Extension Service Volunteer Metro Master Gardeners (http://metromastergardeners.org/)
Unfortunately, this is a very difficult perennial weed to control no matter what the management system (conventional or organic). This is why we strongly recommend controlling perennial weeds like this before planting as much as possible.
There is no OMRI approved herbicide that will work on Himalayan - won't even make a dent in the plant. This introduced blackberry weed grows "new" plants from buds breaking on buried roots and from seeds (dropped from birds or in a seed bed from history of plants present). The only way to stay ahead of these weeds is to keep pulling them. If they are in the row then hoeing doesn't work well as it destroys the raised beds (likely used raised beds for the blueberry plants) and the blueberry roots are shallow. Hand pulling thus works best. An organic mulch will not suppress this weed (can't cover them up). Weed mat or polyethylene porous landscape cloth may work, but as soon as it gets worn the blackberry will come through. If you keep pulling the young plants the roots there will die due to starvation - but this takes time.
-Dr. Bernadine Strik, Extension Berry Crops Professor, Oregon State University