Blackberry is a troublesome scrub weed in Northland, both in pastures and forests. The hooks can trap woolly sheep, and make pruning and thinning in forests difficult. Seedlings are generally killed by grazing, so it does best to fence-lines, among logs and in other places where it gets some protection when young. There is considerable genetic variability in the species with respect to leaf shape and susceptibility to herbicides like Glyphosate. Blackberry is one of the most favoured foods of goats, so a pasture system with some goats present tends to have less problems with blackberry. Even sheep and cattle will eat blackberry when it is a seedling, so having good grazing management can help prevent new plants getting established, though once the plants become woody, they are less likely to be eaten.
The preferred method of controlling blackberry is spraying. Goats will graze blackberry and keep it in check, but they need to be well fenced and confined to ensure they do eat it. Because goats will rarely eliminate blackberry, spraying of grazed bushes will still be required.
The best time to spray blackberry is from flowering until early leaf fall when ample soil moisture is present and the blackberry is growing actively. This is usually in the period of January to May and coincides with sap flowing back down to the roots as the plant builds up a reserve for the following year. Variable control will be achieved if blackberry is sprayed in the spring. Where goats have grazed the blackberry one years uninhibited growth should be allowed before spraying.