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Toward the middle of summer, woody perennial weeds that were small in April turn monstrous. Blackberries, Scotch broom, English ivy, and other introduced plants settled nicely in the maritime Northwest and are continual nuisances in landscapes. Perennial weeds come back year after year, dying down to the roots in winter. Unlike morning glory, these woody shrubby invaders form permanent branch and truck structures and never disappear from sight.
Blackberries begin ripening in late July. Juicy, fragrant, and delicious in pies and jam, they do have some redeeming characteristics. One of my favorite childhood memories is learning to bake blackberry pie for my grandfather. He extracted the berries from their thickets; I made pies. Grampa always went out well-clothed for blackberrying, because the blackberry that is so common along roadsides grows skin-ripping thorns.
In the maritime Northwest we generally see either the Himalayan blackberry (Rubus discolor) or the Evergreen blackberry (Rubus laciniatus.) Both of these were introduced, probably as food sources. The Himalayan blackberry originated in Asia, then was taken to England. The Evergreen blackberry originates in Europe, does keep its leaves evergreen throughout winter, and has distinctly different leaves from the Himalayan. Evergreen blackberry leaves are deeply incised, and easy to distinguish from the other plant.
Both these blackberries enjoy their immigrant status. If confronted by an infestation of these shrubby weeds, several different techniques will help with control. Total eradication of these weeds isn't possible. Blackberries, and any plant in the Rubus family, will set huge quantities of seeds. Birds spread those around. However, the real problem with blackberries is that the stems can get up to 25 feet long, and they root where they touch ground. This explains why blackberry patches can quickly become fairy-tale thickets, daring the picker or walker to venture in. The arched canes grow, touch tips, and root, thus being able to stride across the landscape.
Another constant and irritating invader is Scotch broom, (Cytisus scoparius). The introduction on Vancouver Island is described as "in 1850, by Captain Walter Grant, from some seeds he had picked up in the Sandwich Islands (Hawaii) from the British consul." (Pojar, Plants of Coastal British Columbia, 1994.) Three plants germinated at Sooke and now colonize southern Vancouver Island. Scotch broom grows so well in this area that it's driven out many native plants. The seeds and flowers contain several toxic alkaloids and shouldn't be eaten.
Digging out these weeds by shovel or mattock, getting as much of the root system as possible, gives a good start on management. A prickly, stickery, tiring job it is, but this removal does help. Blackberries come back from roots left in the soil; broom will usually not regenerate from roots. (But zillions of seedlings will be there to contend with.)
On small patches, cut blackberries down to the ground before digging out the roots. Then watch the roots for regrowth and treat that new growth with glyphosate (sold as Round-up.) Treat it when the new growth is about a foot tall so there's enough live tissue to respond to the chemical. Another technique involves cutting the stem off about a foot from the ground and painting undiluted glyphosate in the fresh-cut, still damp stem. This method is recommended by Washington State University specialists for action on a number of different woody plants, including Russian olive.
If a large acreage must be cleared of woody weeds, rent a bulldozer!
If English ivy (Hedera helix) has taken over a woods, start clearing by cutting the stems and digging out roots. Planted as a landscape ornamental, ivy has taken over uncountable acres of forests, choking out native vegetation.
If you plan to spray the foliage of any of these woody weeds, mid-August and into September is a good time to act. The plants are then beginning to move carbohydrates from the leaves back to the roots for winter, and herbicides are more effective then. Several different brushkillers containing glyphosate are registered for this use. Check the label to be sure the problem weed is listed; read directions carefully. Be careful to keep these and any herbicide off desirable plants, including the trunks and stems. Many of these weed killers are non-selective and will damage or kill any green plant they touch.
Woody, shrubby weeds need management; keep chopping out seedlings and root stock after the initial clean up.
Hortsense: Managing plant problems with Integrated Pest Management
