Blackberries: a thorny issue
Step away from the weed killer - at least until mid-June or later. That's what OSU Extension Agent Chip Bubl advises landowners who are thinking about embarking on a blackberry control project this year.
Newcomers to the Pacific Northwest on this side of the Cascades are amazed at the blackberry thickets seemingly everywhere. Longtime residents are willing to put up with them because of the abundant high-quality fruit, but only to a point. If ignored for a couple of years, a nice berry patch can easily turn into a thorny monster. That is why discussions of blackberries in Oregon usually revolve around ways to control them.
As Bubl tells it, there is no point in spraying herbicides until summer - poisons won't be carried into the roots until the plant is done with its burst of springtime growth. The fresh leaves may turn yellow if you spray too soon, but the plant will recover.
This is an excellent time to hand-cut canes or dig up roots of blackberries, however. The ground is easy to work, and the weather is getting more inviting. If you aren't faced with acres of a solid blackberry thicket, slip on the workgloves and have at it.
The Columbia River Youth Corps is very familiar with helping various agencies control blackberries. Kevin Staley, 28, is leader of the high school students who work on the CRYC crew.
'We don't spray - zero chemicals,' said Staley. 'We go at it with weedeaters with metal blades. After we knock down and chop up the canes, we rake it and dig out the roots.' Staley said the CRYC just completed a big blackberry removal project on the Hogan Ranch for the watershed council. A seven-member crew took three days to clear out three acres of blackberries, then three more days to plant 'a whole bunch of native trees.' He said the tool they use to dig roots is a 'havel hoe,' which has a heavy digging blade. The crew works any time of year, but now is particularly good - before the leaves start growing.
You can make significant progress by hand digging blackberries in early spring. 'Once you get it down to a dull roar, mow every seven to ten days,' Bubl said. Mowing will control sprouts from large pieces of root left behind, or seeds. Young plants can also be pulled out by hand, or hoed as a follow-up.
When EuroAmerican settlers first arrived in the Northwest by the thousands in the mid-1800s, there were no blackberry thickets here. The native blackberry, called dewberry or trailing blackberry, sprawls low over the ground in open woodlands - offering a tripping hazard to the unwary.
During a flurry of introducing exotic plants and animals from all over the world, settlers brought in Himalayan and evergreen blackberries. Pleased with the Northwest's mild wet climate, the two species quickly escaped cultivation, and we've been battling them ever since. These non-native blackberries can swallow up large areas in 10-foot-high thorny thickets in just three or four years. Blackberries are in the rose family, so it's no surprise they do well here.
The Himalayan species is the most common. Besides fruit for cobblers, blackberry thickets provide food and shelter to some birds and wildlife species. Large infestations can hinder wildlife, however, and its aggressive growth and big thorns aren't usually considered attributes. Beneficial native plants can be overwhelmed in open habitat - the thickets overtake many species until there is nothing left but blackberries. Once it's established, sun-loving plants cannot break through. Blackberries do suffer in the shade and have trouble getting started in grass.
Nonnative blackberries excel where there has been a disturbance: roadsides, dikes and berms, pastures, exposed soil, or after logging. The initial plant spreads quickly because the canes, which can grow 10-20 feet in a season, arch out from the main root mass and start new 'daughter' plants where the tip of the cane touches the ground. In addition, the roots ball send out side roots that sprout; and then there are the berries, loaded with seeds.
If you prefer to use herbicides rather than the chore of digging, then cut or whack the canes back anytime before the spring growing season. Bubl said to choose a calm, dry day to spray that isn't too hot. Starting in late June, use a herbicide with triclopyr (Crossbow or Garlon 3a). It doesn't kill grass but will kill any other type plant, so use care in application. The slightest breeze will carry the volatile poison to neighboring vegetation. 'The better coverage on leaves, the better the results,' said Bubl. The Nature Conservancy recommends coloring herbicide, in order to apply evenly but not to overdo it.
Fall is the best time to use a herbicide with gylcophosphate (Roundup, Rodeo). You may not see any results from spraying until the next growing season, when the plants will obviously be dead.
Bubl recommends a safe option to use near water, or on blackberries that are growing among desirable plants: Cut the canes back, and then paint herbicide immediately onto the stem cut. This will kill the roots without disturbing the soil or getting poison into the water. There will be no mist floating onto nearby plants, either.
For more information on blackberry control, the local Extension Office in St. Helens is very helpful and has publications available. Web sites, such as the Nature Conservancy, offer additional advice.