Knapweed is a persistent pest

Spotted knapweed is a persistent, invasive pest that is pushing many of our native plants aside, using precious water and nutrients.

There are two seasons when it is most vulnerable: spring, when it first starts growing, and right now - late summer - when it has gone to seed. Property managers can kill it now before it can spread any more seeds.

It's too late to use any chemicals; you must pull it out of the ground - carefully so as not to spread the seeds, knock off the excess soil, stuff it into a black plastic bag (white won't do - you need the heat generated in the black plastic to kill the seed), tie it shut and leave it out in the sun, then take or send the bag to the landfill as garbage.

Knapweeds, both spotted and diffuse, are tough customers. If you don't get all the seeds in that black plastic bag, and a few of them drop to the earth, they will get pushed into the soil by all your thrashing around and can lay there for five years - or more - waiting for just the right conditions to sprout. That's why it takes up to eight years to completely remove spotted or diffuse knapweed from a given site.

Russian knapweed is even worse, it's a creeping perennial that reproduces from seed and vegetative root buds. That is, after it goes to seed in fall it will die back and go to sleep for the winter. That leaves viable seeds in the soil for the next generation of plants, plus the mother plant waiting for spring.

The root stalk of Russian knapweed can go as deep as 20 feet or more in search of water and nutrients. Even if you see it starting up in spring and pull it, you have to get a lot of the mother root or the plant will just generate a new head, poke it into the sunlight, and away it goes.

A chemical poison can be used to kill Russian knapweed, but it must be applied with the utmost care. The best method is to use a small dripper of Roundup, 2-4D, or Escort and apply it to the growing plant ONLY. Don't broadcast it in hopes of getting on the target, you'll just kill native plants while doing so, and cause serious biological problems on the land.

It takes unlimited patience to win the battle with knapweed. Wyoming and Montana know that to be so, as they have all but lost the battle. It's reported to have spread to Forest Service and Bureau of Land Management lands in such magnitude that it will be very costly to eliminate it in a very long-term effort.

That almost happened along Highway 97 south of Bend a few years back. Knapweed near Lava Butte was spreading into the forest. But the concentrated efforts of ODOT and county and federal weed-control teams stopped it.

The City of Sisters has a very effective weed-control plan in place that, if followed, will stop the spread of knapweed. The city's WEED AND BRUSH REMOVAL, Section 8.16.010 states:

The owner or occupant of any real property within the corporate limits of the city shall cut, close to the ground, and remove or destroy all brush, weeds, thistles, grass, bushes, and rank or noxious vegetable growth, growing to a height of six (6) inches or more upon said real property at least twice in each year, once between May 15 and June 15, and once between July 15 and August 15.

Unfortunately, this order does not say "how" to remove those weeds. NEVER mow, or use a weed-whacker on knapweed. They must be pulled by hand or killed with a chemical. When knapweed is mowed, the roots release some very nasty enzymes and cause serious problem with soil chemistry.

And when you pull knapweed, wear gloves. Those same enzymes are said to cause problems with human biology as well. However, if pulled early in the spring, there is not much chemical released, and in the late summer, most of the moisture has left the stalks; it's those seed heads containing thousands of seeds that have to be stopped from sprouting.

The use of a weed-whacker or rotor-tiller will only spread the seeds.

Keep in mind the penalty of leaving knapweed to grow and reproduce on your property. Section 8.16.050 of the Sisters weed code says: "Any person violating any of the provisions of this Chapter shall upon conviction be punished by a fine not exceeding One Hundred Dollars ($100) for each day the person or persons is in violation of this Code." And the County code is even more expensive.

Those weed signs posted along county roads by retired County Forester Dan Sherwin and the Deschutes County Weed Board way back in 2002 have been very effective in getting people to look for knapweed on their property, and leave no question of who is responsible to remove them.

Ed Keith, present county forester, is keeping a close eye on knapweed as well. He has been issuing letters to land-owners asking them to clean up their property so we don't fall into the weed pit that's plaguing other states in the West.