June 27, 2003 at 11:29 a.m.
Writing about weeds is difficult for several reasons. First, even with the best colored pictures it's hard to identify one from another because they are so similar. Another reason is that the best time to identify many weeds is when they flower or go to seed. By that time the area is well seeded for another season.
I would like to dwell on four areas of weed problems.
The first area is the unattended. We don't spend much time on them until they move out of their territory. These are along fence lines, abandoned cow yards, ditches, around old buildings, etc. Weeds like nettles, thistles, ragweed, leafy surge, burdock, mustard, pig weed, and the list goes on. One comment about such weeds is that once they become invasive you can always spray and destroy them.
Then there are lawn weeds. The two weeds that continue to cause problems are creeping Charlie and crab grass. Crab grass can be controlled by using a pre-emergence about two weeks before the weed seeds are set to sprout. This is usually about the time the lilacs bloom in May. The best time to control Creeping Charlie is in early autumn after the summer temperatures have cooled off. Use a broadleaf herbicide once or twice during this period.
The third category of weeds is in our perennial gardens. This includes weeds in our flower beds, berry patches, asparagus beds, etc. I imagine the reason I have so much trouble with weeds in my asparagus and raspberries is because they are so hard to get rid of without injuring the plants.
One of the worst weeds I have is bindweed. This weed loves perennial gardens and raspberry and asparagus stands because it often goes undetected until it has a head start in the garden. Bindweed also goes by the name of field bindweed, blackweed, wild buckwheat, climbing knotweed and wild morning glory. It was also called "devils guts." In 1922, it was proclaimed California's worst weed and it grows wild in every sate except Florida.
You can easily identify this weed because the stem, leaves and flowers resemble the morning glory. It becomes a serious problem when it spirals around the plants, especially if it is permitted to flower.
The bindweed reduces crop yield by competing for moisture, nutrients and light. The twining nature of bindweed entangles the crop and makes harvesting difficult. It also carries diseases as an alternative host for beet and aster yellows, tobacco mosaic and tomato spotted wilt. The main reason that this is such a serious weed is that a little seedling can sink a vertical root several feet into the ground in a single season.
A new weed to my asparagus and raspberry patch is called cleaves. It also goes by the names white hedge, catch weed, scratch weed and gripe weed. You can't miss this weed if you are pulling it with gloves on because it sticks to everything. It isn't hard to pull up but it is very invasive and spreads quite fast.
There are many other weeds, some have already been mentioned, that invade our perennial gardens. It would take several pages to list them all.
The fourth category of weeds are the garden weeds. They sometimes don't get as much notice because we give more attention to the garden on a daily basis. We also mulch, till, hoe, etc., to keep the weeds under control. However, I would like to mention one weed called barnyard grass. This weed is now ranked third among the world's worst weeds. One reason is because barnyard grass may consume 60 to 80 percent of available soil nitrogen in a single growing season. It can be recognized easily because it grows in clumps of up to 15 stems called tillers.
The only way I know to control this weed is to dig the clumps up and remove them from the garden. The clumps left in the garden can survive several days in the sun. When rain comes, they are in business again.
For more information on the U of M Extension Service web page go to www.extension.umn.edu and search. Or, you may call our Yard and Garden Line anytime and leave a message at (612) 624-4771. A Master Gardener will return your call. The Master Gardeners also staff the Extension Office on Monday from 4:30 to 8 p.m. Call (651) 674-4417 or drop in with your samples and gardening questions.