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Q&A with Sandy Feather: How to fight the war on weeds
Saturday, August 02, 2008
Q. I have a large flower bed in the front of my house with a combination of English ivy and various shrubs. When I first bought the house, it looked very lovely. But starting two years ago, it became overrun with weeds that grow very fast. I have been pulling them out and trying to get the root and also sprinkling the area with Preen. Nothing seems to be holding the weeds back. How can I get the upper hand on them?

A. The weeds that got out of control last summer produced seeds that have germinated and grown this year. This has been a great season for weeds. The frequent rain we had through June and early July created favorable conditions for seemingly every weed seed in the soil to germinate. This is especially true if there are areas of the ivy bed that have thinned out, where you can see the soil. Weeds are just waiting to exploit openings like that.

The best place to start is to go back over the bed and pull or dig out as many weeds as you can, preferably before they go to seed. Try to get the roots, or those weeds will grow right back. If you know you have some tough customers such as Canada thistle, you may also make very directed applications of a non-selective herbicide such as Roundup (glyphosate).

Because Roundup is nonselective, you cannot get it on any plant you want to keep. Roundup can be applied with "the glove of death." This is a chemical-resistant glove worn next to your skin, covered with a cotton glove. Mix the Roundup according to label directions in a small bucket. Dip your glove-covered hand into the bucket and squeeze out the excess so that none of the herbicide mixture is dripping from it. Then grasp the weed near the base with the herbicide soaked glove and slide it up to the top so that you cover it thoroughly with the herbicide.

It takes 10-14 days for Roundup to completely kill treated weeds. It is systemic and will translocate to the root system during that time. If you pull treated weeds prematurely, they may return because the Roundup may not have had time to kill the roots completely. If you do drip Roundup onto part of a desirable plant, simply prune that part of the plant and dispose of it.

Once you have removed all of the standing weeds, you can make an application of Preen (trifluralin) or corn gluten meal (sold under names like Without Weeds WOW) to the bed when it is dry. These are pre-emergent herbicides that keep seeds from germinating; they do not have any effect on existing weeds or weeds that grow back from roots, rhizomes (underground stems), or stolons (stems that grow right along the ground). If any of the herbicide granules have gotten stuck on the foliage of plants you want to keep, brush them off so they do not damage them. Then water the pre-emergent herbicide in. This activates pre-emergent herbicides and washes them down into the soil to protect them from exposure to sun.

It also would be a good idea to apply an inch or two of mulch to cover any bare areas in the bed. You also may wish to replant ivy in any bare areas to fill them in faster. Weed seeds are less likely to survive if they germinate under a dense ground cover. Water transplants in thoroughly and make sure the soil has settled around them before applying pre-emergent herbicides.

Once the weeds are under control, check the bed on a weekly basis and pull any small weeds as they appear, to keep them from getting out of control again.

Send questions to Sandy Feather by e-mail at slf9@psu.edu or by regular mail c/o Penn State Cooperative Extension, 400 N. Lexington Ave., Pittsburgh 15208.
First published on August 2, 2008 at 12:00 am
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