Article by Cynthia Drake

Garden Weed Control
Post and Pre-emergent Control of Weeds in the Landscape

Before deciding the method of control you intend to use to treat the weed problem you are dealing with, you must know what varieties of weeds you will be treating in the garden. Providing you have made the correct identification of the weeds in the landscape, elimination will be the next task at hand.

The proper control for an annual weed may not be the same as that for a perennial or biennial weed. Sometimes the best way to deal with an annual weed is through hoeing or pulling. A control method that does not require a license is the use of "weed oil". There are numerous herbicides that result in quick kill for annuals. Some are Montar 560, Weed Boomer, Buctril, and Diquat. As with any chemical, read the label and follow the directions explicitly. The best overall method for dealing with annual weeds has to be pre-emergent herbicides. It is much easier and more cost effective to prevent weed infestations than to treat for them once the weeds become established. The following pre-emergent herbicides do a good job in controlling annual and perennial weeds: Ronstar, Balan, Deverinol. Dacthal DCPA, Beta San 12.5G, and Eptam.

Perennial and biennial weeds are more work to control and require a lot of homework on your part than do annual weeds. Timing of any garden application or treatment of these weeds is critical. Generally, you want to apply the herbicide while the plant is actively growing. Water stress, dormancy, and both flowering and seed setting stages will affect the amount and effectiveness of control you will achieve. In the past few years there have been exciting advances in the development of selective herbicide materials that will allow you to remove weeds from a planting without harming the cultivated plants you wish to keep. To rid groundcover and garden planting beds of unwanted grasses you might try Fusilade or Poast. For weeds around the base of woody trees and shrubs try Round-Up or Weed Boomer. Effective ways to remove broadleaf weeds from turf areas include treatment with Trimec, Buctril, Mecomec 2.5, and Super-d Weedone. Weeds in "iceplant" can be controlled with Iceplant Weeder and in some cases Poast can be effective against grass infestations as well. Treflan and Surflan are excellent in many landscape situations. Again, pre-emergent controls are better and results in less dramatic measures.

A word of warning: Use pre-emergent herbicides after planting and not before. Also, do not cultivate the ground after application. Disturbing the treated area in this manner will completely negate the effects of the herbicide. Always apply pre-emergent materials as called for in the directions to achieve the best results.

Herbicides come in many different formulations. You will find most forms come in water soluble powders, granules, or wetable powders. The liquid forms are found in emulsifiable concentrates, water soluble concentrates or suspensions. With some of the liquid forms you may need a product called an adjuvant. This is a chemical that aids the herbicide in its ability to get inside the weed and do a better job of killing it. Another interesting "tool" that can be used in liquid herbicide application is an indicator dye. You add this product to your herbicide mixture. The area you sprayed will be tinted by the dye thus showing you where you did (or didn't) spray.

Remember, effective weed control is only as good as the chemical you choose to use. You can not know the right herbicide to use unless you can properly identify the weed you wish to control.

The products mentioned in this article are not meant as written recommendations, only as a general guide. Many of the products mentioned require the person using the chemicals to have a Pest Control Applicators License. See your supply house, dealer, or County Agricultural Department for more and specific information.

Recommended for your library:

Solving Weed Problems: How to Identify and Eradicate Weeds Effectively from Your Lawn and Garden, by Peter Loewer

One person's weed may well be another's treasure, but whether you are a home gardener or a giant of agribusiness, there are some plants you need to get rid of in order to improve your desired crop. In Solving Weed Problems, horticulturist Peter Loewer helps identify which plants truly are weeds, then shows you the best ways to eliminate them. Elegantly illustrated, this handbook recounts a short history of weeds and how they got to America, and lists the most stubbornly pernicious species of the twenty-first century. Plus, it gives you important facts on the pollination and germination of weed seeds, their longevity, and their methods of dispersal. Find out which herbicides - chemical or organic - work best in every situation. Even find out the special circumstances when you may actually want to cultivate rather than eradicate certain weeds. (5 1/2 x 8 1/4, 288 pages, illustrations)

Invasive Plants: Weeds of the Global Garden (21st Century Gardening Series, Handbook No. 149), By John M. Randall and Janet Marinelli

This book is refreshingly simple. Excellent pictures of around 50 species of invasive plants. The text explains weed environmental impacts, origins and distribution within the USA, and how to control the problem. It is designed to be understood by all, layman and professional alike. It probably has wider application than the authors intended, although the title hints at their broad understanding of environmental weeds as an international problem. They knew we are needing simple on the ground solutions for identification and control of these species that threaten natural ecosystems everywhere.

One word of advice on buying books, BE SURE to check the place of publication as many of the books are from England or the East Coast and therefore may not be applicable to your area.

Remember, you can't control weeds unless you can identify them, so start that weed collection now as well as adding to your library.

For more Garden Horticulture read previous installments of this column in our magazine archives.

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Cynthia Drake is a landscape consultant, designer, and pest control sprayer. She was educated at University of Tennessee where she studied ornamental horticulture, entomology, and plant pathology. Cynthia has a teaching credential with Mesa Jr College, in ornamental horticulture. She is also a member with many professional organizations including the Professional Grounds Management Society, California Association of Nurserymen, San Diego Association of Professional Horticulturists, Southern California Turfgrass Council, California Women for Agriculture, and many more.