Landscape
And
Nursery
Dialog
Mary Ann Rose
Commercial Landscape
& Nursery Specialist
The Ohio State UniversityAugust, 1997
Helping Your Garden Center Customers Choose Weed Control Products for the
Keywords: garden center, herbicides, weed control, marketing
A lthough they may be packaged under many different trade names, there are relatively few weed control chemicals available for homeowner use compared to what is available for the ornamentals industry. This is probably a good thing, since some herbicides when used improperly could wreak havoc in the home landscape, but are nonetheless safe and effective when applied by a professional.
Most of the homeowner products are applied post-emergence, that is, to existing weeds. There are only a few products that prevent weed seed germination (preemergence herbicides). Some products selectively kill broadleaf or grass weeds. Other products are non-selective = kill anything green. Homeowners should be warned to treat these chemicals with respect since improper use can be a disaster!
A discussion of some of the most useful herbicidal active ingredients follows, with some examples of commercial formulations. Active ingredients, as opposed to inert ingredients, are the herbicidal components of weed control products. Active ingredients are listed with their concentration on product labels; usually both the long, descriptive chemical name (e.g., 2,4-dichlorophenoxyacetic acid) as well as the 'common' chemical name (e.g., 2,4-D) appear.
Selective, broadleaf herbicides. 2,4-D and other phenoxy-herbicides are available in homeowner formulations (e.g., Ortho Weed-B-Gone) and are commonly used for broadleaf weed control in turf. The broadleaf herbicides, while used in the vicinity of ornamentals, are not labeled for use in ornamentals because they may injure them severely. Injury to ornamentals is easy to identify by the presence of twisted or distorted leaves - 'the growth regulator effect'. Homeowners need to use even more care when applying products containing Dicamba (e.g., Ortho Weed-B-Gone formula II), another growth-regulator-type product, to lawns. Dicamba may be taken up by the roots of ornamentals growing in turf. Particularly where mature trees in turf are declining, avoid use of turf products containing dicamba.
Control of grassy weeds. Compared to controlling broadleaf weeds, grass problems are a breeze! Fluazifop-p-butyl (e.g., Fertilome Over-the-Top Weed and Grass Killer) and sethoxidim are two active ingredients that are highly effective on annual grasses and some perennial grasses, but may be used over-the-tops of a great many ornamental plants. This allows these chemicals to be used in ornamental beds. Typical situations where they are very useful include grass-infested groundcover or mixed landscape beds. Frequently extension offices receive calls about controlling grassy weeds in Iris, - both chemicals are useful for this purpose. Products that contain selective grass herbicides will not be effective on broadleaf weeds. Unfortunately we do not have a good chemical to control existing broadleaf weeds in beds.
Preventing weed growth. Only one preemergence chemical is available for use by homeowners in landscape beds. Trifluralin (e.g., Preen) is a granular product that may be applied to beds, including a wide array of annuals, once soil is firmly settled around the plants. Be sure to advise customers to thoroughly water in the granules immediately after applying. Failing this, most of the chemical will vaporize and weed control will not be achieved. Weed control from the product is fairly short-lived, approximately 6 weeks. Trifluralin is particularly useful in annual plantings that will cover bare soil within a six-week period, eliminating the need for reapplication. If the customer wishes to use mulch with this product, it is preferable to apply the mulch over the herbicide layer.
Non-selective weed control. Glyphosate (e.g., Roundup, Kleeraway) is the best-known chemical for non-selective weed control. It is the safest, and most effective product for perennial weed control because it is translocated, which means it moves into the plant and down to roots. Share the 'glove trick' with customers who have problem broadleaf weeds growing inside ornamental beds: pull a cotton glove over your rubber-glove clad hand; using a 30% to 50% solution of Roundup Concentrate (ready to use, dilute formulations are too dilute), saturate the outer, cotton glove with the solution and wipe onto weeds. Do not allow the glyphosate solution to drip onto ornamentals.
Products containing Triclopyr (Ortho Brush-B-Gone) are more effective than Roundup on woody perennials and vines like poison ivy; however they must be used even more cautiously near ornamentals as a spot treatments only. Other non-selective products are available that are excellent for controlling annual weeds. Products containing diquat or glufosinate-ammonium (Finale) are useful for spot weed control along beds and patios. An advantage to these products is that they kill weeds more quickly than glyphosate, but are less effective on perennials. With the exception of triclopyr, the above-mentioned non-selective products may be used for site preparation. After weeds are thoroughly killed there is no concern with soil residual from those products.
Total vegetation control. A few soil sterilants are available to homeowners that kill all vegetation present and prevent regrowth for relatively long periods of time (e.g., sodium chlorate). 'Total vegetation control/kill' are common buzz words for this type of herbicide. These products are very hazardous to ornamentals and are intended for use under fences, gravel paths or similar situations. They should not be used where roots of trees grow into the treated area.
