Wednesday, July 27, 2011

I know with 100 degree weather it is hard to think about winter weeds.

Received today from Michelle Wallace Horticulture Agent Co-op Ext office in Durham

Preen for Garden Weed Control -- Just what’s in that stuff anyway?

Preen herbicide has long been used in home gardens for pre-emergence control of many annual weeds. The active ingredient, trifluralin, is labeled for use around many woody and herbaceous ornamental plants as well as many vegetable and fruit crops. Although, not the most efficacious herbicide, Preen controlled many of our most common landscape weeds including henbit, chickweed, oxalis, crabgrass, and annual bluegrass, without injuring landscape plantings. This product is still widely available in garden centers throughout the country. However, look closely at the label – the Preen you purchase today may not be the same product you previously used.

Today the Preen name is used to identify a diverse product line that includes preemergence and postemergence herbicides. Several Preen products contain 2,4-D for broadleaf weed control in lawns; these products should not be used in landscape beds. The active ingredient in Preen Weed Preventer for Southern Gardens is dithiopyr – the same ingredient found in the herbicide Dimension. This is safe on most ornamentals but should not be used around any food crops. There is Preen Mulch Plus Premium that contains isoxaben plus trifluralin (think Snapshot TG); not to be confused with Preen Plus Mulch Midnight Black that contains trifluralin (but no isoxaben). The isoxaben-containing mulch will damage pansies but the trifluralin-containing product will not. Confused yet? There is also Preen Brush Weed Killer that contains 2,4-DP + 2,4-D + dicamba; Preen Weed and Grass Killer that contains glyphosate (same ingredient as Roundup); and an organic product for vegetable gardens, Preen Vegetable Garden Weed Preventer, that contains corn gluten meal. Many different active ingredients, all sold under the Preen name can lead to confusion.

So, if you go to the garden center to purchase Preen for weed control in your garden or lawn – READ THE LABEL. Make sure you purchase the right product for the right job.

Labels and material safety data sheets for the Preen products are available from the manufacturer’s web site at

Joseph C. Neal
Professor and Extension Specialist -- Weed Science
Department of Horticultural Science
262 Kilgore Hall
Box 7609, NCSU
Raleigh, NC 27695-7609
919-515-9379 (phone)

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