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Ingredients of Preen
Preen herbicides target lawn and garden weeds.
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The Preen brand refers to a line of garden, yard and turf weed-control products for the home. Except for Preen Vegetable Garden Organic Weed Preventer, which contains 100 percent corn gluten meal, the products contain herbicidal chemicals in varying combinations and strengths. Preen's weed and feed product also includes fertilizer.
Trifluralin
The active ingredient in Preen Garden Weed Preventer, Weed Preventer Plus Plant Food and Preen Mulch Plus is trifluralin, used to control broadleaf weeds. Although rated as having low toxicity to humans, this herbicide is highly toxic to aquatic wildlife and should not be applied so heavily that runoff occurs. Both weed preventers contain 1.47 percent trifluralin, and Mulch Plus has 0.0032 percent. Preen Mulch Plus also contains isoxaben, which kills broadleaf weeds. Weed Preventer Plus Plant Food provides 9 percent nitrogen, 12 percent phosphate, 9 percent potash and 6.5 percent sulfur, along with 8 percent chlorine.
Chemical Combinations
Preen's products for lawn weed control include various combinations and percentages of herbicides to combat weeds and crabgrass (Digitaria ischaemum and Digitaria sanguinalis). Herbicides include 2,4-D, mecoprop-p, dicamba and dithiopyr. Preen Lawn StepSaver Weed Control Plus Fertilizer, for example, contains all four herbicides, while Preen Lawn Crabgrass Control contains only 0.19 percent dithiopyr. These pose little to no risk to people, honeybees and other wildlife, according to the California Statewide Integrated Pest Management's pesticide database. Mecoprop and 2,4-D pose little risk to aquatic life, while dicamba poses medium risk, and dithiopyr poses high risk.

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