InterLinc: Clopyralid and Compost Fact Sheet

Fact Sheet

Clopyralid and Compost

What is clopyralid?

Clopyralid (pronounced clo-PEER-a-lid) is an herbicide designed to kill broadleaf weeds, such as clover, thistle, and dandelion. Clopyralid is sold for use on turf by several manufacturers under a variety of trade names, such as Confront, Lontrel, Momentum, and "Weed & Feed" fertilizers. The source of clopyralid in compost are clippings treated with these products.

Why is clopyralid a problem in LinGro compost?

Gardeners may inadvertently damage sensitive plants through misapplication of LinGro compost with clopyralid. Clopyralid is very slow to break down during the composting process. In soil, it has a half life of 2-14 months. When composted, the half life is greater than 1 year. Other chemicals appear to break down quickly in compost and do not present the same problems as clopyralid.

What plants are sensitive to clopyralid?

Plant families sensitive to clopyralid include:

Legumes, such peas, beans, lentils, and clover
Solanaceous, such as tomatoes and potatoes
Composite, such as sunflower, petunias, daisies, and asters
Other plants, such as carrots, carnations, lupines, and lettuce.

There is no evidence that clopyralid harms other gardening plants, including trees, lawns, and shrubs.

Does exposure to clopyralid in LinGro compost pose a health threat?

No. According to the EPA, it is not harmful to people or animals at the low levels present in compost. In fact, people that have applied this herbicide to their lawns have a much higher concentration of clopyralid than is in the compost. The primary environmental concern from this herbicide is its effect on sensitive plants. Vegetables grown in soil treated with clopyralid-contaminated compost are safe to eat.

What do plants damaged with clopyralid look like?

Plants damaged by clopyralid will show:

Stunted growth: the main growth tip stops growing and the lateral buds begin to grow
Reduced fruit set
Cupping of leaves
Failure of secondary leaves to grow after the seed leaves emerge
In legumes, compound leaves stay single

Is compost still good for your garden and landscape?

Unequivocally "YES". Compost is still the best thing you can do for your lawn, garden, and landscape.

Compost builds healthy, biologically active soil.
Compost increases porosity and water-holding capacity of the soil.
Compost decreases bulk density of the soil.

What should you know to prevent clopyralid damage?

Mix LinGro compost thoroughly with existing soil.
Be aware that the desire for weed-free lawns could cause damage to vegetable gardens and broad-leaf ornamentals.
Ask your lawn maintenance company not to use clopyralid-containing products in their treatments of your lawn.
Practice waste reduction at the source by mulching clippings on the grass. It will reduce mowing time, save money, and return nutrients to the soil.

What should you do with LinGro compost you currently have?

Clopyralid is very persistent in compost, but will dissipate faster when mixed with soil. Mix compost thoroughly with existing soil. Over time, the herbicide will dissipate. Keeping gardens moist encourages degradation. Current research indicates that the levels of clopyralid in LinGro compost should not harm sensitive plants if properly applied and incorporated into the soil.

How should you use compost this year?

Mix compost thoroughly with top soil. Use compost at the recommended rates, listed below:

For a new lawn, spread 1 inch of compost and till into the top 4 to 6 inches of soil prior to seeding.
For an established lawn, top dress with up to a 1/4 inch of compost two to three times during the growing season. (Treat bare spots like new lawn)
For planting shrubs, blend with soil at a rate of 3 parts soil to one part compost.
For flower and vegetable gardens, apply 1 inch of compost and till into 6 inches of soil.

What's happening in other parts of the nation? For more information...

• University Pullman: www.puyallup.wsu.edu/soilmgmt/Composts.htm
• Grass Roots Recycling Network: www.grrn.org/dow
• Dow AgroScience: www.dowagro.com