June 27, 2009

1 - Spurge weed management in lawns.

Yard and Garden June 27, 2009


I have a beautiful lawn with the exception of milkweed. I see that it is progressing rapidly and I cannot find anything that will eliminate it without harming my lawn. Trent E.

- Rio Rancho, NM


I wonder if you have real milkweed or another weed with milky latex. Milkweed plants do grow in New Mexico, but these are tall plants that can be managed and weakened by mowing. I spoke with the Sandoval County NMSU Extension Agent. Some chemical or manual removal by digging may be necessary, but mowing will help. He said true milkweed was not common in lawns in your county, but the spurge plants are common.

Other plants that many people call "milkweed" are actually members of the spurge family (this includes the Christmas poinsettia, ornamental houseplant spurges called Euphorbias, and many weeds). Many New Mexico lawns are plagued by one or more of the several low-growing spurge weeds that grow under the level of the lawn mower. All spurge plants release milky latex when the stems are broken, just like milkweeds and a few other plant families.

There are several low-growing spurge weeds common in New Mexico. You can find pictures and information about them on the NMSU Weed web site at NMSU Weeds. Spurge is a very persistent weed because each plant produces thousands of seeds. These seeds are first produced when the plant is very small and then throughout the summer, so this is a very difficult weed to manage.

Management of spurge weeds in lawns begins with proper mowing, irrigating, and fertilizing. A healthy lawn will compete well with the spurge (a poor competitor that prefers bare ground without competing plants). However, spurge can get established in flowerbeds, areas at the edge of the lawn and over-grow the lawn causing problems. Any place in the lawn damaged by scalping when mowing, disease, or insects becomes a place where the spurge can begin growing and cause problems. Management of these other problems becomes an important aspect of spurge management.

Dr. Jamshid Ashigh, NMSU Extension Weed Specialist said that there are some chemical measures available if spurge is already growing in your lawn. He recommended postemergent herbicides labeled for use on spurge. These ingredients: 2,4-D, dicamba, mcpp, or mcpa. He also suggested preemergent herbicides containing pendamethalin, rifluralin, or benfluralin. Spurge is an annual weed (dies each fall) and must reestablish by seed in the spring, preemergent herbicides that prevent seed germination are an effective means for managing spurge. These products must be applied before the seed germinates and it may be necessary to make a second application as the chemical breaks down and looses effectiveness. The product label will give you information about application. If you choose to use one of these products it is important to follow the label directions exactly and to choose a product that says it controls spurge in your type of lawn (warm season or cool season lawn grass). Dr. Ashigh strongly recommends techniques to prevent seed formation and maintenance of a healthy lawn to minimize the impact and reproduction of spurge. Contact your local NMSU County Extension Service for help in properly identifying your weed and for information about herbicides.

Some people prefer not to use chemicals, but spurge is very difficult to control mechanically. Dr. Ashigh said that there are no effective organic chemicals for spurge control. He recommends pulling the plants by hand if chemical control is not an acceptable method in your location.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.


For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook page.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!