Sue has spotted spurge taking over her lawn. This spurge is a low-lying plant, with reddish spots on its small leaves, that can extend its creepers up to three feet. It is a summer annual, germinating late spring to early summer and going to seed in the fall. It is a prolific seeder and returns with new plants year after year.
Sue originally pulled out all the weeds, fertilized in the fall and then used a fertilizer/weed killer combination this spring. As the temperature rose to 75 to 85 degrees, seed germination took off. She wondered whether there was anything to use to eliminate the spurge, rather than hand-pulling, which leaves holes in the lawn.
Fertilizer/weed killer combos are meant more to kill weeds than fertilize, providing minimal amount of nitrogen for grass. I always advise fertilizing with a lawn food that doesn’t contain weed killer, so that the lawn will get the nitrogen it needs. The best defense against weeds is a strong healthy lawn. Healthy grass will fill in any holes left after pulling weeds. However, with the heat, she shouldn’t apply full strength nitrogen lawn fertilizers now because the grass will burn although she could use a slow-release or organic fertilizer.
Also, as the temperature rises, lawns need more water. With summer heat, she may need to apply 2 inches or more of water per week.
Here is a link to the “Water Efficient Landscape Guide” that shows how to measure how much water your irrigation system applies each week and how much is actually needed to replace what’s lost through evapotranspiration: https://wrcc.dri.edu/washoeEt/docs/sp9302.pdf.
Next spring, before soil temperature warms to 55 to 60 degrees, Sue could apply a pre-emergent herbicide to prevent the seeds from germinating. Products containing one of the following active ingredients: pendimethalin, dithiopyr, or prodiamine, are suitable for home lawn use. Pre-emergents are some of the least damaging products to non-target plants and to critters.
There are also post-emergent herbicides that kill broadleaf weeds in a lawn. Don’t use them when it’s hot, because they can volatilize off and damage trees, shrubs and flowers. Always with any pesticide, read the label and make sure the weed, in this case, spurge, is listed as one of the weeds the product controls. Follow directions exactly and wear the correct protective gear. Be sure to keep animals and children off the site for the length of time listed on the label. For detailed information on all kinds of pesticides go here and search by active ingredient.
— JoAnne Skelly is an Associate Professor and Extension Educator, Emerita, University of Nevada Cooperative Extension. She can be reached at skellyj@unr.edu.
