Two types of spurge belonging to the genus, Euphorbia (family Euphorbiaceae), may become a problem at this time of the year in landscapes and turfgrass. These are prostrate spurge (E. prostrata) and spotted spurge (E. maculata). Both are summer annuals meaning that they develop throughout the growing season and produce seeds in late summer to early fall. Both may flourish by lack of competition presented by poorly maintained or drought stressed turfgrass, or by the lack of weed suppression through poor mulching practices in landscapes.
As its common and scientific names indicate, prostrate spurge is an extremely low-growing plant, hugging the ground while forming large, almost perfectly round mats measuring over 2' in diameter. Individual leaves are oval, less than 1/4" in length, and may have an oval purple spot along the midrib. The spots on the leaves sometimes cause this plant to be incorrectly identified as "spotted" spurge. True spotted spurge has a more upright growth habit with stems sometimes creeping over the tops of summer dormant turfgrass plants. While the leaves are oval-shaped, they are much larger compared to prostrate spurge; the older, noticeably hairy leaves are commonly over 1/2" in length. The purplish spots are fan-shaped and appear to arise from the leaf petiole.
As with other spurges, white, milky, latex-like sap will ooze from wounded leaves or broken stems. Contact with the sap should be avoided since it contains polycyclic diterpene esters which are known to cause inflammation of the skin and severe damage to eyes. Indeed, the medical literature includes reports of permanent blindness resulting from accidental exposure to the sap. The sap accounts for some common name confusion with some spurges being called milk purslane (true purslane is in the Portulacaceae family).
Both prostrate and spotted spurges are susceptible to a wide range of pre- and post-emergent herbicides; however, since both are flowering, hand pulling and destroying the plants may be the best option since it provides immediate relief from seeding. Gloves and protective eye-gear is recommended to avoid accidental contact with the sap. More long-term cultural management options include increasing competition in lawns using good turfgrass management practices; and suppressing seed germination in landscapes by proper mulching.