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Technical experts from FMC, Prime Source and Nufarm give the lowdown on how lawn care operators can combat three tough weeds.

Common purslane

A summer annual, common purslane can be found in areas where the turf or soil has been disturbed. It grows low to the ground, laterally and can form in mats. The leaves and stems of purslane are thick and fleshy like a jade plant. Stems and leaves grow from a central point and stay prostrate along the ground. Stems are purple, while the leaves are green. It produces yellow flowers in the summer.

Because it’s found in weakened turf areas, fertilizing will help reduce competition and thicken the canopy. It also can be managed with summer weed control programs, through postemergent herbicides that include 2,4-D, carfentrazone and dicamba. An organosilicone surfactant on its own can cause common purslane plants to lose water from leaf tissue and desiccate.

Yellow foxtail

Yellow foxtail is a summer annual grass with flat blades that can’t be rolled between the fingers. It has a hairy ligule at the base of the leaf, and scraggly hairs often come up about a third of the leaf blade. It may have a maroon or reddish color at the base of the plant. If seedheads are present, foxtails are easy to identify since their spikelike seedheads or inflorescences resemble foxtails. It germinates along with crabgrass and goosegrass in midspring and dies with the first frost in temperate regions. Foxtails often have red to purple stems near the crown of the plant and are less prostrate than crabgrass.

They’re usually found in compacted areas, so maintaining a thick, healthy lawn is the easiest way to prevent foxtail infiltration. All preemergent herbicides and postemergent herbicides that are effective for crabgrass control, like quinclorac, fenoxaprop, mesotrione and topramezone, are also effective for foxtail control.

Knotweed

Often found in very compacted soils where other plants cannot survive, prostrate knotweed is a mat-forming broadleaf annual. Stems of mature plants are very wiry, and leaves are arranged alternately (not opposite) on the stems. This weed is one of the first annuals to emerge in the spring. It will germinate before soil temperatures get to 57 or 58 degrees F, before crabgrass. Featuring narrow leaves and a rounded stem, knotweed can produce ocreae that look like a membrane at the base of the leaf where the leaves join to the stem.

Culturally, lawn care operators can aerate in the fall or spring. In the fall, it’s beneficial to seed affected areas to establish turf in the competitive environment. Postemergent herbicides with pyridine or that contain a protoporphyrinogen oxidase inhibitor active ingredient, like carfentrazone or flumioxazin, can be effective.

Sources: Ken Hutto, Ph.D., product development manager for herbicides and fungicides for FMC; Bret Corbett, director of technical services for Prime Source; Aaron Hathaway, technical services manager for Nufarm.