How to eradicate summer weeds

In the middle of the season, weeds are coming hard and fast. Accurate identification is essential to proper treatment. Here to help you ID these turf foes are Tina Bond, Ph.D., technical services manager for FMC; Jason Fausey, Ph.D., director of technical services for Nufarm Turf & Ornamentals; David Hillger, Ph.D., field scientist with Corteva Agriscience Turf & Ornamental; and Eric Reasor, Ph.D., Southeast research scientist with PBI-Gordon Corp.

Photo: PBI-Gordon

Wanted: purslane

Characteristics:

• Mat-forming, upright growth habit
• Oblong leaves with a broad, rounded end
• Loves warm locations in late summer

“Look for the thick and dark in color stems on the mature portions of a purslane plant,” Fausey says.

“Leaves are smooth and look like a cactus without the thorns,” Hillger says.

“Purslane has little yellow flowers produced in late summer,” Bond says.

May be mistaken for:

• Spurge
• Knotweed
• Carpetweed

“Carpetweed also has oblong or spatulate leaves,” Reasor says. “However, carpetweed is not as succulent and fleshy as purslane.”

“Spurge has smaller leaves with wiry, thin stems. When spurge is damaged, it exudes a white, milky sap. Purslane does not contain white milky sap,” Bond says.

Photo: PBI-Gordon

Wanted: knotweed

Characteristics:

• First to germinate in spring
• First leaves rolled together have a grasslike appearance
• Thrives in compacted soils
• Upright growth with thin, wiry stems

“Knotweed has a paper-thin membrane around the leaf attaching it to the stem,” Hillger says.

“Since knotweed germinates early, look for the red hypocotyl (stem of a germinating seedling),” Bond says. “Growth is prostrate having thin, wiry stems with alternate lanceolate leaves. Knotweed gets its name from swollen, sheathed nodes.”

May be mistaken for:

• Grass
• Pennsylvania smartweed
• Wild buckwheat
• Spurge
• Lespedeza

“Other plants in this family having ocreas — a larger whitish sheath — include Pennsylvania smartweed and wild buckwheat, but smartweed and buckwheat have upright and vining growth habits, respectively,” Fausey says.

“Spurge and lespedeza are two weeds that look similar to knotweed. Spurge has smaller, oval-shaped leaves with milky sap, and lespedeza leaves have three leaflets per leaf and serrated margins,” Reasor says.

Foxtail (Photo: PBI-Gordon)

Wanted: foxtail

Characteristics:

• Bottle-brush seedhead in clumping form
• Can grow as tall as 3 feet
• Yellow foxtail has a thicker seedhead

“Leaves have rolled vernation (new leaf formation) and taper to a sharp point,” Reasor says.

“When you pull the leaf back, the point where the leaf comes into contact with the stem has a lot of small hairs that stick up,” Hillger says.

May be mistaken for:

• Crabgrass
• Goosegrass

“Crabgrass often has more of a prostrate growing habit than foxtails with the distinct digit- or fingerlike seedheads,” Fausey says. “Goosegrass is a clump-forming annual grass that has flattened white to silverish leaf sheaths with distinguishing fingerlike flowers on the top of stems.”

“Grasses are the most difficult to ID because they look so much alike,” Bond says, “Seedheads can help narrow down the identity, but for yellow foxtail, look for hairy leaf margins and a ligule (thin outgrowth at the junction of leaf blade and sheath). Green foxtail has a green seedhead with long hairs. Crabgrass and goosegrass have similar leaf shapes and stem characteristics, but the ligule separates them apart from each other.”

Photo: PBI-Gordon

Wanted: plantain

Characteristics:

• There are several species of plantain, but most common are buckhorn and broadleaf
• Broadleaf plantain leaves grow in a rosette form
• Buckhorn plantain has slender leaves with noticeable veins
• Contains small green flowers produced on tall stocks

“Broadleaf plantain has round leaves, whereas buckhorn
plantain has narrow, lance-shaped leaves,” Reasor says.

“The broadleaf dock looks similar; however, it can be identified by its wavy leaves and veins that branch out like a tree from the midvein,” Hillger says.

May be mistaken for:

• Buckhorn and broadleaf are often confused for each other
• False dandelion
• Fleabane
• Grass

“When seedlings first emerge, the cotyledons (embryonic leaves) are grasslike in appearance, but once the first true leaves emerge, you will find they are much wider than grass with prominent and distinguishing parallel veins that run down the entire leaf,” Fausey says. “The most evident portion of plantains are the seedheads, which are produced on the end of a long unbranched stalk.”

“They are often confused with other plants that grow in a basal rosette,” Bond says. “These are in the aster family, so their flowers are daisylike and very different than those of plantain. Fleabane has lance-shaped leaves with serrated margins. False dandelion has long slender leaves, but the margins are highly lobed with a central midvein.”

Photo: PBI-Gordon

Wanted: spurge

Characteristics:

• Mat-forming
• Upright growth habit
• May have dark red spots on top of the leaf

“Most spurge species problematic in turfgrasses are summer broadleaf annual weeds that can form dense mats via their prostrate growth habit and prolific seed production,” Reasor says. “Spurge leaves are small and oval shaped.”

“A quick ID for spurge is to break a leaf or stem. If you see white, milky sap, chances are it is spurge. There are many species of spurge, but for the most part, these plants are low growing, mostly with opposite leaves,” Bond says. “Stems can be reddish/pink in color. Flowers are small and white, born in clusters.”

May be mistaken for:

• Lespedeza
• Knotweed
• Purslane

“Spurge is found in similar areas as knotweed and purslane with all these weeds having similar growth habits, but unlike the other weeds mentioned, spurge is the only one that will exude a milky sap when the foliage or stems are injured,” Fausey says.

“Lespedeza has pink flowers and leaves with three oblong leaflets with prominent midveins,” Bond says.