An ounce of prevention equals a pound of cure with summer weeds

Fall is a good time to start thinking about summer weed prevention when temperatures warm up next spring. (Photo: PBI-Gordon)

As summer transitions into fall, lawn care operators (LCOs) must turn their attention to the spring season and make careful decisions regarding weed control products and their application timing. This strategic planning is crucial for effectively managing knotweed, purslane, spurge and foxtail.

First line of defense

Gil Del Rosario

Maintaining healthy turfgrass is the first line of defense against knotweed, purslane, spurge and foxtail, says Gil Del Rosario, Western district leader and market development specialist with Corteva Agriscience. Preemergent herbicide treatments provide preventive control, while postemergent treatments are curative measures that can help improve the spectrum of weed control. Using cultural practices that help maintain healthy turfgrass can minimize weed occurrence and improve overall weed control.

For example, adequate fertilizing and watering promote the growth and health of turfgrass, which in turn prevents weeds from establishing themselves. Other practices, such as mowing at proper heights — 3 to 4 inches for cool-season grass and 2 to 2 1/2 inches for warm-season grass — will help minimize the proliferation of some weeds, like foxtail, which performs poorly in lawns with a higher cut.

Aerating soil to alleviate or minimize compaction and ensuring no empty spaces in the turfgrass stand are additional ways to prevent weeds. For example, knotweed, purslane and spurge have taproots. These three weed species take advantage and invade empty spaces and compacted soils in the turfgrass.

"Whereas preventing emergence of knotweed, purslane, spurge and foxtail might be the best approach for controlling these species," adds Del Rosario, "combining preventative and curative herbicide control tactics with good cultural practices will enhance control."

Preemergent is best

Eric Reasor

For controlling knotweed, purslane, spurge and foxtail, Eric Reasor, Ph.D., Southeast research scientist at PBI-Gordon, advises applying preemergent herbicide treatments in the spring is the most effective approach. These treatments lay the foundation for a robust weed management program for the upcoming season.

Knotweed, purslane and foxtail begin emerging and germinating when soil temperatures hit above 55 F, whereas spurge germination begins when soil temperature hits above 65 F. Reasor says LCOs should time preemergent herbicide applications just before soil temperatures reach 55 F.

"Using multiple or sequential applications of preemergent treatments helps extend the herbicide activity which is essential for late-emerging spurge seedlings," says Reasor.

Rescue applications

Bobby Kerr

Reasor says postemergent treatments help control those weeds the preemergent treatment missed. But he cautions that postemergent applications made too late in the summer may be ineffective.

Bobby Kerr, Ph.D., Quali-Pro technical service manager, agrees, noting proper timing of postemergent applications should coincide with when weeds are most susceptible. When weeds reach full maturation and have woody stems, it will compromise postemergent control.

An exception to this is spurge, which emerges later than knotweed, purslane and foxtail, and therefore is more difficult to control with preemergent herbicide treatments in the spring.

"Spurge is a prolific seed producer, and effective control measures for this weed species require the combined use of preemergent and postemergent herbicide treatments to prevent it from going to seed and replenishing the soil seed bank," says Kerr.

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