Pressure point

Weeds. They rear their ugly (seed)heads when the growing season begins, and superintendents spend much of the rest of the year battling to keep the leafy interlopers at bay. How will last year’s late weather coupled with record cold and snowfall in the early parts of 2015 affect weed growth this season? Industry experts point to a mixed bag of potential problems, with the severity of weed outbreaks and their onset varying according to region.

For example, in the Central and Northeast states, the excessive amount of snowfall brings about the potential for spring drainage issues, says Eric Mauer, Engage Agro USA Northeastern and Mid-Atlantic regional representative and regulatory manager.

“It really depends on when the temperatures begin to rise, the snow starts to melt and the ground begins to thaw,” Mauer says. While not usually considered weeds in a broadleaf sense, moss and algae thrive in soils that drain poorly and retain excess moisture and could be a problem this year, he adds.

Although the Northeast has suffered a number of significant winter storms, the Mid-South and Southeast had a mild winter, says Dr. Ramon Leon, assistant professor, weed science at the University of Florida. “This caused a lot of our warm-season turf species to not have gone completely dormant in the most southern areas, which could make the green-up process more irregular,” he says. On the other hand, winter weed problems have not been as serious as the previous two years, “so we might have a cleaner start this spring,” Leon says.

If the trend of cool weather followed by significantly warmer conditions continues this spring, there may be more irregular and longer weed-emergence patterns. “The turfgrass might get weaker by suffering periods of active growth followed by cold stress or even frost damage,” Leon says. “So, pre-emergent herbicide use and fertilization must be done with caution.”

In the northern Great Plains, the winter of 2013-14 killed significant areas of creeping bentgrass and perennial ryegrass, says Dr. Zac Reicher, professor of turfgrass science and Cyril Bish Professor of Horticulture at the University of Nebraska-Lincoln’s Department of Agronomy and Horticulture (Editor’s note: Reicher was hired by Bayer following this interview). “Then, to compound damage, well-below average temperatures in the second week of May in 2014 killed any new seedlings from proactive early seeding. This left many areas thin throughout the summer and they started to finally fill in during the fall of 2014. I’m afraid a lot of this fall fill-in was from annual bluegrass, and so I expect bumper crops of annual bluegrass in areas killed by winterkill almost 12 to 14 months earlier.”
 

The Transition Zone, where warm-season grasses are common and winter injury is more likely, will be the most impacted by weeds this year, says Dr. Fred Yelverton, professor and extension specialist and co-director of North Carolina State University’s Center for Turfgrass Environmental Research and Education. “Also, in more northern climates where Poa annua populations are high and are used as a desirable turf species, there will likely be more turf loss, particularly on greens that are not covered. The other issue is, that if we have winter injury or winterkill, it could have a big impact on weed populations. Thin turf results in higher weed densities. ”

The long winter, cooler temperatures and soil moisture will delay weed season. Weed germination will likely begin later than normal and will last longer into the growing season, says Dr. Jeff Higgins, Harrell’s vice president of business development. Weeds, such as crabgrass and goosegrass, can be expected to germinate into the summer months.

Typically, pre-emergent applied herbicides are used for preventative weed control and applied in late March or April. However, given the environmental conditions that we are seeing this year, it may behoove superintendents to delay making those pre-emergent herbicide applications until they have a grasp on their turfgrass health and winter survival.”

“This year will mimic last year in the Northeast,” says Mike Dukette, Harrell’s Connecticut sales representative, “a long winter with a late spring start up and cool soil temperatures.” Key factors include proper identification and abiding by the labeled rates. “Those superintendents that have had a sound herbicide program, especially those who split the pre-emergent applications, will have decent control.”

In the South, cool to mild weather, in addition to an absence of regular snowfall, will necessitate the early application of pre-emergent herbicides. In addition, cool and moist weather in Florida will likely require early post-emergent applications targeting annual broadleaf weeds, says Dr. Raymond Snyder, Harrell’s research and development manager. “Southern regions may experience heavy weed pressure due to cool and moist conditions in late winter. Predictions for spring are for moist, warm weather, creating conditions ideal for grassy weeds and sedge. Grassy weeds, such as tropical signalgrass and crabgrass, will be much more aggressive and need immediate post-emergent action.”

There is good news for Midwest superintendents. Dave Gardner, associate professor of turfgrass science at The Ohio State University, expects weed problems to be slightly less than normal this year. “The rationale for this is that last year we had nearly ideal growing conditions for cool-season turfgrass,” he says. “Because of this, there were denser stands of turfgrass in late summer and fall, which should have had the effect of reducing the germination of certain perennial and winter annual weeds.”

These densities should still be high enough this spring to reduce the germination of summer annual weeds, Gardner says. “It’s not to say all will be good, but I don’t anticipate a lot of people calling this their worst year ever for weeds,” he says. “Of course, if we have a drought that affects turfgrass stand density, everything I speculated about above goes out the window.”

John Torsiello is a writer based in Torrington, Conn., and a frequent GCI contributor.