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.”
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Battling back There is no doubt superintendents will face weed problems this year. It comes with the territory. But vigilance and a quick response to any incursions of weeds or unwanted grasses into your playing areas will go a long way to ensure 2015 is not a year to remember, or rather one that you will want to forget. When faced with documented summer annual broadleaf and grassy weeds, Dave Gardner, associate professor of turfgrass science at The Ohio State University, says it is best to use a pre-emergent herbicide. “There is no need for those materials in places not documented to have weed issues. But in areas that, for example, had lots of crabgrass last year, most of that crabgrass seed dropped straight to the ground and will be there to germinate this year.” The key to controlling weeds is speed of response. Younger weeds are easier to control in almost all cases than, for example, tillering crabgrass or broadleaf weeds that have hardened off due to summer stress. “Superintendents need to be aware of the life cycle of the weed they are trying to control,” Gardner says. “One application of a post-emergent herbicide to control crabgrass on June 1 is not going to offer season-long control because there are other crabgrass seeds in that stand that will continue to germinate. So, a post-emergent herbicide combined with pre-emergent herbicide might be warranted.” Similarly, he adds, many perennial broadleaf weeds are only suppressed in the spring, with more permanent control afforded by a fall herbicide application. Early use of pre-emergent herbicide will be key to minimizing weed populations. Dr. Raymond Snyder, research and development manager for Harrell's, suggests shortening application intervals of pre-emergent herbicide applications to ensure that sufficient overlap occurs, thereby reducing the opportunities for weed seed germination. In the South, superintendents can maximize product efficacy by closely reading post-emergent product labels. “This will help to properly select the most effective post-emergent herbicides, utilize adjuvants if necessary, and reduce undesirable phytotoxic effects to turf,” he says. There are a couple of options superintendents may consider this weed season, such as not applying any pre-emergent and waiting until the turfgrass comes out of winter dormancy to see what they have in terms of ground coverage and treat any germinating weeds with selective post-emergent herbicides. “Once the turfgrass has emerged and superintendents have a pretty good understanding of the health and condition of their turfgrass, then they could consider applying a pre-emergent applied herbicide,” says Dr. Jeff Higgins, Harrell’s vice president of business development. “The later this pre-emergent application is made, the greater the chance that crabgrass and other weeds will have already germinated in the canopy.” One option is to apply an herbicide that has early post-emergent activity on juvenile crabgrass (pre-tillered) and provides solid pre-emergent control of crabgrass. Another option would be to tank mix a selective post-emergent herbicide with a residual pre-emergent herbicide to control any established/germinated weeds and create a pre-emergent herbicide barrier for future germinating weed seeds. “If by chance one of these pre-emergent herbicides has already been applied and some thin areas are noted, depending on the specific herbicide that was applied, it may take several weeks (six to 16 weeks) before any seed can be expected to germinate,” Higgins says. “Of course, this puts you into the summer timing for this seeding, which is not optimal for successful germination and establishment. Some seed, such as T-1 creeping bentgrass, can germinate under warmer more temperate conditions and may work out OK in this scenario.” There are very few alternatives to pre-emergent herbicides that can be used on newly seeded cool-season turfgrasses. Tupersan (siduron) can be applied at seeding and will provide short-term preventative control of crabgrass. However, it will not control annual bluegrass (Poa annua), goosegrass or winter annual broadleaf weeds. Tenacity (mesotrione) herbicide can be used on newly seeded Kentucky bluegrass, perennial ryegrass and tall fescue. However, it cannot be applied to annual bluegrass or creeping bentgrass and is used to control those turfgrasses as weeds. Superintendents should not rely on curative measures. “We have to be very proactive and anticipate weed establishment, and this is what a strong pre-emergent herbicide program allows you to do,” says Dr. Ramon Leon, assistant professor, weed science at the University of Florida. “However, we will definitively have to deal with escapes. There are two things we need to keep in mind when dealing with escapes. First, monitoring is critical. We should identify escapes when weeds are small. Second, most of the post-emergent herbicides registered for turfgrass have their most effective control on weeds that are less than 2 inches tall or in diameter. Therefore, by identifying those escapes before weeds reach 2 inches in size, we will have a broad range of herbicides we can choose from that will provide adequate control.” |
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.”
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Strange phenomena Each region of the United States has its particular weed challenges, either due to the availability of weed control alternatives or the weed species are more problematic, says Dr. Ramon Leon, assistant professor, weed science at the University of Florida. However, over the last few years, we have seen a trend in the Transition Zone and in the warm-season turfgrass region in which perennial weed species, such as dallisgrass (pasapalum dilatatum), bull paspalum (paspalum setaceum) and tropical signalgrass (urochloa subquadripara) have been increasing their presence on golf courses. “At this point, it is not clear why we are witnessing such increases,” Leon says. “But we think that a combination of factors, such as the decrease in use of MSMA due to environmental restrictions and a heavy reliance on late post-emergent applications could be factors.” |
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.
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