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Fall can bring pesky weeds, inviting invaders like clover, dandelion, crabgrass and nutsedge where weaknesses still linger in the lawn from summer.
Often, the basic defense against fall weeds is a preemergent herbicide. At least, that’s where traditional weed control programs begin.
But the foundation for healthy, weed-free turf goes much deeper, as the strongest defense isn’t applied to the turf – it is the turf.
“The key to weed suppression is good, healthy turf,” says Jeffrey Johns, president of Coastal Greenery in Brunswick, Ga.
“Instead of being reactive to weeds growing – always spraying herbicides, treating for weeds, looking for the problem spots – the key is to ensure that you’ve got a healthy turf during the summer.
So just as routine car check-ups are the best safeguard against breakdowns, regular lawn maintenance can prevent fall weeds. Proper irrigation, fertilization and mowing year-round can minimize and even eliminate the need for herbicides.
This holistic approach to weed control wards off invasion preventatively instead of just spraying it down. Dave Phelps, sustainability manager at Cagwin & Dorward Landscape Contractors, wants to understand why weeds appear so he can remedy weedy conditions altogether. “Weeds can be looked at as nature’s Band-Aid,” he says.
“They’re the early responders when an ecology is out of balance. They show up to heal that situation and push the succession of the soil and plants forward. It’s important to realize that weeds don’t just show up – they’re there on purpose, with a purpose.”
Those purposes are key to controlling weeds, and the most common culprit is water. Whether in excess or insufficient, water can invite fall weeds: Too much can create a moist haven and too little can open turf to invasion. Strategic irrigation can keep conditions just right.
“Irrigation is key to controlling weeds,” Phelps says. “If you can just irrigate the root zones, rather than spraying water where you don’t want plant growth, then you’ve gone a long way to control weeds.”
The long and short of it.
Just as varying amounts of water and nutrients can make turf weak or strong, the length of grass also contributes to weed control.
“Different grasses throughout the country have different mowing heights, and that’s key,” Johns says.
“Some folks think by mowing their turf grass really low, they don’t have to mow it as often. But the lower you mow that grass, the weaker it becomes.”
Taller grass can add an extra defense against weeds. Though it’s a minor adjustment, Brian Adkins of Color Burst Landscapes explains why it makes a big difference:
“If you cut the grass really high, it doesn’t allow sunshine to get to the dirt, or to the weeds, because photosynthesis happens out on the leaf,” he says. “So if grass is cut correctly at 4 to 4-1/2 inches tall, you see fewer weeds in the fall.”
Proper turf care keeps dandelions from popping up on lawns.
Traditional and organics.
But water alone can’t keep weeds away from weak soil, so fertilization is also key.
Specifically, Phelps says he prefers sheet mulching, where compost, corrugated cardboard and organic woodchip mulch are layered to build up organic matter in the soil.
But any mulch can deter weeds by conserving moisture, promoting nutrient cycling and building organic matter.
“If you’ve got soil that has been abused by synthetic fertilizers and herbicides, there’s no organic matter,” Phelps says. “That’s going to attract weed seeds to heal that situation until you build up the organic matter to inhibit weed growth.”
Just pay attention to what goes into soil throughout the year, because the compounds that perk up lawns one month might wear them down the next.
“You have to be careful about the amounts of nitrogen you’re putting on that turf grass,” Johns says.
“If you put out real heavy, heavy amounts of nitrogen, you’re going to have great green turf in the spring, but in the summer heat, that high nitrogen could cause your turfgrass to turn weak.”
Together, proper irrigation, fertilization and maintenance can ward off most fall weeds. If invaders still sneak past these defenses, herbicides can be used as a last resort.
“The amount of chemicals you’re using to treat weeds should be very minimal,” Johns says.
“If it’s not, that means we haven’t done a good enough job managing that turfgrass through the summer. You’re always going to have weeds pop up, and then you’re just spot treating the areas that need it.
“The key is to minimize the amount of herbicide that you have to utilize.”
In the Dallas market, Southern Botanical prefers to blend organic materials into preemergent applications to reduce its use of traditional products.
“We like to do the preemergent with nutrients to add organic material back into the soil,” says Jason New, Southern Botanical’s vice president of Garden Management.
“So we use corn gluten meal, molasses, seaweed, fish emulsions, things with a little nitrogen. That corn gluten meal will actually pack down and give us a nice preemergent for the fall.” Organic options are growing – but still limited. And of course, there’s a cost associated with alternatives.
An organic selective broadleaf herbicide requires more applications of greater amounts, driving up the price and labor.
“We do offer organic options, but it never happens – mainly because once (customers) get the prices, the cost is just so high,” Adkins says.
The author is a freelance writer based in Cleveland.
Photos courtesy of Bayer
Get ready for fall lawn care by taking these steps
By Rob Golembiewski and Laurence Mudge
With fall around the corner, it is time to start thinking about taking advantage of the cooler weather and preparing lawns for the winter. Management practices vary depending on whether it is a cool-season lawn or warm-season lawn, which is determined by the turfgrass species present. Cool-season lawns usually consist of Kentucky bluegrass, perennial ryegrass, tall fescue, fine fescue, or some combination of each. Warm-season lawns generally will contain bermudagrass, St. Augustinegrass, centipedegrass, or zoysiagrass. In some parts of the country you will find both cool-season and warm-season lawns in the same neighborhood.
It is important to identify the type of lawn you have because it will dictate the cultural practices you implement. Below are guidelines for managing both cool-season and warm-season lawns this fall.
Mowing has the greatest influence on turf health and quality of any cultural practice. Keep in mind the following mowing tips:
- Try to never remove more than one-third of the leaf blade during any one mowing. In other words, mow the lawn when it is 50 percent higher than the desired height of cut. For example, if the desired height of cut is 2 inches, mow when it is 50 percent higher or when the grass is 3 inches tall. Most times of the year this amounts to mowing once per week but could be two times per week in the fall (and spring) when the turf is actively growing.
- Use a mulching mower and return clippings to the lawn to add as much as 1 pound of nitrogen per 1,000 square feet, annually. The clippings will not contribute to thatch as long as the mowing occurs on a regular basis.
Aeration. This is the process of air exchange between the soil and its surrounding atmosphere. All lawns will benefit from annual aeration, especially heavily-used lawns or those growing on heavy clay soils.
Perform fall aeration between August and October during peak shoot growth so the lawn recovers quickly from coring.
Drum-type aerators need two to three passes over the lawn to get desired results. Please note that spikers, machines that punch holes without removing cores, are of less value compared with aerators because they compact the soil around the holes and do not increase the flow of water and nutrients into the root zone.
Renovation. Follow these steps to renovate a lawn without totally killing or removing existing vegetation:
- Adjust the height of cut down (scalp the turf) so as to reduce canopy competition for germinating seeds.
- Power-rake the lawn as many times as necessary to remove accumulated thatch and to expose approximately 50 to 70 percent of the soil surface. It is best to dethatch in multiple directions.
- If soil is compacted, aerate the entire area to open up the surface and relieve compaction.
- Perform minor surface grading to eliminate high and low spots and to prepare the seedbed.
- Apply fertilizer and seed/sod as you would for a new lawn.
- Apply approximately one-quarter inch of organic mulch to enhance seed germination.
- Once seeded, manage as you would a newly planted lawn.
Total renovation involves killing undesirable grasses and weeds. Apply a non-selective herbicide in late summer or early fall.
The effectiveness of the herbicide can be enhanced by skipping a mowing prior to treatment and applying it to actively growing turf. It probably will take two to three applications to kill creeping perennial grasses and weeds.
After killing the grass, you have a choice of removing the dead sod or following the steps above for partial renovation. If you remove all sod, cultivate the soil and follow procedures for establishing a new lawn.
In the transition zone and southern parts of the United States, warm-season lawns are most common and can be further classified based on whether the lawn goes dormant or stays green during the winter.
In addition, sometimes warm-season lawns are overseeded in the fall with a cool-season turf such as perennial ryegrass.
This overseeding provides a green color during the period when the warm-season turf is dormant in the winter months.
For lawns left to go dormant, cultural practices should be followed as outlined above for cool-season lawns with the following exceptions:
- Mowing should be continued until top growth has ceased at the preferred height of cut.
- Do not renovate or aerate in the fall. Both renovation and aeration of warm-season lawns should take place in the late spring or early summer when the turf is actively growing.
- The final late-season nitrogen application should be applied no later than six weeks before the first expected autumn frost date. Fertilize at a rate of one pound of nitrogen per 1,000 square feet with a water soluble nitrogen source (e.g. urea, ammonium sulfate).
- Avoid winter damage by reducing or eliminating irrigation early enough in the fall to allow the warm-season turf plants to “harden off.”
Overseeding is defined as the practice of establishing turf over a dormant warm-season grass, mainly bermudagrass.
The primary turfgrass species used in overseeding programs is perennial ryegrass.
In preparation for overseeding, reduce or eliminate nitrogen fertilization four to six weeks, and irrigation three to four weeks, preceding overseeding. Recommended times to overseed include:
- 20 to 30 days before first killing frost
- When daytime highs are in the low 70s
- When soil temperature at the 4-inch depth is between 72 and 78 degrees.
At the time of overseeding, the warm-season turf should be scalped down to expose the soil surface. If needed, a power rake (dethatcher) may be traversed over the area to increase soil exposure. For lawns, perennial ryegrass should be seeded at a rate of 10 to 15 pounds per 1,000 square feet. L&L
Golembiewski is a Green Solutions Specialist for the Environmental Science division of Bayer CropScience with the responsibility of providing technical support for the Midwest turf and ornamental market. Mudge is the Green Solutions Team manager for Bayer’s turf and ornamentals business.