Many weeds spread thousands of seeds each growing season. Most of these seeds will die after two or three years, but some could germinate after a decade or more in the soil. Soils, in turn, can contain thousands of weed seeds capable of germination each growing season.
Managers who research and source topsoil from producers who sanitize their product should significantly reduce weed pressure. Proper composting organically kills weed seeds by reaching temperatures of 140 °F.
If unable to incorporate new and sanitized topsoil on an unvegetated site, you can consider pre-irrigation in the spring. Pre-irrigation simulates rainfall and germinates the existing weed seeds. After 14 days, you can kill the young weed plants with shallow cultivation, flaming or an organic herbicide and then plant the site with desirable vegetation. This practice can potentially control up to 50% of the weeds on site.
In urban areas, some companies have herded goats to control unwanted vegetation in targeted areas. The grinding motion of goats’ mouths and their multi-chambered stomachs kill many of the plant seeds that other chemical and mechanical weed control measures may leave viable. Goats can, also, access steep slopes, rocky landscapes or remote locations that present unfavorable conditions for mowing, burning, hand pulling and more. Managing vegetation with livestock can cause unpredictable results such as leaving a patchy or nonuniform landscape appearance compared to mowing or chemical control. The grazing method will, also, take more time. For help selecting a targeted grazing contractor, please visit this blog post from University of California’s Department of Agriculture and Natural Resources.
Pulling weeds with a tool or by hand can effectively manage many types of weeds, particularly small populations of annuals and tap-rooted plants. Deep rooted and stem plants such as Phragmites usually survive manual removal. However, filling manually controlled areas with new seed, mulch or other organic material can provide some long-term control for weeds. Manual removal likely requires the most labor of all the glyphosate alternatives.
Shawn Sinn's work at Semper Fi Land Services, Inc. stresses ongoing vegetative maintenance to establish new plant communities. Sinn stated, "A freshly cultivated planting bed is a battleground and we want to put our natives in the best position to win the war."
Semper Fi selects control techniques for invasive weeds based on their life cycle. Semper Fi uses a combination of conservation mowing, selective mowing/cutting and hand pulling fo annual invasive weeds. Conservation mowing in the first native plant growing season treats the entire planting area 3-4 times to a height of 8-12 inches. In the second growing season, Semper Fi reduces mowing to 2-3 times. In the third growing season, Semper Fi transitions from conservation mowing to selective mowing spot invasive weed populations that occur. Sinn said that Semper Fi limits hand pulling of weeds, because it can cause unnecessary soil disturbance and pull invasive seeds to the surface.
Biennial invasive species generally allocate their energy to root growth in the first year and flower and seed production in the second year. Sinn's control techniques for biennials has similarities to annual management, but biennial invasive management requires conservation mowing for at least two years.
Perennial invasives are the hardest to manage because they grow, flower and seed each year. Perennials return after mowing, making this control technique ineffective. Semper Fi resorts to selective herbicide application for perennials. Sinn and his team carefully select the correct herbicide product by factoring the type of plant controlled and the weed's location. For example, to manage a common reed or phragmites population in a wetland, Semper Fi will select an aquatic-approved herbicide that mentions control of grasses on its label. Sinn will make sure this herbicide selectively targets the common reed population by using a backpack or all-terrain vehicle pistol sprayer for application. Lastly, the applicator will spray the common reed population at the most effective time in the fall as opposed to the spring or summer.
Semper Fi, also, conducts controlled burns for young, woody invasive weeds, but not for herbaceous weeds that will likely grow back. Sinn recommends annual prescribed burns once the native species have matured enough to carry a fire, which usually occurs after the third growing season. Sinn elaborated, "Fire is a natural process that has many benefits including nutrient release, woody species reduction and can help with native seed germination as well."
Semper Fi typically provides these natural area management and invasive weed control strategies in four to six visits and one prescribed burn. Most of the time, the frequency of Semper Fi's visits decreases over time as the native plant community matures.
Briefly passing a propane gas burner in close proximity to vegetation will kill it in a couple of days by causing plant cell sap to expand and break through cell membranes and walls. Flaming techniques are most effective on broadleaf weeds and vegetation in bare soils or cracks in sidewalks and parking lots. Similar to pesticides, only trained professionals equipped with proper safety gear should use flaming equipment. The operator of flaming equipment should never operate the equipment near children and pregnant women, since propane releases benzene a known carcinogen by California’s Proposition 65.
Leaves and stems of both broadleaf and grass plants die at temperatures of 205-218 °F. Steaming equipment such as Weedtechnics products have a 12” or 24” closed stainless steel head for application that reduces heat loss and concentrates the steam for precise weed control. Saturated steam usually spares earthworms and other beneficial soil organisms, because the heat does not penetrate the soil deeper than ¼”. Steaming equipment requires multiple treatments for best control, because the treatment does not kill weed roots.
Foaming equipment, such as Foamstream, uses heated water to kill weeds. The foam is primarily a water solution mixed with biodegradable and organic foam. This foam blanket helps denature plant proteins by retaining and concentrating the water's heat on the crown of the weed for a more effective kill rate. The price for foaming equipment usually exceeds steaming equipment, but foaming equipment operates faster and quieter. The capital cost for foaming equipment usually exceeds steaming equipment, but the equipment speed and fewer treatment cycles normally offsets these upfront costs in the long-term.
“The weed control sector is under an irreversible change,” WeedingTech’s Thomas Hamilton said in reference to the risks of glyphosate. “We all know how we got here: (1) increasing concerns on the damaging effects on human health, (2) increasing evidence on the effects to animal ecosystems and (3) increasing evidence of pesticide contamination in water tables.”
Bans of glyphosate and other pesticides by multiple European Union countries, New York State and many US municipalities paved the way for alternatives such as WeedingTech’s Foamstream technology. Foamstream focuses on retaining heat around the weeds for more effective vegetation kill. Similar to a steamer, the equipment applies a mostly water solution at temperatures between 205-212 °F. Unlike the steamer that loses heat quickly, however, Foamstream’s liquid solution includes biodegradable and organic foam to retain heat above 135 °F for 30 seconds after application. Temperatures below 135 °F cause little to no effect on weeds. Foamstream’s heat retention ability allows users to move the equipment relatively quickly compared to steaming equipment that needs to stay near a plant for an extended period of time for most effective control.
Hamilton shared multiple case studies where Foamstream controlled weeds as or more effectively than glyphosate. One study from the University of Pisa monitored the effectiveness of Foamstream, ultra-low volume glyphosate, flaming and nonanoic acid on three weeds of yellow nutsedge, field bindweed and annual bluegrass. Only flaming and hot foam provided above 95% weed control on the experimental sites one to two days after application. The weeds for all four strategies grew back after 29 days. Hot foam’s weed biomass after 29 days, however, was near or less than glyphosate’s weed biomass.
Studies have, also, shown Foamstream's effectiveness on invasive weeds such as Japanese knotweed and mugwort. Glyphosate remains the more cost-effective option for weed control, but Foamstream provides a viable and safe alternative. As Hamilton explained, “We believe we are a market leader [in glyphosate alternatives] because of the speed of Foamstream, its efficacy and our low total cost of operation.”
Spreading organic and inorganic mulches of wood chips, compost, leaf litter, pine needles or gravel at an initial thickness of 3-4 inches can smother and prevent the germination of many weed seeds. Mulch, also, regulates soil temperatures and prevents soil moisture loss. One inch of organic mulch topdressing each year will likely best control weeds. Visit this University of Missouri webpage to select the mulch that best fits your landscape’s aesthetic, biological and functional needs.
Covering a plot of land with a clear plastic tarp allows sunlight to heat the soil, field or garden bed and traps the heat and moisture to encourage seed germination. The plastic tarp prevents water access to the vegetation below, leading to eventual death. This strategy can effectively control weeds in two to three weeks during hot summer months.
Occultation uses black coverings as opposed to the clear coverings in solarization. This strategy takes two to three weeks longer to heat the soil than solarization, because the black plastic absorbs light and heat before the soil. Managers will often choose black coverings over clear coverings, because this covering is thicker and less prone to ripping.
LawnandLand.org lists organic and reduced risk herbicides at bit.ly/MGGbroadleaf. Most of these alternatives are liquid and do not need new training or equipment to apply. Most, also, kill vegetation on contact and work best at temperatures of 80 °F or higher. Managers often need to apply organic herbicides multiple times over the year, because the product does not kill plant roots.
The actions taken by many municipalities, park districts and other land managers to replace glyphosate has caused scientists such as Maggie Reiter to take a different approach to evaluating these alternatives, “As an academic, we usually like to do research that informs policy. This case, we’re sort of back on our heels and trying to provide some data for these tools already in use.”
Reiter’s research focuses on the effectiveness of popular organic herbicides. Reiter attributes the rise in popularity of these products to less barriers to adoption, “Organic herbicides are applied in a similar way to synthetic. We can easily swap one liquid formulation for another.”
Reiter did not need any new equipment to conduct her comparison study between organic and glyphosate herbicides at Ridge Creek Golf Course in Dinuba, CA. The experiment designated four 25-square-foot turfgrass plots for eight different management regimes of untreated control, organic herbicides of Avenger, BurnOut, Finalsan, Suppress and WeedPharm and glyphosate herbicides of Ranger PRO and Ranger PRO + Fusilade II. Image 2 shows aerial images of the different plots over a 35-day period.
“The organic herbicides of Avenger, Finalsan, Suppress and WeedPharm have very similar patterns of efficacy and injury,” explained Reiter. Within a day or two, the four products turned the landscape brown by killing the leaves of grass and broadleaf weeds. The vegetation on these plots, however, started to green up and reestablish after two weeks. BurnOut had minimal effect on the greenery. Meanwhile, glyphosate products killed vegetation after a week and reached peak control after two or three weeks. Vegetation started to reestablish on the glyphosate-controlled plots 35 days after application.
In summary, organic herbicides provide fast control on small annual broadleaf weeds. At this time, however, glyphosate still provides the most cost-effective control for weeds. The effectiveness of organic herbicides will increase if supplemented with other cultural practices such as mowing, “That’s the backbone to IPM, the idea of incorporating different strategies.”
The cutting of stems below the waterline can completely deprive oxygen for some aquatic weeds such as Phragmites. Both heavy specialized machinery and hand-held tools have successfully drowned Phragmites with rhizomes located at least six inches below the water surface.
The “cutting-to-drown” method made a difference for the Lambton Centre summer camp in Lambton Shores, Ontario. “For years, the lake wasn’t accessible to campers due to Phragmites,” said Dr. Gilbert.
Dr. Gilbert’s Invasive Phragmites Control Centre, the Wood Drive Coastal Wetland Restoration Project, the Lambton Shores Phragmites Community Group and the Lambton Centre collaborated to manage Phragmites with herbicide treatment on shorelines and a Truxor DM5000 “cut-to-drown” treatment in the lake. One “cut-to-drown” treatment can increase Phragmites mortality by 90% in about a half a meter depth of water. The “cut-to-down” method can achieve 100% mortality in deeper water depths of 0.70 meters.
"Generally, Phragmites doesn't go further than a meter and a half depth of water due to the oxygen diffusion, so cutting the straws of Phragmites that are used for oxygen diffusion will kill the plant," said Dr. Gilbert. Phragmites has a higher chance of survival in shallower waters.
Dr. Gilbert recommends removing cut stalks from the water, because the stalks can resprout at the nodes, “Plant material that is removed can be laid out to dry on land, burned or piled to provide habitat for wildlife such as muskrats.”
Dr. Gilbert stressed that successful Phragmites control like the work at Lambton Centre requires persistence and diligence, “Do not ignore Phragmites. It will eventually become problematic. The quicker an infestation is dealt with, the easier and less costly it will be to manage,” said Dr. Gilbert.