Kurt Vollmer, Dwayne Joseph, and Alan Leslie University of Maryland
Figure 1. A flame treatment is applied to control emerged weeds in soybean.
Starting clean or weed-free is the key to a good weed control program, especially when noxious weeds, such as Palmer amaranth are present. While conventional growers can use soil-active herbicides to manage these weeds, control is more complicated in organic systems. Flame weeding is a non-chemical tactic that has been shown to control several grass and broadleaf weed species. The majority of flame weeding treatments are applied to emerged weeds; however, studies have also shown flame treatments to have detrimental effects on the seeds of certain weed species post-dispersal. Furthermore, seeds from species such as horseweed (marestail) and Palmer amaranth tend to germinate from shallower depths in the soil profile, and may be more readily controlled by flaming on or near the soil surface. Cultivation/tillage is another tactic that can be used to control weeds in both conventional and organic systems. However, cultivation can lead to additional weed emergence and cannot be used when the soil is wet. Flame weeding may help to supplement weed control when cultivation is not an option.
In 2023, a study funded by the Maryland Soybean Board was conducted at sites in Caroline and Kent county Maryland to evaluate flame-weeding as an integrated tactic for early-season weed control in soybean (Table 1). All plots were flamed immediately after planting followed by 1 or 2 additional flame treatments or flame treatments integrated with a cultivation treatment when weeds reached 3” in height. In addition, different walking speeds (1 and 2 mph) were tested to determine if longer flame exposure improved weed control. All flame treatments were made using a propane-powered Inferno Flame Weeder (Neversink Farms, Figure 1), and cultivation was done using a 25cc 2-cycle gas-powered cultivator (Craftsman).
Results from both studies showed that flame treatments affected overall broadleaf density, but cultivation was needed to attain higher levels of control. Flame treatments alone helped to reduce weed density at the Kent County study relative to the untreated check, with three subsequent flame treatments showing a reduction in broadleaf weed density compared to one or two flame treatments (Figure 2).
Figure 2 (left). Broadleaf weed density at the Kent County site 5 weeks after planting. Figure 3 (right). Palmer amaranth density at the Caroline County site 4 weeks after planting. Values followed by the same letter are not significantly different according to Student’s T-Test (α = 0.05).
While a diversity of species were present at the Kent County site, Palmer amaranth was the dominant species at the Caroline County site. At this site both treatment and walking speed had an effect on Palmer amaranth density 4 weeks after planting. While the majority of flame treatments did not differ from one another, Palmer amaranth density was lower with 3 subsequent flame treatments at 1 mph compared 3 subsequent flame treatments at 2 mph (Figure 3). Similar results were observed with the flame followed by cultivation followed by flame treatment suggesting that longer flame exposure may be needed for effective Palmer amaranth control. It should also be noted that Palmer amaranth varied in height at the time of postemergence applications, with flame treatments having a reduced effect on larger weeds (Figure 4).
Figure 4. Palmer amaranth injury following flame weeding.
While results from both sites showed that flame treatments can reduce weed density, weed control was not maintained at acceptable levels throughout the growing season. In the case of the Caroline County site, the level of the Palmer amaranth infestation was too high to produce a viable crop. These results suggest that preemergence flame treatments are not a viable option for weed management compared to postemergence flame treatments. However, additional research is needed to determine how postemergence flame treatments may be better integrated into a more comprehensive weed control program.
The program will start at the seed building and proceed to the fields.
Dr. Vijay Tiwari will discuss the small grain variety trials and his wheat breeding program. Dr. Nidi Rawat will then discuss fusarium research and prevention in wheat and barley. Next, we will have Dr. Alyssa Koeler touching on other small grain pathogens and Dr. Kurt Vollmer will bring us up to date on weed control in wheat. Finally, we will hear from Dr. Kelly Hamby on insect threats and control.
We also have a commercial variety strip trial organized by the Maryland Crop Improvement Association (MCIA) and industry reps will be on hand to discuss their entries.
Dinner will be served at 6:30, sponsored by Nagel Farm Service.
Cerruti R2 Hooks$ and Dwayne Joseph* $Professor and Extension Specialist, *Post-Doctoral Fellow, CMNS, Department of Entomology
INTRODUCTION
Mowing is a relatively inexpensive mechanical weed management option that imposes minimal disturbances to the soil. Several types of commercial mowers including rotary, flail, reciprocating sicklebar and reel can be used to suppress weed growth. Still, mowing is generally not thought of as a formable integrated weed management (IWM) tool as it is not congenial to most cropping systems or all land types. For instance, having a smooth soil surface free of rocks or other obstructions is a necessity for mowing operations, and if mowing close to the ground, the soil surface should be even. Some have declared that mowing is primarily used to limit seed production and restrict unsightly weed growth in un-tilled herbaceous and woody perennial crops. It is important for managing vegetation in pastures, meadows, rangelands, grassed waterways, field margins, turf, orchards, tree plantations, vineyards, golf greens and lawns as well as conservation reserve land and roadsides (Fig. 1). In conservation ecology, mowing may be used to shift plant succession and encourage native plant establishment while discouraging undesirable vegetation. In some non-cropping environments, the mower is used primarily for aesthetic reasons. Still, preventing weeds from reaching maturity beyond crop fields is of critical importance as it can prevent these areas from serving as nurseries for weed proliferation. For example, several species of arable weeds are frequently present in field boundaries such as road verges and some can colonize and reproduce in crop fields. Mowing can be deployed to prevent these and other weeds from producing seeds. However, mowing is ineffectual in destroying vegetative (asexual) structures such as rhizomes (below ground stems), stolons (above-ground stems) corms, tubers and bulbs in which very small structures may result in a new plant. This suggests that mowing may not be compatible with all weed types. Still, it can contribute to an IWM program especially if used in concert with other management tactics.
Fig. 1. Transportation maintenance specialist mowing an interstate roadside. Attribute: Oregon Department of Transportation (CC).
MOWING EFFECTS ON WEEDS
Mowing defoliates plants and because leaves collect carbon dioxide and sunlight, defoliation alters their competitive ability. Mowing can reduce weed vigor, growth, survival and reduce or prevent seed production. Mowing kills existing shoot growth. However, mowed plants can produce additional shoot material and there is also potential of new stem development from previously dormant lateral buds. Still, this may be desirable as new stems grow at the expense of below-ground stored food. As such, repeated cutting hastens food depletion and death of some plants. Under frequent mowing, a plant must generate enough photosynthates under limited leaf area to fuel normal plant function while not depleting carbohydrates stored within the roots. Mowing can also delay flowering of some weed species and impact weeds indirectly by changing their environment. For example, light, temperature and soil moisture among other abiotic factors may change in a mowed plant community. This can occur because mowing creates vegetative gaps by removing plant parts that form a canopy and shades the soil surface. As a result, light intensity and quality changes at the soil surface. Further, the average daily soil temperature and diurnal temperature range at the soil surface increases. These abiotic changes on the ground can favor the germination or emergence of one or more weed species that would have otherwise remained dormant or suppressed. Plant residue that remains after mowing may also change abiotic conditions at the soil surface and subsequently influence the weed community. Mowing also changes the competitive relationships between neighboring weeds and other plants because different plants are impacted varyingly by mowing, some may die or regrow at different rates. As such, mowing can change the flora in an area. Thus, understanding how mowing impacts the biology of different weeds is important as it can be used to manipulate a plant community so that it favors native or other desirable plants.
WHEN to MOW
Fig. 2. Plumless thistle, Carduus acanthoides Attribute: Andreas Rockstein (CC)
Properly timed mowing can suppress unwanted vegetation while favoring desired plant flora. Integrated weed management should target the susceptible stages in a weed’s life cycle and if mowing is being conducted to prevent seed production, it should always be done prior to flower formation. Mowing weeds during this stage can weaken them as they have invested a lot of energy into producing reproductive structures. Mowing to limit weed seed production is usually initiated well after mowing designated to minimized weed-crop competition and yield reductions. Oftentimes, a single mowing will not prevent seed production. New stems below the initial cut can flower and produce seeds. Thus, two or more mowing may be required to inhibit seed formation. However, some weeds such as common ragweed are able to survive repeated mowing. As a general rule of thumb, if only one mowing per growing season is allowed, it should be timed to match weed flowering. Certainly, mowing can be challenging when several weeds with different flowering phenologies co-infest the same site. For instance, mowing timed to prevent viable seed production of one weed species may fortuitously be timed to spread viable seeds of other species. This suggests that tradeoffs may persist when multiple weed species are present in a habitat and mowing is the option. Further, developing seed heads should be mowed before viable seeds are formed. Thus, timing is critical and should precede anthesis, pollination and fertilization. Some viable seeds can form less than 7 days after anthesis. For example, mowing musk thistle within 2 days after anthesis prevented viable seed production. However, mowing was ineffectual if it was conducted 4 or more days following anthesis. The production of viable seeds can occur so instantaneously that if weeds are not mowed before flowering, the benefits may only be cosmetic, especially if the delay results in more weed seeds being deposited into the soil seed bank. Still, variation exists among weed species relative to the best phenological stage to mow. For example, a six-year study in MD found that mowing plumeless thistle (Carduus acanthoides; Fig. 2) at the full bloom stage reduced plant densities compared to mowing it at the full bud or post bloom stage. In the same study, musk thistle (Carduus nutans; Fig. 3) declined only when mowed after the bloom stage. Some weeds have the ability to compensate for mowing effects. They may deploy several strategies to survive mowing such as increasing their photosynthetic rate and tillering, and obtaining greater nutrients.
Fig. 3. Musk thistle, Carduus nutans Attribute: Gertjan van Noord
Properly timed mowing helps minimize weed re-infestation, population increase and seed dispersal of new weed species within fields or from field borders into neighboring crop fields. If mowing is poorly timed, it can spread viable weed seed including herbicide-resistant weeds beyond the current field of infestation. Weed seed dispersal by mowing has been reported to be greatest when mowing and seed set coincide. A study showed that early mowing of chervil (Chaerophylum aureum L.), a weed that infests pasture, reduced seed production by decreasing shoot density and seed set. However, mowing it later resulted in seeds spreading outside the study site. Relative to this, some studies have shown that mowing practices can enhance seed dispersal of some weed species especially those that are favored by disturbances. Mowing may spread weed seeds by blowing them from the mowed area or transporting them on different mower parts. Thus, cleaning mowers between sites may help prevent weed spread.
Fig. 4. Common ragweed (Ambrosia artemisiifolia). Attribute: F. D. Richards (CC)
The regularity of mowing weeds is partially contingent on their tolerance to mowing which is a function of their growth rate, foliage replacement ability and its potential to increase photosynthesis to compensate for leaf loss following mowing. Further, multiple mowing will be required to mitigate seed production if weeds being targeted set seed or emerge in flushes over an extended time period. However, for weeds such as common ragweed, time of mowing and stage of growth may be more important than mowing frequency. Common ragweed can tenaciously regrow after most of its above ground tissues has been removed (Fig. 4). A study demonstrated that despite a substantial loss in aboveground plant tissue, surviving ragweed plants were able to reach the flowering stage after four clippings during the growing season. Similarly, spotted knotweed (Centaurea stoebe) produced tillers and flowers following 3 clippings in a single summer.
Mowing height is also critical as the blades must be low enough to cut off developing seed heads. However, if plants are initially mowed too low, later forming seeds may develop so close to the ground that a second mowing misses them. In addition, conditions may favor the regrowth of mowed weeds. Some annuals such as horseweed will sprout new stems below the cut. This growth may be managed by cutting high at the initial mowing and markedly lower at the next mowing so as to cut off any stems that have sprouted. This strategy is most effective if by the second mowing, the stem is hard and woody, and incapable of developing new sprouts beneath the cut.
MOWING and PERENNIAL WEEDS
Perennial weed control can be costly as well as time consuming. Perennial weeds are typically managed with herbicides and/or aggressive tillage. However, being dependent on herbicides to suppress perennial weeds encourages the development and spread of herbicide-resistant weeds; and an intensive tillage program increases the risk of soil erosion and on-farm energy use. A primary reason that perennial weeds are so resilient is their ability to store reserves in their underground storage organs. This allows above ground regrowth to occur after disturbances. Additionally, the resources in these storage organs are passed on year after year. As such, control measures should target and destroy the underground storage network or disrupt them by reducing or eliminating their ability to translocate resources formed during photosynthesis to other plant parts. Tillage can be used to weaken and destroy the underground storage organ. If it weakens it, the plant becomes more susceptible to other management tactics such as growing a competitive crop and mowing. As such, management tactics that are timed to deplete the food reserves of perennials are most likely to prevent regrowth and spread. For example, the lowest root carbohydrate reserves in Canada thistle occurs just before flowering, when the plant is in the “bud to bloom” stage. Repeated mowing coupled with a competitive crop can deplete carbohydrates reserves from Canada thistle roots and frequent mowing can kill young shoots before they replenish their reserves.
In addition to preventing seed production of perennial weeds, repeated mowing may starve their underground parts. Cutting the leaves and other above ground plant parts reduces biomass accumulation and eliminates the food producing organs as photosynthesis occurs within the leaves, although in some instances, photosynthesis occurs within the plant’s stem. Regrowth that occurs following a cutting drains sustenance from the stored food supply of the weed. As such, repeated mowing can reduce reserves housed in the storage organs. Still it is important to note that using this repeated mowing protocol may not result in the quick death of a perennial weed patch. Effective mowing of large infestations may be a long-term commitment. It may require two or more years of repeated mowing to fully kill a perennial weed stand. The best time to initiate mowing is generally when the underground root reserves of weeds are at a reduced level. This generally occurs when weeds are between full leaf development and flower occurrence. Interestingly enough, these tips related to mowing time can be applied to the timing of herbicide applications for managing perennial weeds as these weeds may also be most vulnerable to herbicides during this stage of their development.
In perennial crops such as forages, weeds and crops are mowed concurrently. The aim is usually to suppress weed competition and seed production while harvesting and managing crop biomass and maintaining pleasing aesthetics. In non-cropland habitats such as field borders typically perennial vegetation is mowed to maintain ground cover and prevent erosion. When crops are planted in rows such as orchards and fruit tree systems, weeds and other vegetation between crop rows are mowed to limit competition with the crop. However, it is important to maintain a stand of “beneficial” vegetation in the inter-row areas as this helps prevent erosion.
MOWING and COVER CROPPING
Crops are sometimes planted without tillage into terminated cover crops. Relative to weed control, the main purpose of the “leftover” cover crop residue or mulch is to suppress weeds within the crop row. To this point, weed control in the between row area may be inadequate in a mulch system especially if the crop is not planted at narrow row spacing and/or the biomass of the residue is inadequate. This is more of a problem in the between row area because the crop’s canopy may not contribute to shading the soil in this area. This suggests that overall weed suppression in a mulch system may be more satisfactory if weeds in the between row area can be subjected to an additional management tool. Fortunately, several implements such as high-residue cultivators exist and can be readily used in established crop fields with cover crop residue without jamming (Fig. 5). Mowing can also contribute to weed suppression in a mulch system. Relative to this, a study examining cultivation as a weed suppression tool in a herbicide-killed rye mulch system found that two inter-row cultivations provided adequate weed suppression in dry beans when field margins were mowed to prevent seed production by dandelion, Taraxacum officinale.
Fig. 5. A) Cultivator operating in bean field with rye cover crop. Attribute: agriculture.hiniker.com & B) High-residue cultivator. Attribute: Univ. of Delaware Carvel Research & Education Center, M. Walfred
Mowing typically contributes to short term weed suppression. As such, it may only be effective in a fast-growing crop particularly one in which a cover crop mulch has restricted weed establishment. Notwithstanding, in some situations, mowing can reduce the effectiveness of a mulch by speeding up its decomposition. Mowing clips cover crops into smaller pieces which break down more rapidly than thick mats. Differences in mowed residue fragment size and decomposition rate influence the duration of residual weed control from cover crop residue. For example, mowing residue (e.g., barley, crimson clover, hairy vetch, rye, subterranean clover) with a sicklebar at or after the mid- to late-bloom stages suppressed yellow foxtail, common lambsquarters, and redroot pigweed better than flail mowing (Fig. 6). It is believed that this occurred because flail mowing left smaller fragments of residue on the soil surface. Though mowed cover crop residue can provide some weed suppression, the duration and level of weed control by mowed residue is inconsistent and often will not provide good suppression the entire cropping cycle.
Mowing may also be done in concert with a living mulch (e.g., cover crop that lives the entire duration of the crop life cycle). A study found that mowing buckwheat living mulch between tomato rows after the critical weed control period suppressed weed seed production. The critical period for weed control is the period in the crop growth cycle during which weeds must be controlled to prevent unacceptable yield losses. A field experiment was conducted in Illinois to study the combined effect of mowing and growing a summer annual cover crop on Canada thistle growth. The study showed that a sudangrass or sudangrass-cowpea mixture alone or combined with mowing suppressed Canada thistle shoot density and mass to less than 20% of initial shoot and mass compared to buckwheat or fallow treatments. However, intensive management must be continued for several years to eliminate patches.
INTEGRATING MOWING with HERBICIDES
Several investigations have been conducted to examine impacts of combining mowing with other weed management tactics. Relative to this, a between row mowing tactic in combination with herbicide applications and crop canopy shading was evaluated in soybean and field corn. The investigation showed that if properly timed, mowing weeds located in the between row area close to the surface < 3.8 cm (1.5 inch) two or more times can kill or suppress annual grass and broadleaf weeds, such as giant foxtail, common ragweed and waterhemp species. During the investigation, weeds within the soybean rows were managed with herbicides and those that “escaped” treatment were suppressed by early crop shading and competition. It was suggested that this management strategy which consists of a) planting a competitive crop, b) banding herbicide(s) over the crop row and c) mowing weeds between crop rows close to the soil surface before crop canopy closure can be successfully used in competitive crops such as corn, soybean and grain sorghum which closes their canopy and shade weeds early in their cropping cycle. Thus, the implementation of husbandry practices that enhances crop competitiveness with weeds is critical to the success of this management plan.
Unfortunately, between row mowing is not adaptable to most cropping systems especially those grown in very narrow row spacing (e.g., drilled grain) and are weakly competitive and lack the ability to form a closed canopy. In addition, many producers will lack the equipment needed for mowing between crop rows. However, if it can be used in combination with herbicides, it is expected that the amount sprayed can be reduced by 50 percent or more as sprays are only banded within the crop row. Mowing has also been investigated for its ability to supplement herbicides and cultivation in peanuts. After weeds had grown 20 cm (7.9 inch) above the peanut canopy, a tractor pulled rotary mower was used to cut off seed heads just above the canopy 8 and 13 weeks after planting. The mowing prevented peanut shading by bristly starbur, sicklepod and Florida beggarweed. Mowing and applying herbicides in the within row areas of citrus trees are the most widely used weed control practices in Brazil. However, a three-year study in Brazil indicated using ruzi grass, Urochloa ruziziensis as a cover crop, combined with within row glyphosate and an ecological mower is a more sustainable IWM option for citrus trees. An ecological mower cuts the cover crop in the between row areas and the resulting residue is launched within the crop rows. Eco-mowing, which involves placing the cuttings from cover crops under the canopies of citrus trees rather than leaving them in the middle rows, is also being researched in Florida.
A study was conducted to test whether integrating early season mowing with a systemic herbicide application would improve the control of perennial pepperweed (Lepidium latifolium, Fig. 7). Mowing alone did not reduce weed biomass or its density the following year. However, mowing followed by application of an herbicide to re-sprouting plants reduced biomass in three different environments (high desert, roadside and floodplain habitats). The combination of mowing and the herbicide, chlorsulfuron reduced pepperweed biomass > 99% at all three sites and glyphosate + mowing > 80% at two sites, one year after application. It was noted that an initial mowing increased the effectiveness of glyphosate to a level where it became an effective control option.
Fig. 7. Perennial pepperweed (Lepidium latifolium) an invasive noxious weed. Attribute: J. N. Stuart (CC).
ADVANTAGES OF MOWING
Mowing may be repeated over a longer period than some herbicide treatments or cultivation. Further, mowing can be used to suppress weeds that have become too large to be managed with herbicides or cultivation; and mowing has fewer off site environmental effects. Thus, it can be an option where ground cover is desired and herbicide use would be restricted or undesirable. Mowing may also be used in circumstances where concerns exist regarding herbicide contamination of water bodies. Mowing can also be used during situations where weather conditions such as wind speed causes herbicide drift or reduces its efficacy. To this point, mowing is advantageous in highly populated or suburban housing areas where the public is concerned about herbicide exposure. Mowing can be used as a substitute in field conditions where cultivation might damage root systems or lead to soil erosion. Mowing limits erosions caused by wind and water by allowing live vegetation and plant residue to remain on the soil surface. Moreover, mowing is compatible with other soil and plant conservation measures such as no-till practices and land conservation programs. Fields can also be mowed faster following a heavy rainfall event compared to cultivation which requires much drier soil conditions.
NEGATIVE ASPECTS of MOWING
Weed species vary in their response to mowing height and frequency and some readily accommodate mowing. “Weeds adapted to mowing tend to grow short, in a rosette form, creeping above the soil surface or show high plasticity and softness of aerial parts and stems and become difficult to mow and also escape hand weeding.” Thus, if multiple weed species of varying height persist in a habitat, mowing may become more of a challenge. Mowing can favor weeds that develop and reproduce below the mowing height and repeated mowing of similar weeds can cause a shift: 1) in biotype from an upright growing form to a more prostrate form, and 2) to a community of weeds that are tolerant to mowing. For example, mowing was correlated with differences in plant size and degree of erectness caused by genetic differences between mowed and un-mowed broadleaf plantain (Fig. 8). This suggests that an integrated or more holistic approach should always be the goal of any weed management program as weeds will adapt to a single management approach. Further, though mowing may reduce aboveground competition, if it fails to kill weeds, they may still compete with crop plants for resources such as space, nutrients and water below the soil. Moreover, weeds that form rosettes or mats and/or grow close to the ground are naturally adapted to mowing. This is why weeds such as dandelion, bermudagrass, crabgrass, goosegrass and buckhorn plantain, once established, are immune to mowing. Additionally, wheel traffic that occurs during mowing can compact some soils such as silty clay loam. Mowing can also be noisy and though vegetation remains on the surface, it may still raise dust.
Fig. 9. Buckhorn plantain (Plantago lanceolata). Attribute: Clemson University Extension
Mowing is a relatively inexpensive form of mechanical weed control that can reduce the use of tillage, herbicide and manual weeding. It may serve as an alternative to herbicide and cultivation or part of an integrated approach. However, mowing to manage weeds has not been well studied compared to other IWM tools and is more popular in habitats with perennial stands of vegetation. Consequently, limited information is available on mowing use in crops. As such, it is not adaptable to numerous cropping systems; and partially for this reason, it is used mainly for aesthetic reasons and preventing seed production in perennial stands of vegetation neighboring cropland. Still, research has shown that mowing can be used jointly with other weed management tools such as applying herbicides, cover cropping and growing competitive crops. Mowing may also be used to successfully manage perennial weeds by removing the aboveground plant parts and consequently reducing food reserves in their storage organs. This, however, may take multiple years and the integration of other weed management tactics. Some research has found that combining mowing with herbicides enhances perennial weed control. Still, there are advantages and disadvantages of using mowing as a weed management tool. Mowing generally does not have any negative environmental effects. However, many weeds especially those that grow close to the ground such as buckhorn plantain are naturally tolerant of mowing (Fig. 9). As with any IWM program, it is important to “keep weeds guessing” by utilizing different management tactics; and mowing is no exception to this rule. For example, repeated use of mowing as a single weed management tactic may result in a selection pressure or shift to weed species or genotypes that can reproduce even if repeatedly mowed. These species may overtime become more difficult to manage. As such, in those situations where mowing is practical, one should consider making it part of an overall IWM program. Financial support for the publication of this article is via USDA NIFA EIPM grant award numbers 2021-70006-35384 and NESARE – Research for Novel Approaches (LNE20-406R).
A series of workshops will be held in March for farmers interested in learning how to use integrated weed management (IWM) techniques to control troublesome weeds in their fields. This is the fifth year for the workshop series, which is a collaborative effort between the University of Maryland, Virginia Tech, and the University of Delaware.
Education regarding weed identification and integrated management strategies continues to be critically important to enable early intervention and effective management options. 2022 is shaping up to be especially challenging with anticipated shortages of many commonly used herbicides. The 2022 workshop series will provide tactics to manage important weeds given limited herbicide availability and increased input prices. Material covered will target row-crop production systems, but tactics learned may be applicable to other systems. Specific dates, times, and locations for each workshop will be as follows:
March 10: Ag Service Center, 26737 Radio Station Way, Leonardtown, MD 20650 from 8am-1pm;
March 14: Sudlersville Volunteer Fire Department, 203 N Church St, Sudlersville, MD 21668 from 8am-1pm;
March 15: Olde Dominion Agricultural Complex 19783 US Highway 29, Ste. G. Chatham, VA 24531 from 12pm-5pm;
March 24: Virtual via Zoom from 8 am-11am.
These workshops are free, but participants will need to register at https://go.umd.edu/IWM.
Pesticide credits will be available for MD, DE, and WV. Two hours of CCA continuing education credits will be offered for each session.
For more information, contact Kurt Vollmer at (443) 446-4260 or Ben Beale at (301) 475-4481.
Kelly Nichols, Agriculture Agent | kellyn@umd.edu University of Maryland Extension, Montgomery County
Japanese stiltgrass is an invasive grass that is typically seen in wooded areas. It likes shaded, wet areas and can easily take over the forest understory. Unfortunately, it can also creep into pastures and hay fields. The leaves of Japanese stiltgrass are wider and shorter than most of our common pasture grasses. There is also a distinctive silvery midvein that is slightly off-center from the middle of the leaf (Figure 1). Japanese stiltgrass also has a shallow root system, so it can be pulled out easily. For more information on how to identify stiltgrass, visit USDA’s National Invasive Species Information Center website.
Figure 1. Japanese stiltgrass.
The one (and only one) positive thing about this invasive is that it is an annual, so there’s no perennial root system to contend with. However, as an annual, stiltgrass spreads by seeds. Seedheads start to form in mid-September through October. Once they are visible but before they produce hard seed (Figure 2), mow the area to prevent the seeds from maturing and becoming viable. Stiltgrass will likely not have enough time to regrow and set more seeds before the first frost.
Figure 2. Japanese stiltgrass seed head emerging.
Herbicides are another option. A broad spectrum herbicide such as glyphosate, can be used to control stiltgrass; however, keep in mind that broad spectrum herbicides will injure or kill any plant that it touches. So, this would be an option for spot-spraying heavily infested areas.
Prowl H2O®, which contains the active ingredient pendimethalin, is labeled for applications on established grass that has at least 6 tillers. Prowl H2O is a pre-emergent herbicide, and must be applied before the stiltgrass emerges in order to suppress germination. Stiltgrass can germinate as early as when the soil temperature is about 50 °F, so Prowl H2O will need to be applied earlier than when we may be used to when controlling other summer annual weeds. While Prowl H2O is a good option, re-seeding restrictions of 10 months for pasture grasses and 6 months for alfalfa may make it a challenge for reseeding after the stiltgrass is gone. (Remember, Prowl H2O is a pre-emergent herbicide, so it will prevent grass and alfalfa seeds from germinating, too.) If Prowl H2O is used, manage the bare areas so that weeds cannot take over before re-seeding can be done.
Once a control method is implemented, re-seed bare areas so they are not left for stiltgrass and other weeds to fill back in. Following your nutrient management plan can also be helpful to provide the hay and pasture grasses the fertility they need to compete with the stiltgrass.
Amanda Grev, Forage & Pasture Management Specialist | agrev@umd.edu University of Maryland Extension
When it comes to something like mowing or clipping pastures, there are certainly two sides to the fence: those that think mowing or clipping pastures is just something that has to be done, and those that think it is a waste of time and fuel and offers little benefit. In truth, the reality is that both sides are right—the need to mow or clip is usually site and time specific and will depend on several factors. Sometimes the decision is easy, and sometimes the decision is less clear, so what are the arguments for or against mowing or clipping?
Eliminating Seed Heads. Mowing pastures is a strategy often used to eliminate seed heads in an effort to keep forages in a vegetative state and promote additional growth. As plants mature to a reproductive stage, they become less palatable to livestock and forage quality quickly decreases. Removing the stem and seed head through clipping or mowing encourages the plants to divert energy away from reproductive growth back to vegetative growth and the production of new leaf material, which will be higher in quality for livestock and will continue to capture sunlight and provide energy for the plant. Keeping plants in a vegetative state not only maximizes forage quality but also maintains a higher growth rate and stimulates tillering and root growth, promoting a denser stand.
One caution with this strategy—if eliminating seed heads is your main goal for mowing, be sure that there are enough seed heads present to validate this. Looking at a field from a “windshield” view often gives off the appearance that there are a lot more seed heads present than there really are, so be sure to go through the field and look at the seed head density from above. You may find that there are less seed heads present than you initially thought.
Promoting Even Grazing. This concept goes along with removing the seed heads and resetting the forages back to vegetative growth, as doing so can also promote a more even grazing distribution by livestock. Particularly if livestock have already been grazing selectively, mowing or clipping can eliminate forages that are heading and lower in quality and prevent the underutilized areas from becoming overly mature. By evening out the pasture, promoting uniform regrowth, and keeping the forage in a vegetative growth state, you can help minimize selection by livestock.
This is especially true for continuously grazed pasture where livestock have the ability to be more selective. For rotational grazing systems with frequent rotations, you may find this less necessary. With smaller paddocks and more frequent moves, livestock will already be less selective about what they eat and paddocks are more likely to be grazed evenly. Although this requires additional management, the return on this is less clipping, and less fuel and time spent doing so. So is the mowing worth it? In the long run, improving your management with rotation, adequate rest, and appropriate stocking rates will likely be more viable than continuously clipping underutilized areas.
Providing Weed Control. Mowing is often listed as a cheap, easy way to control weeds. Recognizing that there is a huge range in tolerance for weeds, particularly in pasture, most producers can probably still agree that certain weeds are more problematic than others and that some do have a negative impact on forage production and can lower the ability of the pasture to meet the nutritional needs of livestock. Mowing pastures is a form of mechanical weed control, and there are times when mowing or clipping can be useful, particularly if you have pastures with heavy weed pressure. In these cases, mowing can help eliminate competing vegetation and open up the canopy to favor the growth of desirable forages. Although mowing itself will not immediately control weeds or brush, it can prevent weeds from going to seed and help control their growth over time.
Of course the type of weeds present is an important consideration. Weed response to mowing will vary based on the time of clipping and the weed species present. Consider a pasture with an abundance of annual weeds; while mowing might help with their control in the short term, the presence of these weeds might be indicative of poor cover providing an opportunity for these species to fill in, in which case maintaining better cover would be a better focus for more success long term. For those harder-to-eliminate perennial weeds, although mowing may not be killing them outright, every time the plant is mowed it has to use additional energy for regrowth, draining its energy reserves and weakening the plant over time.
On the flip side, when considering mowing as a weed control strategy, be sure not to overlook the hidden costs. Factoring in time, along with fuel, maintenance, depreciation, and storage of equipment, most agricultural economists will place a minimum cost of $15 per acre on mowing. That’s really not all that cheap, especially when the results may be more temporary. It’s not that mowing can’t help control weeds, it’s that the number of mowings and the timeliness of each mowing are critical for long-term control. Effective control may require mowing two to three times each season over two or more years in order to fully prevent seed production and exhaust plant energy reserves. If we use the $15 per acre minimum, then we’ve spent $60 to $90 or more per acre for weed control.
In addition to the cost, recognize that mowing also removes some desired forage. Depending on the forage species and density, each inch of forage that is cut may remove 75 to 400 pounds of grazeable dry matter per acre. While mowing forage stands that have slowed or stopped growing can promote new, high-quality regrowth, repeated mowing over the season will reduce total available forage to some extent.
Controlling Pink Eye. Mowing or clipping can be a strategy to help control pink eye in cattle. While forage seed heads themselves do not necessarily cause pink eye, they can be an irritant and aggravate the condition. However, you may have a hard time justifying mowing for this reason unless you have an active pink eye problem. If pink eye is presently an issue, keeping seed heads under control using clipping or mowing could be justified to reduce possible eye irritations. However, that is usually only the case with high amounts of seed heads present, and controlling flies should be the first priority.
Maintaining Aesthetics. If aesthetics is your primary reason for mowing or clipping, the reality is you might be better off leaving it alone. Taller forages produce more live roots, which can provide some drought resilience. They can also help keep the canopy closed, shading out some weeds and keeping soil surface temperatures cooler and wetter, which can promote more growth from cool-season forages. They also have the added benefit of providing some wildlife habitat, especially for certain pollinator species. Pastures were never meant to look like mowed lawns, and keeping them as such is an added cost that has to be paid for by the enterprise.
All things considered, what is your primary reason for mowing? If your reason is to improve or maintain quality or to get on top of some persistent weed issues then you may find it useful. Mowing or clipping is one of the many tools we have for pasture management and it can have benefits. However, those benefits must be weighed against the costs that are associated with mowing pastures to determine if it is economical. In some cases, mowing will have a low return on investment, and you may be better off focusing on other things and reducing the time and money spent mowing.
Kurt Vollmer, Wee Management Specialist | kvollmer@umd.edu University of Maryland Extension
Despite a less than ideal Memorial Day weekend, I’m sure many of us are grateful for the rain. While corn was planted several weeks ago, many places went for weeks without significant rainfall. As a result, many fields lacked adequate moisture to properly activate any preemergence herbicides that were applied. The amount of moisture required to activate a particular herbicide depends on its water solubility (Table 1). The lower the water solubility the more rainfall or irrigation is needed to activate the herbicide and move it into the root zone. Soil-active herbicides such as atrazine, Princep, Balance Flexx, and Prowl need more than 0.75 inches of water to become activated. Under ideal conditions (good activation, no excessive moisture, and sensitive weed species), most preemergence products will provide control for about 3 to 4 weeks after application. Therefore, it’s a good time to start scouting fields to see if an early postemergence application is needed. Remember, preemergence herbicides will not control weeds once they’re up!
Along with products you are considering for postemergence weed control, be sure to include a soil-active herbicide in the tank mix to help extend residual weed control. Group 15 herbicides such as Dual and Outlook can extend control of grasses, pigweeds, and other small-seeded broadleaf weeds. The addition of atrazine can help to improve the efficacy of certain postemergence herbicides as well. Finally, always be sure to consult the label for the proper application rates and tank mix requirements for your crop and soil type.
Table1. The Relative Amount of Water Needed to Activate Common Herbicides and the Duration of Residual Weed Control.
Trade Name
Amount of Water Required to Activate (inches)
Duration of Residual Weed Control (weeks)
Atrazine
> 0.75
4-5
Balance Flexx
> 0.75
2-4
Callisto
0.33
2-4
Dual II Magnum
0.33 – 0.5
4-5
Harness
0.5 – 0.75
2-4
metribuzin
0.33
2-4
Outlook
0.33
2-4
Princep
> 0.75
4-5
Prowl
> 0.75
4-5
Valor
> 0.75
4-5
Zidua
> 0.75
4-5
*Table adapted from the 2021 Mid-Atlantic Weed Management Guide.
Kurt Vollmer, Weed Management Specialist University of Maryland
This is a quick reference chart to check herbicide efficacy for some of the most problematic weeds in corn production: marestail, common ragweed, waterhemp, and Palmer amaranth.
Kurt Vollmer, Weed Management Specialist University of Maryland
This is a quick reference chart to check herbicide efficacy for some of the most problematic weeds in soybean production: marestail, common ragweed, waterhemp, and Palmer amaranth.
