Kurt Vollmer, Weed Management Specialist | kvollmer@umd.edu University of Maryland Extension
Italian ryegrass has been giving us trouble the past couple of years. I’ve had several reports of ryegrass control failures following glyphosate applications. Last year, seeds from 49 ryegrass populations from Maryland and Delaware were screened for glyphosate-resistance by Dr. Caio Brunharo’s lab at Penn State. Out of 40 populations screened, all were controlled by glyphosate at 2 lb. ae/A.
This indicates that recent troubles controlling ryegrass may be due to application issues rather than glyphosate-resistance. This species can be particularly tricky to manage this time of the year, so it’s important to remember:
Cold weather affects glyphosate uptake and translocation. Applications should be made when the temperature is greater than 55°F and consistently remain above 45°F for 3 to 5 days to be effective.
Higher rates will be needed to control ryegrass compared to other species (1.25 to 1.5 lb. ae a/A).
Plants should be less than 6” but no more than 8” tall at the time of application.
Other components in the tank can also affect glyphosate performance.
Include a spray grade ammonium sulfate (8.5lb. to 17lb. /100 gal) in the tank to abate water quality issues. UAN and high rates of triazine herbicides (>0.25 lb. ai/A), such as atrazine, that are included in the tank can also reduce glyphosate absorption and translocation.
If glyphosate alone fails, try tank mixing or alternative herbicides. Last year at the Lower Eastern Shore REC, 98% ryegrass control was achieved with glyphosate (1.25 lb. ae/A) + clethodim (0.121 lb. /A) + nonionic surfactant (0.25%v/v) + AMS (8.5lb./100 gal) or sequential applications of paraquat (1 lb/A) + crop oil (1%v/v) + AMS (8.5lb./100 gal) made 14 days apart (Figure 1). In trials conducted in Pennsylvania, glyphosate + 0.02 lb. rimsulfuron/A also controlled ryegrass greater than 95%. Always consult the label for important information such as tank mixing and plant back intervals before applying any pesticide.
Figure 1. Italian ryegrass response 22 days after application to a) non-treated, b) glyphosate + clethodim, c) paraquat fb paraquat plots. Images: K. Vollmer, University of Maryland.
Kurt Vollmer, Weed Management Specialist | kvollmer@umd.edu University of Maryland Extension
Many may be preparing to apply certain postemergence herbicides to soybeans in the next couple of weeks. Those planning to spray Liberty (glufosinate) or Enlist One (2,4-D), should be aware that time is running out to spray these herbicides this season. The crop cutoff stage to apply Liberty in soybeans is “R1” and Enlist or Enlist Duo is “through R1.”
In addition, many may want to apply one of these products as a rescue treatment to control large weeds. At this time of year, it is likely that these weeds are beyond the label recommended growth stage. Some may have previously applied glufosinate and want to follow up with 2,4-D or vice versa. However, research has shown that tank mixing these products will provide better control of larger weeds compared to individual products alone. Both of these products can be applied over the top of E3 soybeans. Consider using the maximum-labeled rate for each herbicide. Liberty can be applied at maximum rate of 43 fl oz/A per application (87 fl oz/year) and Enlist One can be applied at a maximum rate of 2 pt/A (6 pt/year). Be sure to include 1.5 to 3 lbs of ammonium sulfate, apply at a spray volume of 15 gal/A, and follow all label instructions concerning drift.
This event will be the third stop on the Delmarva Weed Tour and will include tours of corn and soybean herbicide research trials, integrated weed management projects for watermelon and hemp production, and tours of demonstration plots for organic weed management in corn and soybean.
Date: Wednesday, June 28th, 2023
Time: 4PM – 6PM
Location: Wye Research and Education Center
211 Farm Lane, Queenstown, MD 21658
Pesticide credits will be available for MD and DE.
Kurt Vollmer, Extension Weed Management Specialist | kvollmer@umd.edu and Alan Leslie, Agriculture Agent University of Maryland Extension
Italian ryegrass is a winter annual weed that often needs to be managed prior to soybean planting. In Maryland, populations of Italian ryegrass have been confirmed to be resistant to group 1 (Axial, Select) and group 2 (Harmony, PowerFlex) herbicides, but recent populations have appeared to develop resistance to glyphosate (Figure 1). With limited herbicide options, preplant control of Italian ryegrass will be challenging for growers. In the fall of 2021 through spring of 2022, a study sponsored by the Maryland Soybean Board was conducted at a farm site in Talbot County, MD to evaluate different herbicides and application timings for controlling suspected herbicide-resistant Italian ryegrass. This study had two objectives: determine the optimum application timing and herbicides to control Italian ryegrass ahead of planting soybeans. Italian ryegrass seed will germinate in both the fall and the spring, therefore herbicide treatments were applied in the fall, spring, and in the fall followed by a second application in the spring. Herbicide selections consisted of glyphosate applied alone and glyphosate plus either clethodim (Select Max), flumioxazin (Valor), or saflufenacil (Sharpen). Valor and Sharpen can be applied preplant in both winter wheat and soybean to control many different weeds and Select Max is an herbicide that is used to control many annual and perennial grasses after they emerge.
Figure 1. Herbicide-susceptible and herbicide-resistant Italian ryegrass following a glyphosate application.
Our results showed application timing and herbicide selection had a significant effect on Italian ryegrass control, density, and height, but there appeared to be no additional benefit when these two factors were combined. In the spring of 2022, Italian ryegrass density and height were lower with sequential herbicide treatments compared to single applications in the spring or fall (Table 1). This was reflected in improved control with sequential compared to single applications. With multiple germination periods, it is likely that two applications will be needed to provide better control of both early and late emerging Italian ryegrass.
Table 1. Italian ryegrass response to three different herbicide application timings.a
Application timing
Control
Density
Height
%
Plants m-2
cm
Fall
44
b
12
a
20
a
Spring
48
b
16
a
25
a
Sequential
81
a
4
b
15
b
a Means with the same letter do not differ significantly according to Fisher’s LSD (α = 0.05).
Italian ryegrass density and height were lower when Roundup was applied with Select Max compared to all other treatments, regardless of application timing (Table 2). This was reflected in a significant improvement in control with this treatment; however, no treatment provided over 95% control. These results indicate this Italian ryegrass population to be glyphosate-resistant (Figure 2). Tank mixing glyphosate and other herbicides did not always improve control. Sharpen is a broadleaf-selective herbicide that is commonly used to help control glyphosate-resistant weeds like marestail, but it will not control Italian ryegrass. Although, Valor can provide residual control of this weed, including it with Roundup did not significantly improve control over Roundup plus Sharpen or Roundup alone. The combination of Roundup plus Select Max appeared to have a synergistic affect; however, previous research at this site showed Select Max alone provided no more than 30% control. Additional research is currently being conducted to evaluate the level of resistance to these different herbicide groups. Moving forward, additional strategies, including non-chemical ones, will likely be needed to manage this weed before planting soybeans and other summer crops in Maryland.
Figure 2. Italian ryegrass response in June of 2022 following a previous glyphosate application.
Table 2. Italian ryegrass response in spring to selected herbicide treatments.a
Herbicide(s)
Group
Rate (fl oz a-1)
Control
Density
Height
%
plants m-2
cm
Roundup
9
36
38
b
16
a
25
a
Roundup + Select Max
9 + 1
36 + 16
87
a
2
b
13
b
Roundup + Sharpen
9 + 14
36 + 2
49
b
16
a
23
a
Roundup + Valor
9 +14
36 + 2
58
b
12
a
23
a
a Means with the same letter do not differ significantly according to Fisher’s LSD (α = 0.05).
Cerruti R2 Hooks$ and Dwayne Joseph* $Professor and Extension Specialist, *Post-Doctoral Fellow, CMNS, Department of Entomology
Introduction
Mechanical cultivation and hand weeding are organic producers most preferred choices for weed control. However, repeated cultivation has a negative influence on soil structure and organic matter content, and can make conditions more susceptible to soil erosion. In addition, repeated cultivation promotes new weed flushes. On the other hand, hand weeding, which may require a ready supply of field workers, can be expensive, especially if conducted over large areas and in less competitive crops that require multiple hand weeding tasks. For commercial producers who mostly rely on herbicides, concerns may arise regarding herbicide-resistant weeds, the potential risk to the groundwater supply, and their effect on food quality. This suggests that alternative weed management tools should be considered. Multiple studies have examined effects of flaming on annual weeds; and successful application of propane flaming to manage weeds has been reported in crops such as cotton, field corn, cabbage, carrots, sweet corn and onions. This suggests that weed flaming may be a formidable tactic for incorporation into an integrated weed management (IWM) program. Its successful integration could result in reduced usage of cultivation, hand weeding and herbicide sprays.
Flame weeding or flame cultivation involves using propane burners to create intense heat to manage weeds in the interrow region of row crops or across the whole field in fallow situations. Flame-weeding systems range from handheld flamers for small-scale production to tractor-mounted systems for large-scale, row-crop flaming (Fig. 1). Covers or reflectors used to contain the heat energy close to targeted weeds improve energy efficiency by reducing heat loss. Very brief periods [e.g., 125 millisecond (ms)] of exposures to high temperatures interfere with plant cellular processes such as photosynthesis. Practicing flaming to manage weeds was developed for field crops, fruits and vegetables during the 1940s. However, as interest in low priced herbicides became more prevalent, flaming popularity took a hit. After its almost complete disappearance in the 1970s, flame weeding has regained interest, especially in organic production.
Fig. 1. Tractor equipped with propane tank and burners. Attribute: Ian Abbott (CC).
How does flaming impact weeds?
Flaming differs from burning in that plant tissues are not incinerated, but rapidly heated causing denaturation and aggregation of cellular proteins. The extent to which heat from the flames penetrates plants depends on the flaming technique and environmental factors such as leaf surface moisture. Denaturation of the plant cells starts at roughly 40 °C, depending on exposure time. An increase of temperature above 50 °C inside the plant cells can result in the coagulation of membrane proteins leading to loss of membrane integrity. Lethal temperatures are reported to range from 55 to 94 °C. Plant cells comprise 95% water; and if plant tissue reaches temperatures above 100°C for a split second, it causes water boiling and cell membrane rupture, resulting in loss of water and plant death. Exposure times in the range of 65–130 ms are sufficient to kill many annuals. Plants may survive flaming by avoidance or heat tolerance. To optimize propane flaming as a weed control tool, the effective dose (ED) of propane required to control targeted weed species must be known. Depending on the desired level of weed control, a propane dose can be used to kill weeds or reduce their competitiveness with crops. For fast-growing crops, pre-emergence flame weeding can provide sufficient weed suppression to allow the formation of full crop canopy, which impedes later weed emergence. In addition to open flame units that target emerged weeds, flames may be directed to the soil surface. Direct heat to the soil surface increases soil temperatures to the weed seed thermal death point. The thermal death point is the temperature at which a seed will not germinate after heat application. Many soil attributes influence the efficacy of direct heat and contribute to variations in treatment efficacy. These include planting depth, soil texture, soil moisture thermal conductivity, soil chemical properties and soil porosity. The efficacy of flaming is determined by the amount of heat transferred from the burner and the duration of time that weeds are exposed to the heat. The amount of heat transferred by the flamer to weeds is determined by the number of burners for a given working width, the nozzle size, and gas pressure; as well as exposure time which is determined by application speed.
What influences the flamer?
Timing. The efficacy of flame weeding is influenced by several factors, including the plant’s growth stage, the physical location of its growing point during flaming, the presence of protective layers of hair or wax and lignification, and the time of day. Multiple studies have shown that plants are more heat sensitive when flamed in the afternoon than early morning. One study compared the effectiveness of flaming at 8 a.m., 12 p.m., 4 p.m., and 8 p.m., and reported better weed control at the noon and 4 p.m., treatment periods. It was suggested that differences in weed control among flaming times could not be explained by differences in temperature, relative humidity or the presence/absence of dew. Thus, in general, it is believed that flaming will be more effective if conducted during the afternoon period. Though, afternoon flaming may result in better weed control; it is important to note that crops are also more vulnerable to injury during this period. Adjusting the angles of torches and positioning the flames below the crop canopy may reduce risk of crop injury during flaming.
Plant type. Weeds susceptibility to flaming varies among species and in general, dicots are more effectively controlled with flaming than monocots. Further, annual weeds are more vulnerable to flame weeding than biennials and perennials. Annual broadleaf and grass species also differ in their response to flaming. Leaves of annual broadleaf species may turn brown and die within a few days after flaming, resulting in no regrowth whereas leaves of grass species may turn white shortly after flaming, leaving an appearance of a dead plant. However, within a week, grass species begin to recover with the growth of new leaves. These varying responses to flaming between broadleaf and grass species are due to the physical positioning of their growing point at the time of flaming. The growing point in grass species during early growth stages is typically below the soil surface and as such, are protected from flames. In contrast, the growing point of broadleaf species is above the ground where it is exposed to the flame. Grasses also have a sheath that protects their growing point. Weeds with unprotected growing points, such as lambsquarters, have been found to be more sensitive than those with protected growing points, such as shepherd’s purse (Capsella bursa-pastoris) and that barnyardgrass (Echinochloa crus-galli) and green foxtail (Setaria viridis) are more tolerant to flaming than velvetleaf (Abutilon theophrasti; Fig. 2) and ivyleaf morningglory (Ipomea hederacea). Broadleaf weeds in their vegetative growth stages require propane doses ranging from 30 to 60 kg ha-1, whereas a vegetative grass such as barnyardgrass can require up to 79 kg ha_1 to achieve the same level of control. Relative to this, crops in the grass family such as maize and sorghum exhibit higher tolerance to flaming than broadleaf crops such as soybean and sunflower when treated at early growth stages.
Plant growth stage and size. A plant’s tolerance to flaming varies according to its maturity/growth; and developmental stage is probably the most important factor. The growth stage of weeds at the time of flaming helps determine their sensitivity to heat. The growth stage establishes the type and degree of protective layers, the lignification level and location of growing points. Relative to this, flaming is more effective on most weeds at an early growth stage. Smaller plants typically have thinner leaves, lower biomass and fully exposed meristems (not protected by surrounding leaves). In contrast, older seedlings or bigger plants have larger and thicker leaves and greater surface area and biomass, which requires higher temperature and longer exposure to achieve control. Further, they possess larger amounts of food reserves (soluble sugars, proteins and lipids) in stems and roots, providing them with the increased capacity for regrowth. Another critical part of young plants that determines their heat tolerance is the growing point in the shoot apex. In older plants, the shoot apex is often protected by surrounding leaves. The tolerance of different plant parts to flaming can also be influenced by protective layers of hair and/or wax, lignification level and their overall plant water status.
Relative to the growth stage, four weed species [green foxtail (Setaria viridis, Fig. 3), yellow foxtail (Setaria pumila), redroot pigweed (Amaranthus retroflexus) and common waterhemp (Amaranthus rudis)] exhibited more tolerance when flamed at the flowering stage compared with earlier vegetative stages; and popcorn plants flamed at the 2-leaf stage had the highest yield loss. In comparison, flaming popcorn plants at the 5- or 7-leaf stage had less of an effect on ear size. One study found that plant size had a greater influence upon sensitivity to flaming than plant density, with small weeds being more sensitive than large weeds. For example, 42 kg ha−1 of propane killed 95% of individuals within a solid stand of white mustard plants with 0-2 leaves. However, 74 kg ha−1 was required to kill 95% containing 2-4 leaves.
Fig. 3. Green foxtail (Setaria viridis). Attribute: Dick T. Johnson (CC).
Advantage. Flaming can be a viable weed management alternative to hand weeding and cultivation. From an economic standpoint, labor cost associated with hand weeding is more expensive, time-consuming and labor intensive (Fig. 4). Further, flaming can be used when the soil is too moist or stony for hand or mechanical weeding. In comparison with cultivation, flame weeding does not disturb the soil surface or bring buried weed seeds to the surface which makes it compatible with the stale seedbed technique. Further, in some instances, flaming can be as effective or better than cultivation. A study conducted to compare flaming to mechanical cultivation on weed control in popcorn reported that weed control was better with flaming than cultivation. Moreover, flaming helps reduce concerns regarding direct effects of weed suppression tactics on soil, water, and food quality. For instance, flaming does not leave chemical residues on plants, soil, air or water, and produces no hazardous drifts or chemical carry-over to the next season. Flaming does not contribute to herbicide-tolerant or resistant weeds and weeds are less likely to become resistant to flaming. As such, flaming in some situations is a more feasible alternative to using herbicides or mechanical cultivation.
Fig. 4. Wheat plots being hand-weeded. Attribute: Fred Miller, Arkansas Agri Media (CC).
Disadvantage. The main disadvantages of flame weeding are the lack of residual weed control, the lack of selectivity for crop safety, low speed of application, increased application costs, and applicator safety. The efficacy of flaming may be reduced when environmental conditions such as dew is present. It should also be noted that flaming is not as efficient as chemical control. However, it can be repeated as needed during the growing season and more importantly integrated with other weed management tactics. In addition, postemergence flaming can damage the cash crop. For heat-resistant crops such as cotton, corn, and sugarcane, flames can be directed to the plant’s base during certain growth stages. This technique, is called selective flaming and controls intra-row weeds. For heat-sensitive crops, postemergence flaming can be applied using a covered flamer to help protect crops from the heat. This technique, also known as parallel flaming, controls weeds between the crop rows. Flaming may also be incompatible for conservation tillage and cover cropping as the heavy plant residue that remains on the soil surface may ignite during flaming. Another drawback is that most flame weeding systems are designed to treat a lower number of rows per pass compared to chemical treatments which makes the process slower.
Summary
Flame weeding uses propane burners to generate combustion temperatures of up to 1,900 degrees Celsius, which raises the temperature of exposed weed leaves very rapidly and kills them without burning. Flaming in the absence of killing weeds can severely reduce their growth, thereby making them less competitive with crops. Weeds and other plants’ susceptibility to flaming will vary according to species, plant size and growth stage during flaming. Broadleaves are generally more sensitive than grasses, and older and larger plants require higher energy rates for control than younger and/or smaller plants with fewer leaves. Flaming before crop emergence has been the predominant thermal weed control method in slow-germinating row crops such as onion, leek, carrot and corn. However, preemergence flaming may be of limited value in fast emerging crops because the crop may easily emerge before most weeds. As such, preemergence flaming would only control a fraction of the weeds that will emerge during the cropping season. Still, flaming has shown good results after weed emergence and before crop emergence in crops such as potato, sugar beet, carrot and cayenne pepper. When conducted postemergence, vulnerable crops such as soybean and sunflower must be protected from flaming. Other crops such as corn and sorghum have some tolerance to flaming. Flaming similar to other weed management tactics should not be viewed as a stand-alone tactic. However, it can be successfully incorporated into an IWM plan and thus be used in concert with other tools. For example, weeds in corn were controlled through integration of tillage and flaming.
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).
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.
Ray Weil1, Kevin Conover2, Mia Godbey1 1Dept of Environmental Science and Technology and 2Central Maryland Research and Education Center University of Maryland, College of Agriculture and Natural Resources
Weed control is almost invariably cited as one of the biggest challenges for the organic production of grain crops. Synthetic herbicides cannot be used in organic farming, leaving tillage as the main weed control option. Tillage is also the main method of terminating cover crops in organic farming, although roller-crimping can work under some circumstances. The lack of chemical means of weed control makes low disturbance or no-till organic farming extremely difficult if not impossible on a commercial scale.
This spring we conducted a preliminary trial to access the efficacy of a new organically-approved herbicide called Weed Slayer® (based on Eugenol, an essential oil from cloves, molasses, and a biological surfactant mixture). This product comes in two parts, the Clove Oil product, and the microbial surfactant product, that must be mixed together in equal parts. The manufacturer, Agro Research International, recommends a rate of 1-3 quarts/acre of each part in 20-25 gallons water/acre.
We established a cover crop stand that initially included 12 species (originally 4 legumes, 4 brassicas, and 4 kinds of grass) planted in fall 2019, but because of the very dry conditions in August-October 2019 and winter killing of the radish, we ended up with a few plots of good cover crop biomass (>3,000 lbs/acre dry matter) consisting of mainly red, white and crimson clovers, hairy vetch, annual ryegrass, and cereal rye with the occasional turnip or kale. The covers were allowed to grow into full flowering. On May 27, soybeans were “planted green” in and the plots were sprayed with three herbicide treatments: 1) RU: the normal rate of Glyphosate, 2) WS1: the recommended rate of 1 quart/acre each part of Weed Slayer®, and 3) WS2: a rate of 2 quart/acre rate of each part of Weed Slayer® (Figure 1).
Figure 1. Appearance of sprayed multi-species cover crop plot 7 days after treatments were applied.
We used the Canopeo app (canopeoapp.com) to measure the green cover percentage at 2 and 7 days after spraying at 6 locations within the tire tracks and within the untracked middle area of each plot. On day 7 we also measured the green cover of the unsprayed cover crop at the edge of the field (to serve as a control). We did this in two blocks about 80 feet long and 45 ft wide. At four weeks after spraying, visual observations were made to access any possible regrowth of the cover crop.
Results. Two days after spraying, the effect of the tractor tire tracks was quite evident, with less remaining green foliage in the tracks than in the untracked middle rows of the plot (Figure 2). In the untracked area, the 1 quart/acre rate of Weed Slayer® had about 25% green area remaining, which was greater than the 18% green area for the Round-Up and the 2-quart rate of Weed Slayer®. In the tire tracks, less than 10% green area remained for all three treatments.
Figure 2. Percent green (living foliage) area two days after herbicide treatments were sprayed on multi-species cover crop. Measurements were made in the tractor tire tracks (right) and in the untracked middle row (left) of the plot.
By the 7th day after application, there was no difference among the three spray treatments in green cover in the tire tracks where the only detectable green foliage was that of the emerging soybean seedlings (data not shown). There was also very little difference in the untracked middle of the plot with Round-Up and Weed Slayer®2X exhibiting statistically the same percent green area (Figure 3), which was almost entirely due to the emerged soybean seedlings. The Weed Slayer® 1 quart/acre rate had about 5% green area, which was statistically greater than the Round-Up plots, and about half due to cover crop and half to soybean seedlings. The grasses were killed earlier than the legumes by both herbicides, but by day 7 all cover crop species appeared to be nearly completely killed. Most of the green cover by day 7 was due to the soybean seedlings. However, visual inspections four weeks after the spray treatments revealed some re-growth of the hairy vetch in the Weed Slayer® plots but not in the Round-Up plots. No grass regrowth was observed.
Figure 3. Percent green (living foliage) area seven days after herbicide treatments were sprayed on multi-species cover crop. Measurements shown are for the untracked middle rows (right) of the plot.
Weed Slayer® currently costs about $60/acre for the 1 x rate (purchased online in a package of 1 gallon of each part). This is expensive by conventional grain production standards, but feasible for organic grain which brings about twice the price per bushel as conventional. An affordable, effective organic-certified burn-down herbicide for grassy species (and some broadleaves) could open up important opportunities for no-till and cover cropping practices not currently practical in organic farming.
Kurt Vollmer, Extension Weed Management Specialist
University of Maryland
As the 2020 planting season begins, marestail is bolting and common ragweed has started to emerge (Fig. 1). Populations of marestail in the region are resistant to glyphosate and ALS-herbicides (Group 2, i.e. Classic), and populations of common ragweed are resistant to glyphosate, the ALS-herbicides, and PPO-herbicides (Group 14, i.e. Reflex). Herbicides such as 2,4-D, dicamba, and Gramoxone will provide control of emerged weeds, but they are most effective when applied to weeds less than 4 inches tall. Now is the time to spray these weeds. If you have already burned down your field, scout before planting to make sure these species have not escaped or emerged since your burndown application. If they have, consider adding Gramoxone to your at planting application. Dicamba can be used prior to planting Xtend soybeans or 2,4-D can be used with Enlist crops. Always consult the label for application instructions and approved tank-mixes.
Common Ragweed. Photo by Kurt Vollmer.Marestail. Photo by Kurt Vollmer.
Dr. Amanda Grev, Pasture & Forage Specialist University of Maryland Extension
As things are greening up this spring, you may notice a few not-so-friendly plants popping up around your fields, especially given the milder weather this past winter. If you haven’t already done so, now is the time to scout your pastures and hayfields in search of winter annual and biennial weeds. When it comes to weed control, timing of herbicide application is critical and it is important to spray when weeds are most susceptible to achieve maximum effectiveness.
Winter annuals typically germinate in the fall, overwinter, and complete their reproductive cycle in the spring or early summer. Common winter annual species include chickweed, purple deadnettle, field pennycress, henbit, horseweed/marestail, shepherd’s purse, and the mustard species. Annuals are best controlled during the seedling and early vegetative stage when they are young and actively growing. Herbicide applications will be more effective if made at this stage while they are still vegetative and more susceptible and will prevent them from flowering and producing seed. At this time of year, these winter annuals are growing rapidly and have already or will soon begin to flower and set seed. If the winter annuals in your fields have moved beyond this stage, an application may offer some control but you may also want to take note of those weedy areas now and target them later this year with a late fall application.
Biennials live for two growing seasons, with the first year consisting of only vegetative growth as a seedling and rosette and the second year consisting of vegetative growth and also reproductive growth in the form of an elongated flower stalk. Common biennial species include burdock, bull thistle, musk thistle, and wild carrot. These weeds are best controlled during the seedling and rosette stage, and should be treated now while they are smaller and more susceptible and before they begin to bolt.
There are a number of herbicides available for control of broadleaf weeds. Herbicide selection should be based on the type of forage and weed species present. The most common herbicides used for control of broadleaf weeds in grass hay or pasture are the plant growth regulator herbicides, which includes products containing 2,4-D, dicamba, triclopyr, aminopyralid, picloram, or a mix of these (see the table below for a list of common products). These products are safe if applied to grass forages at the labeled rates but can kill or injure desirable broadleaf forages (i.e. clover) in grass-legume mixed pastures.
If weedy annual grasses such as crabgrass, foxtail, panicum, and Japanese stiltgrass are problematic, pendimethalin (Prowl H2O) now has a supplemental label that allows for its use on established perennial pastures or hayfields grown for grazing, green chop, silage, or hay production. It may be applied to perennial grass stands or alfalfa-grass mixed stands. Prowl H2O may be applied as a single application in the early spring, or for more complete control it can be applied as a split application with the first application in early spring and the second application after first cutting. Keep in mind, this herbicide is a pre-emergent herbicide, meaning it will only control weeds if applied prior to germination. If soil temperatures in your area are already above 50°F it is likely that crabgrass and stiltgrass has already germinated, but a split application of Prowl H2O now and after first cutting can help control foxtail. There are currently no herbicides labeled to control emerged weedy grasses in grass stands or alfalfa/grass mixes.
Note that if forages were recently seeded and are not yet established many of these herbicides can cause severe crop injury. Most herbicide labels for cool-season perennial grasses state that the grasses should be well established with at least 4-5 inches of growth, although some labels are more restrictive than this. In addition, some of these herbicides have haying or grazing restrictions following application. Always read and follow the guidelines listed on the product label for proper rates, timing, residual effects, and any grazing or harvest restrictions following application.
Lastly, remember that while herbicides can be a useful tool for weed management in pastures and hayfields, they are not the only option for weed control. A program that integrates several different control strategies is generally more successful than relying on a single method. For maximum results, include cultural practices such as selecting adapted species and maintaining optimum soil fertility, mechanical practices such as timely mowing or clipping to suppress weed seed production, and biological practices such as utilizing livestock for controlled grazing or browsing. And remember that weeds are opportunistic; the best method for weed control is competition with a healthy, dense stand of desirable forage species.
Product
Active Ingredients
Application Rate*
General/Restricted Use
2,4-D
2,4-D
1 to 2 qt/A
General
Banvel/Clarity
dicamba
0.5 to 2 pt/A
General
Crossbow
2,4-D + triclopyr
1 to 6 qt/A
General
GrazonNext HL
2,4-D + aminopyralid
1.2 to 2.1 pt/A
General
Grazon P+D
2,4-D + picloram
2 to 8 pt/A
Restricted
Milestone
aminopyralid
3 to 7 fl. oz/A
General
PastureGard HL
triclopyr + fluroxypyr
0.75 to 4 pt/A
General
Prowl H2O
pendimethalin
1.1 to 4.2 qt/A
General
Remedy Ultra 4L
triclopyr
0.5 to 4 pt/A
General
Stinger
clopyralid
0.7 to 1.3 pt/A
General
Surmount
picloram + fluroxypyr
3 to 6 pt/A
Restricted
WeedMaster
2,4-D + dicamba
1 to 4 pt/A
General
*For use in established grass pasture or hayfields
