Most broadleaf weeds have netlike veins in their leaves and nodes containing one or more leaves. They may have showy flowers. Broadleaf weed seedlings… Annual broadleaf weeds are more competitive with soybeans than are annual grasses. Annual broadleaf weeds also vary greatly in their potential to reduce soybean yield. You should strive to obtain excellent control of the more competitive species such as cocklebur, lambsquarter, jimsonweed, and smartweed. A fairly high population of the less competitive species such as …
Most broadleaf weeds have netlike veins in their leaves and nodes containing one or more leaves. They may have showy flowers. Broadleaf weed seedlings emerge with two leaves. Because of differences in their leaf structure and growth habits, they are easy to distinguish from grasses.
A weed’s life cycle has great impact on the selection and success of a given control procedure, so it is important to learn the life cycle characteristics of a weed when you first learn its identity.
Annual weeds germinate from seeds, grow, flower, produce seeds and die in 12 months or less. Annual weeds are further categorized by the season in which they germinate and flourish. Winter annuals sprout in the fall, thrive during the winter and die in late spring or early summer. Summer or warm-season grasses, such as crabgrass and goosegrass sprout in the spring and thrive in summer and early fall.
Perennial weeds are weeds that live more than two years. They reproduce from vegetative (non-seed) parts such as tubers, bulbs, rhizomes (underground stems), or stolons (above ground stems), although some also produce seed. Perennial weeds are the most difficult to control because of their great reproductive potential and persistence.
Proper identification of weeds targeted for control is necessary in order to select effective control measures, whether cultural or chemical. Further assistance with weed identification is available from any Clemson Extension office or the Clemson Home and Garden Information Center.
Life Cycle & Description: Common chickweed (Stellaria media) is a winter annual broadleaf weed that commonly infests thin or dormant lawn areas. It germinates in the fall, grows during the winter and produces seed from spring to early summer, then dies.
Common chickweed (Stellaria media) with small white flowers is a winter annual weed.
Karen Russ, ©2015 HGIC, Clemson Extension
You can identify common chickweed by its flat, mat-forming growth habit and small egg- to football-shaped leaves that are arranged in pairs. The stems have a single line of hairs running along their length. Small clusters of white, five-petaled flowers occur at the ends of stems in the spring. Common chickweed reproduces by seed and creeping stems.
Sticky chickweed (Cerastium glomeratum), or mouse-ear chickweed, is a mat-forming branched winter annual with fuzzy, opposite leaves that resemble mouse-ears, hence, the common name. The stems are also covered with dense hairs. The white flowers are arranged in clusters at the end of the stems. It is hairy, spreading or erect, and larger than common chickweed. The empty seed cases, which are almost transparent and have 10 teeth, are noticeable. Sticky chickweed reproduces by seed.
Perennial mouse-ear chickweed (Cerastium vulgatum) looks like sticky chickweed, but it has creeping stems that often take root to produce new plants. It reproduces by seed and by producing new plants from ground-hugging stems that root at the nodes (the point of attachment of the leaves).
Control: Hand pulling is a simple, practical approach for small areas. Improve the health and density of the lawn by fertilizing at the right time and with the correct amount; maintaining an appropriate soil pH; mowing at the recommended height; and watering properly. Apply a 2- to 3-inch layer of mulch to ornamental bed areas to suppress germinating weed seeds. Since this weed reproduces by seed, control it before seeds are produced. Pre-emergence herbicides are available depending on the kind of turfgrass and ornamental plants grown. Optimum timing of post-emergence herbicides is mid-autumn. See Table 1 for pre- and post-emergence control products. Apply all chemicals according to directions on the label. See Table 2 for turfgrass tolerance to each herbicide.
Life Cycle & Description: Dandelion (Taraxacum officinale) is a deep-rooted, stemless perennial weed that is probably one of the most widely recognized weeds. It has a long taproot and a basal rosette (circular cluster of leaves radiating from the stem of a plant at ground level) of slightly to deeply cut leaves with lobes that point back towards the base. The rosette remains green year-round. Yellow flowers appear mainly in the spring on long, smooth, hollow stalks. A second bloom occurs in the fall. The leaves and flower stalks exude a milky juice when broken. The flowers give rise to a “puff” ball or globe of parachute-like brown seeds.
Seedlings emerge from late spring to early fall, with most emerging in early summer, several weeks after the seeds are shed. Dandelion will grow in almost any soil type and is most commonly found in sunny areas. It reproduces by seed and from new plants that develop from pieces of broken taproots.
Common dandelion (Taraxacum officinale) is a perennial broadleaf weed that spreads by wind-blown seeds.
Joey Williamson, ©2015 HGIC, Clemson Extension
Carolina falsedandelion (Pyrrhopappus carolinianus) is a winter annual or biennial with erect branching flowering stems. The leaves are alternate, sharply pointed with leaves that may be deeply lobed or lack lobes. The basal leaves are attached to the stem with petioles; leaves on the stem do not have petioles. In late spring, bright yellow flowers similar to dandelion occur on the ends of stems. The flowers give rise to a “puff” ball comprised of a cluster of brown seeds with a parachute attachment of a long stalk of hairs. It reproduces by seed.
Catsear dandelion (Hypochoeris radicata) is also a perennial weed that produces a basal rosette of leaves. Unlike dandelion, the leaves are densely hairy and have irregular to rounded lobes on the leaf margins. The flower stalk bears two to seven bright yellow flowers that look similar to dandelion. The leaves and flowers also excrete a milky juice when broken.
Control: Handpulling can be done with the aid of a tool that removes the entire taproot, especially when the soil is moist. Maintain a dense, healthy turf which crowds out weeds naturally and reduces the chances for invasion. Mulch ornamental bed areas with a 2- to 3-inch layer of mulch to suppress weed seed germination and growth. Remove the flowers before they reach the “parachute stage” to eliminate seed production. There are many herbicides available depending on the kind of turfgrass in your lawn. Optimum timing of postemergence herbicide use is mid-fall. See Table 1 for pre- and post-emergence control products. Apply all chemicals according to directions on the label.
Life Cycle & Description: Florida betony (Stachys floridana) is a fast-spreading nuisance of lawns and landscaped beds. It grows in full sun to partial shade and tolerates a wide variety of soil conditions ranging from wet to dry. Florida betony is often called “rattlesnake weed” because it produces white, segmented tubers that resemble a rattlesnake’s tail.
Distinctively shaped Florida betony (Stachys floridana) tubers.
John D. Byrd, Mississippi State University, www.forestryimages.org
This cool-season perennial weed emerges from seeds and tubers during the cool, moist months of fall. Throughout the winter months, the plants grow and spread rapidly, often reaching heights of less than 2 feet. Florida betony has square stems and lance-shaped leaves with slightly toothed or serrated edges arranged oppositely on the stems. From late spring to early summer the weeds bear white to pink trumpet-shaped flowers occurring in whorls of three to nine in the leaf axils (the upper angle formed where the leaf joins the stem). In response to the onset of high summer temperatures or cold winter temperatures, Florida betony growth stops and the plant becomes nearly dormant. Florida betony reproduces primarily from tubers but also from seeds and rhizomes.
Control: Maintain a healthy, dense lawn by fertilizing and liming according to soil test results and mowing at the proper height and frequency. Healthy lawn grasses can out-compete Florida betony for light, water and nutrients and reduce the level of infestation.
Suppress growth by applying a 2- to 3-inch layer of mulch such as pine straw or pine bark around shrubs and trees. Using landscape fabric weed barriers beneath the mulch layer will further hinder its emergence. Pull or dig out all plant parts, especially the tubers, when the soil is moist. Hoe or cut the top growth down to soil level repeatedly to “starve” the plant.
Spot-treat with herbicides when Florida betony is actively growing during the cool fall months. Pre-emergence and post-emergence herbicides are available depending on the kind of turfgrass and ornamental plants grown. See Table 1 for post-emergence control products. Apply all chemicals according to directions on the label. See Table 2 for turfgrass tolerance to each herbicide.
Life Cycle & Description: Japanese clover (Lespedeza striata) or common lespedeza is a wiry, ground-hugging summer annual that has oblong leaflets that occur in triplets, or threes. A noticeable midvein runs down the center of each leaflet. A parallel arrangement of veins is attached at 90-degree angles to the midvein. The pink to purple single flowers appear in mid- to late summer along the branching stems. Japanese clover reproduces by seed.
Control: Handpulling is a simple, practical approach for small areas. Improve the health and density of the lawn by fertilizing at the right time and with the correct amount; maintaining an appropriate soil pH; mowing at the recommended height; and watering properly. Apply a 2- to 3-inch layer of mulch to ornamental bed areas to suppress germinating weed seeds.
Postemergence herbicides are available depending on the kind of turfgrass in your lawn. Optimum timing of postemergence herbicide use is early summer. See Table 1 for post-emergence control products. Apply all chemicals according to directions on the label. See Table 2 for turfgrass tolerance to each herbicide.
Common lespedeza (Lespedeza striata) prostrate growth habit.
Photo courtesy of: Ted Bodner, Southern Weed Science Society, Bugwood.org
Life Cycle & Description: Both buckhorn, or narrow-leaved plantain (Plantago lanceolata), and broadleaf plantain (Plantago major) are perennial weeds that reproduce by seeds. Both produce a rosette or cluster of leaves at ground level and have fibrous root systems. The leaves of buckhorn plantain are narrow and lance-shaped (2 to 10 inches long – about five times as long as wide), often twisted or curled. Raised, parallel veins can be found on the underside of the leaf.
As the name suggests, the leaves of broadleaf plantain are broad and egg-shaped – 1½- to 7-inches long – with several main veins running parallel to the leaf margins. The petioles are sometimes tinged with red at the base.
Both plantains produce erect flower stalks from June to September. Buckhorn plantain produces a cone-like spike of white flowers perched at the top of the leafless flower stalk. Broadleaf plantain produces white-petaled flowers along the length of a leafless flower stalk that may be 2- to 18-inches long. Seed germinates in late spring through midsummer and sporadically in early fall.
Buckhorn plantain (Plantago lanceolata) is a perennial broadleaf weed.
Joey Williamson, ©2015 HGIC, Clemson Extension
Control: Handpulling is a simple, practical approach for small areas. Improve the health and density of the lawn by fertilizing at the right time and with the correct amount; maintaining an appropriate soil pH; mowing at the recommended height; and watering properly. Apply a 2- to 3-inch layer of mulch to ornamental bed areas to suppress germinating weed seeds. Postemergence herbicides are available depending on the kind of turfgrass in your lawn. Optimum timing of post-emergence herbicides is mid-autumn. See Table 1 for pre- and post-emergence control products. Apply all chemicals according to directions on the label. See Table 2 for turfgrass tolerance to each herbicide.
Life Cycle & Description: Common vetch (Vicia sativa) is a winter annual, broadleaf weed that reproduces by seeds that germinate in the fall or early winter. As with all weeds, vetch can quickly invade thin turf areas, especially in sunny areas or moderate shade where there is good soil moisture. It is normally upright and vining, but may have a prostrate growth habit. Vetch grows slowly during the winter, but more rapidly during any period of warm winter weather. It resumes rapid growth in spring and produces violet-purple flowers, which are followed by seedpods. Being a cool weather weed, the plants die as temperatures increase in late spring and early summer.
Common vetch (Vicia sativa) is a sprawling, vining weed.
Barbara H. Smith, ©2019 HGIC, Clemson Extension
Control: Keeping a thick and vigorous growing turf is the best way to reduce the encroachment of vetch. First, select a turfgrass cultivar adapted for your area and light conditions, and then properly fertilize, mow, and water to encourage dense growth. For more information on growing healthy turfgrass, see HGIC 1201, Fertilizing Lawns; HGIC 1205, Mowing Lawns; and HGIC 1207, Watering Lawns. In landscape beds, vetch can be hand dug and suppressed with the use of mulch. A 3-inch mulch layer is ideal to reduce weed growth.
Cultural controls should be implemented before applying herbicides for vetch control. However, after taking steps to use the best lawn care techniques, chemical control may still be necessary to further reduce common vetch. Herbicides should be chosen according to turfgrass species and all label instructions followed. Chemical controls for common vetch should be applied in fall or early spring for best results. Keep in mind that herbicide effectiveness is reduced as weeds mature.
Three-way herbicides are the most commonly used broadleaf weed killers on bermudagrass, zoysiagrass, centipedegrass, St. Augustinegrass, and tall fescue to control common vetch and almost any broadleaf weed in the lawn. The active ingredients of three-way herbicides include the following broadleaf weed killers: 2,4-D, dicamba, and mecoprop (MCPP) or MCPA. A three-way herbicide will give good control of common vetch.
Atrazine may be used to control common vetch in centipedegrass and St. Augustinegrass only. Atrazine is a post-emergence broadleaf weed killer that also controls several common grassy weeds and has some pre-emergence activity. Atrazine will give excellent control of vetch.
A recent herbicide combination of thiencarbazone, iodosulfuron, and dicamba, as found in Celsius WG Herbicide, is selective to control many broadleaf weeds and several grass weeds in all four of the common warm-season grasses, but it cannot be used in fescue lawns. Apply when common vetch is actively growing and again 2 to 4 weeks later if needed. The addition of a non-ionic surfactant, such as Southern Ag Surfactant for Herbicides, will increase control. Celsius WG Herbicide is safe to apply during spring green-up of warm season grasses. Celsius WG will give good control of vetch.
Metsulfuron can be used for common vetch control in bermudagrass, centipedegrass, St. Augustinegrass, and zoysiagrass. Quali-Pro MSM Turf Herbicide is a product that contain metsulfuron, and Quali-Pro Fahrenheit contains dicamba along with metsulfuron, but these are packaged for landscape professionals. Metsulfuron will give excellent control of vetch.
Do not apply metsulfuron to lawn if over-seeded with annual ryegrass or over-seed for 8 weeks after application. Do not plant woody ornamentals in treated areas for one year after application of metsulfuron. Do not apply metsulfuron herbicides within two times the width of the drip line of desirable hardwood trees or if temperature is over 85 °F. For these professional products, a non-ionic surfactant (such as Southern Ag Surfactant for Herbicides) is required at 2 teaspoons per gallon of spray mix for best control. See Table 1 for herbicides and specific products. See Table 2 for turfgrass tolerance to each herbicide.
Landscape Bed Weed Control
Glyphosate: When herbicides are applied to beds intended for future planting of ornamentals, care must be taken as various herbicides may injure the plants to be installed. For planned beds, glyphosate has far less soil activity (a few days) as compared with the three-way herbicides or atrazine (a few weeks). Glyphosate is the safest choice for spray application in existing flower and shrub beds, so long as care is taken to prevent drift to non-target plants. Glyphosate applications are much less apt to move through the soil, be absorbed by roots, and injure existing woody ornamental shrubs.
Glyphosate can be used for spot treatments around ornamental plants in landscape beds. Glyphosate is a non-selective herbicide that should be used with caution. Do not allow glyphosate spray mist to contact ornamental foliage or stems as severe injury will occur. A cardboard shield may be used to prevent glyphosate spray from drifting to nearby ornamentals. Examples of products containing glyphosate in homeowner sizes are:
- Roundup Original Concentrate,
- Roundup Pro Herbicide,
- Martin’s Eraser Systemic Weed & Grass Killer,
- Quick Kill Grass & Weed Killer,
- Bonide Kleenup Weed & Grass Killer 41% Super Concentrate,
- Hi-Yield Super Concentrate,
- Maxide Super Concentrate 41% Weed & Grass Killer,
- Super Concentrate Killzall Weed & Grass Killer,
- Tiger Brand Quick Kill Concentrate,
- Ultra Kill Weed & Grass Killer Concentrate,
- Gordon’s Groundwork Concentrate 50% Super Weed & Grass Killer,
- Zep Enforcer Weed Defeat III,
- Eliminator Weed & Grass Killer Super Concentrate,
- Monterey Remuda Full Strength 41% Glyphosate,
- Knock Out Weed & Grass Killer Super Concentrate,
- Southern States Grass & Weed Killer Concentrate II,
- Total Kill Pro Weed & Grass Killer Herbicide,
- Ace Concentrate Weed & Grass Killer.
Natural-based, Burn-down Herbicides: For those who would prefer not to use glyphosate for weed control in landscape beds or areas to be kept free of weeds, several non-selective, burn-down herbicides are available that are based on more natural products. This does not mean that they are safer for the individual doing the spraying – caution is always advised. Even natural products may irritate or burn the skin or injure the eyes, especially in the concentrated form. Read the product label for safe use and protective clothing (such as coveralls). It is advisable to wear rubber boots to prevent contact when walking through areas being sprayed, as well as wearing protective goggles and a pair of rubber or top quality dish washing gloves to help protect your hands and forearms from exposure, especially when mixing and adjusting the sprayer nozzle. Also keep in mind that sprayer wands often leak.
Please note that burn-down herbicides do not translocate into the root system, which means that for perennial and tougher to kill weeds, the weeds may regrow from the roots and require additional sprays for control. These products control actively growing, emerged, green vegetation. However, by being persistent with the spraying of any weed regrowth, even the toughest of weeds can be controlled. Do not allow sprays to contact desirable plants.
Examples of plant essential oil-based herbicides include:
- SafeGro WeedZap (contains 45% cinnamon oil & 45% clove oil) (OMRI)
- St Gabriel Organics BurnOut II (8% clove oil & 24% citric acid) (OMRI)
Examples of orange oil (d-limonene) based herbicides include:
- Avenger AG Burndown Herbicide (55% d-limonene) (OMRI)
- Worry Free Weed and Grass Killer (70% d-limonene) (OMRI)
Examples of fatty acid-based herbicides include:
- Monterey Herbicidal Soap (22% ammoniated soap of fatty acids)
- Finalsan Total Vegetation Control (22% ammoniated soap of fatty acids)
- Garden Safe Weed & Grass Killer RTU (premixed) (3.68% ammoniated soap of fatty acids)
Examples of pelargonic acid herbicides include:
- Scythe Herbicide (57% pelargonic acid)
- BioSafe Weed Control (40% ammoniated nonanoate)
- BioSafe Weed Control RTU (premixed) (5% ammoniated nonanoate)
- BioSafe AXXE Broad Spectrum Herbicide (40% ammoniated nonanoate)
- Mirimichi Green Pro Concentrate (40% ammoniated nonanoate) OMRI
- Mirimichi Green Pro RTU (premixed) (5% ammoniated nonanoate) OMRI
Note: Pelargonic acid is a fatty acid which occurs naturally as esters in the oil of pelargonium. It is often called nonanoic acid. The ammonium salt of nonanoic acid, ammoniated nonanoate, is an herbicide.
Examples of acetic acid-based herbicides include:
- Summerset Brand All Down Concentrate (23% acetic acid & 14% citric acid)
- Vinagreen (20% acetic acid)
Table 1. Examples of Herbicides for Broadleaf Weed Control in Turfgrass and Landscape Beds.
Table 2. Turf Tolerance to Herbicides for Common Vetch Control.
|Herbicide||Bermudagrass||Centipedegrass||St. Augustinegrass||Tall Fescue||Zoysiagrass|
|(3- way) 2,4-D + MCPP + dicamba||S||I||I||S||S|
|dicamba & metsulfuron||S||S||S||NR||S|
|thiencarbazone, iodosulfuron, & dicamba 1||S||S||S 2||NR||S|
|S = Safe at labeled rates
I = Intermediate safety, use at reduced rates
NR = Not registered for use on and/or damages this turfgrass
D = Fully dormant turf only.
Note: Do not apply post-emergence herbicides, except Celsius WG Herbicide, to lawns during the spring green up of turfgrass.
1 This mix of active ingredients requires the addition of
2 teaspoons of a non-ionic surfactant (that is, a wetter-sticker agent to aid in weed control at 0.25% by volume) per gallon of water, such as Hi-Yield Spreader Sticker. 2 Spot treatments to St. Augustinegrass at temperatures above 90 degrees may cause temporary growth regulation.
Note: Read and follow all label instructions when using herbicides. Herbicides containing 2,4-D should be applied at a reduced rate on St. Augustinegrass and centipedegrass to prevent damage to these lawns. The product labels will give the rate to use for each type of turfgrass. If a second application is needed, it is safest to apply the herbicide in spot treatments. Repeated applications of a three-way herbicide should be spaced according to label directions. Do not mow within 48 hours after application of most herbicides. Most post-emergence herbicides need to dry on the leaf surface before irrigation or rainfall occurs. See Table 1 for turfgrass tolerance to herbicides.
Most herbicides should not be applied during spring transition (green-up of lawn) or when air temperatures exceed 90 ºF as this can cause severe damage to the turfgrass. A newly seeded lawn should be mowed a minimum of three times before applying an herbicide. Rainfall or irrigation a day or two prior to herbicide application reduces the chance of turfgrass injury and enhances weed uptake of the herbicide.
Pesticides are updated annually. Last updates were done on 7/21 Joey Williamson.
Originally published 09/99
If this document didn’t answer your questions, please contact HGIC at [email protected] or 1-888-656-9988.
Robert F. Polomski, PhD, Associate Extension Specialist, Clemson University
Bert McCarty, PhD, Turf Specialist, Clemson University
This information is supplied with the understanding that no discrimination is intended and no endorsement of brand names or registered trademarks by the Clemson University Cooperative Extension Service is implied, nor is any discrimination intended by the exclusion of products or manufacturers not named. All recommendations are for South Carolina conditions and may not apply to other areas. Use pesticides only according to the directions on the label. All recommendations for pesticide use are for South Carolina only and were legal at the time of publication, but the status of registration and use patterns are subject to change by action of state and federal regulatory agencies. Follow all directions, precautions and restrictions that are listed.
Annual Broadleaf Weed Control
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Estoy de Acuerdo / I agree
Annual broadleaf weeds are more competitive with soybeans than are annual grasses. Annual broadleaf weeds also vary greatly in their potential to reduce soybean yield. You should strive to obtain excellent control of the more competitive species such as cocklebur, lambsquarter, jimsonweed, and smartweed. A fairly high population of the less competitive species such as prickly sida and tropic croton may not seriously reduce soybean yields.
Annual broadleaf weeds can be controlled with preplant-incorporated, preemergence, and postemergence herbicides. The best application method to use depends upon the weed species present and compatibility with your overall production system. This section discusses the various herbicide options.
Soil-Applied Herbicides for Broadleaf Weeds
Grass control herbicides. Soil-applied grass herbicides also control certain broadleaf weeds. Prowl, Sonalan, Treflan, and Vernam control annual grasses plus certain small-seeded broadleaf weeds such as pigweed and lambsquarter (Table 1). If the predominant weed problem is annual grasses plus pigweed, lambsquarter, or both, one of these preplant-incorporated herbicides plus cultivation may be adequate.
Command controls prickly sida, tropic croton, jimsonweed, lambsquarter, smartweed, spurred anoda, and velvetleaf. Note that Command does not control pigweed. Dual or Lasso will control pigweed.
Lexone, Sencor, Salute, and Turbo. These products containing metribuzin normally control many annual broadleaf weeds. Notable exceptions include cocklebur and morning glory. Lexone, Sencor, and Turbo can be preplant incorporated or applied preemergence. Salute should always be incorporated.
Salute is a packaged mixture containing trifluralin plus metribuzin (the active ingredients in Treflan and Sencor, respectively). Turbo is a packaged mixture containing metolachlor plus metribuzin (the active ingredients in Dual and Sencor, respectively).
Soybeans have a narrow margin of tolerance for metribuzin. Therefore, be extremely careful when selecting the application rate of a product that contains metribuzin. This can be a problem in fields with varying soil types. Miles Inc., makers of Salute, Sencor, and Turbo, offer a free soil testing program called SURE. The SURE program recommends a specific rate of Salute, Sencor, or Turbo based upon soil texture, organic matter content, and application method (preplant incorporated or preemergence). SURE has proven to be very helpful in selecting the proper metribuzin rate to avoid crop injury.
There are several restrictions on the use of metribuzin. Specific restrictions vary depending upon application methods and tank mixes, but in general this herbicide should not be used on sands or loamy sands with less than 1 percent organic matter or any soil with less than 1/2 percent organic matter. Certain varieties of soybeans, such as Asgrow 6520 and Coker 156, are very susceptible to metribuzin injury. Before applying a product containing metribuzin to a new variety, check with your seed dealer to determine the variety’s sensitivity to metribuzin. Increased soybean injury will also be observed when metribuzin is used in conjunction with soil-applied organophosphate insecticide/nematicides; see the product labels for details.
Canopy. Canopy is a packaged mixture containing 6 parts metribuzin to 1 part chlorimuron (Classic). Because it contains a high percentage of metribuzin, the use restrictions discussed previously for Lexone, Salute, Sencor, and Turbo also apply to Canopy. Canopy can be applied in various preplant-incorporated or preemergence tank mixes.
In contrast to metribuzin alone, Canopy provides better control of large-seeded broadleaf weeds such as cocklebur and morningglory. Canopy normally controls most annual broadleaf weeds. In fields heavily infested with cocklebur or morningglory, cultivation or a postemergence herbicide may also be needed.
Some rotational restrictions apply when using Canopy. However, there have been no documented cases of Canopy carryover to agronomic crops in North Carolina. Carefully follow label directions for sprayer cleanout after using Canopy.
Lorox. This preemergence herbicide controls common ragweed, pigweed, and lambsquarter but is inadequate for control of most other broadleaf weeds.
Lorox should not be used on sand, loamy sand, or gravelly soils or on any soil with less than 1/2 percent organic matter. Lorox is somewhat safer on light- textured soils than is metribuzin. However, injury may occur if excessive rates are applied or if heavy rainfall is received shortly after planting. Do not use on soils with more than 3 percent organic matter.
Scepter, Squadron, and Tri-Scept. Scepter can be applied in various preplant-incorporated or preemergence tank mixes. The most consistent and broadest spectrum control is obtained when Scepter is tank-mixed with Prowl or Treflan and incorporated.
More rainfall is required to activate a preemergence application of Scepter than is required for most preemergence herbicides. For good control, 3/4 to 1 inch of rainfall is needed within 7 to 10 days after application. For this reason, incorporated applications perform more consistently.
Soil-applied Scepter controls most broadleaf weeds. Major exceptions are tropic croton, hemp sesbania, spurred anoda, and volunteer cowpea. Morningglory control is variable but usually adequate, especially when followed by cultivation.
Soybean tolerance of Scepter is normally good. However, slight to severe crop stunting has occasionally been noted. Heavy rainfall and waterlogged soils shortly after planting appear to enhance the problem. To reduce the potential for crop stunting, avoid deep incorporation and shallow planting, especially on sandy soils.
Squadron is a packaged mixture containing pendimethalin (Prowl) and imazaquin (Scepter); Tri-Scept is a packaged mixture containing trifluralin (the active ingredient in Treflan) and imazaquin. Weed control and crop tolerance with Squadron or Tri-Scept are similar to that with a tank mix of Prowl or Treflan plus Scepter.
Squadron can be preplant incorporated or applied preemergence. Incorporated applications are generally preferred, especially in fields with moderate to heavy infestations of annual grasses. Tri-Scept should always be incorporated.
Note the 11-month rotational restriction for corn. Although not widespread, some carryover to corn has been noted in North Carolina. Carryover has generally been confined to very sandy soils where Scepter, Squadron, or Tri- Scept was incorporated the previous year, where rainfall the previous growing season was below normal, and where soil pH was well below optimum levels. In light of the potential for carryover to corn, the 11-month restriction should be adhered to closely. Do not plant cotton or vegetables the year after applying Scepter, Squadron, or Tri-Scept.
Broadstrike + Dual and Broadstrike + Treflan. These packaged mixtures contain flumetsulam plus Dual or Treflan. Broadstrike + Dual can be preplant incorporated or applied preemergence; Broadstrike + Treflan can be preplant incorporated only.
In addition to the weeds normally controlled by Dual or Treflan, Broadstrike + Dual or Broadstrike + Treflan control a number of broadleaf weeds. Notable exceptions include hemp sesbania and giant ragweed. Broadstrike + Dual and Broadstrike + Treflan may not adequately control moderate to heavy infestations of cocklebur, common ragweed, and morningglory. Crop tolerance of Broadstrike + Dual and Broadstrike + Treflan appears to be good. There are significant rotational restrictions for both herbicides.
Postemergence Herbicides for Broadleaf Weeds
All common annual broadleaf weeds can be controlled with postemergence herbicides. However, weed species vary in their response to the different herbicides, and proper weed identification and herbicide selection are essential for satisfactory results.
In addition to proper herbicide selection, timeliness of application and proper application methods are essential. The most common cause of poor results with postemergence herbicides is application when the weeds have grown beyond the optimum size for treatment. As a general rule, postemergence broadleaf herbicides should be applied when weeds are in the two- to four-leaf stage or 2 to 3 inches tall. This normally occurs 2 to 3 weeks after planting.
Weather conditions are also important to the success of postemergence herbicides. For best results, weeds should be actively growing and not under moisture stress. When weeds are under moisture stress, they are tough and less herbicide is absorbed into the plant, resulting in less control.
Many of the postemergence broadleaf herbicides act through contact, meaning that there is little to no translocation or movement of the herbicide within the plant. Consequently, thorough spray coverage is necessary for good results. See Table 9 for recommended application pressures and volumes. Postemergence herbicides should be applied using either flat fan nozzles or hollow cone nozzles. Flood nozzles give poor spray coverage and should never be used to apply postemergence herbicides. Most postemergence herbicide labels also specify not to use CDA (controlled droplet applicator) sprayers. See specific labels for application directions.
Spray adjuvants are normally used with postemergence herbicides.
Basagran. Basagran gives excellent control of cocklebur, jimsonweed, and smartweed, and good control of prickly sida, spurred anoda, velvetleaf, and giant ragweed. Although control may be inconsistent, Basagran plus crop oil concentrate usually controls small common ragweed and lambsquarter. Crop tolerance is excellent.
Blazer. Blazer controls most broadleaf weeds. Exceptions include prickly sida, sicklepod, spurred anoda, velvetleaf, and volunteer cowpea.
Blazer normally causes some soybean leaf crinkling and leaf bronzing or leaf burn. Addition of crop oil concentrate or higher rates of surfactant increase the amount of leaf burn. This injury is temporary and the soybeans recover quickly and grow normally.
Basagran Plus Blazer, Storm. A tank mix of Basagran plus Blazer is a very effective, broad-spectrum treatment. Application of 1 pint of Basagran plus 1 pint of Blazer plus an adjuvant has proven to be acceptable in most situations. However, the rate of Basagran and Blazer can be increased to 2 pints and 1.5 pints per acre, respectively, if needed. The best rate of each herbicide to use in the tank mix depends upon the weed species and weed size; see the product labels for details.
Storm is a packaged mixture containing the active ingredients found in both Basagran and Blazer. Applying 1.5 pints of Storm is equivalent to applying 1 pint of Basagran plus 1 pint of Blazer. One pint per acre of crop oil concentrate is always recommended with Storm.
Classic. Classic will control many broadleaf weeds. Major exceptions are lambsquarter, prickly sida, and tropic croton. Control of spurred anoda and velvetleaf also may not be adequate. Classic may be tank-mixed with several other herbicides to expand the spectrum of control.
Soybean tolerance of Classic is normally good, but some leaf distortion and yellowing and minor crop stunting may be noted, especially when applied to soybeans under stress conditions. The soybeans usually recover and grow normally.
See Table 14 for rotational restrictions following Classic application. No documented cases of Classic carryover to agronomic crops have been observed in North Carolina. See the label for specific directions on sprayer cleanout.
Cobra. Cobra controls most annual broadleaf weeds. Major exceptions are lambsquarter, sicklepod, smartweed, and spurred anoda. Morningglory control often is inconsistent. Cobra applied at the full labeled rate (12.5 ounces per acre) usually causes moderate to severe soybean leaf burn. Although the soybeans usually recover and grow normally, the injury often is unacceptable to growers. For this reason, Cobra at the full labeled rate is generally not recommended. Several tank mixes containing Cobra at low rates (6 ounces per acre) are registered.
Pinnacle. Pinnacle controls lambsquarter, pigweed, smartweed, and velvetleaf. Because the spectrum of control is limited, Pinnacle is normally tank-mixed with another broadleaf herbicide to expand the range of species controlled. Carefully follow label directions for herbicide and adjuvant rates when applying tank mixes containing Pinnacle.
Reflex. Reflex controls most common broadleaf weeds. Major exceptions are prickly sida, sicklepod, spurred anoda, and velvetleaf. Unless treated when smaller than 1/2 inch, lambsquarter will not be controlled. Soybean tolerance of Reflex is normally good. Although the Reflex label mentions rotational restrictions, carryover to agronomic crops has not been observed in North Carolina.
Typhoon is a packaged mixture containing fomesafen and fluazifop (the active ingredients in Reflex and Fusilade, respectively). Typhoon at the recommended rate of 3.2 pints per acre is equivalent to 1.5 pints of Reflex and 12 ounces of Fusilade DX per acre.
Scepter. Scepter applied postemergence controls cocklebur and pigweed excellently. Control of other broadleaf weeds will be inadequate. See the section on sicklepod control.
Soybean tolerance of Scepter applied postemergence is excellent. See the most recent label for rotational restrictions.
Scepter O.T. Scepter O.T. is a packaged mixture of imazaquin and acifluorfen (the active ingredients in Scepter and Blazer, respectively). Applying 1 pint of Scepter O.T. per acre is equivalent to applying 1/3 pint of Scepter plus 1 pint of Blazer. Scepter O.T. gives excellent control of cocklebur and pigweed and will control other weeds normally controlled by 1 pint of Blazer.
Pursuit. Applied postemergence, Pursuit controls cocklebur, pigweed, jimsonweed, and smartweed. Morningglory control is usually acceptable but can be inconsistent.
Pursuit kills weeds very slowly, and it may take as long as 3 weeks to kill morningglory. In some cases, the weeds do not die completely but rather stop growing and the soybean canopy fills in above them. In addition to controlling certain broadleaf weeds, a postemergence application of Pursuit usually gives adequate control of broadleaf signalgrass, foxtails, seedling johnsongrass, and shattercane, and it sometimes gives adequate control of rhizome johnsongrass. Pursuit does not control common ragweed, lambsquarter, prickly sida, sicklepod, and certain other weeds.
Soybean tolerance of Pursuit is good. See Table 14 for rotational restrictions. Do not plant cotton or most vegetable crops the year following a Pursuit application.
Postemergence-Directed Herbicides for Broadleaf Weeds
Although not widely used in North Carolina, postemergence-directed herbicides are effective, economical tools for controlling late-emerging weeds or weeds that have escaped at-planting or early-season postemergence overtop herbicides. Directed applications are also very effective as a component of a sicklepod management program.
Herbicides and tank mixes labeled for postemergence-directed application to soybeans include Gramoxone Extra, Lexone, Lorox, 2,4-DB (Butyrac, Butoxone, and others), Lorox plus 2,4-DB, Sencor, and Sencor plus 2,4-DB. A surfactant should be added according to label directions to all of these herbicides and tank mixes except 2,4-DB applied alone.
For postemergence-directed treatments to be effective, the weeds must be shorter than the crop. The soybeans should be at least 8 inches tall (12 inches for Lexone) and the weeds should be 3 to 4 inches tall or less, depending upon the herbicide and application rate selected. Precision application is necessary to avoid unacceptable crop injury. The spray solution should contact no more than the lower 1/4 to 1/3 (or about 3 inches) of the soybean plant. Nozzles should be mounted in a manner that allows good control of the spraying height. Do not use booms with drop nozzles. Mount the nozzles on a cultivator frame or use a sliding shoe spray rig. Shielded sprayers are particularly effective. Use regular flat fan nozzles (or offset flat fan nozzles for banding) and a maximum pressure of 25 psi. For additional details, see Extension Service publication AG-259, Application of Directed Postemergence Herbicide in Cotton and Soybeans.
Depending on the herbicide chosen, directed sprays will control a broad spectrum of annual grasses and broadleaf weeds. 2,4-DB is effective on cocklebur and morningglory; treatment is suggested when weeds are 3 inches tall or less, although much larger weeds can be killed if spray coverage is good on the lower portion of the weeds. Gramoxone Extra controls pigweed and annual grasses up to 3 inches tall. Lexone or Sencor controls most species of broadleaf weeds up to 3 inches tall and annual grasses up to 1 inch tall. Lorox is effective on most annual broadleaf weeds and grasses up to 4 inches tall. A directed application of Lorox plus 2,4-DB has been very effective on a wide range of weed species in on-farm tests. For optimum yields, weeds must be controlled for the first 4 to 5 weeks after soybean planting. Weeds that emerge later have little direct effect on yield but may interfere with harvesting and add foreign matter to the harvested product.
Although you should strive for good early-season weed control, situations arise where a salvage treatment is necessary. Remember that salvage treatments are not a substitute for good early-season control.
2,4-DB (Butyrac, Butoxone, and others) can be applied over the top of soybeans at rates up to 1 pint per acre from 7 to 10 days before bloom up to mid-bloom. Application before or after this time period may result in severe crop injury. Application to soybeans under drought stress will also increase injury and reduce the chances of the crop recovering from the injury. This is a risky treatment and should be considered only as a salvage operation to remove cocklebur and morningglory when harvesting would otherwise be impossible.