NMSU: Managing Weeds in Alfalfa
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Authors: Respectively, Extension Weed Scientist/Assistant Professor, Department of Extension Plant Sciences; IR-4 Program Coordinator, Department of Extension Plant Sciences; Forage Agronomist, Agricultural Science Center at Tucumcari, all of New Mexico State University.

Managing weeds is a critical component of alfalfa production, and under New Mexico growing conditions, effective weed management will pay for itself if the market for alfalfa exists.

Weeds are plants that interfere with the management objectives for a particular crop or situation. Weeds negatively impact alfalfa production by competing for space, nutrients, sunlight, and moisture, and also play a major role in production of premium alfalfa, because they can reduce the quality of harvested alfalfa. Weeds affect alfalfa stands differently at the various stages of alfalfa production: prior to establishment, in the seedling stage and in established stands.

In establishing an alfalfa stand, it is critical that the field be free from perennial weeds. Weeds such as field bindweed, silverleaf nightshade, yellow nutsedge, and johnsongrass are extremely aggressive and will outcompete seedling alfalfa should the field be planted prior to their control. Taking time to manage any perennial weed prior to alfalfa establishment will pay for itself in reseeding costs or excessive weed control costs in the future.

During the seedling stage, weeds exert their greatest impact. If competition from weeds is high enough, it can cause failure of crop establishment. Light to moderate weed infestations can reduce alfalfa growth, which will delay production. In seedling alfalfa, weed type/pressure varies with the timing of seeding. In areas with mild winters, winter annual weeds may cause problems in alfalfa planted in late summer or early fall. However, weed control in New Mexico and the southern high plains is generally much easier to achieve in fall-planted alfalfa than in alfalfa planted in the spring.

In established stands of alfalfa, weeds reduce the quality of forage. A California study showed that in fields with high weed infestation forage protein content was as low as 9%. However, when the weeds were controlled alfalfa protein content increased to over 20%. The vigor of an established stand depends on how well the weeds were managed during the previous stages of production. Once a healthy alfalfa stand is established, problems associated with weeds lessen because the alfalfa becomes much more competitive. Weeds can become a problem in established stands because of factors such as poor soil fertility, improper irrigation and/or harvest management, disease and insect pressures, and other practices. Aside from standard crop rotation practices, growers report that weeds are the main reason many fields are taken out of production.

Principles of Weed Management

Weed Identification

Developing a management plan requires that growers first properly indentify the weeds. Weeds typically found in alfalfa fields are divided into three major classes: broadleaves, grasses, and sedges. Broadleaves usually have a taproot system, two cotyledons (embryonic leaves), and netted veins on the leaves. Grasses usually have a fibrous root system, a single cotyledon, and leaves with parallel veins. Sedges are often confused with grasses, but unlike grasses they have stems that are triangular in cross-section.

Weeds in each of these classes are also grouped according to their life cycles. Annual weeds, either winter or summer, complete their life cycles in one year. Winter annuals germinate in the fall and complete their life cycles the following spring, while summer annuals germinate in the spring and complete their life cycles in the fall. Biennial weeds such as musk thistle complete their life cycles in two years. Annual and biennial weeds spread through seed production only, so the key to effective management is to not let them set seed. Perennial weeds are capable of coming back year after year because they have vegetative reproductive structures such as rhizomes, stolons, or underground roots with adventitious buds, crowns, or tubers.

Perennials are difficult to manage because, in most cases, management plans have to deal with both vegetative reproduction and seed production. There are two groups of perennials: simple perennials and creeping perennials. Simple perennials such as common mallow and dandelion spread only by seed and have no normal means of spreading vegetatively. However, if the roots of some species are cut or broken, each piece could send out roots and stems to form a new plant. Creeping perennials, such as bindweed or johnsongrass, may reproduce not only by seeds but also by creeping roots, creeping aboveground stems (stolons), or creeping underground stems (rhizomes). Some of the more common weeds found in New Mexico alfalfa fields during different stages of alfalfa production are listed in Table 1.

Table 1. Some of the Common Weeds Associated with the Different Stages of Alfalfa Production

Common name prior to establishment

Scientific name Class Life cycle*
Bermudagrass Cynodon dactylon Grass CP
Field bindweed Convolvulus arvensis Broadleaf CP
Johnsongrass Sorghum halepense Grass CP
Purple nutsedge Cyperus rotundus Sedge CP
Silverleaf nightshade Solanum elaeagnifolium Broadleaf CP
Texas blueweed Helianthus ciliaris Broadleaf CP
Yellow nutsedge Cyperus esculentus Sedge CP
Fall-seeded seedling alfalfa
Downy brome (cheatgrass) Bromus tectorum Grass WA
Flixweed Descurainia sophia Broadleaf WA
London rocket Sisymbrium irio Broadleaf WA
Rescuegrass Bromus catharticus Grass WA
Shepherdspurse Capsella bursa-pastoris Broadleaf WA
Tansymustard Descurainia pinnata Broadleaf WA
Spring-seeded seedling alfalfa
Dodder Cuscuta spp. Broadleaf SA
Green foxtail Setaria viridis Grass SA
Kochia Kochia scoparia Broadleaf SA
Pigweed species Amaranthus spp. Broadleaf SA
Russian thistle Salsola iberica Broadleaf SA
Sandbur (grassbur) Cenchrus spp. Grass SA
Yellow foxtail Setaria glauca Grass SA
Yellow nutsedge Cyperus esculentus Sedge SA
Established alfalfa stands
Bermudagrass Cynodon dactylon Grass CP
Common mallow Malva neglecta Broadleaf SP
Dandelion Taraxacum officinale Broadleaf SP
Dodder Cuscuta spp. Broadleaf SA
Downy brome (cheatgrass) Bromus tectorum Grass WA
Flixweed Descurainia sophia Broadleaf WA
Green foxtail Setaria viridis Grass SA
Johnsongrass Sorghum halepense Grass CP
Kochia Kochia scoparia Broadleaf SA
London rocket Sisymbrium irio Broadleaf WA
Pigweed species Amaranthus spp. Broadleaf SA
Plantain Plantago spp. Broadleaf SP
Purple nutsedge Cyperus rotundus Sedge CP
Rescuegrass Bromus catharticus Grass WA
Russian thistle Salsola iberica Grass SA
Shepherdspurse Capsella bursa-pastoris Broadleaf WA
Tansymustard Descurainia pinnata Broadleaf WA
Whorled milkweed Asclepias spp. Broadleaf CP
Yellow foxtail Setaria glauca Grass SA
Yellow nutsedge Cyperus esculentus Sedge CP
*WA = Winter annual, B = Biennial, SP = Simple perennial, SA = Summer annual and CP = Creeping perennial

Management Options

Successful weed management requires an integrated approach that includes multiple strategies. There are four general weed management strategies used in alfalfa: (1) preventive, (2) mechanical, (3) cultural and (4) chemical management. Sustainable weed control requires a system that integrates these management strategies. The following will provide a basis for consideration.

Preventive weed management

The most important part of integrated weed management is preventive management. Growers can prevent weeds from getting into the field. Strategies such as managing weeds in the fencerow or along ditches, controlling weeds before they set seeds, planting certified seed, and taking time to remove weeds from harvesting equipment when going from field to field reduce the potential spread of weeds such as field bindweed, johnsongrass, sandbur, and other troublesome weeds.

Cultural weed management

The central theme of cultural weed management is giving alfalfa the competitive edge against weeds. Begin by ensuring the field is free of any major weed problems before planting. Planting certified seed and varieties suited for the area are two other ways the grower can improve chances of good establishment. Maintaining proper field fertility and managing any disease or insect problem also helps alfalfa establishment prior to weeds. When using flood irrigation, growers can give alfalfa a competitive edge by knowing when to turn the water off. By not overwatering, growers reduce ponding, which drowns alfalfa and favors weed invasion. If irrigation occurs soon after cutting alfalfa, the added moisture can favor summer annual grasses because there will not be enough regrowth from the alfalfa to shade out the competing grasses. Irrigating prior to cutting, then harvesting the alfalfa as soon as possible allows the alfalfa to be more competitive. Although ideal in some ways, this is not always possible due to irrigation schedules. Proper harvest management (particularly during the last cutting of the season) allows alfalfa plants to store root energy prior to harvesting and, therefore, helps maintain a dense and healthy alfalfa stand.

Mechanical weed management

Although quite effective in row crop production, mechanical weed management offers little help in managing weeds in alfalfa. Fields heavily infested with winter annual mustards often are cut prematurely to eliminate the mustards. However, the mustards produce lateral branches from below the cut stem, produce new flowers, and go to seed anyway.

Chemical weed management

Growers may opt to use herbicides to manage weeds. A list of currently registered herbicides for alfalfa in New Mexico and some information regarding their usage is given in Table 2. Be sure to read and understand the label before using the product. Pay particular attention to information such as timing of application, rates of application, types of weeds controlled, harvest or grazing restrictions, and rotation restrictions. Many times, an herbicide's poor performance or nonperformance can be traced to improper use and failure to follow label directions.

Table 2. List of Herbicides Registered for Use on Alfalfa in New Mexico (2008)a b

Common name Example of trade namec Weed Timing
Grass Broadleaf Prior to establishment Seedling Established
Benefin Balan DF Yes Yes Yes No No
Bromoxynil Buctril No Yes No Yes No
Buctril 4EC
2,4-DB Amine Butoxone 200 No Yes No Yes Yes
Butoxone 7500
Butyrac 200
Clethodim Select 2E Yes No No Yes Yes
Diuron Karmex DF Yes Yes No No Yes
EPTC Eptam 7E Yes Yes Yes Yes Yes
Flumioxazin Chateau Yes Yes No No Yes
Glyphosate Roundup Yes Yes Yes No No
Hexazinone Velpar DF, L Yes Yes No No Yes
Imazamox Raptor Yes Yes No Yes Yes
Imazethapyr Pursuit 2S Yes Yes No Yes Yes
Pursuit DF
Metribuzin Lexone DF Yes Yes No No Yes
Sencor 4F, DF
Metam-Potassium K-PAM HL Yes Yes Yes No No
Metam-Sodium Metam CLR 42% Yes Yes Yes No No
MCPA MCP Amine 4 No Yes No No Yes
Norflurazon Solicam DF Yes Yes No No Yes
Paraquat Gramoxone Extra Yes Yes Yes No Yes
Pelargonic acid Scythe Yes Yes Yes No Yes
Pendimethalin Prowl H2O Yes Yes No Yes Yes
Pronamide Kerb 50W Yes Yes No Yes Yes
Pyraflufen-ethyl ET Herbicide No Yes Yes No No
Sethoxydim Poast Yes No No Yes Yes
Poast Plus
Terbacil Sinbar Yes Yes No No Yes
Trifluralin Treflan 4EC, MTF Yes Yes No Yes Yes
Treflan 5
Treflan TR–10
Trilin 4EC, 10–G
TRI–4 EC, DF
a Note Table 3
b The list is current as of December 2008; however, labels change frequently, and the herbicide's current label should be reviewed for the most recent conditions or restrictions before it is used. Read all labels carefully and comply with their site-use directions. For the very latest label information on a given herbicide, contact the manufacturer, Extension services in your area, or the company or distributor that sells the product.
cOther trade names of the above mentioned active ingredients alone or in combination may be available in the market. (Notice: Mention of herbicide trade names does not constitute endorsement of any material).

When using chemical control, growers need to be advised that repetitive usage of a single herbicide or of a particular herbicide family with the same site of action could select for herbicide-resistant weed biotypes. Therefore, make sure to rotate herbicides with different sites of action and do not make more than two consecutive applications of herbicides with the same site of action against the same weed. If possible, combine herbicides based on the label direction. Mixing two or more herbicides can delay/prevent the development of herbicide resistance in weeds and dramatically increase the spectrum of weed control, since no single herbicide controls all weeds commonly found in alfalfa.

If you have been relying on one particular herbicide for several years and notice that some weed species that were effectively controlled in past seasons are now abundant, or that some species are now present that you have not dealt with before, this could be an indication that a herbicide-resistant biotype or a shift in weed species has developed.


The following information on herbicides can help producers develop an effective alfalfa weed management program. Most chemical labels can be accessed at either http://www.greenbook.net or http://cdms.net.

Herbicide
Common Name
Example of Trade name Timing Rates of application
Benefin Balan DF Incorporate pre-plant 2.0–2.5 lb Balan DF/acre
Comments: A pre-plant herbicide that must be incorporated within 4 hours following application if the soilis moist, and within 8 hours under dry soil conditions. This herbicide will not control mustard species but can be effective on small-seeded broadleaf weeds and annual grasses.
 
Bromoxynil
Buctril Post-emergence 1.0–1.5 pt Buctril/acre
Buctril 4EC 0.5–0.75 pt Buctril 4EC/acre
Comments: Buctril and Buctril 4EC are labeled only for seedling alfalfa. Make applications after the alfalfa has at least four trifoliate leaves. Applications made when temperature is expected to exceed 80°F at and 3 days following application can result in unacceptable crop injury. Be sure to read the label for harvest and crop rotation restrictions. Studies have shown that this herbicide is not very effective when applied alone, but control is improved when it is tank-mixed with 2,4–DB Amine.
 
Clethodim Select 2E Post-emergence 6-8 Fl oz. Select 2E/acre
Comments: Clethodim is a grass herbicide with no activity on broadleaf weeds that may be applied to seedling and established stands of alfalfa. Always add a crop oil concentrate at 1.0% v/v to final spray solution. Do not apply within 15 days of grazing, feeding, or harvesting alfalfa for forage or hay. Select offers control of several winter annual Bromus species as well as sandbur and the summer annual foxtails.
 
2,4–DB Amine Butoxone 200 Post-emergence 4.0–6.0 pt Butoxone 200/acre
Butoxone 7500 1.33–2.0 pt Butoxone 7500/acre
Butyrac 200 2.0–6.0 pt Butyrac 200/acre

Comments: 2,4-DB Amine is a "Restricted Use Pesticide," so the applicator is required to be certified. Some broadleaf crops such as cotton are as sensitive to 2,4-DB Amine as many weeds, and only a trace of the chemical as spray drift, vapor drift or contaminant in soil or water may cause serious damage. Thus, follow label precautions carefully to minimize the possible unwanted crop injuries.
      In seedling alfalfa: Apply in spring or fall when seedling alfalfa has at least two trifoliate leaves and weeds are less than 3 inches tall. Do not graze treated fields for 60 days following application.
       In established stands: Certain winter annual mustards are better controlled using a late fall/early winter treatment. The grazing restriction for treated fields is 30 days.
      Do not apply this herbicide if daytime temperature is expected to exceed 90°F or drop below 40°F within the 2 or 3 days following application. Field research in New Mexico showed this to be an inconsistent treatment; sometimes it works and other times it doesn't appear to provide any control. In seedling stands, the addition of bromoxynil has improved 2,4DB Amine's efficiency, but erratic results still are observed.

 
Diuron Karmex 80DF Pre/Post-emergence 1.5–3.0 lb Karmex 80DF/acre
Comments: While there is some post-emergence activity with this herbicide, uptake from the soil by susceptible plants is the main mechanism for activity. Uptake requires some form of incorporation, usually irrigation or rainfall, within 2 weeks of application. Studies have shown that if the incorporation occurs sooner than 2 weeks post-application, control improves. The strength of this herbicide is its mustard control, for which applications must be made following the alfalfa's fall dormancy and before regrowth occurs in the spring. Do not make applications to frozen ground. Be sure to read all crop rotation restrictions on the label.
 
EPTC Eptam 7E Incorporate pre-plant 3.5–4.5 pt Eptam 7E/acre (seedling alfalfa)
Pre-emergence 2.25–3.5 pt Eptam 7E/acre (established stands)
Comments: As a pre-plant-incorporated treatment, it is important to incorporate 3–4 inches deep immediately following the application. In established stands, the herbicide is usually applied by chemigation. The strength of this herbicide is its activity on yellow and purple nutsedge.
 
Flumioxazin Chateau Pre/Post-emergence 0.25–10 oz. Chateau/acre
Comments: While there is some post-emergence activity with this herbicide, weeds mainly are controlled by residual activity of Chateau. Applications should be made as soon as possible after cutting and removing alfalfa to minimize injury to alfalfa regrowth. Chateau may be applied to established alfalfa with a maximum amount of regrowth of 6 inches or less for the pre-emergence control of the weeds. Application to alfalfa with greater than 6 inches of regrowth may result in unacceptable crop injury.
 
Glyphosate Roundup 4S Post-emergence 4 pt Roundup 4S/acre
Comments: In conventional alfalfa, this herbicide is for site preparation and spot treatment only. Glyphosate is a nonselective herbicide, so any alfalfa that comes in contact with it will be killed or severely damaged. Application rates depend on the weed species. Adding a surfactant and nitrogen fertilizer improves efficacy, as does reducing the total sprayer output volume to about 10 gal/acre of total spray solution.
      In Roundup Ready alfalfa, glyphosate can be applied at any stage of alfalfa production based on the label direction. However, in order to prevent or delay the occurrence of herbicide-resistant weed species, and control the glyphosate tolerant weed species, it is recommended to apply glyphosate in a mixture with other registered alfalfa herbicides, such as Pursuit, based on the label direction.
 
Hexazinone Velpar DF Pre/Post-emergence 1/3–2.0 lb Velpar DF/acre
Velpar L 1.0–6.0 pt Velpar L/acre
Comments: Application rates are based on soil type and organic matter content. Make applications to wellestablished stands in the fall after the onset of dormancy and before the field begins regrowth in the spring. Do not make applications to frozen ground. Moisture is necessary within 2 weeks after application to activate the herbicide in the soil. Do not graze for 28 days after application. Be sure to observe all crop rotation restrictions on the label.
      Field studies have shown that at low application rates, this herbicide will not only control winter annual mustards, but also provides partial to complete control of winter annual grasses. At higher rates, residual control of some weed species may continue into summer and fall. Hexazinone is also available in mixture with Diuron (e.g., VELPAR ALFAMAX).
 
Imazamox Raptor Post-emergence 4.0–6.0 fl oz Raptor/acre
Comments: Apply Raptor when the majority of weeds are 1–3 inches tall. In seedling alfalfa Raptor should be applied when seedling alfalfa is in the second (2nd) trifoliate stage or larger. In established stands, raptor can be applied in the fall, winter or spring to dormant or semi-dormant alfalfa or between cuttings. Any application should be made before significant alfalfa growth or regrowth (3 inches) to allow Raptor to reach the target weeds.
      Do not make sequential application of Pursuit herbicide followed by Raptor (or Raptor followed by Pursuit) within a 60-day timeframe due to increased potential alfalfa crop response.
 
Imazethapyr Pursuit 2S Post-emergence 3.0–6.0 fl oz Pursuit 2S/acre
Comments: The key to obtaining good weed control with Pursuit is applying the product to small weeds. Applications can be made to seedling stands when alfalfa has at least two trifoliate leaves and when the majority of the weeds are 1–3 inches tall. With established stands, applications need to be made in accordance to the weed size. The standard rate of 4 fl oz/acre has shown outstanding control of winter annual mustards. This product also can provide extended control of annual grasses and mixes well with clethodim and sethoxydim.
    When using Pursuit, remember:
  • It is critical that an adjuvant, either a surfactant or a crop oil concentrate, be added to the spray mixture according to the label directions.
  • Studies have shown that adding a liquid fertilizer solution (such as 28% N, 32% N or 10-34-0) improves the product's performance. Apply 1–2 qt/acre.
  • The following cropping rotations apply to the use of Pursuit:
        Peanuts      Anytime       Wheat        4 months      Field corn      8.5 months
        Cotton       18 months    Lettuce      8 months      Chile              40 months
These rotation restrictions frequently change, so be sure to check the most current label for any adjustments.
 
Metribuzin Lexone 75DF Pre/Post-emergence 0.5–1.33 lb Lexone 75DF/acre
Sencor 4F 0.75–2.0 pt Sencor 4F/acre
Sencor 75DF 0.5–1.3 lb Sencor 75DF/acre
Comments: Make a single application in the fall to well-established alfalfa stands following the beginning of dormancy and before regrowth begins in the spring. To become activated, the herbicide requires moisture within 2 weeks after application. Do not use on soils with a pH greater than 7.5. The labeled grazing restriction is 28 days.
 
Metam-Potassium K-PAM HL Incorporate pre-plant 30–60 gallons/acre
Metam-Sodium Metam CLR 42% Incorporate pre-plant 15–74.5 gallons/acre
Comments: K-PAM HL and Metam CLR 42% are soil fumigants for control of several weed species, soilborn fungi, nematodes and insects. These products are applied following harvest of the previous crop and 14 to 21 days before alfalfa is planted. In some locations, fall application is preferred as the products will dissipate over the winter, which allows planting in favorable springtime conditions. These products will suppress or control pests that are in the fumigated zone at time of treatment; however, application rates will vary depending on the soil texture and the depth of treatments.
 
MCPA MCP AMINE 4 Post-emergence 1 pt MCP AMINE 4/acre
Comments: MCPA is registered for broadleaf weed control in alfalfa and should be applied in late fall following frosts when alfalfa is dormant.
 
Norflurazon Solicam DF Pre-emergence 1.25-2.5 lb. Solicam DF/acre
Comments: Rates of application are based on soil texture. Do not apply to alfalfa less than 5 months old. On young alfalfa, apply no more than 1.25 lb of product the first time, with a second application of 1.25 lb later in the year if needed. Incorporation is necessary to activate this pre-emergence herbicide, either through rainfall, irrigation, or tillage. Rotation restriction: Only cotton, soybeans, peanuts, and asparagus may be planted in fields previously treated with Solicam DF, with peanuts showing a greater sensitivity to the herbicide. Solicam DF may be tank-mixed with several of the registered alfalfa herbicides.
 
Paraquat Gramoxone Extra Post-emergence Application-dependent rates
Comments: Paraquat is a "Restricted Use Pesticide," so the applicator is required to be certified. Paraquat can be used at two times:
      1- Before planting or emergence of alfalfa, but after weeds emerge: Apply after weeds have emerged, but before seedling alfalfa has emerged. This herbicide will kill any emerged alfalfa. Application rates of 2.0–3.0 pt of Gramoxone Extra plus surfactant must be applied in 20 gal of water per acre. If applied by air, reduce the spray solution to 3 gal/acre of total spray mix. This application will control emerged annual weeds and burn off emerged perennial weeds. Do not allow grazing on treated areas.
      2- Between cuttings: Apply 12.8 fl oz of Gramoxone Extra plus surfactant in 20 gal of water per acre. Applications must be made within 5 days following alfalfa cutting. If seedling stands are allowed to regrow more than 2 inches before application, the application will injure the stand but will not likely kill the plants. In first-year alfalfa, make no more than two applications; established stands can tolerate up to three applications in one year. Do not apply by air. A harvesting restriction of 30 days is associated with the use of this herbicide.
 
Pelargonic acid Scythe Post-emergence Application-dependent rates 3–10%
Comments: Pelargonic acid is a contact, non-selective, broad-spectrum herbicide that can be used for burndown before planting or emergence of alfalfa, but after weeds emerge, and between cuttings but before regrowth. This herbicide will damage emerged or green alfalfa.
      For best control or burndown use the indicated rate of this product in 75 to 200 gallons of spray solution per acre through boom, hand-held or high volume equipment. Use 3–5% solution for annual weeds and vegetation, 5–7% solution for perennial herbaceous and late stage annuals, and 7–10% for maximum vegetation burndown.
 
Pendimethalin Prowl H2O Pre-emergence 1.0–4.0 qt Prowl H2O/acre
Comments: Apply to established alfalfa grown for forage/hay. For seedling alfalfa, Pendimethalin can be applied at 1 to 2 pints per acre, once alfalfa has reached the 2nd trifoliate stage of development, but prior to reaching 6 inches in growth. In established alfalfa, pendimethalin can be applied: 1) in the fall after the last cutting, 2) during the winter dormancy, 3) in the spring or between cuttings, but before the alfalfa reaches 6 inches in regrowth. Application made after the alfalfa exceeds 6 inches in height may result in poor weed control. Do not apply this product less than 50 days prior to harvest for forage or hay.
     For optimum dodder control the highest labeled rate should be used. Be sure to read the label for harvest and crop rotation restrictions.
 
Pronamide Kerb 50W Pre/Post-emergence 1.0–4.0 lb Kerb 50–W/acre
Comments: Pronamide is a "Restricted Use Pesticide," so the applicator is required to be certified. Application rates depend on the weed species to be controlled and whether there is furrow or overhead irrigation. Apply during the fall or winter months before the soil freezes. Optimum herbicidal activity is achieved when applications are made at air temperatures 55°F or lower and are followed by water incorporation. In seedling alfalfa, do not apply this product before the trifoliate leaf stage. Field studies conducted in the state have not shown this option to be very effective or consistent. Be sure to observe all restrictions on the label.
 
Pyraflufen-ethyl ET Herbicide Pre-Plant burndown 0.5–2.0 fl oz ET Herbicide/acre
Comments: Pyraflufen-ethyl must be applied at least 30 days prior to planting for contact (burndown) broadleaf weed control. For best results use this product for control of annual or perennial herbaceous broadleaf weeds less than 4 inches in height, or rosettes less than 3 inches in diameter. Addition of a crop oil concentrate or nonionic surfactant is recommended for optimum control.
 
Sethoxydim Poast 1.5 E Post-emergence 1.5–2.5 pt Poast/acre
Poast Plus 1.0 E 1.5–3.75 pt Poast Plus/acre
Comments: Sethoxydim controls only grass weeds. Application rates are based upon the grass species to be controlled and the county and state in which you live. The addition of a crop oil concentrate is critical. The addition of UAN solution or ammonium sulfate also improves control. Ground applications must be made with equipment calibrated to deliver at the rate of 10 gal/acre of total spray solution. Applications are most effective to young, actively growing weeds, so growers may need to irrigate before making the application.
 
Terbacil Sinbar 80W Pre/Post-emergence 0.5–1.5 lb Sinbar/acre
Comments: Apply to well-established stands in the fall after the beginning of dormancy and before the field begins regrowth in the spring. Do not make applications to frozen ground. To become active, the herbicide requires moisture within 2 weeks after application. There is no grazing restriction with the use of this herbicide. Be sure to observe all crop rotation restrictions on the label.
     Low application rates have proven effective when applied to young, actively growing winter annual mustards.
 
Trifluralin Treflan 4EC, MTF Pre-emergence 1.5–4.0 pt Treflan 4EC/acre
Treflan 5 1.2–3.2 pt Treflan 5/acre
Treflan TR-10 20 lb Treflan TR-10/acre
Trilin 4EC 1.5–2.0 pt Trilin 4EC/acre
Trilin 10-G 20 lb Trilin 10-G/acre
TRI-4 EC 1.5–2.0 pt TRI-4 EC/acre
TRI-4 DF 1.4–1.66 lb TRI-4 DF/acre
Comments: When considering the use of trifluralin, be sure to read the label: certain formulations can be water incorporated, while others must be incorporated using "incorporation equipment that will ensure thorough soil mixing with a minimum of damage to established alfalfa." Use of the granular formulations, Treflan TR-10 and Trilin 10-G, requires specific application equipment and an incorporation requirement of 3 days following application. Use of Treflan 4EC, MTF, and Treflan 5 includes an option for "surface application which is activated by rainfall or irrigation," in which higher rates can be applied in the fall for control of winter annual grasses. Such applications must be made between August 1 and October 1. Observe a 21- day grazing restriction.
     According to its label, two applications of Treflan TR-10 at the rate of 20 lb Treflan TR-10/acre can be used to control dodder. The first application must be made in the spring prior to weed germination. The second application should be made 60 days following the first, or after at least two cutting cycles. Applications can be made both with ground and aerial application equipment. Incorporate within 3 days after application.
     When considering the use of an herbicide, nothing can take the place of reading the label and making applications according to label directions. Pay attention to label information on controlled weed species, timing of application, rates of application, and methods of incorporation. Also note other directions such as worker protection standards, requirements for personal protective equipment (PPE), restricted entry interval (REI), storage and disposal and sprayer cleanup.


Critical reviews of this article by Dr. Brent Bean, Dr. Calvin Trostle and Mr. Richard N. Arnold are acknowledged.


Original authors: Richard D. Lee, former Extension weed scientist; R. Darrell Baker, former Extension agronomist; and Shane T. Ball, former Extension Agronomy Specialist.


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Revised and electronically distributed April 2009, Las Cruces, NM.