Weed Control

Glyphosate (Roundup PowerMax, Durango DMA, Touchdown Total, etc.) provides a means of controlling quackgrass before forage establishment. Because spring seedings should be made before quackgrass reaches the four- to five-leaf stage, the recommended stage of development for treatment with glyphosate, fall applications are encouraged to control quackgrass and other perennial grasses before making spring seedings.

Fall applications of glyphosate are recommended between October 1 and November 15. Glyphosate should not be applied, however, if the average daily air temperature has dropped below 55°F for a seven-day period before application (glyphosate works best if soil temperature is 65° to 75°F). Spring applications can be made before late spring or summer seedings. Because glyphosate will not control weeds that germinate after application, this treatment should be used in combination with other weed control measures.

Scouting new legume seedings for weeds should be done shortly after the seeding emerges because herbicides for annual broadleaf weeds must be applied when the legume is 1 to 3 inches tall and weeds have two to four true leaves. In established hayfields scouting can be done at the time of each harvest. This should provide adequate information for decisions on dormant or between-cuttings herbicide applications.

Though it is relatively easy to show the value of herbicides during legume establishment, it is more difficult to deter-mine their value in established stands. To be economical, herbicide applications on established legumes must control the weeds, and the stand must have the potential for increased legume yields. If the legume stand is so poor that total forage yields decline when the weeds and/or grasses are controlled, the economics are questionable.

In a good stand, the removal of weed competition should increase the quantity and quality of the forage produced. Although the potential of a legume stand is difficult to evaluate, it is suggested that clear stands should have a minimum of five healthy crowns per square foot to justify herbicide application. Because grasses are sensitive to many of the herbicides available for use in established legumes, the guidelines given in Table 4.11.1 are for clear stands; in some cases, label restrictions limit their use to clear alfalfa.

Roughstalk bluegrass is a perennial, cool season grass that heads in May and early June and then goes dormant in summer. This weedy grass is a problem in established alfalfa because it matures prior to first cutting harvest and the mature, somewhat woody stems of the bluegrass reduce palatability and quality of first cutting dry hay. Its presence in alfalfa that is harvested and preserved as haylage is perhaps of less concern than in dry hay.  Research results show that seeding a perennial forage grass with alfalfa suppresses bluegrass and probably other weeds. The results show that the recommended seeding rate (4 – 6 lb. of seed per acre) for timothy or orchardgrass is adequate for this purpose.

Herbicide Resistance Management

Herbicide resistance management involves the use of crop rotation and cultivation along with herbicide rotation and/or use of herbicide combinations that include herbicides with different sites of action (how they affect weeds). These practices will help manage existing herbicide resistant weed populations and delay development of new resistant weed populations.

To effectively utilize herbicides with different sites of action, everyone involved in decisions about weed management must have site of action classification readily available. The Weed Science Society of America (WSSA) has approved a numbering system to classify herbicides by their site of action (Mallory-Smith, C.A. and Retzinger, E.J. 2003. Revised classification of herbicides by site of action for weed resistance management strategies. Weed Technol. 17:605-619). A group number is given to all herbicides with the same site of action. These “GROUP NUMBERS” are included in the “Chemical weed control tables” in each crop section. Since herbicide resistance management is most effective when practiced across all crops in rotation, a list of all herbicides in this guide with their “GROUP NUMBERS”  and mode of action/site of action and chemical families for site of action GROUPS can be found in the tables below.

Table 4.11.1. Chemical weed control in forage crops.

Situation

Amount of Product(s) per Acre

Remarks and Limitations

Legume seedings without small grain companion crop

Quackgrass

22-44 fl. oz. Roundup PowerMax

or 24-48 fl. oz. Durango DMA

GROUP 9 HERBICIDES• Apply these or other glyphosate products as preplant foliar sprays in the fall or spring when quackgrass is at least 8 in. tall (4- to 5-leaf stage) and actively growing. Fall applications should not be made in fields that have been tilled during the summer or mowed after August 15. Delay tillage for at least 3 days after spraying. Will not control weeds germinating after application. The low rates may not provide long-term quackgrass control. Labels include all forage grasses and forage legumes. Do not graze or harvest forage within 8 weeks after application.

Nutsedge, annual grasses, and broadleaf weeds

3.5–4.5 pt. Eptam

7-E

GROUP 8 HERBICIDE Preplant only. Apply to a dry soil surface and incorporate immediately. Will not control wild mustard, wild radish, or ragweed.

Annual grasses and broadleaf weeds

4 oz. *†Pursuit
or 5 oz. Raptor

GROUP 2 HERBICIDES• Apply postemergence when seedling alfalfa is in the second trifoliolate stage or larger and when weeds are 1-3 in. tall. Use crop oil concentrate or nonionic surfactant and add 1-2 qt./A of liquid fertilizer to spray solution. Add 1-2 pt. Butyrac 200 if ragweed or lambsquarters are a problem.

 

2–2.5 lb. Balan DF

GROUP 3 HERBICIDES• Apply preplant and incorporate within 8 hr. Use 2 lb. on coarse and medium soils and 2-1/2 lb. on fine soils. Will not control quackgrass, nutsedge, wild mustard, wild radish, and ragweed.

Annual grasses

1.5 pt. Poast Plus

GROUP 1 HERBICIDE• Labeled for alfalfa only. Apply when annual grasses are 2–4 in. tall. Add 1 qt./A of an oil concentrate-surfactant blend. Do not apply Poast Plus within 7 days of grazing, feeding, or cutting for undried forage, or within 14 days of cutting alfalfa for dry hay.

 

9-16 fl. oz. *Select Max

GROUP 1 HERBICIDE• Apply when annual grasses are 2–4 in. tall. Add adjuvants according to label instructions. Do not apply *Select Max within 15 days of grazing, feeding, or harvesting (cutting) alfalfa for forage or hay.

Annual broadleaf weeds

1-1.5 pt. of 2 lb./gal. Bromoxynil

GROUP 6 HERBICIDE• Labeled for alfalfa only. Apply when alfalfa has a minimum of 4 trifoliolate leaves. Weeds should not exceed the 4-leaf stage or 2 in. in height, whichever comes first, or apply before rosettes are 1 in. in diameter. Applications should not be made when temperatures exceed 70° F at, and 3 days following application. Do not cut alfalfa for feed or graze within 30 days following treatment.

 

2 qt. Butyrac 200

GROUP 4 HERBICIDE• Apply postemergence when weeds are no more than 2–3 in. high or rosettes are less than 2 in. across. Will not control wild radish. Do not graze or feed seedling alfalfa, clover, or birdsfoot trefoil within 60 days after application. There is no preharvest interval for haylage or dry hay; however, harvested forage should not be fed within 60 days after application.

Annual grasses and broadleaf weeds in Roundup Ready Alfalfa

22-44 fl. oz. Roundup PowerMax

GROUP 9 HERBICIDE• For use with Roundup Ready alfalfa only. Apply 22 to 44 fl. oz. up to 4 trifoliolate leaves. Apply up to 44 fl. oz. from 5 trifoliolate leaves up to 5 days before first cutting. Up to 10 percent of the alfalfa seedlings might not contain the Roundup Ready gene and will not survive after the first application of this product.

Legume seedings with small grain companion crop

Quackgrass

22-44 fl. oz. Roundup PowerMax
or 24-48 fl. oz. Durango DMA

GROUP 9 HERBICIDES• Apply these or other glyphosate products as preplant foliar sprays in the fall or spring when quackgrass is at least 8 in. tall (4- to 5-leaf stage) and actively growing. Fall applications should not be made in fields that have been tilled during the summer or mowed after August 15. Delay tillage for at least 3 days after spraying. Will not control weeds germinating after application. The low rates may not provide long-term quackgrass control. Labels include all forage grasses and forage legumes. Do not graze or harvest forage within 8 weeks after application.

Nutsedge and annual grasses

__

No herbicides currently available

Annual broadleaf weeds

1 pt. of 2 lb./gal. Bromoxynil

GROUP 6 HERBICIDE• Labeled for alfalfa only. Apply when alfalfa has a minimum of 4 trifoliolate leaves. Weeds should not exceed the 4-leaf stage or 2 in. in height, whichever comes first, or apply before rosettes are 1 in. in diameter. Applications should not be made when temperatures exceed 70° F at and 3 days following application. Do not cut for feed or graze within 30 days following treatment.

 

1/4-1/2 pt. *MCP Amine 4

or 1/2 pt. MCPA-4 Amine

GROUP 4 HERBICIDES Recommended for red clover seedings only. Small grain should form a protective canopy over the red clover seedlings. Do not use more than 6 gallons of water per acre unless injury can be tolerated; higher spray volumes may injure red clover.

Established alfalfa

Chickweed, henbit, yellow rocket, and other broadleaf weeds

4-6 oz. *†Pursuit

GROUP 2 HERBICIDE• Apply in fall or spring to dormant, or semi-dormant alfalfa, or between cuttings before 3 in. of growth or regrowth. Will reduce growth and competitive effect of perennial grasses such as bluegrass, orchardgrass, and timothy.

Chickweed, bluegrass1, and other annual grasses and broadleaf weeds

2-3 pt. *Gramoxone SL 2.0

GROUP 22 HERBICIDE• Apply to established (at least 1 yr. old) alfalfa stands in the spring before new alfalfa growth starts. Add a nonionic surfactant to spray tank. Do not cut or harvest within 42 days of application.

1 pt. *Gramoxone SL 2.0

GROUP 22 HERBICIDE• Apply to alfalfa stands within 5 days after cutting. Add a nonionic surfactant to spray tank. Do not cut or harvest within 30 days of application.

Grass and broadleaf weeds in Roundup Ready alfalfa

22-44 fl.oz. Roundup PowerMax

GROUP 9 HERBICIDE• For use in Roundup Ready alfalfa only. Apply up to 44 fl. oz. per cutting up mto 5 days before cutting.

Sorghum or sorghum-sudangrass hybrids

Nutsedge and annual grasses

__

No herbicides currently available

Broadleaf weeds

2 qt. *†AAtrex 4L

or 2 qt. *†Atrazine 4L

GROUP 5 HERBICIDE• Apply after sorghum or hybrid has completely emerged and weeds are less than 1-1/2 in. tall. Do not apply to straight sudangrass. Do not graze or feed forage from treated areas for 21 days following application.

*Restricted-use pesticide

†Not for use in Nassau and Suffolk Counties

• Refer to Section 4.11.1 for information on herbicide resistance management and site of action groups.

Table 4.14.1. Chemical weed control in grass pastures

Situation

Amount of Product(s) per Acre

Remarks and Limitations

Summer annual broad-leaf weeds: lambs-quarters, pigweeds, etc.

2 pt. of 3.8 lb./gal. 2,4-D formulation1
or 1/2 pt. Banvel/Clarity

GROUP 4 HERBICIDESApply to small, actively growing plants in spring or early summer

Winter annual and biennial broadleaf weeds: shepherdspruse, common burdock, spotted knapweed, bull thistle

2–3 pt. of 3.8 lb./gal. 2,4-D formulation1

or 1/2 pt.- 1pt. Banvel/Clarity

GROUP 4 HERBICIDES• Apply to rosettes or other fall growth in fall or early spring. Use low rate for winter annuals and high rate for biennials.

Simple perennial broadleaf weeds: tall buttercup, chicory, dandelion, curly dock

3–4 pt. of 3.8 lb./gal. 2,4-D formulation1

or 1/2 pt.- 1pt. Banvel/Clarity

GROUP 4 HERBICIDES• Apply to rosettes or other fall growth in fall or early spring.

Creeping perennial broadleaf weeds: horsenettle, common milkweed, leafy spurge, Canada thistle

4 pt. of 3.8 lb./gal. 2,4-D formulation1
        +
2 pt. Banvel/Clarity

GROUP 4 HERBICIDES• Apply after weeds have reached the bud stage in mid- to late summer (before killing frost).

Bedstraw plus a wide variety of annual, biennial, and perennial broadleaf weeds.

2 qt. Crossbow

GROUP 4 HERBICIDES• Apply to actively growing bedstraw in fall before killing frost., Do not allow lactating dairy animals to graze treated areas until the next growing season following application of this product and do not harvest hay for 14 days after application. For other livestock, there are no grazing restrictions following application of this product. During the season of application, withdraw livestock from grazing treated grass at least 3 days before slaughter.

1For other 2,4-D formulations, use Table 7.2 to calculate the amount of herbicide needed per acre.

•Refer to Section 4.11.1 for information on herbicide resistance management and site of action groups.

 

NOTE: In pastures treated with 2,4-D or Banvel/Clarity, the following restrictions must be followed: 2,4-D—Do not graze lactating dairy animals for 7 days after treatment. Remove meat animals from treated areas for 3 days before slaughter if less than 14 days have elapsed since treatment. Do not cut treated grass for hay within 30 days after application. Banvel/Clarity—Do not graze lactating dairy animals for 7 days after treatment with up to 1 pt./A, and 21 days after 2 pt./A, of Banvel/Clarity. Do not harvest hay for lactating dairy animals before 37 days after application of 1 pt./A of Banvel or Clarity and before 51 days after application of 2 pt./A of Banvel or Clarity. Remove meat animals from treated areas 30 days before slaughter. There is no waiting period between treatment and grazing for non-lactating animals.