UC IPM: Information about Herbicides for Seedling Alfalfa

UC Pest Management Guidelines

Common name

Amount/Acre

R.E.I.+

P.H.I.+

(trade name)

(hours)

(days)

When choosing an herbicide, consider the environmental impact.

PREPLANT

Before Weeds Emerge

BENEFIN

1.2–1.5 lb a.i.

—

(Balan) 60DF

MODE OF ACTION: A dinitroaniline (Group 3)¹ herbicide.

COMMENTS: Incorporate shallow (2-inch depth) once within 4-8 hours after application and again before planting. Do not use on high organic soils. See label for rotational restrictions.

EPTC

2–4 lb a.i.

—

(Eptam) 7EC

MODE OF ACTION: A thiocarbamate (Group 8)¹ herbicide.

COMMENTS: Incorporate immediately 3–4 inches. Use low rate on sandy soil, high rate on heavy soil. Can be water-run or through sprinklers. To avoid crop injury, water-run only on flat ground; i.e., flood irrigation, not in furrows or on corrugations. Also, if applied through sprinklers on hot days, a significant amount of the material may be lost through evaporation.

After Weeds Emerge

GLYPHOSATE

(Roundup Ultra Max)

Annuals: 0.25–1.5 lb a.i.

—

Perennials: 2–5 lb a.i.

...OR...

(Touchdown)

Annuals: 0.24–1 lb a.i.

—

Perennials: 0.75–3.75 lb a.i.

MODE OF ACTION: A glycine (Group 9)¹ herbicide.

COMMENTS: In conventional alfalfa, apply anytime before planting to kill existing weeds. No soil residue. Do not mow or till before application. Do not apply just before rain or irrigation. High rate for annuals is only suggested for filaree control.

PARAQUAT*

0.638–1.01 lb a.i.

—

(Gramoxone Max)

MODE OF ACTION: A bipyridylium (Group 22)¹ herbicide.

COMMENTS: Apply to emerged weeds. Do not use in soils that lack clay minerals, i.e., peat, muck, pure sand. For use in certain northern counties only (see label). Always use a nonionic surfactant with paraquat.

2,4-DB*

0.5–1.5 lb a.i.

—

(Butyrac)

MODE OF ACTION: A phenoxy-carboxylic-acid (Group 4)¹ herbicide.

COMMENTS: Apply late fall or early winter when weeds are 3 inches or shorter. Rates vary with formulation and weed size. Apply between 40°–90°F. Do not graze or harvest within 60 days for seedling alfalfa. Restricted use from Mar 15 - Oct 15 in some Central Valley counties. Check with your County Agricultural Commissioner.

PELARGONIC ACID

(Scythe)

3–10% volume/volume

—

MODE OF ACTION: Unknown

COMMENTS: A nonselective contact herbicide for control of emerged weeds. Can be used anytime before alfalfa emergence. Weed size and growth stage determine the rate needed for control: large perennial weeds require the highest rate. This material can also be used during winter dormancy to control winter weeds but cool weather reduces its efficacy. Because this is a contact herbicide, good spray coverage is essential for satisfactory weed control.

Herbicide combinations

BENEFIN

1.2–1.5 lb a.i.

—

(Balan) 60DF

MODE OF ACTION: A dinitroaniline (Group 3)¹ herbicide.

...PLUS...

EPTC

3–4 lb a.i.

—

(Eptam) 7EC

MODE OF ACTION: A thiocarbamate (Group 8)¹ herbicide.

COMMENTS: Incorporate immediately, preferably in the same operation as application, to a 2- to 3-inch depth, so the disk or ground-driven tiller should be set to 4–6 inches. When planting on flat ground, broadcast these herbicides and incorporate by disking twice at right angles at a speed sufficient to mix the soil, or by using a power driven rotary tiller set at 2-3 inches. EPTC has a relatively short soil life; under cropping conditions expect it to last 1–2 months. Benefin has a moderate soil life and may persist 3–5 months. Fall application of benefin and incorporation to 3-inch depth will cause growth retardation of the alfalfa.

POSTPLANT (Roundup-ready alfalfa only)

GLYPHOSATE

0.75–1.5 lb a.i.

(Roundup WeatherMax)

22–44 fl oz

—

MODE OF ACTION: A glycine (Group 9)¹ herbicide.

COMMENTS: In Roundup-ready varieties, over-the-top applications can be made at any stage of growth. Do not use more than 132 fl oz/acre/year.

POSTPLANT (Conventional and Roundup-ready alfalfa)

BROMOXYNIL

0.25-0.375 lb a.i.

30–spring alfalfa

(Buctril)

60–fall/winter alfalfa

MODE OF ACTION: A nitrile (Group 6)¹ herbicide.

COMMENTS: A contact herbicide that has no soil residual. Apply when alfalfa is in the second trifoliolate leaf stage. Broadleaf weeds should be 2 inches or less. Thorough coverage is essential for best control. Do not apply when temperatures exceed 80°F. Combining with sethoxydim (Poast), clethodim (Prism), imazethapyr (Pursuit), or 2,4-DB (Butyrac) will broaden control. When combined with the herbicides requiring oil adjuvants, crop injury will increase. Nonionic surfactants have shown to be less injurious to crop than oil concentrates.

Alfalfa injury symptoms: leaf burn. Weed symptoms: browning and necrosis within 2-4 days.

2,4-DB*

0.5-1.5 lb a.i.

(Butyrac 200)

MODE OF ACTION: A phenoxy-carboxylic-acid (Group 4)¹ herbicide.

COMMENTS: A foliar-applied systemic herbicide that has no soil residual. Apply when alfalfa is in the second trifoliolate leaf stage. Broadleaf weeds should be 3 inches or less. Weed control increases with clear and warm conditions. If significant rainfall or irrigation occurs before 4 days after application, crop injury may occur. Can be combined with sethoxydim (Poast), clethodim (Prism), bromoxynil (Buctril), or imazethapyr (Pursuit). When mixed with herbicide requiring an adjuvant, nonionic surfactants have shown to be less crop injurious than oil concentrates. Restricted use from Mar 15 - Oct 15 in some Central Valley counties. Check with your County Agricultural Commissioner.

Alfalfa injury symptoms: leaf narrowing and plant twisting. Weed symptoms: twisting, epinasty and chlorosis in 2-10 days.

PARAQUAT*

0.19–0.3 lb a.i.

(Gramoxone Max)

MODE OF ACTION: A bipyridylium (Group 22)¹ herbicide.

COMMENTS: A contact herbicide that has no soil residual. Apply when alfalfa is in the third trifoliolate leaf stage. Broadleaf weeds should be between 1 to 3 inches and grasses below 6 inches. Thorough coverage is essential for best control. Rate increases with larger alfalfa size: use the 8 fl oz rate (0.19 lb a.i.) if alfalfa has at least 3 trifoliate leaves and 12.8 fl oz (0.3 lb a.i.) if alfalfa has 6 trifoliate leaves. Tank mixing information with other herbicides is limited. Always use a nonionic surfactant.

Alfalfa injury symptoms: leaf bleaching to browning. Stand reduction on smaller seedlings. Weed symptoms: bleaching and necrosis in 1-3 days.

PRONAMIDE*

0.5–2 lb a.i.

25 – below 1.5 lb a.i.

(Kerb) 50WP

45 – 1.5-2 lb a.i.

MODE OF ACTION: A benzamide (Group 3)¹ herbicide.

COMMENTS: A contact herbicide that is also taken up by the roots. Apply when alfalfa is in the first trifoliolate leaf stage. Control is best when applied before weed germination; some postemergent control on seedling weeds. Control is dependent upon adequate moisture following application. Tank mixes with bromoxynil (Buctril) or imazethapyr (Pursuit) can be helpful on emerged broadleaf weeds.

Alfalfa injury symptoms: occasional white speckling of leaves. Weed symptoms: leaf browning and necrosis and root inhibition in 2 weeks.

SETHOXYDIM

0.09-0.47 lb a.i.

See label

(Poast)

MODE OF ACTION: A DIM (Group 1)¹ herbicide.

COMMENTS: A systemic herbicide that has no soil residual. Can be applied when alfalfa is in the first trifoliolate leaf stage. Control is best when alfalfa is in the 3rd trifoliolate leaf stage and grass weeds are between 2-6 inches tall, growing vigorously before tillers develop. Control is reduced when grasses are moisture-stressed. Oil adjuvant is required. Can be combined with bromoxynil (Buctril), 2,4-DB (Butyrac) and imazethapyr (Pursuit) herbicides. Oil concentrate adjuvant will increase crop injury when mixed with bromoxynil (Buctril) or 2,4-DB (Butyrac).

Alfalfa injury symptoms: none observed. Weed symptoms: chlorosis followed by necrosis at growing point in 6-10 days.

CLETHODIM

0.095-0.25 lb a.i.

(Prism)

MODE OF ACTION: A DIM (Group 1)¹ herbicide.

COMMENTS: A systemic herbicide with no soil residual. Apply when alfalfa is in the first trifoliolate leaf stage. Control is best when alfalfa is in the 3rd trifoliolate leaf stage and grass weeds are between 2-6 inches tall, growing vigorously before tillers develop. Control is reduced when grasses are moisture-stressed. Oil adjuvant is required. Can be combined with bromoxynil (Buctril), 2,4-DB (Butyrac) and imazethapyr (Pursuit) herbicides. Oil concentrate adjuvant will increase crop injury when mixed with bromoxynil (Buctril) or 2,4-DB (Butyrac).

Alfalfa injury symptoms: none observed. Weed symptoms: chlorosis followed by necrosis at growing point in 6-10 day

IMAZETHAPYR

0.047–0.094 lb a.i.

(Pursuit)

MODE OF ACTION: An imidazolinone (Group 2)¹ herbicide.

COMMENTS: A systemic herbicide with soil residual. Apply when alfalfa is at least in the second trifoliolate leaf stage. Control is best when broadleaf weeds and some grass weeds are less than 3 inches in height and growing vigorously. Weed control is greatly reduced when plants are moisture stressed. Can be combined with sethoxydim (Poast), clethodim (Prism), bromoxynil (Buctril), or 2,4-DB (Butyrac) herbicides. Oil adjuvants will increase the potential of crop injury when used with bromoxynil (Buctril) or 2,4-DB (Butyrac). Using a nonionic surfactant may be a safer choice.

Alfalfa injury symptoms: temporary growth reduction. Weed symptoms: chlorosis followed by necrosis in 1-2 weeks.

IMAZAMOX

0.032–0.047 lb a.i.

(Raptor)

MODE OF ACTION: An imidazolinone (Group 2)¹ herbicide.

COMMENTS: A systemic herbicide with soil residual that controls broadleaf and grass weeds. Has the same mode of action as imazethapyr (Pursuit), and it is not recommended that these two products be applied alternately. Apply when alfalfa is at least in the second trifoliolate leaf stage. Control is best when broadleaf weeds and grass weeds are less than 3 inches in height and growing vigorously. Control is reduced when weeds are moisture-stressed. Does not adequately control prickly lettuce, annual sowthistle, and fiddleneck but can be tank mixed with another herbicide to broaden the spectrum of weeds controlled. Must use an adjuvant. Useful tank mixes include bromoxynil (Buctril) and 2,4-DB (Butyrac). Oil adjuvants will increase the potential of crop injury when used with bromoxynil (Buctril) or 2,4-DB (Butyrac). Using a nonionic surfactant may be a safer choice.

Alfalfa injury symptoms: temporary growth reduction. Weed symptoms: chlorosis followed by necrosis in 1-2 weeks.

HEXAZINONE

0.25–0.375 lb a.i

(Velpar)

MODE OF ACTION: A triazinone (Group 5)¹ herbicide.

COMMENTS: A contact herbicide that also has a soil residual. Use caution on sandy soil. Apply when alfalfa is between the sixth to ninth trifoliolate leaf stage with multiple stems, and root length is greater than 6 inches. Has both pre- and postemergent activity on small broadleaf weeds less than 2 inches in size. This ideal timing required for treatment of larger alfalfa and smaller weed size, however, is difficult to achieve. See label for additional restrictions. Useful tank mixes include sethoxydim (Poast) and clethodim (Prism).

Alfalfa injury symptoms: leaf burn and chlorosis. Weed symptoms: chlorosis and necrosis in 1-2 weeks.

+	Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment until the field can be grazed or cut. In some cases the R.E.I. exceeds the P.H.I.; the longer of these two intervals is the minimum time that must elapse before harvest may take place.
¹	Group numbers are assigned by the Weed Science Society of America (WSSA) according to different modes of action. Although weeds may exhibit multiple resistance across many groups, mode of action numbers are useful in planning mixtures or rotations of herbicides with different modes of action. For more information, see http://www.plantprotection.org/HRAC/.

UC IPM Pest Management Guidelines: Alfalfa
UC ANR Publication 3430
Weeds for Seedling Alfalfa
W. M. Canevari, UC Cooperative Extension, San Joaquin County

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How to Manage Pests

UC Pest Management Guidelines

Alfalfa

Herbicide Treatment Table for Seedling Alfalfa

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