Preemergence

benefin + oryzalin (XL 2G)

Bulb iris, tulip, and narcissus

Rate 1.5 to 3 lb ai/A

Time Apply 2 to 4 weeks after planting but before weeds germinate, then incorporate immediately with shallow cultivation (1 to 2 inches) or with overhead water.

Remarks Application equipment must be calibrated precisely. Although registered for commercial plantings, product may perform erratically along ridges where granules may not be distributed evenly.

Caution Do not apply to tulips emerged more than 0.75 inch.

Site of action (both) Group 3: microtubule assembly inhibitor

Chemical family (both) dinitroaniline

bensulide (Prefar 4-E)

Field flowers, bulbs, and ornamentals

Rate 5 to 9 lb ai/A (5 to 9 quarts/A)

Time Apply fall through spring to weed-free soil.

Remarks See label for rates for grass species. Can persist up to 18 months. See label for replanting sensitive crops. Inhibits seedling root growth.

Caution Do not exceed 25 lb ai/A per year.

Site of action Group 8: lipid synthesis inhibitor but not an ACCase inhibitor

Chemical family Organophosphorus

clethodim (Envoy and others)

Dahlia, daylily, and iris

Rate 0.1 to 0.25 lb ai/A

Time Apply to actively growing grasses.

Remarks Identify grasses and adjust rates for susceptibility, and stage of weed growth as label instructs. Add a nonionic surfactant containing at least 80% active ingredient at the rate of 1 pt per 50 gallons (0.25% v/v). Use of crop oil concentrate is not recommended as injury to flower and foliage may occur.

Caution Do not exceed 0.5 lb ai/A per season. Do not apply if rain is expected within 1 hour. Rotational grass crops such as corn and cereals may not be planted within 30 days of the last application. Grazing any plant product or residue is prohibited.

Site of action Group 1: acetyl CoA carboxylase (ACCase) inhibitor

Chemical family Cyclohexanedione

dimethenamid-P (Tower)

Daylily, iris, lily, and narcissus

Rate 1 to 1.5 lb ai/A (1.3 to 2 pt/A)

Time Apply after final hilling operation, before bulbs or weeds emerge.

Remarks Use lower rates on coarse soils low in organic matter and higher rates on fine-texture soils high in organic matter. Allow soil to settle around bulbs after planting before applying herbicide. In fall-planted daffodil, iris, or lily, make an initial application following planting establishment; then make a sequential application in late winter or early spring before weed seed germination.

Site of action Group 15: inhibits very long chain fatty acid synthesis

Chemical family Chloroacetamide

diuron (Diuron 80WDG)

Bulb iris and narcissus

Rate 3.2 lb ai/A (4 lb/A)

Time Apply once after planting but no later than 4 weeks before bulbs emerge.

Remarks Diuron is most effective when applied before weeds emerge; it will not consistently control large, emerged weeds.

Caution Do not replant treated areas to any crop within 1 year after last application. Do not use on sand or loamy sand soils.

Site of action Group 7: photosystem II inhibitor

Chemical family Substituted urea

fenoxaprop (Acclaim Extra)

Daylily, iris, and peony

Rate 0.06 to 0.17 lb ai/A (13 to 39 fl oz/A)

Remarks Apply adjusted rates, depending on number of grass tillers (see label). Ensure thorough coverage to actively growing, susceptible grasses. Repeat after grass begins active growth, but do not exceed 120 fl oz/A per season.

Site of action Group 1: acetyl CoA carboxylase (ACCase) inhibitor

Chemical family Aryloxyphenoxypropionate

glyphosate (several products)

Iris, narcissus, and tulip

Rate Consult labels.

Time Apply to actively growing weeds at least 2 weeks before bulbs emerge.

Remarks Adding a surfactant improves activity. Consult label for specific rates, times of application, and perennial species controlled.

Caution Do not exceed 8 lb ae/A per year.

Site of action Group 9: inhibits EPSP synthase

Chemical family None generally accepted

isoxaben (Quali-Pro Isoxaben 75 WG)

Bulbous iris, gladiolus, hyacinth, lily, narcissus, and tulip

Rate 0.5 lb ai/A (0.66 lb/A)

Time Apply to weed-free soil.

Remarks Make single application within 30 days after planting and before bulbs or weeds emerge. Do not exceed 0.5 lb ai/A. Chemical stability is adequate when left on soil surface for 21 days, but must be activated with rainfall or sprinkler irrigation of 0.5 inch or more.

Caution Do not apply to newly transplanted bulbs until soil is settled. Postemergence application to tulip may result in severe injury.

Site of action Group 21: inhibits cell wall synthesis Site B

Chemical family Benzamide

napropamide (Devrinol 50DF)

Dahlia, daylily, gladiolus, iris, lily, narcissus, and tulip

Rate 4 lb ai/A (8 lb/A)

Time Apply after October 15 or final hilling operation, before bulbs or weeds emerge. In spring, apply before summer annual weeds germinate; do not apply to tulips showing more than 2 inches top growth.

Remarks Apply in a minimum carrier of 10 gal/A. Use a lower rate on coarse soils low in organic matter. Allow soil to settle around bulbs after planting before applying herbicide.

Site of action Group 15: inhibits very long chain fatty acid synthesis

Chemical family Acetamide

oryzalin (Surflan and others)

Bulbous iris, hyacinth, narcissus, and tulip

Rate 0.75 to 1.5 lb ai/A

Time Apply in the fall, 2 to 4 weeks after planting and final hilling, but before weeds emerge. Can reapply at 0.75 lb ai/A in early spring (late February to early March) to weed-free soil.

Remarks Herbicide is stable on soil surface up to 21 days but must be activated to be effective. A single rain or sprinkler irrigation of 0.5 inch or more is necessary to activate.

Caution Do not apply to tulip varieties that have emerged 0.75 to 1 inch. Plow deeply before planting any crop.

Site of action Group 3: microtubule assembly inhibitor

Chemical family Dinitroaniline

paraquat (Gramoxone SL 2.0)

Iris, narcissus, and tulip; Washington only

Rate 0.47 to 0.94 lb ai/A

Time Apply as a broadcast application prior to bulb emergence.

Remarks Supplemental label for Washington. Foliage emerged at application will be severely injured. Add a nonionic surfactant or crop oil concentrate as label specifies, taking care to avoid anionic formulations that form insoluble precipitates.

Caution Restricted-use herbicide. Identify grasses and adjust rates for susceptibility and stage of weed growth as on label. Do not apply more than twice per season.

Site of action Group 22: photosystem I electron diversion

Chemical family Bipyridilium

pendimethalin (Pendulum Aquacap)

Crocus, daylily, lily, iris, narcissus, gladiolus, and tulip

Rate 2 to 4 lb ai/A (2.1 to 4.2 quarts/A)

Time Apply after final hilling operation, before bulbs or weeds emerge.

Remarks The product requires 0.5 inch of rainfall or irrigation to incorporate within 30 days of application. Use a lower rate on coarse soils low in organic matter. Allow soil to settle around bulbs after planting before applying herbicide.

Site of action Group 3: microtubule assembly inhibitor

Chemical family Dinitroaniline

prodiamine (Prodiamine 65 WG)

Daylily and tulip

Rate 0.65 to 1.5 lb ai/A (1.0 to 2.3 lb/A)

Time In the fall or spring before weeds germinate or after weeds are removed.

Remarks Will not control emerged weeds. May be applied to newly-transplanted and established ornamentals as broadcast or over-the-top spray. Is most effective when applied to soil free of clods, weeds, and debris such as leaves and mulch. Is most effective when the product is activated in the soil before weed seeds germinate and within 14 days after application. Is activated when the treated area receives at least 0.5 inch of irrigation or rainfall, or shallow (1 to 2 inches) mechanical incorporation.

Site of action Group 3: microtubule assembly inhibitor

Chemical family Dinitroaniline

sethoxydim (Segment)

Dahlia, daffodil, gladiolus, iris, and tulip

Rate 0.28 to 0.47 lb ai/A (2.25 to 3.75 pints/A)

Time Apply at optimum growth stage listed on label.

Remarks Identify susceptible grasses and add 2 pints/A nonphytotoxic crop oil concentrate to improve leaf absorption. Control often is erratic on grasses stunted or stressed from drought, high temperatures, or low fertility. Resistant grasses include annual bluegrass and all fine fescues, but quackgrass can be suppressed.

Site of action Group 1: acetyl CoA carboxylase (ACCase) inhibitor

Chemical family Cyclohexanedione

S-metolachlor (Pennant Magnum)

Iris, lily, narcissus, and tulip

Rate 1.2 to 2.5 lb ai/A (1.3 to 2.6 pints/A)

Time Apply after final hilling operation, before bulbs or weeds emerge.

Remarks Apply in a minimum carrier of 10 gal/A. Use lower rates on coarse soils low in organic matter and higher rates on fine-texture soils high in organic matter. Allow soil to settle around bulbs after planting before applying herbicide.

Caution Restricted-use herbicide in WA, to protect groundwater.

Site of action Group 15: Inhibits very long chain fatty acid synthesis

Chemical family Chloroacetamide

trifluralin (Treflan HF and others)

Bulbous iris, dahlia, gladiolus, hyacinth, narcissus, and tulip

Rate 0.5 to 1 lb ai/A

Time Apply to the soil surface 2 to 4 weeks after planting, but prior to the emergence of annual weeds.

Remarks Use lower rate on coarse soils low in organic matter and higher rates on fine-texture soils high in organic matter. Do not apply to newly transplanted ornamentals until soil has been settled by packing and irrigation or rainfall and no cracks are present or injury may occur. For fall planted bulbs, an additional application can be made in late winter or early spring to weed-free soil. Do not make preplant applications to areas where gladiolus corms less than one inch in diameter will be planted or injury may occur.

Site of action Group 3: microtubule assembly inhibitor

Chemical family Dinitroaniline