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
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
diquat (several products)
Bulb iris, lily, narcissus, and tulip
Rate 0.38 to 0.5 lb ai/A (1.5 to 2 pints/A)
Time Apply as a broadcast application prior to bulb emergence or for pre-harvest desiccation.
Remarks Foliage emerged at application will be severely injured. Add a nonionic surfactant as label specifies, taking care to avoid anionic formulations that form insoluble precipitates. Reapply as needed at no less than 5-day intervals, up to three applications.
Caution Do not apply more than twice per season.
Site of action Group 22: photosystem I electron diversion
Chemical family Bipyridylium
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 Restricted-use herbicide in Washington to protect surface and groundwater. 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
linuron (Lorox 50DF)
Tulip, daffodil
Rate Up to 1.0 lb ai/A (2 lb/A Lorox 50DF) depending on soil type
Time After planting of bulbs, settle the soil with sprinkler irrigation (rainfall will serve the same purpose); then apply Lorox before bulbs emerge.
Remarks Lorox must be activated within 2 weeks of application for optimum control with rain or irrigation of 0.5 inch or more. Add a surfactant to increase contact activity if weeds are present. Do not exceed a total of 2 lb Lorox/A. One application per season.
Caution Do not apply through irrigation systems. Note ground and surface water advisories on main label. Toxic to fish and aquatic invertebrates. Do not apply directly to water or to areas where surface water is present or to intertidal areas below the mean high-water mark.
Site of action Group 7: photosystem II inhibitor
Chemical family Urea
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; supplemental label Washington only, expires 03/24/2022
Rate 0.47 to 0.94 lb ai/A
Time Apply as a broadcast application prior to bulb emergence.
Remarks Restricted use pesticide due to acute toxicity. For retail sale to and use only by certified applicators - not to be used by uncertified persons working under the supervision of a certified applicator. 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 Bipyridylium
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, iris, narcissus, 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
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 Washington to protect surface and 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