dimethenamid-P (Outlook)
Rate 0.56 to 1 lb ai/a (12 to 18 oz/a product on coarse soils, 14 to 21 fl oz/a product on medium and fine soils).
Time Apply preemergence to weeds when hops are dormant or in early vegetative stages of growth. Incorporate with rainfall, sprinkler irrigation, or by mechanical means soon after application to maximize weed control.
Remarks Controls numerous annual grass weeds and certain broadleaf weeds when applied prior to emergence. Only one application allowed per season. Do not apply more than 21 oz/a per growing season. Preharvest interval is 60 days. If planting a cover crop between hop rows, be aware of possible injury to small grains or direct applications to hop rows only.
Caution Contact of spray mixture with hop foliage may cause injury to hops. May only be applied by ground (banded) application (including postemergence-directed). Has not been tested on all soil types in the Pacific Northwest so test on a small area of field to confirm crop safety on the local soil type.
Site of action Group 15: inhibits very long chain fatty acid synthesis
Chemical family Chloroacetamide
flumioxazin (Chateau SW, Redeagle, Tacoma, Tuscany SC, Warfox)
Rate 0.19 lb ai/a (6 oz/a of 51% ai products).
Time Apply to dormant hops November thru February in a 1- to 1.5-foot band to each side of the hop row. Rain following application will improve preemergence weed control.
Remarks Do not apply more than 6 oz/a in a single application. Do not apply more than 6 oz/a during a growing season. Do not add an adjuvant. If weeds have emerged at the time of application, tank mix with a labeled herbicide such as paraquat or glyphosate to improve control of emerged weeds. Controls numerous broadleaf and some grass weeds when applied prior to emergence.
Caution Do not allow spray to contact green stems, foliage, flowers, or cones because unacceptable injury may occur. Preharvest interval is 30 days. Avoid spray or drift outside the area. Do not mow or rake over treated area as dust created by mowing may drift onto sensitive crops or vegetation and damage crop foliage.
Site of action Group 14: protoporphyrinogen oxidase inhibitor
Chemical family N-phenylphthalimide derivative
glyphosate (several trade names)
Rate Consult labels
Time Apply to actively growing weeds.
Remarks Glyphosate will injure and kill hops, so avoid all contact with hop foliage. Remove any sucker that may be growing in area to be sprayed. Use a low-pressure, coarse spray to minimize drift within the hop yard. Glyphosate controls many perennial weeds if applied at the weed growth stage stated on the label.
Caution Do not allow spray to contact green hop stems or foliage. Any crop receiving spray will be killed. Preharvest interval is 14 days.
Site of action Group 9: inhibits EPSP synthase
Chemical family None generally accepted
indaziflam (Alion)
Rate 0.045 to 0.065 lb ai/a (3.5 to 5 fl oz/a product). Use the lower rates on soils with less than 1% organic matter content. Do not use on sand soils.
Time Apply preemergence to weeds when hops are dormant or in early bud stage of growth.
Remarks Controls numerous annual grass weeds and broadleaf weeds when applied prior to emergence. Can be applied as an early spring dormant application and/or as a fall dormant application after hop harvest. Do not apply more than two applications for a total of 7 to 10 fl oz/a in a 12 month period depending on soil organic matter. Only apply to hop vines where the soil has completely settled around the vines and there are no open roots. Apply in a minimum of a 2 foot band on each side of the hop row.
Caution Use only on hops that have been established at least one year. Do not use on soils with greater than 20% gravel content. Early spring dormant application can be made to hop shoots that are in the bud stage up to 2 inches tall. Do not allow spray to contact green stems, foliage, flowers, or cones or unacceptable injury may occur.
Site of action Group 29: inhibits cellulose biosynthesis
Chemical family Alkylazine
norflurazon (Solicam DF)
Rate 2 to 4 lb ai/a (2.5 to 5 lb/a Solicam DF), depending on soil texture
Time May be applied immediately after planting new hops. On established fields, apply to soil surface in fall after hop yards have been worked for the last time, or within 1 week after stringing in the spring.
Remarks Use lower rate on coarse soils and higher rate on fine soils. Note recropping interval on label. Preharvest interval is 60 days. If planting a cover crop between hop rows, be aware of possible injury to small grains or direct applications to hop rows only.
Site of action Group 12: bleaching; inhibits carotenoid biosynthesis
Chemical family Pyridazinone
paraquat (several trade names)
Rate 0.5 lb ai/a in at least 10 gal/a water. Add nonionic surfactant or crop oil concentrate to spray mix.
Time For control of winter annuals, apply before hops begin to grow in spring. Apply after hop vines are at least 6 ft tall; direct spray to basal 2 ft of plants.
Remarks Direct spray around base and in interspaces of hops. Re-treatment or spot treatment may be necessary.
Caution A restricted-use herbicide. Do not let spray contact green portions of plant, because injury may result. Do not exceed three applications per season. Preharvest interval is 14 days. Do not graze animals in treated hop yard. Hop vine refuse and silage may be fed to livestock. Follow all safety precautions on label.
Site of action Group 22: photosystem I electron diversion
Chemical family Bipyridilium
pelargonic acid (Scythe)
Rate Apply in a total water volume of 75 to 200 gal per acre. Apply as a 3-5% (v/v) solution on young, small annual weeds and 5-7% (v/v) solution on perennial herbaceous weeds or annual weeds over 6 inches tall. For difficult to control weeds and maximum vegetation control use 7-10% (v/v).
Time Apply before hops emerge to control winter annual or early emerged weeds. Apply after hop emergence, but don't allow spray to contact emerged hops. Small weeds are easier to control than larger weeds. Warm weather promotes rapid activity on plants.
Remarks Apply as a spot treatment or as a directed and shielded spray avoiding contact with all desirable vegetation. Contact of spray or spray drift with emerged vegetation will result in damage. Repeat applications are required to control new weeds emerging from seed or underground vegetative parts. Broadleaf weeds are generally controlled better than grass weeds. Repeated use may select for grasses.
Caution Pelargonic acid is a nonselective herbicide. Any spray contacting desirable vegetation will likely result in damage.
Site of action Group 26 unknown. Disrupts cell membranes causing leakage from the cells and rapid wilting.
Chemical family Carboxylic acid
pendimethalin (Drexel Aquapen, Prowl H2O, Satellite Hydrocap)
Rate 1 to 4 lb ai/a (1.1 to 4.2 quarts/a product), depending on soil texture
Time Apply prior to target weed emergence when hops are dormant or in vegetative stages of growth. Apply the spray directly to the ground beneath the vines and/or in areas between rows with ground equipment. Apply in a single application or sequential applications with an interval of 30 days or more.
Remarks Controls many annual grass weeds and certain broadleaf weeds when applied prior to weed emergence. Use lower rate on coarse soils and higher rate on fine soils. Do not exceed a maximum total of 4.2 quarts/a per year. Preharvest interval is 90 days. Note recropping interval on label. If planting a cover crop between hop rows, be aware of possible injury to small grains or direct applications to hop rows only.
Caution Do not apply over the top of vines with leaves or cones. Contact with hop foliage or cones by spray mixture may cause injury.
Site of action Group 3: microtubule assembly inhibitor
Chemical family Dinitroaniline
trifluralin (several trade names)
Rate 0.5 to 0.75 lb ai/a
Time Apply and incorporate when crop is dormant.
Remarks Use lower rate on coarse soils, higher rate on fine soils. Must be incorporated 1 to 2 inches with equipment that ensures soil mixing without injuring hop crowns. This treatment will not control mustards, prickly lettuce, horseweed (marestail), salsify, or nightshades.
Caution Do not spray over hop crowns. Take care that incorporation equipment does not injure hop crown buds that are needed to initiate hop bines. Disking operations that move additional treated soil onto the hop crown may delay emergence. Avoid exposing untreated soil when ditching for furrow irrigation.
Site of action Group 3: microtubule assembly inhibitor
Chemical family Dinitroaniline