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Weed Management in HopsRick BoydstonUSDA-ARS, Prosser, WA

Outline – Weed Management New hop yards Established hop yards What’s coming next

Why Control Weeds? Weeds compete with hops fornutrients and water. Also for lightin new plantings. Can harbor other pests (insect,mites, pathogens) Can impede airflow and preventdrying of foliage – promotes somediseases Impede stringing/training Impede harvest operations

Weed Management in New Hop Yards Control perennial weeds in years precedingplanting of hops – especially broadleaf perennials(Canada thistle, field bindweed, perennialsowthistle, red sorrel, goldenrod, horsenettle,etc.)Herbicides – avoid using long residual herbicides inpreceding crop that could persist and injure newhopsTillage – effective, but should avoid spreadingrhizomes to noninfested areas

Canada thistlePerennial sowthistleField bindweed (morning-glory)Red sorrelHorse nettleGoldenrod

Weed Management in New Hop Yards Preplant tillage, fertilizer, & compost Design planting arrangement and trellis system that allowsclose cultivation to hop rows Plant rhizomes (free of weeds) or starts – avoid usingrhizomes dug from fields with perennial weeds Apply preemergence herbicide-Pendimethalin (Prowl H2O)Norflurazon (Solicam) - on new hops in PNW onlyDimethenamid-P – (Outlook) PNW only!-Glyphosate – prior to hop emergence to control earlyemerging weeds

Weed Management in New Hop YardsorTransplants - seedlings Plant after preemergenceherbicides applied. Avoid herbicide in plantingslot/hole Emerged shoots susceptible toherbicide applied over the top(i.e. Prowl and/or Roundup) Minimize soil disturbance(herbicide barrier)rhizomes Can plant before preemergenceherbicides applied (deeper) Avoid herbicide in planting slot/hole

Open and close transplanting slot withminimal disturbance of herbicide barrierAvoid contaminatingtransplanting slot with herbicide –inhibits root growth and/orinjures plantlet

Hop planting(rhizomes)Soil disturbancedisrupts herbicidebarrierApply herbicideafter planting

Weed Management in New Hop Yards Preemergence herbicidesBand or Broadcast?– Depends on cover cropping plans – If broadcast;herbicide choice must be compatible with cover crop– Cultivation plans – may choose to cultivate alleys.Herbicides can reduce amount of cultivation required.Growers choice. Excessive cultivation increases erosion,destroys organic matter, decreases water infiltration &retention. Also can increase & spread verticillium.– Can also mow alleys (cover crops and weeds)

Weed Management in New Hop Yards Once hops are trained and 6 ft tall, weedcontrol practices are similar to established hops

Annual Weed Control Prevent new seed set. Weeds often produce thousands ofseeds per plant. Allowing weeds to set seed results in athousand fold increase in weeds the next season. Alwayscontrol weeds before they set seed.Good weed control programs use a combination of thefollowing: Mechanical cultivation on a timely basis Preemergence herbicides to eliminate weed seedlings as theygerminate and sprout. Postemergence herbicides to control escape weeds. Cover crops to prevent and smother sprouting weeds. Mowing or removing weeds before seed set.

Cover Crops Smother weedsScavenge nutrientsFix nitrogen (legumes)Increase organic matter and biological activityMay reduce plant pathogens and nematodes(mustard, arugula, sudangrass) Be careful about planting a perennial cover inalleys – may become a weed and difficult tocontrol in hops

Weed fabric or plastic mulch? Effective in controlling weeds. Limits ability to amend soil with fertilizers,compost or other organic matter Difficult to change hop varieties May promote mildew and root rots Limits ability to apply fungicides or nematicidesto soil

Weed Management in Established Hops Late winter, early spring –remove winter annual weedswith cultivation or herbicides. Tillage can remove previousyear’s hop residues, but canalso spread verticillium andperennial weeds Glyphosate controls mostemerged weeds. Apply beforehop emergence. (late Feb.early March in PNW)Glyphosate injury on newlyemerged hops

Tillage/CultivationPros Repeated shallowcultivation controlsweeds Prepares bed for covercrop planting Removes previous cropresiduesCons Reduces organic matter Can spread rhizomes,stolons and tubers ofperennials weeds Spreads verticillium Can damage hop crowns Reduces waterinfiltration rate Increases soil erosion

Preemergence Herbicides (Established Hops)Suppress weeds early in the season to reducenumber of cultivations and reduce size of weedswhen postemergence herbicides/desiccants areused later in season Trifluralin (Treflan) - shallow incorporationrequired Pendimethalin (Prowl H2O) Norflurazon (Solicam) – long persistence Flumioxazin (Chateau) – mainly broadleaf weeds Dimethenamid-P – (Outlook) PNW only!

Trifluralin (Treflan, others) Apply prior to weed and hop emergence (onestablished hops only) Requires mechanical incorporation (shallow) Broad spectrum annual grass and somebroadleaf control Misses most mustards and nightshades

Pendimethalin (Prowl H2O, Satellite HydroCap) Apply prior to weed emergence Apply prior to main hop emergence or keep offhop foliage May apply sequential treatments at least 30 daysapart Pre harvest interval 90 days Broad spectrum annual broadleaf and grass weedcontrol If broadcast, may injure small grain cover crops

Norflurazon (Solicam) Apply prior to weed emergence (late fall or early spring) Apply prior to main hop emergence or keep off hopfoliage May apply from before hop emergence to 1 week afterstringing Pre harvest interval 60 days Broad spectrum annual broadleaf and grass weed control Persistent and may injure cover crops if broadcast Adjust rates for soil type (see label) Hops must be established at least 6 months outside ofPNW.

Solicam injuryto hopsSolicam injuryto wheat

Flumioxazin (Chateau) Apply prior to dormant hops (Nov.-Feb.) or after hopstringing and 6 ft tall directed to base of hops. Broad spectrum annual broadleaf weed control Applied to base of hops provides some postemergenceweed control and contributes to sucker burn back atbase. Do not add any adjuvant. Only one, 6 oz/A application allowed per growingseason (choose between PRE or POST application) Pre harvest interval 30 days

Weed Management in Established Hops Burn back or remove early shootsbefore training. Helps reduce powdery mildew (earlyspores on foliage) and downy mildew(flag shoots)

Weed Management in Established HopsRemoval of early shoots First shoots often not thebest to train (less lateralbranching) Removal of early shootsaides in reducing mildew Mowing, flail chopper Desiccants- Aim ( NIS or COC)- Scythe or Axxe (organic acids)- Gramoxone – PNW only! These contact herbicides will alsocontrol many small broadleafweeds postemergence (no soilresidual activity)

Weed Management in Established HopsPostemergence Herbicide Options 2,4-D (many trade names) Clopyralid (Spur, Stinger) Flumioxazin (Chateau) Carfentrazone (Aim) Glyphosate (Roundup, others) Pelargonic acid or nonanoate acid (Scythe/Axxe) Clethodim (Select, others) – annual and perennialgrasses

2,4-D (many trade names) Apply to small broadleaf weeds Up to three applications, 30 days betweentreatments (0.5 lb ae/A each application) Avoid spray contact with new hop foliage andapical buds. Direct applications to rowmiddles. Translocated in susceptible broadleaf weedsand effective on both annuals and perennials 28 day PHI

Clopyralid (Spur, Stinger) Primarily for control of Canada thistle. Alsocontrols other composite (goldenrod, dandelion,horseweed, sowthistle), legume (clover, vetch),nightshade , and polygonaceae (smartweed, redsorrel) species. One or two applications, 21 days betweentreatments (1/3 to 2/3 pt/A) Avoid contact with hop foliage. Can cause leafcupping in hops. 30 day PHI

Carfentrazone (Aim) Non translocated, contact herbicide. Apply tosmall broadleaf weeds ( 4 inches) Directed, hooded applications between rows 0.5 to 2 fl oz/A; Total for season 7.6 fl oz/A Adjust rates for weed species susceptibility (seelabel) Allow 14 days between treatments Apply in 20 GPA or more spray volume and addNIS or COC. 7 day PHI

Carfentrazone (Aim)Adjust rates for weed species susceptibility (see label)

Carfentrazone (Aim) Also used for burn back of hop suckers at baseof plant (after stems of trained hops arebecoming woody – usually about 6 ft. tall) 2 to 3.2 fl oz/A to basal 18 inches Allow 14 days between treatments Apply in 20 GPA or more spray volume andadd NIS or COC. 7 day PHI

Nontreated2 days after Aim treatment

Aim spotting onhop stems

Weeds too large!

Pelargonic Acid (Scythe) or Ammoniumnonanoate (Axxe)Contact, high volume, expensive herbicides for burndown of small broadleaf weeds. Grass weeds regrow.1. Vegetative Burndown: Control of weeds for seedbedor site preparation.2. Directed and Shielded Sprays: Apply in and arounddesirable plants avoiding contact of foliage and greenbark.3. Sucker Control: Burn back of unwanted basal suckergrowth and foliage growth on bines. Apply only tounwanted vegetative parts. Apply before suckersbecome woody. WAIT UNTIL TRAINED HOPS HAVEWOODY STEMS.

Glyphosate Spot spray perennialweeds. Alley ways for control ofemerged weeds. Prior to hop emergence inhop row. Do not spray on hopfoliage. Early spring applicationssafer than fall applications.Glyphosate injury on new growthfrom previous fall application

Postemergence annual andperennial grass weed controlClethodim (Select, Intensity, Section, Arrow,Dakota, others) Do not exceed 0.12 lb ai/A in a single applicationor 0.5 lb ai/A per season Adjust rates for grass species Apply to actively growing grasses (not stressed) 14 or more days between applications PHI – 21 days

What’s on the Horizon?(NOT LABELED)PRE – dormant application Alion (indaziflam) – broad spectrum preemergencebroadleaf and grass herbicide (dormant established hops) Trellis (isoxaben) – broad spectrum preemergencebroadleaf herbicide (dormant established hops)Hop sucker burn-back Venue (pyraflufen-ethyl) – contact postemergencebroadleaf herbicide, hop sucker control (similar to Aim) Rely 280 (glufosinate) – nonselective postemergenceherbicide, hop sucker control after bines 6 ft. tall

Preemergence Weed Control in HopsAlion (PRE)Nontreated

Glufosinate (Rely280) Rely 280 (glufosinate) – nonselectivepostemergence herbicide, hop sucker control Excessive hop injury if apply before hops are 6ft. tall Longer suppression of hop sucker regrowth atbase of plant than Aim or Gramoxone

Glufosinate (Rely280)