Weed Control in Carrot PNVA, Pasco

Rick Boydston

USDA-ARS

Prosser, WA

Carrot Weed Control

Carrots are very susceptible to competition from weeds (reduces carrot size, may cause malformed carrots, harvest losses)

eg. volunteer potato reduced carrot yield by 22 to 91% depending on potato densities.

Weeds can also act as hosts to insect pests, nematodes, and diseases of carrots.

Cultural and Mechanical Weed Control in Carrots

Pre-sowing: • Various types of tillage implements and bedformers • Weeding implements for first flush of weeds

After sowing – pre-germination of carrots: • Flame or steam weeder • Harrow for blind weeding

After germination of carrots: • Various types of tine cultivators • Brush weeder • Steerage hoe (cultivator)• Hand hoe**Early weeding most critical on carrot yield (first 4-6 wks)**

Stale seedbed – a fresh start

• Till soil and form beds• Allow weeds to germinate (irrigate)• Remove/control germinated weeds

– Manual removal – shallow tillage– In dry months, withhold irrigation– Flame– Herbicides

• Plant desirable species (minimal tillage)

Alternative Strategy

• Prepare seedbed just 5-7 days prior to planting carrots to promote weed emergence prior to carrots – followed by flaming before carrots emerge.

Flame weeding• Propane fueled burners• Idea is to just break cell membranes (dark

green color after flaming)• Controls primarily young, emerged annual

broadleaf weeds that have exposed growing points

• Grass and perennial weed control often poor, with re-growth after treatment– Grass weeds: growing point often below-ground– Perennial weeds: re-grow from root tissue

• Energy costs are high

Prototype II in carrot:

–80-90% weeding effectiveness against annual weeds at 800C

–tendency for a higher marketable yield

–fuel consumption < 400 l ha-1

Band steamed

Reduction in numbers of carrot seedlings and weeds by three different weeding implements (Mildura 2002)

Goosefoot tine cultivator

Finger-tine harrow Power rotary harrow

Carrots Weeds Carrots Weeds Carrots Weeds

67% 83% 33% 82% 0% 80%

Power rotary harrow

Herbicides Registered for Carrot

Lorox (linuron) Poast (sethoxydim)Treflan (trifluralin) Fusilade (fluazifop-butyl)Sencor (metribuzin) Select (clethodim)Nortron (ethofumesate)

Prowl H2O (pendimethalin)

Roundup (glyphosate)Gramoxone (paraquat)

Roundup, Gramoxone, Flaming

Prior to crop emergence – stale seedbed

Nonselective

Aim 2EW – carrot stand loss and yield loss when applied at rates of 1 or 2 fl oz/a

Trifluralin (Treflan, others)

Preplant incorporated treatment for control of annual grasses and broadleaves

Soil Texture Treflan 4EC (pints)

Coarse 1

Medium 1.25 – 1.5

Fine 1.5 - 2

Lorox 50DFStatus: Primary carrot herbicide “Do not apply to sand or loamy sand. Do not use

on soils with less than 1% organic matter”Use: PRE and POST control of most broadleaves

and annual grasses; Max. 2 lb ai/a/yrConcerns: POST applications at temp >85F can

burn carrots; some weeds have developed resistance to PS II inhibitors

POST - Wait 2 wks or more after first applicationCarrots must have 2 lvs or more (~3 inches tall)

Sencor 75DF

Triazine, PS II inhibitorUse: POST control of annual broadleaves

when carrots have 5-6 leavesConcerns:

May burn carrots at temp <55 or >85FSensitive varietiesDo not tank mixWeed resistance

Fusilade, Poast, Select

Use: POST grass control; volunteer small grains

Avoid tank mixes with Lorox or Sencor

Avoid applying to water stressed grasses

Always use adjuvants according to label

Prowl H2O (3.8 CS)

Use: 2 pts/acre (max. 2 pts/season)

- Postplant, preemergence w/in 2 days of planting

- Layby as a directed spray before weed emergence.

Chemigation – only prior to carrot emergence.

Possible substitute for Treflan

Prowl H2O (pendimethalin)

Kochia Lambsquarters

Purslane Pigweed sp.Annual grasses

Spotted spurge

Nortron (Ethofumesate)• Labeled in OR and WA• Bayer - sugarbeet, grass seed herbicide• 1.5 – 2 lb ai/a (48 – 64 fl oz/a)• PRE 48 oz coarse soils

64 oz med and fine soils• Early POST (PRE to weeds) – 64 fl oz

(2-4 leaf carrot)

Max 128 fl oz (1 gal) per season

• Rotation crop interval – 12 month• Some carrot leaf fusion at higher doses

Nortron (Ethofumesate)

Kochia Lambsquarters Chickweed

Russian thistleBlack NightshadeSmartweed/ladysthumb

Purslane Redroot Pigweed Volunteer Potato

Nortron –grass weed control

• Barnyardgrass• Green foxtail• Yellow foxtail• Large crabgrass• Downy brome• Wild oat• Volunteer grains

Volunteer potato height (inches) at time of weed removal

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Volunteer potato density (number per 100 square feet)

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• Nortron applied PRE delayed potato emergence, stunted potato growth, and caused epinastic growth on potato.

May 15, 2003 – Delayed potato emergence

Carrot Trial 2003

Nortron also applied POST at 2 leaf stage of carrot (potatoes had 6 leaves).

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Etho1.5/2

Etho 2/2 Etho 4.0 None

Yield of Carrot treated with Nortron - 2003

Yield (% of HW Check)

PRE/POST

POST/POST POST

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Reduced due to potato competition

Summary

• Nortron applied PRE delayed potato emergence and applied POST reduced potato growth in carrots.

• Sequential applications of Nortron 1.5/2 lb ai/a (PRE/POST) reduced number and weight of potato tubers and prevented carrot yield loss from volunteer potato.

• Sequential applications of Nortron and Caparol applied POST also provided good potato control without reducing carrot yields.

Caparol 4F – NOT Labeled

Status: Possible label in 2008

PRE or POST control of broadleaves. Use as a substitute for Lorox (controls many

similar weeds as Lorox)

Volunteer potato - single or sequential POST applications of Caparol at 1 to 2 lb ai/a, were safe on carrot and suppressed volunteer potato.

Mode of action similar to Lorox (PS II inhibitor); potential crop stunting

Dual Magnum – NOT labeled in WA

Status: 24c label in Oregon; growers must Indemnify Syngenta before use

Use: PRE control of nutsedge, annual grasses, pigweeds, and nightshades.Keep rates low to avoid crop damage

Concerns: Stand thinning on sandy soils

Future: Use with Lorox for nutsedge and crabgrass, and resistant pigweed control

Summary

• Organic systems: stale seedbed, flame, cultivation, hand-weed

• Prowl H2O – pre or post directed, 2 pts/a

grass and small seeded broadleaf weeds• Nortron – pre (48-64 fl oz), post (64 fl oz)

volunteer potato suppression, grasses, and selected broadleaf weeds

Future labels?? Caparol – pre and post

Dual – pre for nutsedge, grasses

Crossing paths Crossing paths on their on their respective respective journeys of journeys of destiny, destiny, Johnny Johnny Appleseed and Appleseed and Irving Irving Ragweed nod Ragweed nod “hello.”“hello.”