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: Band steamed 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

Goosefoot tine cultivator Power rotary harrow 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 67% 83% 33% 82% 0% 80%

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 50DF Status: 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/yr Concerns: 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 application Carrots must have 2 lvs or more (~3 inches tall)

Sencor 75DF Triazine, PS II inhibitor Use: POST control of annual broadleaves when carrots have 5-6 leaves Concerns: May burn carrots at temp <55 or >85F Sensitive varieties Do not tank mix Weed 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) Spotted spurge Kochia Lambsquarters Purslane Pigweed sp. Annual grasses

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) Chickweed Kochia Lambsquarters Russian thistle Smartweed/ladysthumb Black Nightshade Purslane Redroot Pigweed Volunteer Potato

Nortron –grass weed control Barnyardgrass Green foxtail Yellow foxtail Large crabgrass Downy brome Wild oat Volunteer grains

Volunteer Potato in Carrot

Carrot Trial 2003 Nortron applied PRE delayed potato emergence, stunted potato growth, and caused epinastic growth on potato. Nortron also applied POST at 2 leaf stage of carrot (potatoes had 6 leaves). May 15, 2003 – Delayed potato emergence

Reduced due to potato competition b POST/POST POST PRE/POST

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