1. Weed Control in Carrot PNVA, Pasco
Rick Boydston
USDA-ARS
Prosser, WA

2. 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.

3. 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)**

4. 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)

5. 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.

6. 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

7. 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

8. 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%

9. 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)

10. 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

11. 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

12. 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)

13. 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

14. 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

15. 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

16. Prowl H2O (pendimethalin)
Spotted spurge
Kochia
Lambsquarters
Purslane
Pigweed sp.
Annual grasses

17. 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

18. Nortron (Ethofumesate)
Chickweed
Kochia
Lambsquarters
Russian thistle
Smartweed/ladysthumb
Black Nightshade
Purslane
Redroot Pigweed
Volunteer Potato

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

20. Volunteer Potato in Carrot

21. 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

22. Reduced due to potato competitionb
POST/POST
POST
PRE/POST

23. 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.

24. 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

25. 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

26. 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

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