2,4-D Amine 500 Mode, Toxicity, Fate, Properties & Regulations

20 MODE OF ACTION:

Foliar absorbed with some root absorption, translocated, post-emergent.

Disrupts cell growth and elongation. Multiple sites of action.

Uptake and translocation:

High concentrations may cause leaf burn and poor translocation leading to poor weed control. Translocated both up and down from the site of application to sources of active growth.

Physiological effects:

Causes twisting, swelling and splitting of soft stems and abnormal growth of leaves often resulting in cupping and inter-veinal chlorosis. Flowers are often deformed and seed viability may be affected. These symptoms may occur at very low dose rates.

Residual Life and Breakdown:

21 SELECTIVITY:

Most grasses are tolerant to 2,4-D. Woody plants have lower tolerances and soft broad leaved species are generally susceptible to rates around 1 kg a.e./ha.

Crop effects are usually only noticeable if applied at the incorrect growth stage and/or excessive rates.

Plant roots absorb polar (salt and amine) forms of 2,4-D most readily and leaves absorb non polar (ester) forms most readily. Salt formulations have negligible vapour pressure are the safer to use in close proximity to sensitive plants whereas ester formulations are generally safer prior to planting susceptible crops.

Crop tolerance:

Varietal sensitivities:

Applying 2,4-D to wheat before the completion of ear development may lead to yield loss and head deformities. Some varieties complete ear development at an earlier growth stage than others. The earliest timing for 2,4-D application therefore depends on the variety as indicated below


VarietyGrowth StageLeaves on the main stem.
AjanaZ155
AmeryZ166
AroonaZ166
ArrinoZ166
BladeZ166
BrooktonZ177
CadouxZ166
CalingiriZ177
CammZ166
CannaZ155
CarnamahZ166
CorriginZ166
CranbrookZ177
CunderdinZ177
DaggerZ177
EraduZ166
GamenyaZ166
GuthaZ155
HalberdZ166
KalannieZ155
KulinZ155
MacheteZ177
NyabingZ166
PerenjoriZ177
SpearZ177
StilettoZ177
TamminZ177
TincurrinZ155
WestoniaZ155
WilgoyneZ166


Effect on Clover Species:

Research done by Nufarm shows that clover tolerance increases at later growth stages and that at 1.4 L/ha minimal to light but acceptable damage to Balansa cv Paradana and subterranean clover cv Mt Barker, Trikkala, Larissa, Woogenellup and Northam occurs. Generally not as safe as MCPA 250 and 500 except on white clover. Few weed control advantages so MCPA is preferred.

Effect on Medic Species:

Damage trials as carried out by Nufarm.

Low rates of 350 mL/ha for barrel medic cv Paraggio, Sephi, Cyprus and Parabinga; gamma medic cv Paraponto; snail medic cv sava; spineless burr medic cv Circle Valley and Serena and strand medic cv Harbinger cause minimal to light but acceptable damage. Higher rates cause unacceptable damage.

Effect on Lucerne:

Death of seedlings or established plants very common especially at low rates of herbicides and even if leaf growth is at a minimum when sprayed. All formulations can cause severe damage, cutting/grazing prior to spraying can reduce damage but damage is usually unacceptable and severe. Herbicide drift onto lucerne can cause damage.

Effect on Native Plants:

Most native plants will tolerate low levels of 2,4-D and drift is not expected to cause significant long term effects on roadside trees or vegetation if reasonable care is taken to avoid exposure.

22 DISEASE AND INSECT EFFECTS:

Vascular diseases usually reduce the translocation of 2,4-D and may reduce efficacy. Leaf diseases may reduce the leaf area available for 2,4-D absorption and consequently reduce efficacy.

Low levels of insect damage may increase the absorption of 2,4-D increasing efficacy but also increasing the risk of crop damage. High levels of defoliation by insects may reduce efficacy due to decreased leaf area to collect spray droplets compared to the size of the plant.

23 PLANT SYMPTOMS:

Initial symptoms are usually apparent in 3-7 days and include twisting of soft stems, cupping of leaves and erection of rosette leaves. Malformed growth may take weeks to develop. Death of young plants usually occurs within a month. Older and woodier plants may take several months to die.

The table below summarises the effects of 2,4-D amines on the most sensitive species tested.
SpeciesGrowth stageFormulationEC25
g a.e. /ha
NOEC
g a.e./ha
Sorghum (Monocot)Seedling2,4-D DMAS (amine)2917
Mustard (Dicot)Seedling2,4-D DEA (amine)50<50
Tomato (Dicot)Vegetative2,4-D DEA
(amine)
3.32.2
Table adapted from EPA 738-R-05-002, June 2005

For sensitive species like Tomato, rates around 5 mL/ha of 2,4-D amine can cause symptoms.

For cereals the ester formulations are less damaging to the crop pre planting than the amine formulations.

SECONDARY EFFECTS:

Sugar contents of sprayed plants normally increase within a week of spraying and this may make the plants more palatable to herbivores including sheep and insects. This may cause stock problems if toxic plants are present.

24 TOXICITY:

Summary:

2,4-D amine is generally of low toxicity to mammals, birds, bees and aquatic organisms.

Details:

Poison schedule: S5.

Mammalian toxicity: Low toxicity.



Acute oral: LD50 735-1646 mg/kg (rats) [For comparison table salt is 3000 mg/kg]

Acute dermal: LD50 1829 to >2000 mg/kg (rabbits)

Skin: Primary irritation. Slight skin irritant.

Skin: Sensitisation. Not a dermal sensitizer.

Eye: Severe eye irritant.

Vapour inhalation: LC50 3.1 to >4.97 mg/L (rat)

Chronic oral toxicity: NOEL 5 mg/kg/day for two years rats and 30 mg/kg/day for rabbits.

Acute dietary toxicity: NOEL 25-67 mg/kg/day.

High doses have caused reproductive effects in test animals.

Data indicates that 2,4-D has low teratogenic potential or is not teratogenic.

Several studies investigated 2,4-D as a carcinogen with varying results. At normal exposure levels it is not expected to be carcinogenic.

Acceptable Daily Intake (ADI): 0.01 mg/kg/day.

Other Species:

Birds: LD50 = 415 to >1000 mg a.e./kg. Moderately to practically non toxic. The acid, amine and ester formulations have similar toxicity. Chronic NOEC for birds is 992 ppm for 2,4-D acid formulation.

Fish: toxicity LC50 >80.24 to 2244 mg a.e./L for acid and amine formulations

NOEC of 14.2 to 63.4 mg a.e./L for 2,4-D acid, 2,4-D DEA and 2,4-D DMAS formulations based on larval fish survival for the fish full life cycle studies.

2,4-D amine and acid formulations are practically non toxic to freshwater and marine fish.

2,4-D acid and dimethyl amine are practically non toxic to tadpoles.

Invertebrates: LC 50 = 25 to 830 mg a.e./L for freshwater and marine invertebrates for 2,4-D acid and amine formulations. That is slightly toxic to practically non-toxic to freshwater marine invertebrates.

Bees: Practically non toxic. LD50 > 10 ug/bee. Moderate doses have impaired brood production.

Arthropods: toxicity.

Earthworms:

25 TOXICITY SYMPTOMS:

26 FIRST AID:

If SWALLOWED: If more than 15 minutes from a hospital, induce vomiting preferably using Ipecac Syrup APF. See a doctor.

If in EYES: Irrigate with plenty of water. Amine and salt formulations are severe eye irritants. See a doctor.

If on SKIN: Rinse with plenty of water, remove contaminated clothing, wash with soap and water.

If INHALED: Remove patient to fresh air. See a doctor.

Advice to doctor: Treat symptomatically.

Contact the Poisons Information Centre on 131126.

27 ENVIRONMENTAL FATE:

Half life in soil: 2,4-D acid has a aerobic soil half life of 6.2 days.

Half life in water: 2,4-D acid has an aerobic half life of 15 days and an anaerobic half life of 41-333 days.

2,4-D acid is stable to abiotic hydrolysis with a half life of 1-2 years.

It has an EPA classification for soil mobility that ranges from intermediate to very mobile. Usually very low mobility in field studies even though laboratory solubility studies indicate 2,4-D is potentially mobile. Rapid degradation in the soil and removal from soil by plant uptake minimizes leaching under realistic application conditions.

Significant ground water contamination not likely but it has been detected in ground and surface waters in the US and Canada. Rarely detected more than 500 mm deep in soils.

Accumulation in milk and tissues.

pH stability:

Photolysis rate: 2,4-D acid half life (DT50) was 12.9 days in water at pH 5 and 68 days in soil.

Hydrolysis half life: Stable to abiotic hydrolysis.

Biodegradation rate: 2,4-D acid half life is 6.9 days in aerobic soils and 15 days in aerobic aquatic environments. 2,4-D amine and salt formulations are similar. Most field studies show an apparent half life of 1.7 - 13 days with an average of 5 days in moist soils. In dry soils the half life is much longer because most of the breakdown is due to microbial activity. The half life in grass and thatch was < 7 days on average. The half life in natural water is 1-2 weeks but may be only a few days in rice paddies.

2,4-D degrades through several low toxicity intermediates to carbon compounds, CO2, water and chlorine or HCl.

UV breakdown rate: Probably has a half life of 2-13 days

28 REGISTERED CROPS:

See HerbiGuide Species Solution tab.

29 REGISTERED WEEDS:

See HerbiGuide Species Solution tab.

30 REGULATION AND LEGAL:

UN number:

Dangerous goods class:

Hazchem code:

NOHSC classification:

Proper shipping name:

Packaging group:

EPG:

CAS numbers: DEA = 5742-19-8, DMA = 5742-19-8, IPA = 5742-17-6, TIPA = 32341-80-3.

31 PROPERTIES:

Water solubility: 170000-720000 mg/L at 25 C at pH ;

Oil solubility: Low.

Octanol:Water ratio: N/A; salt dissociates to acid in water.

Soil organic carbon absorption coefficient (Koc): 31.2-470.9 mL/g.

Soil DT50 aerobic 20 C - 1.7 days.

Soil DT50 anaerobic 20 C - 333 days (aquatic study).

Hydrolysis: 1-2 years sterile water pH 7 buffered.

Photolysis water DT50 13 days (artificial sunlight)

Photolysis soil DT50 68 days

Vapour Pressure: <1 x 10-7 at 26 C.

Dissociation constant: pKa

Melting point: 87-121 C.

Boiling point: C.

Molecular weight: 280-412 g/mole.

Colour: Light brown or amber.

Odour:

Bulk density:

Specific gravity: 1.15-1.23.

pH:

Flammability: Non flammable.

Shelf Life: 60 months (5 years).

(When Stored under Ideal Conditions)

32 COMMENTS:

2,4-D decreases nitrate reductase in the plant and this results in an increased nitrate level. In some plants, such as Capeweed, Radishes, Turnips, and Canola, this may reach toxic levels.

33 REFERENCES:

Ashton, F.M. and Crafts, A.S. (1981) Mode of Action of Herbicides. (Wiley-Interscience publication).

Kearney, P.C. and Kaufman, D.D. (1976). Herbicides. Chemistry, degradation and mode of action. Vol 1 & 2.

Acknowledgments:

Collated by HerbiGuide. For more information see www.herbiguide.com.au or phone 08 98444064.