Atrazine is a translocated, pre and post emergence herbicide that is mainly absorbed by the roots with some foliar absorption. It controls a wide range of weeds in tropical (C4) grass crops, triazine tolerant crops, orchards, vineyards, plantations and fallow situations.
Best residual weed control comes from split applications where an initial dose is applied and a half dose is applied each month until weeds have finished germinating.
For post emergence control of weeds the minimum rate is around 500 g/ha of atrazine900 with 1% spray oil. Weeds must be small and those with more than 4 leaves or more than 3cm tall are not likely to be adequately controlled unless they are very shallow rooted species like Rat or Squirrel-tailed Fescue (Vulpia species or Silver Grass).
Atrazine will survive on dry soil but will have little action until water is present to take it into the roots.
Rainfast in 1 hour for post emergent applications. Rainfast immediately for pre emergence applications.
Frost effects: Reduced post emergence activity on frost affected plants. Frost has little effect on pre emergence activity.
Wind: Because of its generally low levels of post emergence activity, drift due to wind rarely causes damage.
Inversions: Because of its generally low levels of post emergence activity, drift due to inversions rarely causes damage.
Delta T and relative humidity: Avoid application when Delta T is greater than
Soil moisture at application: Good soil moisture before and after application is generally required for good weed control as it acts mainly through root absorption. Rain or irrigation to thoroughly wet soil through the weed root zone is required within 10 days of spraying for best results.
For pre emergent applications no adjuvants are required.
For post emergent applications the mineral spray oils such as DC-Tron, DC-Trate, Spray Plus, Uptake, Ad-here and others at 1-2% provide far better control of most weeds than the esterified vegetable oils such as Hasten and Kwickin or wetting agents or multi purpose products such as LI700.
Results from the Birchip Group showed Radish control of 84-97% with 0.5-2% of mineral oils, 59-69% with 0.3-1% of esterified vegetable oils and 51% with 0.25% of wetting agent.
10 WATER QUALITY:
Pre emergent applications can be applied with liquid fertilisers.
There may be increased fertiliser burn when applied as a post emergent application.
Conventional boom sprays with flat fan nozzles applying 30 L/ha or more for pre emergence applications and 100 L/ha or more for post emergence applications are normally used. Fine nozzles are prone to blockages with many formulations.
Use 50-80 mesh screens to reduce filter blockages.
Carrier volume: 30 L/ha water or more. For post emergence applications 100 L/ha water or more is recommended if using large droplet nozzles.
Nozzles: Flat fan.
Pressure: 150-400 kPa.
Carrier volume: 15 L/ha water or more for pre emergence applications and 25 L/ha water or more for post emergence applications. Rainfall or irrigation after spraying is more critical for good results with aerial applications.
13 SPRAYER DECONTAMINATION:
Clean soon after spraying to reduce the risk of forming dried deposits that may be difficult to remove. Mechanically removed any caked deposits.
Remove filters and clean separately. Rinse with soapy water (eg 500 mL or g of Drive, Dynamo, Omo or Surf per 100 L water) or water plus 0.25% wetting agent and run through boom. Rinse with water.
Remove filters and clean then soak in 500 mL household ammonia in 10 L water for 30 minutes.
Rinse sprayer with soapy water (eg 500 mL or g of Drive, Dynamo, Omo or Surf per 100 L water) or water plus 0.25% wetting agent and run through boom. Add 1 L of household ammonia (3% active ingredient) per 100 L water while filling the tank. Circulate through the system and spray a small quantity through the boom then leave for several hours. Rinse with soapy water or water plus 0.25% wetting agent. Rinse with water. Or use a commercial spray tank and equipment cleaner.
Rinse nozzles and filters in water and replace.
14 HERBICIDE RESISTANCE:
Tolerant plants are expected to occur and may dominate the weed population after repeated applications.
Atrazine resistance in weeds will disappear a few years after the last application of triazine herbicides because the resistant plants are less competitive than the susceptible plants. Rotate to other herbicides when triazine resistance first appears.
15 REPLANTING INTERVALS:
6 weeks for rates up to 500 g/ha
12 weeks for rates up to 1 kg/ha
6 months for rates up to 2 kg/ha
12 months for rates up to 4 kg/ha
At least 6 months for crops not on the label.
Times may be longer under dry conditions and on alkaline soils.
16 WITHHOLDING PERIODS:
Canola (pre emergence)
Canola (post emergence)
Not required when used as directed
All other crops
Not required when used as directed.
17 RE-ENTRY PERIOD:
Wear protective clothing if in contact with the crop before the spray has dried.
18 PROTECTIVE CLOTHING:
Overalls, boots and washable hat.
Atrazine tends to be bound by clays and higher rates are often required on heavy soils.
Crop damage from pre emergent sprays is more likely on light soils.
Atrazine persists longer on alkaline soils.
To reduce the risk of atrazine carry-over into subsequent crops, don't' exceed 2 kg/ha Atrazine900 on soils with a pH less than 6.5, and don't' exceed 1 kg/ha Atrazine900 on soils with a pH greater than 6.5 (and on alkaline soils).
Soil organic matter:
Atrazine tends to leach more in soils with low organic matter and has more activity on plants.
Soil nutrient status:
More atrazine is absorbed by susceptible plants and less by tolerant plants in good nutrient conditions and inactivation in tolerant plants is faster (1296, 1297) so better weed control and greatest crop safety occurs at optimum nutritional levels.
20 MODE OF ACTION:
Inhibits photosynthesis at photosystem 2. Tolerant plants metabolise it.
Uptake and translocation:
Absorbed mainly by roots with some absorption through leaves.
Residual Life and Breakdown:
Half life in moist soil is generally around 4-6 weeks.
Selective or non-selective depending on timing and rate of application.
Tends to provide better control of C3 grasses than broad leaved species. Species in the Fabaceae family are usually more tolerant than others species.
Many C4 species are tolerant.
Some crops have been bred to be tolerant to atrazine.
Damage may occur if applied post emergence with crop oil to stressed crops.
Some varieties of Lupins and wheat are more tolerant than others.
Effect on Clover Species:
Partially tolerant to low rates.
Effect on Medic Species:
Partially tolerant to low rates.
Effect on Lucerne:
Established Lucerne tolerates low rates.
Effect on Native Plants:
Most established native plants are tolerant to low rates.
22 DISEASE AND INSECT EFFECTS:
Crops with root disease or insects that attack roots are more prone to damage.
23 PLANT SYMPTOMS:
Leaf yellowing and death along the edges of leaves followed by overall death. Some plants show strong veinal or inter-veinal yellowing. It usually take 1-2 weeks before effects are noticeable.
No effect on seed germination or radicle elongation at rates up to 4.5 kg a.i./ha.
Slightly to moderately toxic to mammals. Atrazine is absorbed through the gastrointestinal tract, lungs and skin.
Poison schedule - Exempt.
Mammalian toxicity -
Acute oral LD50 - 5100 mg/kg (rats), [For comparison table salt is 3000 mg/kg]
Acute dermal LD50 - 9300 mg/kg (rabbit).
Skin - Mild skin irritant (WHO classification)
Eye - Severe eye irritant (WHO classification)
Vapour inhalation - LC50 - >2 mg/L air (rat).
Chronic oral toxicity NOEL - ppm for two years.
Not carcinogenic, mutagenic or teratogenic (i.e. does not cause cancer or reproductive problems).
It is readily absorbed through the gastrointestinal tract, lungs and skin.
At high doses it can cause neuromuscular effects such as motor incoordination, paralysis of limbs, respiratory distress and hypothermia.
Other Species -
Birds - practically non toxic.
Fish - slight toxicity LC50 > ppm.
Invertebrates - Slight to moderate toxicity.
Bees - toxicity.
Algae - High toxicity. NOEC (No effect concentration) 0.0037 mg/L for Chlamydomonas reinhardtii (Girling et al, 2000).
Highly toxic to duckweed.
Reports of effects on frogs are not likely to occur at levels of atrazine that occur in the field.
The NOEC for crustacea is higher for freshwater species than marine species. The lowest EC50 was 4.3 mg/L for marine copepods and the lowest NOEC was 1 mg/L for pink shrimps. Most other aquatic invertebrates have much higher tolerances.
Bacteria are very tolerant of atrazine. There is no effect on soil microbial activity at 15 kg a.i./ha. There was no effect on bacteria from sewerage sludge at > 100 mg/L so it is not expected to cause problems in treatment plants.
The lowest chronic NOEC in fish was 0.06 mg/L.
The lowest chronic NOEC in aquatic invertebrates (Daphnia magna) was 0.04 mg/L.
No effects were seen on ground beetles at 1.5 kg a.i./ha.
The LC50 for earthworms is 78 mg/kg.
Atrazine doesn't affect N conversion in the soil.
NOEC for birds is 1250 mg/kg.
No effect on seed germination or radicle elongation at rates up to 4.5 kg a.i./ha.
25 TOXICITY SYMPTOMS:
26 FIRST AID:
If SWALLOWED -
If in EYES - Irrigate with plenty of water.
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.
27 ENVIRONMENTAL FATE:
It has a half life of 55 days at 20 degrees and 50% WHC in Mohlin soil. The half life in soil can vary considerably with Australian values ranging from 12 days to 140 days.
It is broken down mainly by chemical processes with some degradation due to micro-organisms, metabolism by plants and UV degradation on surfaces.
It has an EPA classification for soil mobility that ranges from moderately to highly mobile in soils with low clay or organic matter contents.
It has a leaching index of 10. (For comparison, trifluralin is 0-1 and chlorsulfuron is 25-30).
Ground water contamination risk is high in some situations. Most of the atrazine in aquatic ecosystems enters via surface runoff. 80-90% of the atrazine that occurs in streams, lakes and ground water is due to a few post-application run off events (or storms) within a few weeks of application. In the US about 2% of the atrazine applied to the catchment is eventually discharged into the sea (USGS, 1999).
Bubb and Barnes (2000) have Australian results on atrazine in the environment.
Ecosystems are not likely to be affected with atrazine concentrations below 0.05 mg/L in the water (Giddings & Hall, 1998; Huber, 1993).
Accumulation in milk and tissues - does not accumulate in milk or tissues. Traces of the breakdown products (particularly 2-chloro-4,6-diamino-s-atrazine) are occasionally found in milk.
In soil atrazine is moderately absorbed by the clay and organic matter and degrades mainly by chemical dealkylation (to form the more mobile desethylatrazine) and dechlorination reactions
28 REGISTERED CROPS: (Button)
29 REGISTERED WEEDS: (Button)
30 REGULATION AND LEGAL:
OPP Chemical Code:
Dangerous goods class (ADG): Not classed as a dangerous good.
Proper shipping name:
International Maritime Dangerous Goods Code (IMDG):
Water solubility at 25 C. - 33 ppm at pH. Moderately soluble, slightly hydrophilic.
Oil solubility -
Octanol:Water ratio at 25 C. - at pH 5;
Vapour Pressure at 25 C. -
Dissociation constant - pKa
Melting point - C.
Molecular weight -
Half life in water - days at pH5 and 35 C.
Bulk density -
2100 tons of active ingredient was sold in Australia in 1998.