Picloram

Description

Picloram is a colourless crystal. It is very soluble in acetone, ethanol, benzene, and dichloromethane. It is a systemic herbicide used for general woody plant control, sold under the trade names Tordon and Grazon. It also controls a wide range of broad-leaved weeds, but most grasses are resistant. It is used in formulations with other herbicides such as bromoxynil, diuron, 2,4-D, MCPA, triclorpyr, and atrazine. It is also compatible with fertilisers. Picloram, in the pyridine family of compounds, is a systemic herbicide used for control of woody plants and a wide range of broad-leaved weeds. Most grasses are resistant to picloram, so it is used in range management programs. Picloram is formulated either as an acid (technical product), a potassium or triisopropanolamine salt, or an isooctyl ester, and is available as either soluble concentrates, pellets, or granular formulations. The materials in this document refer to the technical acid form unless otherwise indicated. Picloram is stable under acidic, neutral and basic conditions. Picloram is formulated either as an acid (technical product), a potassium or triisopropanolamine salt, or an isooctyl ester, and is available as either soluble concentrates, pellets, or granular formulations and related manufacturing impurities.

Chemical properties

Picloram is a colorless powder. Chlorine odor.

The Uses of Picloram

Picloram is a dicot-selective, persistent herbicide and in salt form is used to control a variety of annual weeds on crops, perennial broadleaved herbs, and woody species in combination with 2,4-D or 2,4,5-T. It can persist in an active form in the soil from several months to years, and can also be released from the roots of treated plants into the soil, where other nontarget species may take it up and die. Picloram is of great use in the management of unwanted vegetation in rangeland, grass pastures, and forestry as well as non-cropland and rightsof- way sites, such as around industrial and military installations, roads, railways, airports, under power lines, and along pipelines. Additional uses in some countries include in rice, sugarcane, cereals, and oilseed rape.

The Uses of Picloram

Herbicide.

The Uses of Picloram

Systemic herbicide used to control most broad-leaved weeds on grassland and noncrop areas. Use as a pesticide is restricted

The Uses of Picloram

It is used as a herbicide and defoliant.

Definition

ChEBI: Picloram is a pyridinemonocarboxylic acid that is pyridine-2-carboxylic acid which is substituted by a chloro group at positions 3,5 and 6, and by an amino group at position 4. It is a systemic herbicide used to control deeply rooted herbaceous weeds and woody plants in rights-of-way, forestry, range lands, pastures, and small grain crops. It has a role as a herbicide and a synthetic auxin. It is an aminopyridine, a pyridinemonocarboxylic acid, a chloropyridine and an organochlorine pesticide. It is functionally related to a picolinic acid.

General Description

Fine beige crystals or white powder. Odor of chlorine.

Air & Water Reactions

Insoluble in water.

Reactivity Profile

Picloram may be sensitive to prolonged exposure to light. Aqueous solutions may be decomposed by light. Picloram is incompatible with strong oxidizing agents, strong acids, acid chlorides and acid anhydrides.

Health Hazard

The toxic effects from ingestion or inhalation of dusts of picloram in test animals were mild. The acute oral LD50 values inrats and rabbits are 2900 and 2000 mg/kg,respectively. Maternal toxicity in rats wasobserved at a dose level of 750 mg/kg/day.Oral administration of picloram in rats andmice caused tumors in thyroid and liver.

Fire Hazard

Flash point data for Picloram are not available; however, Picloram is probably combustible.

Agricultural Uses

Herbicide: Picloram is a systemic herbicide used for control of woody plants and a wide range of broad-leaved weeds along roads, power lines and long right-of-ways. Most grasses are resistant to picloram, so it is used in range management programs to control noxious weeds and brush. It is used to prepare sites for tree planting. Picloram is formulated either as an acid (technical product), a potassium or triisopropanolamine salt, or an isooctyl ester, and is available as either soluble concentrates, pellets, or granular formulations. During the Vietnam war, a herbicide named Agent White was used to control vegetation. It was a mixture of 2,4-D, triisopropanolamine salt and picloram. A U.S. EPA restricted Use Pesticide (RUP).

Trade name

ACCESS®; AMDON®; AMDON GRAZON®; BOROLIN®; GRAZON® Picloram; K-PIN®; PATHWAY®; TORDON®[C]; TORDON® 101 MIXTURE; TORDON® 10 K; TORDON® 22 K

Biochem/physiol Actions

Picloram (4-Amino-3,5,6-trichloropyridine-2-carboxylic acid) is a chlorinated systemic herbicide widely used for woody plant and broad-leaved weed control. Picloram induces direct somatic embryogenesis of Lilium longiflorum var. Ceb-dazzel.

Safety Profile

Moderately toxic by ingestion. Questionable carcinogen with experimental carcinogenic, neoplas tigenic, tumorigenic, and teratogenic data. An experimental teratogen. Mutation data reported. When heated to decomposition it emits very toxic fumes of Cland NOx.

Potential Exposure

A potential danger to those involved in the manufacture, formulation or application of this herbicide.

Environmental Fate

Soil. Degrades in soil via cleavage of the chlorine atom at the m-position to form 4- amino-5,6-dichloro-2-picolinic acid. Replacement of the chlorine at the m-posi-tion by a hydroxyl group yields 4-amino-3-hydroxy-5,6-dichloropicolinic acid (Hartley and Kidd, 1987). Other soil metabolites reported include carbon dioxide, chloride ions, 4-amino-6- hydroxy-3,5-dichloropicolinic acid (Meikle et al., 1974), 4-amino-3,5-dichloro-6-hydroxypicolinic acid and 4-amino-3,5,6-trichloropyridine (Goring and Hamaker, 1971). Youngson et al. (1967) reported that degradation increased with an increase in temperature and organic matter
The half-lives for picloram in soil incubated in the laboratory under aerobic conditions ranged from 29 days to 3 years with an average of 201 days (Meikle et al., 1973; Yoshida and Castro, 1975; Merkle et al., 1976). In field soils, the half-lives for pi
Groundwater. According to the U.S. EPA (1986) picloram has a high potential to leach to groundwater.
Plant. Picloram degraded very slowly in cotton plants releasing carbon dioxide (Meikle et al., 1966). Metabolites identified in spring wheat were 4-amino-2,3,5-trichloropyridine, oxalic acid and 4-amino-3,5-dichloro-6-hydroxypicolinic acid (Redemann et al., 1968; Plimmer, 1970). In soil, 4-amino-3,5-dichloro-6-hydroxypicolinic acid was the only compound positively identified (Redemann et al., 1968)
Photolytic. The sodium salt of picloram in aqueous solution was readily decom-posed by UV light (λ = 300–380 nm). Two chloride ions were formed for each molecule of picloram that reacted. It was postulated that degradation proceeded via a free ra

Metabolism

Chemical. Picloram is generally stable to hydrolytic degradation but will decompose in hot, concentrated alkali solutions. It undergoes photodecomposition when irradiated with UV light and, to a lesser extent, with sunlight. Degradation via photolysis is thought to primarily involve cleavage of the ring structure and liberation of substituent chlorine atoms producing oxamic acid and 3-oxo-β-alanine. Decarboxylation is not thought to be a major pathway in photolytic degradation.
Plant. Hall et al. (16) have shown that in rapeseed plants (Brassica spp.) >25% of picloram is metabolized 24 hours after treatment.
Soil. There is only limited microbial degradation in the soil. If picloram remains on the soil surface, it may undergo photolysis.

Shipping

UN2588 Pesticides, solid, toxic, Hazard Class: 6.1; Labels: 6.1-Poisonous materials, Technical Name Required.

Toxicity evaluation

Mammalian Toxicity. Studies conducted on dog, rat, steer, and human males indicate that most, if not all, of orally administered picloram is quickly excreted unmodified in the urine. The acute oral LD₅₀s for male rat, mice, rabbit, guinea pig, sheep, and cattle are >5000, 2000–4000, ca. 2000, ca. 3000, >1000, and >750 mg/kg, respectively.
Weed Resistance/Modified Crop Tolerance. Weed resistance to picloram has been reported in populations of yellow starthistle (Centaurea solstitialis) (48) and wild mustard (Sinapis arvensis) (34). No crops with modified tolerance toward picloram are currently in production.

Incompatibilities

Incompatible with oxidizers (chlorates, nitrates, peroxides, permanganates, perchlorates, chlorine, bromine, fluorine, etc.); contact may cause fires or explosions. Keep away from alkaline materials, strong bases, strong acids, oxoacids, epoxides. Compounds of the carboxyl group react with all bases, both inorganic and organic (i.e., amines) releasing substantial heat, water and a salt that may be harmful. Incompatible with arsenic compounds (releases hydrogen cyanide gas), diazo compounds, dithiocarbamates, isocyanates, mercaptans, nitrides, and sulfides (releasing heat, toxic and possibly flammable gases), thiosulfates and dithionites (releasing hydrogen sulfate and oxides of sulfur). This material is acidic. Reacts with hot concentrated alkali (hydrolyzes), strong bases. May attack metals.

Waste Disposal

This chlorinated brush killer is usually formulated with 2,4-D and the disposal problems are similar. Incineration @ 1000C for 2 seconds is required for thermal decomposition. Alternatively, the free acid can be precipitated from its solutions by addition of a mineral acid. The concentrated acid can then be incinerated and the dilute residual solution disposed in an area where several years’ persistence in the soil can be tolerated.