Aatrex / atrazine

WSSA Resistance Group: 5

Crop/non-crop registration: Corn

Sensitive weeds: Annual BLW (broadleaf weeds); widespread resistant populations to atrazine in NY State include common ragweed, lambsquarters, redroot pigweed and common groundsel.

Application method: PPI, PRE and POST-before weeds attain 4 cm (1.5") in height.

Absorption & Translocation: Actively absorbed by roots via apoplasm (including xylem) and readily absorbed by foliage in POST applications;translocated to top of plant accumulating at growing points and leaf margins.

Mode of Action: Inhibition of photosynthesis and ATP formation by blocking electron transport.

Metabolic pathway inhibited: Inhibition of photosynthesis by binding to the QB-binding niche on the D1 protein of the photosystem II complex in chloroplast thylakoid membranes, thus blocking electron transport from QA to QB; this stops CO2 fixation and production of ATP and NADPH2 which are required for plant growth; however, plant death often results from other factors (e.g. lipid peroxidation).

Basis of Selectivity: Metabolized to non-toxic compounds by tolerant species.

Symptoms: Interveinal chlorosis of leaves and yellowing margins within several days of application which ultimately results in wilting and necrosis; older leaves are more damaged than younger leaves; browning of leaf tips; root growth not affected; sub-lethal levels can cause greening in some species (e.g. radish); control of susceptible species within 2 weeks.

Residuality: Intermediate to long (persistence increases in dry, cool weather, sandy soils and higher soil pH); thus rotation to soybean the following year may be a problem; typically no persistence problems occur

Toxicity: Oral LD50 = 3090 mg/kg - slightly toxic (AATREX NINE-O = 1600 mg/kg - moderately toxic).

Additional comments: Shallow incorporation beneficial under dry conditions; surfactants and oil adjuvants increase rate and amount of foliar absorption.

Images above: Interveinal chlorosis in soybean caused by a pre-emergent (PRE) application of atrazine (left). Atrazine-resistant common lambsquarters

Images above: Atrazine (PRE) on broadleaf and grass crops and weeds (left). Atrazine (PRE) on soybean and winter wheat (right).