Sencor / metribuzin

WSSA Resistance Group: 5

Crop/non-crop registration: Corn, soybeans, barley, winter wheat, established alfalfa, potatoes, established asparagus, carrots, transplant tomatoes

Sensitive weeds: Many annual BLW (broadleaf weeds) and some annual grasses (e.g. foxtails, barnyard grass, witchgrass, crabgrass).

Application method: PPI (not for corn), PRE and POST (not for soybean).

Absorption & Translocation: Readily (most) absorbed by roots via xylem, moderate uptake also by foliage;translocated to top of plant accumulating at growing points and leaf margins (i.e. acropetal movement); uptake and translocation rates increase with transpiration rates.

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: Leaf margin discoloration (chlorosis) develops within several days of application particularly on older leaves; discoloration continues towards the base, followed by crisping and complete browning; older leaves are more damaged than younger leaves; control of susceptible species within 2 weeks.

Residuality: Intermediate (1- 4 months).

Toxicity: Oral LD50 = 1090 mg/kg - moderately toxic.

Additional comments: Heavy rainfall following application may cause crop damage; some potato, soybean, and tomato varieties less tolerant than others; do not use on muck soils; triazine-resistant weeds are not controlled.