Lasso / alachlor

WSSA Resistance Group: 15

Crop/non-crop registration: Corn, soybean, grain sorghum, beans

Sensitive weeds: Most annual grasses; yellow nutsedge; galinsoga, lambsquarters, purslane and black nightshade.

Application method: PPI, PRE or early POST in corn; PPI or PRE in soybean; PPI in beans.

Absorption & Translocation: Absorbed primarily by emerging plant shoots (grass coleoptile, broadleaf hypocotyl or epicotyl, and secondarily by seedling roots;older plants readily absorb alachlor into roots and translocate upward throughout shoots; translocation in established plants irrelevant as alachlor is phytotoxic only to emerging seedlings.

Mode of Action: Not well understood.

Metabolic pathway inhibited: May include inhibition of fatty acid and lipid biosynthesis; as well as gibberellin synthesis; does not inhibit seed germination.

Basis of Selectivity: Metabolized by tolerant species at the seed germination stage by enzymatic breakdown.

Symptoms: Most susceptible grass and BLW (broadleaf weeds) fail to emerge; susceptible grasses that do emerge appear twisted/malformed with leaves tightly rolled in whorl and unable to unroll normally; leaves do not emerge properly from coleoptile and may do so underground; in BLW seedlings leaves may show some cupping and crinkling and shortened leaf midribs producing a 'drawstring' effect on the leaf tip.

Residuality: Intermediate (1-4 months); provides season long control (6-10 wks) with no soil residues in the following year to limit rotations.

Toxicity: Oral LD50 = 1100 mg/kg - moderately toxic (LASSO = 2000 mg/kg - moderately toxic).

Additional comments: RESTRICTED use herbicide (DANGER) due to oncogenicity in rats.