Lorox / linuron
Chemical Name: N'-(3,4-dichlorophenyl)-N-methoxy-N-methylurea.
Chemical Family: Substituted ureas.
WSSA Resistance Group: 7
Crop/non-crop registration: Corn, soybeans, wheat, oats, barley, potatoes, carrots
Sensitive weeds: Many annual grasses and BLW (broadleaf weeds); seedlings of dandelion, plantain and perennial sow-thistle.
Application method: PRE, POST.
Absorption & Translocation: Readily (most) absorbed by roots via xylem, some 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: Differential metabolism, uptake and translocation in tolerant species.
Symptoms: Symptoms first observed in older leaves (foliar veinal chlorosis (yellowing) and leaf-tip dieback) develop within several days of application; later on, have water-soaked wilted appearance which eventually lead to stem collapse, necrosis (brown in BLW, white in grasses) and plant death.
Residuality: Intermediate (1- 4 months).
Toxicity: Oral LD50 = 1254 mg/kg - moderately toxic.
Additional comments: Do not use on sandy or coarse-textured soils having less than 2% organic matter; if unusually heavy rains follow application, severe injury may occur to corn, soybeans, carrots and potatoes.
Images above: Linuron (PRE) damage on velvetleaf. Note the water-soaked wilted appearance of older leaves (left). Linuron (PRE) on broadleaf and grass crops and weeds. Note: healthy appearance of corn, soybean, and winter wheat in the front flat and absence of weeds in the two other flats (right).