soil fumigants
See the current edition of the PNW Plant Disease Management Handbook for application details and approved materials.
glyphosate (several product names)
Rate Consult labels
Time Apply to actively growing weeds with 'site preparation' or 'preemergence to crops' uses listed on label.
Remarks See label for specific rates, application times, and perennial species controlled. Use higher rate if annual weeds are more than 6 inches tall.
Caution Do not exceed 8 lb ai/A per year.
Site of action Group 9: inhibits EPSP synthase
Chemical family Glycine
metam sodium (several brands)
Rate 63 to 317 lb ai/A (15 to 75 gal/A product)
Time Apply preplant when conditions will enhance moving from liquid to gas phase in soil.
Remarks Cultivate soil 7 to 10 inches deep before preparing a uniform seedbed using equipment that leaves a smooth surface. Soil moisture must be adequate for seed germination but below field capacity. Apply when temperatures exceed 50°F, with a boom mounted on the front of a rototiller. Incorporate 3 to 4 inches deep; seal surface of soil with a smooth roller power-driven to travel at same speed as tractor. Soil surface must be smooth without cracks where fumigant may escape.
Delay planting until soil is free of metham, usually 14 to 21 days. Plant radish seeds or transplant radish seedlings while protecting from wind and bright sun. Observe for 12 to 24 hr for wilting. Before planting, till the soil surface (3 to 4 inches) while breaking the compacted layer formed during incorporation of metam using a small shank within the seed row.
Caution Restricted use pesticide due to acute toxicity. Pay particular attention to the personal protective equipment required for these products including respirators and face shields, and wear protective clothing. Metam sodium is dissolved in water for application. Activity depends on several soil factors that enhance conversion and movement from the liquid to gas phase. Avoid mixing soil from beneath the treated layer. Do not contaminate water, runoff water, or fish habitat. Disrupts cell membranes.