bensulide (Prefar 4-E)
Not for use in Willamette Valley of Oregon; garlic, dry bulb onions and shallots only (Idaho and Oregon only)
Rate 5 to 6 lb ai/a (5 to 6 quarts/a)
Time Fall application, during bed construction: apply after markout when soil temperature is below 60°F. Prepare a good, flat seedbed following standard cultural practices. Apply Prefar 4-E in the fall in 10 to 50 gal of water in 10- to 12-inch bands and bed-up, throwing soil from the furrows over the sprayed band of Prefar 4-E. Allow to remain undisturbed until spring. Prior to planting in spring, drag-off the bed tops being careful not to drag off soil below the level of Prefar 4-E application. Plant in the center of the bed. Do not apply more than 6 lb ai/a per season.
Remarks Shallow mechanical incorporation can be substituted to maintain the herbicide above the onion seed. If mechanically incorporated, use spike-tooth harrow, smizer roller, or similar equipment to maintain shallow and uniform layer of herbicide within the upper 1 inch of soil for sandy soils or the upper 0.5 inch for loam soils. Use low rates on sandy soils. Will not control germinated weed seedlings. Inhibits roots of emerging seedlings.
Site of action Group 8: lipid synthesis inhibitor but not an ACCase inhibitor
Chemical family Organophosphorus
S-metolachlor (Dual Magnum)
Fall preplant for yellow nutsedge control in dry bulb onions; Oregon and Idaho only
Rate and Time West of the Cascades: apply 1.27 lb ai/a (1.33 pints/a) of Dual Magnum in fall. Use low rate on mineral soils and high rate on muck soils. Apply before fall rains begin or after the first light rain. Do not incorporate Dual Magnum with tillage, as this will reduce yellow nutsedge control.
East of the Cascades: apply 1.27 lb ai/a (1.33 pints/a) to 1.9 lb ai/a (2 pints/a) of Dual Magnum after wheat harvest in early fall and then moldboard plow and disk to ensure thorough incorporation in the soil. Adjust the rate according to soil texture. To reduce risk of crop injury, apply at least 130 days before planting onion seed, sets, or transplants. Fall preplant (plow-down) application should not exceed 2 pints/a. Total preplant and postemergece applications should not exceed 2.5 pints/a.
Remarks Indemnified SLN labels OR-040009 and ID-990016 available at farmassist.com. Dual Magnum inhibits roots and shoots formation.
Caution Recent experience at the OSU Malheur Experiment Station indicates onions may be injured if Dual Magnum is not sufficiently incorporated in fall, and if weather remains cold and wet after onions are planted in spring. Similarly, chances of crop injury increase if the weather during winter and spring remains dry. Risk of crop injury is greater on light-textured soils and at higher application rates. Tank-mixes with other pesticides may increase potential of crop injury. Only one application in fall is recommended. No more than 2 pint/a in a single fall preplant application. Avoid areas with shallow groundwater and directly applying to water.
Site of action Group 15: inhibits very long chain fatty acid synthesis
Chemical family Chloroacetamide