Annual Grass and Broadleaf Weeds in New Plantings and Established Crops

napropamide (Devrinol DF-XT, Devrinol 2XT, Devrinol 10G)

Rate 4 lb ai/A (8 lb/A of 50% products)

Time In furrow-irrigated mint, it is most effective to apply late in the fall to allow winter rain to carry herbicide into soil. In sprinkler-irrigated mint, apply any time before weeds emerge. May be applied to newly planted mint immediately after planting.

Remarks There is some evidence that napropamide breaks down with continued exposure to sun. This photodecomposition can be minimized by rain, sprinkler irrigation, or mechanical incorporation. November through February treatment must be incorporated or irrigated in if no rain falls within 2 weeks of application. Treatments outside of this November through February window must be incorporated or irrigated in within 24 hours if no rain falls. Results are best if mechanically incorporated within 24 hours after application regardless of time of year applied.

Caution Napropamide has injured mint that was not rotovated before herbicide application. Will not control emerged weeds. Do not apply to ground that is frozen or heavily covered with leaves or trash.

Site of action Group 15: inhibits very-long-chain fatty acid synthesis

Chemical family Acetamide

sulfentrazone (Spartan 4F and other trade names)

Rate 0.14 to 0.375 lb ai/A (4.5 to 12 oz/A) depending on soil type and organic matter. Reduce application rate by 25% for new plantings. Do not apply more than 12 oz/A per year.

Time Apply to dormant mint in spring after any cultivation and before new growth emerges, or postharvest in fall or winter after any cultivation when mint is dormant. Split applications may be used for preemergence sequential control of winter annual and summer annual weeds. May be applied to new mint plantings before weeds emerge and mint begins growth.

Remarks Adjust rate for soil type, soil organic matter content, and soil pH. Will not adequately control most grasses. In new plantings, reduce application rate 25% from the rate for established plantings with the particular soil characteristics. Apply with a registered burndown herbicide to control weeds emerged at application. A surfactant is recommended with these tank-mixes to increase control of emerged weeds. Overhead moisture required after application to activate the herbicide. Foliage that persists during dormancy may be discolored. Foliage on new growth may be discolored temporarily. May be tank mixed with other labeled herbicides to broaden weed control spectrum.

Caution Do not apply to soils classified as sand and with less than 1% organic matter content. Applications to stressed mint may injure crop. Applications to emerged mint will severely injure exposed plant tissue. Do not cultivate after applying. Do not exceed 0.375 lb ai/A in a 12-month period. Do not mix with fertilizers. Note re-cropping restrictions on the label.

Site of action Group 14: protoporphyrinogen oxidase inhibitor

Chemical family Triazinone

terbacil (Sinbar WDG)

Rate 0.8 to 1.6 lb ai/A applied preemergence to mint or 0.8 to 1.6 lb ai/A plus recommended surfactant or nonphytotoxic spray oil applied postemergence to small, actively growing weeds (1 to 2 lb/A Sinbar)

Time West of the Cascades, apply before crop emerges in spring or in fall after last cultivation. East of the Cascades, apply before emergence any time after the first settling rain in fall. Do not apply when ground is frozen. Make postemergence applications before broadleaf weeds are 2 inches tall or across, and grasses are 1 inch tall or across. If not applied preemergence, two postemergence treatments may be made.

Remarks Almost all spring terbacil application failures result from inadequate moisture to activate the chemical during the time when weeds are germinating and growing. If moisture is inadequate to activate the chemical, irrigation must follow fall or winter treatment as soon as soil thaws in spring (or promptly after spring treatment). On soils with good subsurface moisture, best results are by applying 0.75 to 1 inch of overhead moisture before weeds are more than 1 inch high. If subsoil is dry, or if weeds have germinated and their roots penetrate deeply into the soil, 1.5 to 3 inches of irrigation may be required. For furrow-irrigated or rill-irrigated mint, take care to thoroughly wet across the entire bed after applying, or weed control may be poor. Control under those conditions may improve by applying in fall, for activation by winter rain, or by incorporating terbacil into top 1 inch of soil during final bed preparation before crop emerges in spring. This is especially true if spring rain is erratic or inadequate to activate terbacil. For fall application west of Cascades, apply early, before weeds emerge. Results have been poor after weeds, such as groundsel and prickly lettuce, develop a taproot. For postemergence application, apply before broadleaf weeds are 2 inches tall or across and before grasses are 1 inch tall or across. Add 0.5 to 1 pint of surfactant per 25 gal of spray mixture, 1 gal/A of nonphytotoxic superior-type spray oil, or 1 quart/A of surfactant-oil mixture (such as Herbimax or MorAct). Two applications of terbacil (preemergence + postemergence or postemergence + postemergence) may be made within 1 year, but the total applied should not exceed 1.6 lb ai/A in any 1 year. This treatment will not control green foxtail. Terbacil resistant common lambsquarters and redroot pigweed are present in many fields in the PNW.

Caution Do not apply within 60 days of harvest. Unless otherwise directed, do not use on sand, loamy sand, or gravelly soils or on soils with less than 1% organic matter. If used on soils with these conditions, limit use to a small area to determine crop response prior to treating larger areas. Do not exceed 1.6 lb ai/A total per season. Residues can persist after mint plow-out and can injure later crops. Do not replant treated areas to any other crop within 2 years after last terbacil application. Deep plowing (10 to 12 inches) helps reduce injury from carryover. Mint sometimes has been injured when terbacil was applied before, with, or after certain insecticides, especially organophosphates such as Dyfonate. Injury usually has been with applications less than 3 weeks apart and has been especially severe on new stands or on mint emerging from shallow, weak roots, particularly on sandy or gravelly soils. To minimize the possibility of injury, follow the labels of both products carefully. Avoid closely timed applications, especially to weak mint on coarse soils. Mint stressed by double cutting, drought, high salt content of soils, insects, diseases, or other factors may be injured.

Site of action Group 5: photosystem II inhibitor

Chemical family Uracil