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Mint
Revised October 31, 2008
MINT—Annual Grass and Broadleaf Weeds in New Plantings and Established Crop • terbacil
Rate 0.8 to 1.6 lb ai/A applied preemergence to mint or 0.8 to 1.2 lb ai/A plus recommended surfactant or nonphytotoxic spray oil applied postemergence to small, actively growing weeds
Time
West of Cascades, apply before crop emerges in spring or in fall after last cultivation. East of Cascades, apply before emergence any time after the first settling rain in fall. 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 are from inadequate moisture to activate the chemical 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 in 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 yr, but the total applied should not exceed 1.6 lb ai/A in any 1 yr. This treatment will not control
green foxtail.
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 injure later crops. Do not replant treated areas to any other crop within 2 yr 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 wk apart. Injury has been especially severe on new stands or on mint emerging from shallow, weak roots and 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
• sulfentrazone
Rate 0.14 to 0.375 lb ai/A (4.5 to 12 fl oz/A product)
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 emergence and mint begins growth.
Remarks
Adjust rate for soil type 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. Some foliage may be discolored temporarily. May be tank-mixed with other labeled herbicides to broaden weed control spectrum.
Caution
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-mo period. Do not mix with fertilizers. Note recropping restrictions on the label.
Site of action
Group 14: protoporphyrinogen oxidase inhibitor
Chemical family
Triazinone
• sulfentrazone + glyphosate
Rate 1.15 to 3.06 lb ai/A (32 to 85 fl oz/A Spartan Advance)
Time
Apply preemerge to new mint plantings.
Remarks
Consult label to determine rate for soil pH, percentage of organic matter, and texture.
Caution
Do not exceed 3.105 lb ai (86.4 fl oz) Spartan Advance per 12-mo period. Applications made to mint that has emerged will result in severe injury to exposed plant tissue. Do not apply on sand soils with less than 1% organic matter. Preharvest interval is 92 days.
Site of action
(sulfentrazone) Group 14: protoporphyrinogen oxidase inhibitor; (glyphosate) Group 9: inhibits EPSP synthase
Chemical family
(sulfentrazone) triazinone; (glyphosate) none generally accepted
MINT—Annual Grass and Broadleaf Weeds in Established Crop • diuron
Rate 0.6 to 2.4 lb ai/A
Time
Apply to mint during late-winter dormant period or after flaming in spring before new growth emerges.
Remarks
Soil organic matter determines application rate. Treatments to growing mint often injure crop. Diuron works best applied to moist soils and followed by 0.5 to 1 inch of rain or overhead irrigation to move herbicide into the weed root zone before weeds germinate. If weeds are present at time of application, a surfactant at 0.25% v/v or a crop oil concentrate at 1% v/v may enhance control. Weeds larger than 2 inches tall or across at time of treatment may not be controlled. May be tank-mixed with other herbicides provided mixture is not applied to actively growing mint. Tank-mixes and sequential treatments with other herbicides can increase the risk of crop injury. Use lower rate of diuron unless experience indicates it is safe to use higher rates.
Caution
Do not use on sand, loamy sand, gravelly soils, or exposed subsoils or if soil organic matter is less than 1%. Do not apply to soils that have a high salt content and/or high water table or poor drainage that retards mint root development, resulting in a shallow root system. Do not cultivate after treatment. Do not apply to actively growing mint. Do not apply to mint established less than one growing season in the field or to mint stressed from low fertility, drought, winter injury, insects, disease, or damage from other herbicides or other causes. Do not apply to snow-covered or frozen ground.
Site of action
Group 7: photosystem II inhibitor
Chemical family
Substituted urea
• paraquat
Rate 0.49 to 0.75 lb ai/A (1.3 to 2 pints/A Gramoxone Max or Firestorm) or 0.5 to 0.75 lb ai/A (2 to 3 pints/A Gramoxone Inteon) + nonionic surfactant or crop oil concentrate
Time
Apply to dormant mint from November through mid-February.
Remarks
Apply in at least 10 gal/A water by ground or 5 gal/A by air. Always add nonionic surfactant or crop oil concentrate as specified on label. Weeds should be succulent and growing and less than 6 inches tall or across at application. Weeds that germinate after application will not be controlled.
Caution A restricted-use herbicide.
Do not apply after mint begins spring growth. Mint foliage present at application may be burned. Use a full-face shield, rubber gloves, and apron when handling concentrate. Avoid working in spray mist. Wear waterproof footwear and clothing when spraying or contacting plants wet with spray.
Site of action
Group 22: photosystem I electron diversion
Chemical family
Bipyridilium
• oxyfluorfen
• paraquat
Rate 0.25 lb ai/A + 0.375 lb ai/A (1 pint Goal 2XL) or 0.5 pint GoalTender + 1 pint/A Gramoxone Max or 1.5 pints/A Gramoxone Inteon
Time
Apply only to established dormant mint after a hard frost or not before early December. Use higher rates for
dandelions or weeds over 4 inches tall or wide.
Remarks
This combination is more effective on many weeds than either herbicide alone. Paraquat particularly improves performance on grasses.
Caution Paraquat is a restricted-use herbicide.
See cautions for each herbicide.
Site of action
(oxyfluorfen) Group 14: protoporphyrinogen oxidase inhibitor; (paraquat) Group 22: photosystem I electron diversion
Chemical family
(oxyfluorfen) diphenylether; (paraquat) bipyridilium
• trifluralin
Rate 0.5 to 0.75 lb ai/A
Time
Apply to dormant, established peppermint and spearmint.
Remarks
Application rate depends on soil type. Must be soil-incorporated 1 to 2 inches deep with equipment that ensures thorough soil mixing and minimum damage to mint. This treatment will not control mustards
, prickly lettuce
, horseweed
(marestail)
, salsify
, mallow
, or nightshade
.
Caution
Take care to avoid exposing untreated soil when ditching for rill irrigation. Do not plant sugar beets, red beets, or spinach for 12 mo after applying. Do not plant corn, sorghum (milo), or oats for 14 mo after applying.
Site of action
Group 3: microtubule assembly inhibitor
Chemical family
Dinitroaniline
• clomazone
Rate 0.5 lb ai/A (1.3 pints/A product)
Time
Apply to soil surface before weeds emerge and mint begins new growth.
Remarks
Will not adequately control most grasses. Only one application per season allowed. Off-site movement of spray drift or vapors of clomazone can whiten or yellow some plants. Before applying, check adjacent properties and avoid spraying within 300 ft of desirable plants. Overhead moisture after application required to move herbicide into soil. Some, usually temporary, mint discoloration may occur when mint emerges. All use is at the user’s and/or grower’s risk; users should review the vegetable disclaimer at the end of the label before using. May be tank-mixed with other labeled herbicides to broaden weed control spectrum.
Caution
Do not apply more than once per season. Preharvest interval is 84 days. Do not exceed 0.5 lb ai/A (1.3 pint/A Command 3ME). Do not allow particle or vapor drift. Note crop restriction intervals on label.
Site of action
Group 13: inhibits DOXP synthase
Chemical family
Isoxazolidinone
• pendimethalin
Rate 0.71 to 1.9 lb ai/A (1.5 to 4 pints/A Prowl H2O or 1.7 to 4.6 pints/A Pendimax 3.3). Rate depends on soil texture.
Time
Apply to dormant established peppermint and spearmint before weed seedlings emerge.
Remarks
Apply by ground in 10 to 40 gal/A of water or by air in at least 5 gal/A water. Adequate rain or irrigation after application and before weed seedlings emerge will enhance control.
Caution
Do not apply to mint in first year of growth and establishment. Do not apply if mint has broken dormancy. Mint growing under stress conditions is more susceptible to herbicide damage. Preharvest interval is 90 days. Refer to main labels for crop rotation restrictions. Do not exceed 1.9 lb ai/A per season.
Site of action
Group 3: microtubule assembly inhibitor
Chemical family
Dinitroaniline
• flumioxazin
Rate 0.128 lb ai/A (4 oz/A product)
Time
Apply to established dormant mint between November 25 and March 1.
Remarks
Use for residual preemergence weed control and to aid postemergence burndown of many annual and perennial weeds where established mint is dormant. To control emerged weeds, tank-mix with paraquat
and apply with a nonionic surfactant. A spray-grade nitrogen source (either ammonium sulfate at 2 to 2.5 lb/A or 28 to 32% nitrogen solution at 1 to 2 quarts/A) may be added to increase burndown of emerged weeds. Controls broadleaf weeds better than grasses.
Caution
Applications to nondormant mint may result in unacceptable crop injury. Do not exceed 0.128 lb ai/A (4 oz/A product) in a single application or 0.255 lb ai/A (8 oz/A product) in a single growing season. Do not reapply within 60 days of the first application. Preharvest interval is 80 days. Do not apply to stands established longer than 3 yr. Do not apply south of Ladd Canyon in Union or Baker counties in Oregon. Note crop restriction intervals on label.
Site of action
Group 14: protoporphyrinogen oxidase inhibitor
Chemical family
N-phenylphthalimide
MINT—Annual Grass and Certain Annual Broadleaf Weeds • napropamide (
Rate 4 lb ai/A
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.
Remarks
There is some evidence napropamide breaks down with continued exposure to sun. This can be avoided by rain, sprinkler irrigation, or mechanical incorporation. November through February treatment must be incorporated or irrigated in if no rain falls within 2 wk of application. Treatments other than in November must be incorporated or irrigated in within 24 hr if no rain falls. Results are best if mechanically incorporated within 24 hr 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
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