239-Weed Control Guide for Wild Blueberries

Fact Sheet No. 239, UMaine Extension No. 2025


Prepared by David E. Yarborough, Extension Blueberry Specialist, and Jennifer L. D’Appollonio, Assistant Scientist, The University of Maine, Orono, ME 04469. Revised January 2019.

NOTICE: It is unlawful to use any pesticide for other than the registered use. Read and follow the label on the product container. The user assumes all responsibility for a use inconsistent with the label.

This fact sheet is to be used only during 2019. Use in subsequent years may lead to improper and illegal use of pesticides. When this guide is outdated, please request an updated version from your Extension office or on the Maine Wild Blueberries website.

WARNING! Pesticides are potentially hazardous. Handle carefully! Read and follow all directions and precautions on labels. Store in original labeled containers out of reach of children, pets, and livestock. Dispose of empty containers at once, in a safe manner and place. Do not contaminate forage, streams, ponds or groundwater recharge areas.

Groundwater is a major natural resource. Pesticides have been detected in the groundwater of all states. A sound application program including site-specific selection, adherence to label directions, sprayer calibration mixing accuracy, spill and back-siphon prevention, proper waste disposal, integrated pest management, and judicious pesticide use can prevent groundwater contamination.

Trade names are used for identification. No product endorsement is implied, nor is discrimination intended against similar materials. Cooperative Extension makes no warranty or guarantee of any kind concerning the use of these products.

Weed Management

The primary goal of weed management is to optimize yield by minimizing weed competition. Weeds reduce yields by competing with the crop for water, light and nutrients. No one method or chemical will control all weeds; each tends to reduce some weeds while encouraging others. Therefore, a combination of cultural techniques, the wise use of herbicides and careful monitoring of the weed situation in a field forms the basis of a sound weed management program.

Do not expect chemicals to completely control all weeds. The selection of herbicides should be made on the basis of what specific weed species are present in the field.

For additional information on the use of pesticides and other methods of weed control, refer to Wild Blueberry fact sheets entitled Weed Management in Wild Blueberry Fields (No. 236), Weed Resistance Prevention Practices for Wild Blueberries (No. 257), Glyphosate for Weed Control in Wild Blueberries (No. 237), Hexazinone for Weed Control in Wild Blueberries (No. 238), Postemergence Grass Control for Wild Blueberries (No. 235), Tribenuron Methyl for Bunchberry Control in Wild Blueberries (No. 255), and Mesotrione Use in Wild Blueberries (No. 256). For detailed information on granular calibration refer to Calibration of Granular Applicators for Herbicide Impregnated Fertilizer Applications (No. 234). When using Velpar, review Hexazinone Best Management System for Wild Blueberry Fields (No. 250) for use precautions that will minimize leaching into groundwater. These publications can be found on the Wild Blueberry website at: Maine Wild Blueberries website or by request from Cooperative Extension by calling 1-800-897-0757 x 1.

Preemergence herbicide rates are based on the amount of commercial product per acre or the percent solution for spot treatment. To achieve good weed control application, equipment must be calibrated so that the required amount is applied accurately and uniformly. Under application may result in poor weed control and over application can cause severe crop injury.

Postemergence non-selective herbicides listed for herbaceous weeds, some herbicides for woody weeds applied to weed foliage with wiper applicators, and selective postemergence herbicides should be applied at the proper stage of weed growth.

Postemergence grass herbicides are selective, so may be applied as a broadcast spray when grasses are small without injury to blueberries, but are more effective as a spot treatment.

Cultural Weed Control Methods for Wild Blueberries
Weeds Controlled Method Comments
Most weeds, especially grasses Test soil for pH and reduce with sulfur if above 4.0 Add nitrogen or phosphorus fertilizer only if leaf analysis indicates a deficiency. Maintain soil pH at 4.0.
Most weeds except grasses Hand pulling Effective against spot infestations. Pull before any weed flowers go to seed.
Weeds spread by seed or vegetative parts carried on equipment, especially mechanical harvesters Field sanitation Steam clean and inspect equipment before entering a field.
Bracken fern, sweet fern, dogbane, seedling or sprouting trees, flowering weeds Mowing above blueberry plants Most successful if done during the vegetative year. Cut flowers off before they go to seed.
Coniferous trees, some weeds spread by seed Fire pruning When burning with straw or hay, use weed-free material.
Weeds that form crowns at or above ground level Cut or mow woody weeds three times in the non-crop year Mow or cut plants to ground level.
Some weeds spread by seed Mulching on bare spots Apply mulch 2″ to 4″ deep. Use one of the following: bark, woodchips, shavings, sawdust, peat or sand.

 

This Fact Sheet is Intended as a Guide

Refer to the product label for details regarding soil type, soil moisture, temperature, stage of weed
growth and product limitations.

Chemical Weed Control Methods for Wild Blueberries, Preemergence Weed Control

Problem Material Rate Product/a Comments & Limitations
Annual and perennial weeds Hexazinone
(Velpar L CU, Tide Hexar 2SL liquid 2 lbs active/gal)
4 to 12 pts.

Do not exceed 8 pts. per acre per season if treated with Hexazinone within the past eight years.

Apply in spring after pruning in nonbearing year before blueberries emerge. Use lower rates on poorly drained soils and steep slopes. Moisture is required to activate; most effective in high temps/humidity. Avoid contact with blueberries. May be impregnated on fertilizer and applied after emergence up to tip-dieback. Maintain a 50 foot buffer from any well head or water reservoir and do not apply to flooded fields.

 

450 day PHI.

(Velpar DF CU 75% active) 1.2 to 3.6 lbs.

Do not exceed 2.4 lbs. per acre per season if treated with Hexazinone within the past eight years.

(Velossa liquid 2.4 lbs active/gal) 3.3 to 10 pts.

Do not exceed 6.6 pts. per acre per season if treated with Hexazinone within the past eight years.

Annual and perennial weeds Mesotrione
(Callisto, Explorer, Meso 4 SC liquid
4 lbs active/gal)See nonbearing year/bearing year Callisto 24c label, expires 12/31/22
Non-bearing year: 6 oz. preemergence
or
Bearing year: 4 oz./a prebloom (24C label)
Apply preemergence before blueberries emerge.

Do not exceed 6 oz per acre per season in nonbearing year; or 4 oz per acre per season in bearing year.

May be applied in the bearing year pre bloom to crop up to 60 days before harvest with SLN 24c label.

Grasses only Terbacil
(Sinbar WDG 80% active)
2 to 3 lbs.
Minimum 20 gpa water
Apply nonbearing year in spring after pruning or in crop year before bud-break.  Do not use on soils with less than 1% organic matter, in sand or loamy sand with <3% organic matter, or where roots are exposed. Use higher rate on heavy soil or soils high in organic matter. Moisture required to activate. May be impregnated on fertilizer; see 2ee label.

 

Annual and perennial weeds Diuron
(Karmex DF 80% active)
2 lbs. Apply non-bearing year only in late spring after pruning or in crop year before bud-break. Do not use on soils with <2% organic matter or on foliage or exposed roots.

Moisture is required to activate.

(Direx 4L, Diuron 4L liquid 4 lbs. active/gal) 1.6 qts.
Resistant grasses and herbaceous broadleaf weeds Pronamide
(Kerb SC liquid
3.3 lbs active/gal.)
2.5 to 5 pts. Apply in a single application in late fall/early winter before soil freezes or snow. Most effective in soils with <4% OM and when temp is <55°F; rain/snowmelt or irrigation is required to move into root zone.

May only be applied during the fall or winter of either year.

Do not apply more than 5 pts or 4 lbs per acre per season.

(Kerb 50W 50% active) 2 to 4 lbs.
Resistant grasses and herbaceous broadleaf weeds Rimsulfuron
(Matrix SG, Solida
25% active) See Matrix supplemental label, expires 3/31/20
4 oz. Apply in prune year only, pre-emergence broadcast spray. Do not use on frozen/snow covered soil, soils classified as Sand or pre-emergence on soils with >6% OM. Spray solution should be pH 5-7 for best results.

Do not apply more than 4 oz per acre per season. 21 day PHI.

Resistant
grasses, herbaceous broadleaf weeds and sedges
Carfentrazone + Sulfentrazone
(Zeus Prime XC liquid
0.35 lb active/gal carfentrazone,
3.15 lbs active/gal sulfentrazone)
 7.7 to 15.2 oz. Do not tank mix with flumioxazin or other products containing sulfentrazone.  Maintain spray solution between pH 5-9. Best results with moist soil and ½-1” rainfall/irrigation within 14 days. Availability decreases with finer soils and increases with higher pH. Do not apply on sand with <1% OM.

Do not apply more than 15.2 oz per acre per season. 3 day PHI.

Apply in non-bearing year before blueberry emergence.

Resistant herbaceous broadleaf weeds Flumioxazin
(Chateau SW 51% active)
12 oz. Moisture necessary to activate in soil for residual weed control. Valent® tank cleaner available for removing flumioxazin residue from spray equipment.

Do not apply more than 12 oz per acre per season. Do not apply in spring of crop year since delayed emergence and injury to blueberry could occur.

Apply after pruning in fall only.

Resistant grasses, broadleaf weeds and sedges  Glufosinate
(Rely 280 liquid 2.34 lbs active/gal)
 29 oz. Avoid contact with blueberries; plants will burn back. Add to spray tank last; may require an antifoam agent. For best results, apply on a warm, sunny humid day.

Do not apply more than 164 oz. per acre per season. 14-day PHI.

Apply to weeds postemergence but preemergence blueberry.

Chemical Weed Control Methods for Wild Blueberries, Postemergence Weed Control
Problem Material Rate Product/a Comments and Limitations
Broadleaf, herbaceous and woody perennial weeds Glyphosate
(use rate based on 41-49% glyphosate)
(Roundup, Touchdown and other formulations will vary in percentage of glyphosate – adjust use rates accordingly)
Wiper: Sponge – herbaceous 10% v/v, woody 20% v/v Rope/wick – 33% v/v or directed spray: 2% v/v

Add 8.5 lbs. per 100 gallons ammonium sulfate to increase effectiveness on woody weeds only

Avoid contact with blueberries. Will kill nearly all actively growing plants. Apply with wiper (10 to 33% solution) or as directed spray (2% solution). See labels for surfactant guidelines; do not use surfactant for wiper applications.

Do not apply more than 6 lbs acid equivalent for all formulations per acre per season. 14 day PHI.

Resistant grasses and herbaceous broadleaf weeds Rimsulfuron
(Matrix SG, Solida
25% active)See Matrix supplemental label, expires 3/31/20
 4 oz.  Apply in prune year only as an early post-emergence directed spray. Post-emergence spray may result in temporary chlorosis or stunting. Do not use on soils classified as Sand. Spray solution should be pH 5-7 for best results.

Do not apply more than 4 oz. per acre per season. 21 day PHI.

Grasses only Sethoxydim
(Poast liquid 1.5 lbs. active/gal)
Spot application: 2 oz. in 1 gal water plus 1.5 oz COC or 0.5 oz surfactant/gal.

Broadcast: 1.5 to 2.5 pts plus 2 pt/a COC

Grass control only. Must add crop oil concentrate (COC) or surfactant. Do not apply when grass is drought-stressed. Multiple applications must be at least 14 days apart.

Do not apply more than 5 pts. per acre per season. 30 day PHI.

Grasses only Fluazifop-P butyl
(Fusilade DX liquid 2 lbs active/gal)See supplemental label, expires 8/31/20
Spot application: 0.75 oz. in 1 gal water plus 1.5 oz. crop oil concentrate or 0.5 oz. surfactant/gal.

Broadcast: 1-1.5 pt. plus 2 pt. COC/25 gal. water or 1/2 pt. surfactant/25 gal. water

Grass control only. Must add crop oil concentrate or surfactant. Do not apply when grass is drought-stressed. Do not apply if rainfall is expected within 1 hour. Use of other herbicide within 5 days may cause crop injury/reduced control.

Do not apply more than 48 oz per acre per season.

May only be applied in the non-bearing year. 10 month PHI.

Grasses only Clethodim
(Select 2 EC, Arrow 2 EC, Clethodim 2EC, Intensity, Shadow liquid
2 lbs active/gal)
Spot application: Mix 0.33 to 0.65 oz in 1 gal water plus 0.5. oz surfactant

Broadcast: 6 to 8 oz. plus 0.25% v/v surfactant in 5 to 40 gal/a water

Grass control only. Apply as broadcast spray minimum 30 psi. Spot application, treat to wet but do not allow runoff. Must add surfactant. Crop oil concentrate not recommended. Multiple applications must be at least 14 days apart. Do not apply when grass is drought-stressed. Use higher rates for perennial grasses.

Do not apply more than 32 oz. per acre per season.

May only be applied in the non-bearing year.

Grasses only Clethodim
(Select Max liquid 0.97 lb active/gal)See bearing year supplemental label, expires 5/2/19
Spot application: 0.44 to 0.85 oz in 1 gal water plus 0.33 oz surfactant

Broadcast: annuals 9 to 16 oz, perennials 12 to 16 oz plus NIS at 0.25% v/v in 5-40 gal water

See comments above.

Do not apply more than 64 oz. per acre per season.

May be applied in the non-bearing year, or crop until 5/2/19. 45-day PHI.

Grasses only Clethodim
(Shadow 3EC, Section 3 liquid, 3 lbs. active/gal)
Spot application: 0.44 to 0.85 oz in 1 gal. water plus 0.33 oz. surfactant

Broadcast: 4 to 5.33 oz. plus NIS at 0.25% v/v in 5-40 gal. water

 See comments above. AMS not recommended.

Do not apply more than 21.33 oz. per acre per season.

May only be applied in the non-bearing year.

Bracken Fern only Asulam
(Asulox liquid
3.34 lbs active/gal)See 24c label, expires 1/31/20
1 gal.

Use of non-ionic surfactant at 0.25% v/v may improve uptake of the Asulox

For bracken fern control; bracken should be in full frond prior to application. Use Asulox only as a spot treatment. Do not apply more than once every other year. Control will be observed the year following application of the Asulox. No visible control symptoms will be observed the year of application.

Do not apply more than 1 gal per acre per season.

May only be applied in the non-bearing year.

Bunchberry only Tribenuron methyl
(Express TotalSol 50% active)See 24c label, expired and to be renewed in 2019
0.8 to 1 oz. plus non-ionic surfactant at 0.25% v/v Apply in fall after blueberry harvest, up until killing frost. Do not use COC or methylated seed oil (MSO). Do not use in solutions below pH 6.0.

Do not apply more than 1 oz per acre per season.

May only be applied after harvest and before pruning.

Annual and perennial weeds Mesotrione
(Callisto liquid 4 lbs. active/gal) 

 

 

 

See nonbearing year/bearing year Callisto 24c label, expires 12/31/22

6 oz, 3 oz or 2 oz*

Add COC at 1% v/v postemergence only.

Add 8.5 lbs. per 100 gallons ammonium sulfate to increase postemergence effectiveness.

 

4 oz

Apply postemergence after weeds emerge. May be applied one, two or *three times with 14 days between applications.

Do not apply more than 6 oz. per acre per season in a non-bearing year or 4 oz. during crop year.

 

 

Apply prior to bloom in crop year. 60 day PHI.


Information in this publication is provided purely for educational purposes. No responsibility is assumed for any problems associated with the use of products or services mentioned. No endorsement of products or companies is intended, nor is criticism of unnamed products or companies implied.

© 2019

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