Weed Management for Wild Blueberry


Fact Sheet No. 239, UMaine Extension No. 2025

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 When this guide is outdated, please request an updated version from your Extension office or on the Maine Wild Blueberries website.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.

Why Manage Weeds?

Why Culturally Manage Weeds? To increase yield and reduce pesticide exposure to off-target organisms such as bees.


Weeds Compete with Wild Blueberry for:

  • Water
  • Light
  • Nutrients

The method for controlling one weed – may encourage another. A combination of careful ID and monitoring of the weed situation in a field, with cultural management and the wise use of herbicides (only when critical) forms the basis of a sound weed management program.


THERE IS NO QUICK FIX. One method will not control all weeds.

Cultural weed control: routine management practices that can prevent pests from developing in the first place.

Chemical weed control: involve the use of naturally derived or synthetic chemicals (pesticides) to kill, attract, repel or otherwise control the growth of pest plants, animals and microorganisms.

ferns

The table below includes pre-emergence and post-emergence herbicides commonly used for specific weeds or types of weeds in wild blueberry fields in Maine. The selection of herbicides should be made on the basis of what specific weed species are present in the field.

Pre-emergence 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.

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

Post-emergence 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.

 

red-orange flowers

Cultural Weed Management Practices for Wild Blueberry

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 of the 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.

blue / purple flower


HERBICIDES with Environmental Persistence**

F1 Extremely toxic to fish B1 Extremely toxic to bees D1 Extremely toxic to birds P1 Extremely toxic to people
F2 Moderately toxic to fish B2 Moderately toxic to bees D2 Moderately toxic to birds P2 Moderately toxic to people

THIS CHART IS NOT A SUBSTITUTE FOR READING AND FOLLOWING THE LABEL. 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 use inconsistent with the label. 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. Check with your processor regarding PHI restrictions or MRL restrictions for export sales.

*Please note: This revised version replaces any previous charts.
**Environmental persistence rankings were estimated using a combination of available evidence, PHI, and REI. LP = low persistence, MP = moderate persistence, HP = high persistence. 
S = systemic, NS = not systemic

Use &

Toxicity

Herbicide

AI/Group & Signal

Timing:

Crop Cycle & Weed Emerg. (Pre or Post)

Rate:

Per/Acre & Max/Acre/yr

PHI

REI

Notes

Bracken Fern ONLY P1

F1

Asulox
(24c label expires 2025)
Asulam

Group 18

Caution Prune Post Spot ONLY: 1 gal

Max: 1 gal

Add NIS at 0.25% v/v

365 12 hrs For bracken fern ONLY. Ferns should be in full frond.
Control symptoms will not be visible until the year after application.
Human & Environment: High for skin and eyes. HP, S
Annual & Perennial weeds   Callisto
(24c label expires 12/31/22)
Explorer Meso 4 SC etc.
mesotrione

Group 27

Caution Prune Pre 3-6 oz or 2 oz*
Max: 2-3 app./6 oz (at least 14 days apart)
60 12 hrs Post-emergence Applications: add COC (1% v/v). To increase efficacy, add 8.5 lbs AMS/100-gal water.
Crop Injury: may occur in dry conditions or over 85°F. See 24C label for revised prune year/crop year application.
Human & Environment: MP, S
Post
Crop Pre 4 oz. (24C label) Add NIS
Max: 1 app/4 oz (0.19 lb ai)
Post
Resistant Grass & Broadleaf P2
F2
Chateau SW flumioxazin
Group 14
  Prune Pre 6-12 oz
Max: 1 app/12 oz
7 12 hrs Activation: Moisture is necessary to activate in soil.
Use Valent® tank cleaner to remove residue from equipment.
Crop injury: and delayed emergence may occur with spring application.
Human & Environment: Moderate reproductive toxicity. LP, NS
Post
Annual & Perennial weeds P2
F2
Direx 4L
Diuron 4L
diuron
Group 7
Caution Prune Pre 1.6 qts
Max:
12 hrs Apply in late spring of prune year pre-emergence.
Activation: Moisture required within 2 weeks post-treatment
Caution: Do not use on soils with <2% organic matter or on foliage or exposed roots.  Do not use near fruit trees.
Human & Environment: LP, S
Karmex DF 2 lbs
Max:
Broadleaf P2 Express TS 50 (24c label expires, Dec. 31, 2020). tribenuron methyl
Group 2
Caution Prune Post 0.8 to 1 oz
Add NIS 0.25% v/v
Max: 1 oz
365 12 hrs Field Conditions: Apply in the spring of a prune year or fall after harvesting and up until killing frost. Fertilizer applications before or after applying Express will help blueberry plants recover.
Caution: Do not use COC or an MSO. Do not use in solutions below pH 6.0.
Human & Environment: Moderate toxicity for skin. MP, S
Crop *Post-Harvest
Grasses P1
F1
Fusilade DX (supplemental label expires 8/31/20) fluazifop-P butyl
Group 1
Caution Prune Post Broadcast*: 1 to 1.5 pt
Spot*: 0.75 oz./1 gal-water
Max: 2 app of 24 oz/app (at least 14 days apart); Total 48 oz (0.75 lb ai)
10 mo. 12 hrs *Add 1% v/v COC or 0.25% v/v NIS
Caution: Do not use if grass is drought-stressed or if rainfall is expected within one hour.
Crop injury: may occur if other herbicides are applied within 5 days, also reducing control efficacy.
Human & Environment:  High aspiration toxicity. HP, S
Crop *Post-Harvest
Resistant Grasses F2 Kerb SC pronamide
Group 3
Caution Prune or Crop Pre 2.5 to 5 pts
Max: 1 app/5 pts (2 lb ai)
24 hrs May only be applied in fall/winter of either year (before ground-freeze or snow).
Field Conditions: Most effective in soil with <4% OM and when temperature is <55°F.
Activation: rain/snowmelt is required to move into root zone.
Human & Environment:  MP, NS
Post
Kerb 50W Prune or Crop Pre 2 to 4 lbs
Max: 1 app/4 lb (2 lb ai)
Post
Resistant Grass & Broadleaf F2 Multiple formulations glyphosate
Group 9
Caution Prune Post Wiper: Sponge 10% v/v herb, 20% woody; Rope/wick-33% v/v.  Directed spray:  2% v/v
Max: 6 lbs a.e. for all formulations (see label)
14 4 hrs Use rate based on 41-49%, adjust accordingly.
Add 1- 2% w/w spray grade AMS to increase efficacy on woody weeds only. See labels for surfactant guidelines; do not use surfactant for wiper applications.
Caution: Avoid contact with blueberries. Will kill nearly all actively growing plants.
Human & Environment: LP, S
Crop
F2 Matrix SG (supplemental label expires 4/30/21)
Solida
rimsulfuron
Group 2
Caution Prune Pre 4 oz
Max: 1 app/4 oz
For spray: use NIS 0.125-0.25% v/v or COC 1% v/v
(spray solution should be pH 5-7)
21 4 hrs Pre-emergence: broadcast.
Early post-emergence: directed spray.
Field Conditions: Do not use on soils with >6% OM.
Caution: Post-emergence spray may result in temporary chlorosis or stunting. Do not use on frozen/snow covered soil, soils classified as Sand.
Human & Environment: MP, S
Post
Grasses P2
B2
Poast sethoxydim
Group 1
Warning Prune Post Broadcast*: 1.5 to 2.5 pts
Spot**: 2 oz. in 1 gal water
Max: 5 pts; 2.5 pts/app (at least 14 days apart)
30 12 hrs *Add 2 pt/a COC
**Add 1.5 oz COC or 0.5 oz NIS/gal.
Must add crop oil concentrate (COC) or surfactant
Caution: Do not apply when grass is drought stressed.
Human & Environment: HP, S
Early Crop
Resistant Grass & Broadleaf P1 Rely 280 glufosinate
Group 10
Warning Prune Post Broadcast: 29 oz
Spot: 1.7 oz in 1 gal water
Max: 164 oz (3 lb ai); 2 app of 82 oz per app
14 12 hrs Foliar-active only. Apply pre-blueberry emergence.
Field Conditions: Apply on a warm, sunny humid day.
Caution: Will burn blueberry plants. Add to spray tank last; may require an antifoam agent.
Human & Environment: Highly toxic for eyes and reproduction. LP, S
Grasses P1
F2
Arrow 2 EC
Intensity
Shadow
Clethodim 2E
and others
clethodim
Group 1
Warning Prune Post Broadcast*: 6 to 8 oz.
Spot: 0.33 to 0.65 oz /1 gal-water. Add 0.5 oz NIS
Max: 32 oz (0.5 lb ai); 8 oz per app (at least 14 days apart).
NA (365) 24 hrs *Add 0.25% v/v NIS in 5 to 40 gal/a water
Use higher rates for perennial grasses.
Apply as broadcast spray minimum 30 psi.
Spot Treatment: Treat until wet but do not allow runoff.
Caution: Do not use COC. Tank mixing with certain post-emergence broadleaf herbicides may reduce grass control. Human & Environment: High aspiration toxicity. HP, S
P1
F2
Select Max
(See supplemental label)
Caution Prune Post Broadcast*: annual 9 to 16 oz, perennial 12 to 16 oz
Spot**: 0.44 to 0.85 oz /1 gal-water.
Max: 64 oz (0.485 lb ai); 16 oz per app (at least 14 days apart).
45 24 hrs *Add NIS 0.25% v/v in 5-40 GPA water
**Add NIS at 0.33 oz/gal water
Spot Treatment: Treat until wet but do not allow runoff.
Caution: Do not apply when grass is stressed. Do not apply post-emergence broadleaf herbicides within 1 day of application.
Human & Environment: High toxicity for aspiration, mutagenicity and carcinogenicity. MP
Crop
P1
F1
Shadow 3EC
Section Three
Caution Prune Post Broadcast: 4 to 5.33 oz
Spot: 0.44 to 0.85 oz in 1 gal water
Max: 21.33oz; 5.33oz /app
NA (365) 24 hrs See notes under Arrow 2 EC. AMS not recommended.
Human & Environment: HP, S
  Sinbar WDG
(2ee label for fertilizer)
terbacil
Group 5
Caution Prune Pre 2 to 3 lbs (Minimum 20 GPA).
Max: 3 lbs
12 hrs Apply pre-emergence in prune year or in crop year before bud-break. Field Conditions: Use higher rate on heavy soil or soils high in OM. May be impregnated on fertilizer (See 2(ee) label).
Activation: Moisture required.
Caution: Do not use on soil with <1 % organic matter, in sand or loamy sand with <3% OM, or where roots are exposed.
Human & Environment: LP, NS
Crop
Annual & Perennial weeds P1 Velpar L CU
Tide Hex. 2SL
hexazinone
Group 5
Danger Prune Pre 4 to 12 pts
Max: Up to 8 pts if treated in past 8 yrs
450 48 hrs Apply in spring of prune year pre-emergence. May be impregnated on fertilizer and applied after tip-dieback.
Field Conditions: Use lower rates on poorly drained soil and steep slopes. Use higher rates on heavier soil or soils high in organic matter.
Activation: Moisture required; high temps and humidity help.
Avoid contact with blueberries.
Caution: Maintain a 50’ buffer from any well head or water reservoir and do not apply to frozen or flooded fields.
Human & Environment: Highly toxic to eyes. HP, S
Velpar DF CU 1.2 to 3.6 lbs
Max: 2.4 lbs if treated in past 8 yrs
Velossa 3.3 to 10 pts
Max: 6.6 pts. if treated in past 8 yrs
Resistant Grass & Broadleaf P2
F2
Zeus Prime XC Carfentrazone & sulfentrazone
Group 14
Caution Prune Pre 7.7 to 15.2 oz
Max: 1 app/15.2 oz (0.41lb ai)
Maintain spray solution between pH 5-9.
3 12 hrs Apply in prune year before blueberry emergence.
Field Conditions: Availability decreases with finer soils and increases with higher pH; do not apply on sand with <1% OM.
Activation: Ideally apply to moist soil with ½-1” rainfall/irrigation within 14 days of application.
Caution: Do not tank mix with flumioxazin or other products containing sulfentrazone.
Human & Environment: Moderate toxicity for liver. LP, S

Prepared by Lily Calderwood, Extension Wild Blueberry Specialist and Brogan Tooley, Research Assistant, David E. Yarborough and Jennifer L. D’Appollonio. The University of Maine, Orono, ME 04469. Revised, February 2020.

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.

© 2020

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