Weeds - 239-Weed Control Guide for Wild Blueberries

Fact Sheet No. 239, UMaine Extension No. 2025 (239 PFD)

Prepared by David E. Yarborough, Extension Blueberry Specialist, and Jennifer L. D’Appollonio-Cote, Research Assistant, The University of Maine, Orono, ME 04469. Revised February 2012.

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 use inconsistent with the label. This fact sheet is to be used only during 2012.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 When this guide is outdated, please request an updated version from your Extension office. 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), 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 in the Wild Blueberry Growers Guide, at your county Cooperative Extension office, from the Wild Blueberry Office at the University of Maine in Orono, or on the web at: http://extension.umaine.edu/blueberries

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. Over application can cause severe crop injury.

Postemergence herbicides listed for herbaceous weeds and some herbicides for woody weeds which are not selective and must be applied to weed foliage with wiper or roller applicators.

Postemergence grass herbicides may be applied as a broadcast spray 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 adjust 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, sweetfern, 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	Flail-mow pruning	Mow plants to ground level.
Some weeds spread by seed	Mulching and/or planting blueberries 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 liquid 2 lbs active/gal)	4 to 12 pts. Do not exceed 8 pts. if treated with Hexazinone within past 8 years.	Apply in spring after pruning in nonbearing year before blueberries emerge.  Use lower rates on poorly drained soils and steep slopes.  Moisture 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. See 2ee label. Maintain a 50 foot buffer from any well head or water reservoir and do not appy to flooded fields. 450 day PHI
	(Velpar DF 75% active)	1.2 to 3.6 lbs. Do not exceed 8 pts. if treated with Hexazinone within past 8 years.
	(Velossa 2.4 lbs. active/gal.)	3.36 to 10 pts. Do not exceed 6.6 pts. per acre per season if treated with Hexazinone withing past 8 years.
	Mesotrione (Callisto liquid 4 lbs. active/gal.)	Non-bearing year: 6 oz. preemergenceor3 oz. postemergence. Add crop oil concentrate at 1% v/v postemergenceAdd 8.5 pounds per 100 gallons ammonium sulfate to increase postemergence effectiveness. Bearing year: 4 oz./a prebloom (24C label)	Apply preemergence before blueberries emerge. Apply postemergence after weeds emerge. May be applied two times with 14 days between applications. Do not exceed 6 fl oz. per acre/a per season in non-bearing year; or 4 fl oz. per acre per season in bearing year. May be applied in the bearing year prebloom to crop up to 60 days before harvest with State 24C label.
Grasses only	Terbacil (Sinbar 80 WP and WDG 80% active)	2 to 3 lb. 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, or where roots are exposed. Use higher rate on heavy soil or soils high in organic matter. Moisture required to activate.
Annual and perennial weeds	Diuron (Karmex XP/DF 80% active)	2 lbs.	Apply nonbearing year only in 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 required to activate Karmex.
	(Direx 4L, Diuron 4L liquid 4 lbs. active/gal)	1.6 qts.
Bunchberry only	Tribenuron methyl (Express TotalSol 24C label 50% active)	0.8 to 1 oz.Use 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.
Bracken Fern only	Asulam (Asulox 24C label 3.34 lbs. active/gal)	1 gal.Use of non-ionic surfactant at 0.25% v/v may improve uptake of the Asulox.	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.
Resistant grasses	Pronamide (Kerb SC 3.3 lbs. active/gal)	2.5 to 5 pts. Do not apply more than 5 pts. per acre per season.	Apply in 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.
	(Kerb 50W 50% active)	2 to 4 lbs. Do not apply more than 4 lbs. per acre per season.

Chemical Weed Control Methods for Wild Blueberries Postemergence Weed Control
Problem	Material	Rate Product/a	Comments & Limitations
Broadleaf, herbaceous and woody perennial weeds	Glyphosate (use rate based on 41% glyphosate) (Roundup and Touchdown 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. Do not apply within 14 days of harvest.
Grasses only	Sethoxydim (Poast liquid 1.5 lbs active/gal)	Spot application: 2 fl oz in 1 gal. water plus 1.5 fl. oz. crop oil concentrate or 0.5 fl. oz. surfactant/gal. Broadcast: 1.5 pt/a to 2.5 pt/a plus 2 pt/a COC.	Grass control only. Must add crop oil concentrate (COC) or surfactant.Do not apply when grass is drought-stressed. Do not apply more than 5 pts. per acre per season. Do not apply within 30 days of harvest.
	Fluazifop-P butyl (Fusilade DX liquid 2 lb active/gal)	Spot application: 0.75 fl. oz. in 1 gal. water plus 1.5 fl. oz. crop oil concentrate or 0.5 fl. oz. surfactant/gal. Broadcast: 1-1.5 pt/a 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 72 fl oz. per acre per season. May only be applied in the on-bearing year.
	Clethodim (Select 2 EC liquid 2 lb. active/gal) (Arrow 2 EC liquid 2 lb. active/gal) (Clethodim 2 EX, Intensity, Section 2 EC, Shadow liquid 2 lb. active/gal)	Spot application: Mix 0.32 to 0.64 fl. oz. in 1 gal water plus 0.5 fl. oz. surfactant. Broadcast: 6 to 8 fl. oz/a 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 fl oz. per acre per season. May only be applied in the non-bearing year.

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.

©2012

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