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Weeds - 250-Hexazinone Best Management System for Wild Blueberries

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Fact Sheet No. 250, UMaine Extension No. 2276

Developed by Hexazinone BMP Committee, Department of Agriculture, Food & Rural Resources, Augusta, Maine.  Prepared by David E. Yarborough, Extension Blueberry Specialist, The University of Maine, Orono, ME 04469. Revised February 2008.

Objective: Handling and applying hexazinone so that potential impact on surface and groundwater is minimized.

Scope: This Best Management System gives guidance in management of hexazinone to minimize runoff and leaching into water bodies.

Purpose: To manage hexazinone use to minimize the potential for surface and groundwater contamination from hexazinone use and to obtain maximum economic yields (MEY) of wild blueberries. Note: the amount of herbicide needed for MEY is always less than the herbicide needed for maximum control of weeds.

Use: This Best Management System provides a number of possible options. Only those best management practices that are most appropriate, determined on a site-specific basis, should be selected and implemented.

Effects on Water Quality: This Best Management System provides guidance on reducing the potential for pollution of water bodies by hexazinone.

Label Considerations: Obtain copies of the current label plus any supplemental labeling from the dealer who sold the product. The label is a legal document that must be read and followed when using the product. The product label and applicable supplemental labels must be in the possession of the applicator when the product is being applied. Read and follow all directions on the label.

Hexazinone Formulations: Velpar® L- 2 lb./gal. liquid hexazinone or DF 75% active dry flowable; may be impregnated on fertilizer only by commercial dealers.

Use Considerations:

  • Determine weed pressure and use the lowest rate of hexazinone needed to provide effective control.
  • Determine potential for groundwater and surface water contamination.
  • Establish good communications with your neighbor to explain wild blueberry management practices.

NOTE: You must be a certified pesticide applicator to apply products containing hexazinone in the state of Maine.


Hexazinone Best Management Practices

Use multiple alternative weed control measures.

  • Use of hexazinone as a broadcast treatment alone will not provide an adequate weed management and will increase the probability of groundwater detections. Adopt other weed management strategies to maintain good weed control. Refer to Weed Management in Wild Blueberry Fields, Wild Blueberry Fact Sheet No. 236 for more details.
  • If overall weed pressure is low, consider not applying hexazinone for a production cycle or using spot applications of hexazinone. Use other weed management techniques to prevent heavy weed pressure the next treatment cycle.
  • If woody weed pressure is low, use alternative preemergent herbicides for a production cycle.
  • If grasses are the major problem, use postemergence applications of selective grass herbicides.
  • To manage weeds taller than blueberries, use a selective wiper application of a nonselective herbicide. For shorter weeds growing among blueberry clones, use a directed spray of a nonselective herbicide.
  • Hand pull or use a string trimmer to cut weeds taller than blueberries before they go to seed. This will reduce weed pressure in the future.
  • Cut woody weeds to the ground at the end of June, July and August to suppress growth.
  • Use mulch in open areas among blueberry clones to reduce weeds and to encourage blueberry spread.
  • If there are large open areas, consider interplanting blueberries, mulching and additional fertilizer to increase blueberry cover. A full cover of blueberry plants will reduce the need for herbicide applications.
  • Sample leaf tissue and follow rate recommendations to prevent excess fertilizer use which will encourage weed growth.
  • Sample soil for pH and apply granular sulfur to reduce pH to 4.0 to reduce weed pressure.

Determine weed species and density, and use the lowest rate of hexazinone needed to suppress weeds and obtain maximum economic yield.

  • The effect of hexazinone on weeds and blueberries will vary with soil type, texture, and amount and timing of rainfall. Following the blueberry harvest, determine weed species and density, and use weed mapping techniques or log observations on data sheets for future reference. Refer to Integrated Crop Management Field Scouting Guide for Wild Blueberries, Wild Blueberry Fact Sheet No. 204 for details on weed mapping. Use guidelines provided by the supplemental label and past experience to determine the lowest rate needed. If, at one to two months after application, you observe blueberry leaf drop throughout the field from the bottom of the stem to the top, your rate is too high. Reduce rates used in future applications. As weeds are controlled, less hexazinone is needed. Weeds not controlled without injury to blueberry plants will need other weed management control strategies. If it is determined that hexazinone is needed, use the practices outlined below.

Do not apply hexazinone to frozen or saturated soil.

Time application to minimize leaching or runoff.

  • Hexazinone should not be applied during or just prior to heavy rain because surface runoff or leaching of hexazinone could occur.
  • Apply liquid hexazinone as close to anticipated blueberry emergence as possible, but do not apply liquid after blueberry emergence. Too early an application of hexazinone will result in less weed control and more hexazinone could leach into groundwater. Application of liquid hexazinone after blueberry emergence will cause injury to blueberry plants and is a violation of the label.
  • It is best to apply hexazinone impregnated on fertilizer after blueberry and weed emergence. Do not apply granular formulations if blueberry leaves are wet because of fertilizer burn or uptake of hexazinone by blueberry leaves.

Calibrate application equipment.

  • Poor distribution of hexazinone increases injury to blueberries, decreases control of weeds and could result in leaching or runoff into ground or surface water.
  • Calibrated application equipment is essential for accurate application.
  • To apply liquid hexazinone at appropriate controlled rates, the following steps are recommended:
    1. Check equipment for leaks.
    2. Check nozzles for proper spacing, height and pressure.
    3. Check nozzle for wear, measure individual output and note any uneven pattern.
    4. Change nozzles that vary from the average by more than 10% or have an uneven pattern.
    5. Select nozzle, pressure and speed that will give desired output. Spray water over a measured area under actual field conditions to determine if output is correct. If not, adjust speed, pressure or change nozzles to get the desired output. For more details, refer to the Blueberry Pesticide Applicator’s Manualhttp://umaine.edu/ipm/pesticide-safety/ from the University of Maine Cooperative Extension Integrated Pest Management Office.
  • Use hexazinone L or DF-impregnated formulations if applying with granular fertilizer up to 1 lb/a active hexazinone. If applying more than 1 lb/a active hexazinone, apply separately from fertilizer.
  • Obtain guarantee of analysis and homogeneity of mixture for Velpar/fertilizer mixtures from your supplier.
  • If field terrain is rough and rocky, do not fill hopper to its limit, and tighten three-point hitch arms to prevent side-to-side movement.

Compare application rate with calibration rate.

  • For all applications, keep accurate records of amount used on each field and check to see if it equals the calibrated amount. If not, recheck calculations and recalibrate.

Use the most accurate placement method of hexazinone available.

  • Do not use an airblast sprayer to apply liquid hexazinone (Prohibited by Board of Pesticides Control).
  • Use ground application over air application, since this will result in more accurate and even placement.
  • When applying liquid hexazinone, use field or foam markers or a GPS system to insure that sprays don’t overlap.
  • When applying liquid or fertilizer impregnated hexazinone, do not apply when wind conditions are conducive to off-target deposition.
  • If you find strips of weeds that are not controlled and/or strips of defoliated blueberry plants, this indicates that the hexazinone has been applied unevenly.

Modify applications to adjust to site conditions.

  • Map sensitive areas, such as wetlands, well heads, rock outcroppings, steep slopes, etc., to identify sites that warrant modifications.
  • Maintain 50-foot buffer from any wellhead or water reservoir as specified by the supplemental label.
  • Reduce rate, or incease set-back beyond required 50 feet in the vicinity of a well, on a site-specific basis taking into account effects of soil texture, slope, depth to bedrock, size of field, vegetative cover and type of well, as discussed in this fact sheet.
  • Do not apply hexazinone over rock outcroppings because they could provide a direct conduit to groundwater.
  • Use reduced rates on slopes that do not have good blueberry cover.
  • Do not apply hexazinone to field roads with vegetative cover, if on a slope.
  • Use other weed management strategies adjacent to or on portions of a field that slope abruptly toward sensitive areas such as wells, reservoirs or waterways.
  • When possible, use mowing or light burning to prune blueberries. This promotes organic matter retention and build-up, especially on course-textured soils.

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.

© 2008

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