238-Hexazinone for Weed Control in Wild Blueberries

Fact Sheet No. 238, UMaine Extension No. 2191

Prepared by David E. Yarborough, Extension Blueberry Specialist, The University of Maine, Orono, ME 04469.  Revised February 2008.

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.

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.


Velpar is a broad-spectrum herbicide, registered since 1983, for use in Maine lowbush blueberry fields. Its generic name is hexazinone; the chemical name is 3-cyclohexyl -6- (dimethylamino) -1-methyl-1,3,5-triazine-2,4(1h,3h)-dione.  Velpar comes in two forms:

  • Velpar L, a water-dispersible liquid with 25 percent hexazinone, or two pounds per gallon (see label at end of fact sheet). Velpar may also be mixed with fertilizer and applied in a granular fertilizer spreader.
  • Velpar DF, a dry flowable powder with 75 percent hexazinone, or ¾ pounds of hexazinone per pound of product. Velpar DF may also be mixed with fertilizer and applied in a granular fertilizer spreader.

When to Use

  • Apply Velpar L as a broadcast spray in the spring, after pruning, but before blueberries emerge. Apply Velpar mixed with the fertilizer after pruning in the spring until the tip die-back stage of blueberry growth.
  • Fall treatment of Velpar is half as effective as a spring treatment and is not a labeled use.

How to Use

  • Apply Velpar with ground equipment using 20 gallons of water per acre or a minimum of five gallons of water per acre for aerial applications.
  • Add the proper amount of Velpar to a spray tank filled with the amount of water to be used and mix well. If foaming is a problem, add a suitable defoaming agent. Follow instructions on the label.
  • Shut off spray booms while starting, turning, slowing or stopping. Otherwise, you may injure blueberries.
  • Do not apply hexazinone to frozen or snow-covered soil.
  • Use lower rates on poorly drained soils, and do not use in fields with standing water.
  • Use lower rates (one pound per acre of hexazinone or less) on steep slopes to reduce erosion potential.
  • Do not use on steep slopes where poor stands of blueberries occur.
  • Overlapping applications may result in injury to blueberries.
  • Place the herbicide properly. Drift may injure or kill off-target plants.

Rates to Use

Because hexazinone’s effect varies with soil types, uniformity of application, time of application and amount of rainfall after application, the rate for the best weed control will vary among fields and from year to year. See the Velpar label for a list of weeds controlled and the amounts of hexazinone needed for their control.

Injury to Blueberries

Most lowbush blueberry clones are resistant to hexazinone at the suggested label rates. However, some are not. Sourtop blueberry is more susceptible to injury from hexazinone than is low sweet blueberry.

Excessive rates of hexazinone will cause leaf drop beginning with the bottom leaves and moving to the top of the stems. Improper sprayer calibration or spray overlap will cause leaf drop when high rates of hexazinone are used. Injury increases with higher rates of hexazinone. Because hexazinone is absorbed by the leaves as well as the roots, treating blueberries after they have emerged or leafed out will cause leaf drop and severe injury. As weeds are controlled, fewer plants are there to take up hexazinone, so injury to blueberries plants may occur.

Effect on Blueberry Growth and Yield

Blueberry yield depends on many factors: soil type, soil organic matter, the extent of blueberry cover, kinds and density of weeds present, precipitation, growing season temperature, winter injury and yield potential of individual clones. With less weed competition, blueberries will have more light, water, and nutrients. The plants will increase stem density and the number of flower buds per stem. This can result in an increase in yield.

Factors Affecting Performance

Some factors that influence hexazinone’s performance are timing, moisture, temperature, soil texture, soil organic matter, and sprayer accuracy.

  • Timing: If hexazinone is applied too early in the season, spring rains can move it out of the top layer of the soil so it will not be in the root zone of the weeds. Delay application until just before blueberry emergence, or use Velpar on fertilizer after emergence for best results.
  • Moisture: After you apply hexazinone, you will need enough moisture to carry the herbicide from the soil surface to the roots. Too much rain may leach the herbicide through the soil past the root zone of the weeds. Applying hexazinone to standing water will injure blueberries.
  • Temperature: Warm temperatures increase hexazinone’s weed-killing action because at high temperatures plant growth and activity increase. The faster the plant grows, the quicker the herbicide is picked up and moved through the plant. Applying hexazinone to frozen soil may cause it to run off if rain occurs before the soil thaws.
  • Soil texture and organic matter: As soil becomes heavier (i.e., increasing from sand to loam to clay), more hexazinone is needed to get the same degree of control. Soils with high organic content adsorb hexazinone and reduce its effectiveness.
  • Sprayer or spreader accuracy:
    • Equipment calibration: Calibration is very important to get the right rates. Adjust output with tractor speed for the desired rate.
    • Nozzle check: Check each nozzle before you use it. Nozzles can become partially or totally clogged. Improper cleaning can cause nozzles to become misshapen or enlarged. Nozzle holes also enlarge with use because of the abrasive action of sprays.
  • Boom height: If the sprayer is too low, skips will occur. When the sprayer is too high, overlapping occurs. Doubling of herbicide may damage blueberry plants, and drifting spray may harm adjoining blueberries or off-target plants.

Persistence in Soil

Hexazinone has a half-life of one month in blueberry soils. However, breakdown varies depending on temperature and moisture. The half-life means that half of the hexazinone will break down within one month. The main reason for this is degradation by the soil microorganisms. Other factors affecting half-life include soil leaching, uptake by plants and breakdown by sunlight.


Hexazinone has low acute toxicity. It has an acute oral LD50 for mice (dose to kill 50 percent of test animals) of 1,690 mg/kg (or 0.026 oz/lb of body weight). Aspirin has the same toxicity level. Hexazinone is a class D compound – not classifiable as to human carcinogenicity.

Groundwater Concerns

Hexazinone has been detected at low levels, in the parts per billion (ppb), range in ground-water in Maine that is under or near to blueberry fields that have been treated with Velpar. All detections were well below the maximum exposure guides of 210 ppb set by the Maine Department of Health and Human Services. The EPA “believes that water containing hexazinone at or below the Health Advisory Level of 400 ppb is acceptable for drinking over the course of one’s life, and does not pose any health risk.”

If there are sensitive areas (i.e., schools, public drinking water supplies, etc.), then reduced rates and setbacks may be needed to prevent detectable levels from occurring in the ground-water. Although the levels detected pose no health risk, people are still concerned when pesticides are found in groundwater.

Maintain a 50-foot buffer from any wellhead or reservoir.

Precautionary Statements and Labels

Read the following precautionary statements and the label samples before using the herbicide.

Fertilizer/Velpar Mixture

Commercial sources in Maine for mixing Velpar and fertilizer include:

Cavendish Agri Services Ltd.
B Road
Houlton, ME 04730
Tel: (207) 532-6705

Precautionary Statements

Hazards to Humans and Domestic Animals, DANGER! Causes eye damage. Corrosive causes irreversible eye damage. Harmful if swallowed. Do not get in eyes or on clothing.

Personal Protective Equipment (PPE): Applicators and other handlers must wear: long-sleeved shirt, long pants, shoes plus socks, protective eyewear. Discard clothing and other absorbent materials that have been drenched or heavily contaminated with this product’s concentrate. Do not reuse them. Follow manufacturer’s instructions for cleaning/maintaining PPE. If no such instructions for washables, use detergent and hot water. Keep and wash PPE separately from other laundry.

User Safety Recommendations: Users should wash hands before eating, drinking, chewing gum, using tobacco or using the toilet.

Environmental Hazards:  Do not apply directly to water, to areas where surface water is present or to intertidal areas below the mean high water mark. Do not apply where runoff is likely to occur. Do not contaminate water when disposing of equipment wash waters.

Physical and Chemical Hazards: Liquid formulation is FLAMMABLE! Keep away from heat, sparks, and open flames. Keep container closed.

IMPORTANT: Injury to or loss of desirable trees or other plants may result from failure to observe the following: Do not apply except as recommended. Do not drain or flush equipment on or near desirable trees or other plants, or on areas where their roots may extend, or in locations where the chemical may be washed or moved into contact with their roots. Do not use on lawns, walks, driveways, tennis courts or similar areas. Prevent drift of spray to desirable plants. Keep from contact with fertilizers, insecticides, fungicides, and seeds.

Thoroughly clean all traces of hexazinone from application equipment immediately after use. Flush tank, pump, hoses, and boom with several changes of water after removing nozzle tips and screens (clean these parts separately).

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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