237-Glyphosate for Weed Control in Wild Blueberries
Fact Sheet No. 237, UMaine Extension No. 2176
Prepared by David E. Yarborough, Extension Blueberry Specialist, The University of Maine, Orono, ME 04469. February 1996. Revised July 2004.
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Glyphosate has the trade name Roundup® registered for use in blueberries in 1986 and more recently as a new product name Touchdown®. It is a broad-spectrum, nonselective herbicide that is effective on deep-rooted perennial species, and on annual and biennial species of grasses, sedges and broadleaved weeds. Glyphosate should be able to kill most plants, provided the herbicide is applied at the right time and is able to reach the roots of the plant. Species such as maple, beech, and ash, which are tolerant to 2,4-D, are sensitive to Glyphosate. However, since Glyphosate is nonselective, extreme care must be exercised to avoid contact with blueberries or other desirable vegetation. Otherwise, severe damage or destruction may result.
Glyphosate is a systemic or translocated herbicide. This means that it moves from the point of contact on the leaves through the plant to the root system with the sugars produced by the leaves. It may take a week or more before injury to weeds appears. Visible effects include a gradual wilting and yellowing of the plant, which advances to a complete blackening of the above ground growth and deterioration of underground roots and rhizomes.
How to Use
Note: All rate recommendations are based on Glyphosate at 36.5 to 48.8 percent of the product. There are many new Glyphosate formulations on the market, so be sure blueberries is on the label of the product you will be using. These products may be sold in a more diluted form, so be sure to check the label and adjust the rate accordingly if you have a lower percentage of Glyphosate.
Glyphosate may be used in a wiper applicator as a directed spray or as a cut stump treatment in established blueberry fields. In order for Glyphosate to kill weeds, it must reach all underground parts.
That means a high percentage of the leaves must be contacted by the herbicide. The more leaves you can contact by wiping or directed spray, the better the control will be. If you use a cut stump application, then the cut must be fresh to allow for uptake of the herbicide.
Allow a minimum of 14 days between the last application and harvest of blueberries.
Avoid drift. Extreme care must be used when applying this product to prevent injury to blueberry plants. Do not allow the herbicide solution to mist, drip, drift or splash since minute quantities of this product can cause severe damage or destruction to the crop, plants or other areas on which treatment was not intended. The likelihood of injury occurring from the use of this product is greatest when winds are gusty or in excess of five miles per hour or when other conditions, including lesser wind velocities, will allow spray drift to occur. When spraying, avoid combinations of pressure and nozzle type that will result in splatter or fine particles (mist) that are likely to drift. Do not apply at excessive speed or pressure. A plastic shield may be used to prevent drift onto blueberry plants.
Wiper applicators include either roller or wick devices that wipe appropriate amounts of herbicide directly on the weed. Equipment must be properly designed, maintained and operated to prevent the herbicide solution from contacting blueberry plants. Equipment must be operated at ground speeds no greater than five miles per hour.
Applications above the crop should be made when the weeds are a minimum of six inches above the blueberries. Better results may be obtained when more of the weed is exposed to the herbicide solution. Weeds not contacted by the herbicide solution will not be affected. This may occur in dense clumps, or when the height of the weeds vary. In these instances, repeat treatment may be necessary.
Performance may be improved by reducing the speed in areas of heavy weed infestations to ensure good leaf coverage. Also, better results may be obtained if two applications are made in opposite directions.
Be sure not to break the plant stem when applying Glyphosate, or the herbicide will not be able to reach the roots, and this will result in poor weed control.
- Do not use wiper equipment when weeds are wet.
- Mix only the amount of solution to be used during a one-day period, as reduced activity may result from use of leftover solutions.
- Clean wiper parts immediately after using this product by thoroughly flushing with water.
A ten to thirty-three percent solution of Glyphosate may be used in roller style wiper applicators. Good results have been obtained with a ten percent solution applied with a hand-held “hockey stick shaped” wiper, which allows good coverage of weed foliage.
Rope-wick applicators allow only a thin film of the solution to be deposited on weeds, whereas wiper applicators provide better coverage. The highest rate of Glyphosate, 33 percent, or one gallon/two gallons of water is needed for the wick-type applicators.
A directed spray involves spraying Glyphosate on weed foliage without hitting blueberry plants. Directed sprays may be made between clones to control weeds that may not be tall enough to be treated with a wiper application. A coarse spray should be used to prevent drift onto the blueberry foliage. A uniform spray should be applied to wet the weed foliage but not to the point of runoff. To help mark the area treated, an agriculturally approved marking dye, such as Blazon Blue, Spray Tracer or Signal, may be added to the spray solution when applying Roundup with hand-held equipment. A plastic shield may be used to prevent drift onto blueberry plants.
Cut Stump Sprays
Applications to cut stumps should be made during periods of active growth and full-leaf expansion. Apply using equipment that ensures coverage of the entire cambium. Apply spray to the surface of the freshly cut surface. Delays in application after cutting may result in reduced effectiveness of the treatment. A plastic shield may be used to prevent drift onto blueberry plants.
Use a one percent solution (one gallon/99 gallons water) for most herbaceous weeds. A two percent solution may be used for harder-to-control perennial species such as dogbane or bunchberry. Mix only the amount of solution you will use in a one-day period as reduced activity may result from the use of leftover solutions. Cut Stump sprays require a 50 to 100% solution.
Nonionic surfactants that are labeled for use with herbicides may be used. Do not reduce rates of this product when adding surfactant. When adding additional surfactant, use 0.5 percent surfactant concentration (2 quarts per 100 gallons of spray solution) when using surfactants which contain at least 70 percent active ingredient, or a one percent surfactant concentration (4 quarts per 100 gallons of spray solution) for those surfactants containing less than 70 percent active ingredient. Read and carefully observe surfactant cautionary statements and other information appearing on the surfactant label.
The addition of one to two percent dry ammonium sulfate by weight or 8.5 to 17 pounds per 100 gallons of water has increased the performance of this product on perennial wooded weeds. The improvement in performance may be apparent where environmental stress is a concern. Low-quality ammonium sulfate may contain material that will not readily dissolve, which could result in nozzle tip plugging. To determine quality, perform a jar test by adding 1/3 cup of ammonium sulfate to one gallon of water and agitate for one minute. If undissolved sediment is observed, pre-dissolve the ammonium sulfate in water and filter prior to addition to the spray tank. If ammonium sulfate is added directly to the spray tank, add slowly with agitation. Adding too quickly may clog outlet line. Ensure that ammonium sulfate is completely dissolved in the spray tank before adding herbicides or surfactants. To reduce corrosion, thoroughly rinse the spray system with clean water after use.
Rainfall or irrigation occurring within six hours of an application or heavy rainfall occurring within two hours of an application may decrease effectiveness. Rain or irrigation can wash the Glyphosate off leaves before it can be taken up. Adequate soil moisture must be present for plant growth because water stress may reduce the effectiveness of the treatment. Some of the newer formulations such as Roundup WeatherMax® herbicide will penetrate the leaf surface within minutes and will be effective 30 minutes after application even with rainfall.
Warm temperatures hasten the action of Glyphosate, because at high temperatures plant growth increases. Therefore, symptoms will occur sooner after summer applications than after fall applications.
Time of Application
Good control is obtained by treating perennials in the spring at the bud or regrowth stage. However, foliage must be fully leafed out and opened to get a good application, and the weeds must be taller than the blueberries for wiper applications. Additionally, fall is a time when herbicides will reach the underground parts through the natural translocation of the plant. Perennial weeds are most susceptible to herbicides in the fall before frost.
Behavior in the Soil
Glyphosate is strongly adsorbed onto soil particles, so leaching is very low. Microbial degradation is the major cause of break down in the soil. The normal half-life, or time it takes to break down 50 percent of the herbicide, is less than 60 days. Glyphosate is relatively non-persistent in the soil, and will provide no preemergence control of weeds so it is not effective as a soil-applied herbicide.
Glyphosate is corrosive to iron and galvanized steel. Do not hold spray mixtures in galvanized or unlined steel tanks (except stainless). Following application, clean sprayer parts by flushing tank, pump, hoses and boom with several changes of water.
Glyphosate is stable under temperatures up to 140 degrees F. It will freeze at -20 degrees F., but will go back into solution upon thawing. It does not require heated facilities.
Handle with care, avoid contact with eyes. It causes substantial but temporary eye injury. It is harmful if inhaled. Do not allow spray to drift onto desirable vegetation. Mix, store and apply Glyphosate in stainless steel, aluminum, fiberglass, plastic or plastic-lined containers.
Note: This fact sheet is prepared as a guide to use. Always read and follow the product label.
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.
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