Effective Herbicide Use in Christmas Tree Plantations By Douglas Lantagne, Melvin Koelling, and Donald Dickman

Using herbicides to control vegetation in Christmas tree plantations

New plantations

Established plantations

---

Introduction

Christmas tree production has developed into an intensive agricultural operation designed to produce a specialty product. Consumer demands and production costs necessitate that growers maximize the production of high quality trees per acre in as few years as possible. This requires an intensive management program that focuses on the factors that affect tree growth, foliage quality and general appearance. Management includes the effective use of herbicides.

Why use herbicides? When properly used, herbicides provide benefits not only during initial establishment and growth of the tree, but also later, during crop rotation. Herbicide use:

• Prepares sites for Christmas tree establishment. Herbicides can be used effectively to control woody and herbaceous vegetation. Pre-establishment treatments facilitate planting as well as reduce competing vegetation.

Increases survival and early growth of newly planted trees. Whether applied as a pre-plant or a post-plant treatment, herbicides can control competing vegetation. This increases the moisture available to planted seedlings and results in increased survival and growth. Maximum growth in the first two to three years after planting is necessary to obtain large, salable trees in as few years as possible.

Increases the supply of nutrients available to the tree. Preventing herbaceous plants from growing makes the nutrients these plants would have used available to the trees. In plantations where herbicides are used effectively, the grower can expect improved foliage color and more rapid growth. Growth is affected most in the first few years after planting.

Eliminates the need for furrow planting. Furrow planting is used by some Christmas tree growers to reduce plant competition. Though furrowing provides some relief from competition, it has some disadvantages. Furrowing physically removes much of the nutrient-rich topsoil from around the newly planted trees. This reduces growth and increases the possibility of soil erosion and the likelihood of rodent injury. Furrowing also makes it more difficult to shear, mow, spray, harvest and clean-up the plantation after harvest. Effective weed and grass control offers the advantage of furrow planting without theassociated disadvantages.

Reduces damage and loss due to rodents. Abundant grass and weed growth is a favorable environment for rodents, especially mice and voles. Mice will often feed on tree bark, causing severe injury or death. Controlling grass and weed growth in the plantation reduces the mouse and vole population by eliminating habitat and so lessens the probability of injury.

Helps develop better quality foliage on the lower part of the tree. Heavy weed growth shades needles on the trees' lower branches and prevents full foliage development. Shading also causes earlier than normal needle loss and may cause some branches to die. This reduces tree quality and prolongs the development of a full-size tree.

Permits easier and higher quality shearing. Heavy grass and weed growth makes shearing and shaping the trees difficult, if not impossible. Lower tree branches are difficult to see and slow the shearing process. Working in heavy grass and weeds is uncomfortable and discourages work crews from doing the best job.

Reduces the probability of foliage diseases. The environment maintained by heavy weed growth - shade, high relative humidity, excessive moisture due to slow drying of dew and rain, and cooler temperatures in the lower part of the tree - favors the development of foliar diseases. Effective weed control helps reduce the occurrence of diseases such as Lophodermium needlecast, brown spot needle disease, Swiss needlecast and Rhizospheria needlecast.

Reduces the likelihood of wildfire in the plantation. Dry weeds and grass are a fire hazard that threatens Christmas tree growing in the same area. Effective weed and grass control will lessen the likelihood or severity of a fire in the plantation.

Promotes better wholesale buyer and consumer

relations. This benefit may be intangible, but it is still real. With increasing emphasis on the production of quality trees, the impression that a clean, well managed plantation makes on potential buyers cannot be overlooked. For choose- and-cut operations, a well manicured plantation makes customers' selections easier and conveys an image of concern about quality. The individual consumer will be more inclined to pay a fair price if he or she in convinced the product is top-of-the-line.

Herbicide characteristics. By definition, herbicides are chemical compounds that affect the germination, growth and behavior of plants.

There is a wide variety of herbicidal materials - some are better adapted to certain uses than others. To choose the appropriation herbicide for a particular situation, the grower must understand some basic herbicide characteristics. These include:

Selectivity or specificity. Herbicides are not equally effective on all types of vegetation. This is fortunate because it makes it possible to control one or moretargeted weed plants without causing significant injury to the Christmas trees. Herbicides are available that control grasses only, broadleaf plants only, or certain grasses and broadleaf plants. Some herbicides are selective in Christmas tree plantations when applied during certainperiods of the year, such as before the trees begin growing in the spring, after they have hardened off in the late summer or when they are dormant.

Mode of activity. Herbicides affect plants in several ways. Some are absorbed through the foliage, while others are applied to the soil and are absorbed through the root systems of actively growing plants. A few herbicides kill only the portion of the plant to which they are applied. Other herbicides, when applied to or incorporated in the soil, prevent the germination of weed and grass seeds.

Residual nature. Herbicide effects vary, in part, because of their residual characteristics. A herbicide is considered to have residual effect if it prevents the regrowth of vegetation for a period of time after application. This time period varies from a few months to more than a year. Several residual herbicides exert pre- emergent control by continuing to kill weeds as their seeds germinate.

Application rate, soil texture (particularly clay content), soil organic matter content, soil moisture level and herbicide solubility affect a herbicide's residualproperties. Many herbicides that are absorbed through foliage have little or no residual effect, whereas those applied to the soil before plant growth usually have residual effect.

Formulation. Herbicides are available in several formulations: solutions, which are completely soluble in water or other solvents, such as fuel oil: emulsions, which are two unlike liquids mixed together; wettable powders, which consist of finely divided solid particles that can be dispersed in a liquid; and granules, which contain crystals of the effective chemical bound together with an inertcarrier. Each formulation has advantages related to its manner of application and the targeted plants' susceptibility to the formulation used.

A herbicide mixture's effectiveness depends on the user's knowledge of the formulation characteristics. For example, soluble herbicides must be mixed with clean water because dirt will inactivate them. Combinations of emulsifiable compounds or wettable powders and water require spray tank agitation to maintain a uniform suspension. Failure to agitate may result in erratic application rates.

Factors influencing herbicide effectiveness

To successfully control vegetation, the grower must understand the factors that influence herbicide effectiveness. Effective control is related to:

Application rate. The amount of herbicide required per acre to obtain effective control depends on severalvariables, including herbicide formulation, soil type and targeted vegetation. Specific application rates for various conditions are stated on the herbicide label. Follow these recommendations to obtain safe, economical and effective results. When preparing the spray mixture, carefully weigh or measure the amount of herbicide.

Equipment calibration. Proper calibration of application equipment is required to obtain good results when using herbicides. Calibration is simply thedetermination of how much material is being applied to a given area of land. MSU Extension bulletin E-916, "In Forest Plantings: Sprayer Calibration for HerbicideApplication," gives recommendations for calibrating spray equipment. Calibrate equipment yearly, especially if it is used frequently. Once equipment is calibrated, it is essential that the same ground speed, pump pressure and nozzle size are maintained during actual application.

Application method. Application method is closely related to application rate and proper equipmentcalibration. Herbicides used in Christmas tree operations are usually applied by broadcast treatments, using ground or aerial equipment, or in 24- to 36-inch bands over each row. For successful results, it is essential that coverage is uniform, regardless of method used. Routinely check and clean screens, filters and nozzles. When using foliar- active compounds, check the label to determine if a wetting agent is recommended. For herbicides that do not form true solutions, be sure to use spray tank agitation to maintain herbicide suspension. Wettable powders especially require agitation. Failure to agitate can cause erratic application rates -areas treated when the tank is full will receive too little herbicide, while those areas treated when the tank is low will receive too much herbicide.

Targeted vegetation. Because of differences in anatomy and physiology, some plants are more affected by herbicides than others. Annual weeds and grasses are easily controlled with pre-emergent products, while perennial grasses and weeds, particularly those with deep root systems, are more difficult to control chemically. Some plants, suchshorsetails and sedges, are especially difficult to control. Because of such differences, growers often combine two or more herbicides in the spray tank. Foliar-active compounds and pre-emergent herbicides with residual properties are often combined to control existing vegetation and to maintain an area clean of vegetative regrowth. Determine the compatibility of various herbicide compounds before preparing tank mixes to avoid interactions that may make each compound less effective. There is also a danger that an improper tank mix could injure or kill trees. Herbicide dealers provide charts that outline the compatibility of many herbicides.

Soil-site characteristics. Soils with high clay or organic matter contents require a heavier application of residual herbicides than coarse-textured sands or gravelly soils. If the amount of herbicide necessary for effective control on heavy soil is applied to a lighter-texturedsoil, the herbicide may injure any trees present. Further, residual herbicides persist longer on heavier soils because clay and organic particles absorb more of the material.

Soil moisture content and the soil's ability to retain moisture also influence herbicide effectiveness. Growers can expect more complete control on moister soils than on sites with dry soils.

Weather conditions. Weather factors at the time of and following application can influence herbicideeffectiveness. Cool and cloudy weather followingapplication of foliar herbicides will reduce their effectiveness. Heavy rain immediately following application will wash away foliar herbicides and therefore reduce their effectiveness. On the other hand, rainfall within a few days of application is necessary to move soil-applied herbicides into the soil solution. If precipitation islacking after application, weeds can germinate and grow before the herbicide can work. Heavy rains however,especially if they occur in a short time, may leach the herbicide from the upper soil or wash it to low-lying areas. In both cases, the herbicide is less effective and may damage trees.

Wetting agents. Wetting agents influence the effectiveness of foliar-applied herbicides. Because many plant leaves are waxy or hairy, they tend to repel herbicide spray droplets. The wetting agent (also called a spreader or sticker) decreases the surface tension of herbicide solutions by reducing the spray droplet size so droplets stick to the plant leaves better. This increases absorption and therefore improves control. Not all herbicide formulations require a wetting agent be added because some already contain these compounds. Check the herbicide label and follow any recommendations given on their use.

Commonly used herbicides

Many compounds are available for use by Christmas tree producers to control herbaceous and woody plants. The following is a list of compounds commonly used as herbicides and a description of characteristics and specific uses of available formulations.

Asulam (trade name: Asulox). Applied as an over-the-top post-emergent in late summer at a rate of 3.34 pounds active ingredient(ai) per acre to control actively growing bracken fern. Control is not evident in the year ofapplication, but braken fern fails to appear the following year. Control will usually last for two or more years. For best results, do not cut or disturb existing bracken fern after application.

Atrazine (trade names: Aatrex, Atrazine). Historical use in both agricultural and tree production. In Christmas tree production it is applied as an over-the-top post-emergent on dormant tress in early spring at rates of 1 to 2 pounds ai/acre. It provides control of vegetation less than two inches tall. It is a root absorbed compound and inhibits plant photosynthesis, causing weeds to die from the top down. Atrazine is available under numerous trade names. Atrazine persists in the soil for up to several years and can buildup with repeated use depending on the rate used, the soil texture and organic matter content. Tree seedling injury has been observed on sites where atrazine had been used in the agricultural production of corn. Atrazine can be mixed with several other compounds to extend pre- emergent control of germinating seeds.

Bentazon (trade name: Basagran T/O). Newly labeled herbicide for Christmas tree production. It is applied as a directed post-emergent spray in early summer at rates of 0.75 to 1 pound ai/acre. It controls a variety of broadleaf herbaceous weeds and sedges through contact action when applied before susceptible plants exceed recommended growth stages. This compound is also effective in controllingyellow nutsedge.

Clopyralid (trade name: Stinger). Newly labeled herbicide for Christmas tree production. It is applied as an over- the-top post-emergent in early summer on actively growing trees at rates of 0.09 to 0.26 pound ai/acre. It controls a number of herbaceous broadleaf weeds such as alfalfa, sweet and red clover, horseweed, sowthistle, Canada thistle and vetch. Applications must be made before susceptible plants exceed recommended growth stages. Control isprimarily through foliage uptake although limited rootuptake can occur.

2,4-D (trade names: Weedone LV4, Weedone 170, numerousothers). Historical use in both agricultural and tree production. 2,4-D is available under many trade names and commercial formulations. In Christmas tree production it is applied as a broadcast spray on actively growing plants for sites being prepared for planting. Rates vary with theformulation being used. Some of the ester formulationsreadily volatilize and the vapors cause severe injury to nearby susceptible crops and ornamental plants as theydrift away from the area of application. 2,4-D controls numerous herbaceous and non-herbaceous broadleaf weeds and many tree species. 2,4-D does not affect grasses. It is used in late-summer as a directed spray in establishedplantations to control invading brush such as aspen, alder, birch, willow and sumac. Mixtures of 2,4-D with picloram, dicamba or 2,4-DP (dichlorprop) provide better control of other tree species.

Dicamba (trade names: Banvel, Trooper). Used as a broadcast spray on actively growing plants at rates of 1 to 8 pound ai/acre for sites being prepared for planting. It controls numerous herbaceous and non-herbaceous broadleaf weeds and many tree species. Dicamba does not affect grass but will damage or kill unprotected Christmas trees. A formulation of dicamba and 2,4-D is also marketed (Banvel 720).

Dichlobenil (trade name: Casoron, Norosac). Applied in late fall or early spring at rates of 4 to 6 pounds ai/acre as a pre-emergent to inhibit seed germination of both grasses and broadleaf weeds. A good rain is needed following application to activate the material. It should not beapplied to newly planted Christmas trees. Formulations of dichlobenil are more commonly used in nurseries that produce container stock.

Fosamine (trade name: Krenite S). Applied in late summer or early fall before leaf coloration at rates of 6 to 12 pounds ai/acre as a broadcast spray to control tree species on sites being prepared for planting. It has little effect on herbaceous plants and kills only that portion of a tree to which it is applied. Control is evident the spring following treatment.

Fluazifop-butyl (trade name: Fusilade 2000). Used in late spring and early summer at rates of 0.25 to 0.375 pound ai/acre as an over-the-top post-emergent to controlactively growing grasses before they reach listed growth stages (e.g., quackgrass should be less than 10 inchestall). Growth stops soon after application, and the plants turn yellow or reddish before dying. It does not control broadleaf weeds or sedges. For effective control of listed grasses a non-ionic surfactant must be added to the spray mixture.

Glyphosate (trade name: Roundup, Accord). Applied in spring, summer or fall as a broadcast application at rates of 1 to 4 pounds ai/acre for control of numerous grasses, broadleaf weeds and tree species on sites being prepared for planting. Applications for site preparation aretypically more effective on perennial plants when applied in late summer or early fall. Also used as an over-the-top post-emergent in early fall at a rate of 1 pound ai/acre for the release of established trees from quackgrass and other late-season grasses and weeds. Chance of injury to the established trees is present if applied improperly or the trees are not dormant. Chance for injury is especially high for Douglas fir. There is no soil residual with the use of this compound. To obtain a residual effect aresidual herbicide can be tank mixed with glyphosate. Add a wetting agent if using the Accord formulation.

Hexazinone (trade names: Velpar, Pronone). Used as a preor post-emergent in spring or early summer at rates of 0.5 to 2 pounds ai/acre in Scotch pine plantations only. For best results, apply when soil moisture is ample, and temperature and relative humidity are high. This herbicide compound provides both contact and residual control ofannual and perennial weeds, grasses and many woody plant species.

Metolachlor (trade name: Pennant). Newly labeled herbicide for Christmas tree production. Applied as a over-the-top pre-emergent in early spring at rates of 2 to 4 poundsai/acre to control annual grasses, certain broadleaf weeds and yellow nutsedge. This compound will not controlestablished weeds.

Oryzalin (trade name: Surflan A.S.). Applied as an over- the-top pre-emergent in early spring at rates of 0.5 to 1.5 pounds ai/acre to established seedlings and transplants to control annual and late-season grasses and some broadleaf weeds. Established vegetation will not be controlled. Approximately 0.5 inch of rain following application is required to activate the herbicide.

Oxadiazon (trade name: Ronstar). Applied as an over-the-top pre-emergent in early spring at rates of 100 to 200 pound ai/acre to control a wide variety of annual broadleaf weeds and grasses. It is commonly used in seedbeds and treenurseries.

Oxyfluorfen (trade name: Goal). Applied as an over-the-top pre- and post-emergent in spring and early summer at rates of 1 to 2 pounds ai/acre to control annual grasses and many species of broadleaf weeds. Applications must be made before trees break bud or after new growth has hardened off.

Pendimethalin (trade name: Stomp). Newly labeled for use in Christmas tree production. Applied as an over-the-top pre- emergent in early spring at rates of 2 to 4 pounds ai/acre to control most annual grasses and certain broadleaf weeds. It will not control established weeds. Application rates vary depending on soil texture, increasing as clay or soil organic matter content increases.

Picloram/2,4-D (trade names: Pathway). This is a ready-to- use liquid for the control of individual tree stems, including hard-to-kill species such as maples and oaks. This formulation can be injected or applied to freshly cut surfaces such as frills, girdles and stumps. Do not apply to the soil surface since picloram is a highly active herbicide and can remain active in the soil for a year or more. Exercise caution in the use of this herbicide near desirable plants. Some formulations of picloram arerestricted use pesticides.

Pronamide (trade name: Kerb). Pronamide is a selectiveherbicide that controls certain broadleaf plants and grasses, particularly quackgrass. It is a soil-appliedherbicide that has little foliar activity and requires rain following application so root uptake can occur. Pronamide is usually used in conjunction with other herbicides to control late annual weeds and grasses. For best results when using pronamide, apply in late fall before soil freeze-up when air temperatures do not exceed 55 degrees F at rates of 1 to 2 pound ai/acre. Pronamide is moreeffective on soils with low levels of organic matter.

Sethoxydim (trade name: Vantage). Applied as an over-thetop post-emergent at rates of 0.19 to 0.4 pound ai/acre to control a wide variety of annual and perennial grasses. It does not control sedges or broadleaf weeds. Grasses must be within recommended size classes for effective control.

Simazine (trade name: Princep). Historical use in bothagricultural and tree production. Simazine is the mostwidely used herbicide in Christmas tree production. It is applied as an over-the-top pre-emergent in late fall or early spring at rates of 2 to 4 pound ai/acre when trees are dormant to control many herbaceous broadleaf weeds and grasses. Simazine will not control established vegetation. It is often combined in a tank mix with one or more other herbicides to obtain a broader spectrum of control. When using simazine, agitation of the spray mixture during application is required to maintain a uniform mixture.

Sulfosate (trade name: Touchdown). Newly labeled herbicide for Christmas tree production. Applied in spring, summer or fall as a broadcast application at rates of 0.5 to 4 pounds ai/acre for control of numerous grasses and broadleaf weeds on sites being prepared for planting. For weed control in established plantations a directed-spray should be used. Chance of injury to the established trees is present if applied improperly. There is no residual soil affect with the use of this compound. To obtain a residual effect simazine or other residual herbicide can be added to the spray mixture. Add a wetting agent is recommended. This compound is similar to glyphosate in mode of action and activity.

Triclopyr (trade name: Redeem). Newly labeled herbicide for use in Christmas tree production. Used as a broadcast spray for site preparation at rates of 0.75 to 1.5 pounds ai/acre or as a directed spray at a rate of 0.5 to 1 pound ai/acre in established plantations to control herbaceous broadleaf weeds and some tree species. It does not control grasses.

USING HERBICIDES TO CONTROL VEGETATION IN CHRISTMAS TREE PLANTATIONS

Preparing areas for planting

Woody brush

2,4-D Amine (Weedar 64, Formula 40). Rate: 1 to 2 ml/injection. Use to inject and treat frills on larger individual trees scattered over a proposed planting area. Space injections or frills 2 inches apart, edge to edge. Treat trees at any time of the year.

2,4-D Amine (Weedone CB), ready-to-use formulation.Apply solution to cut stumps to control sprouting or use as a basal spray on small, scattered, multi-stemmed hardwood brush. Saturate stumps and root collars. Both treatments are effective year round.

2,4-D Ester (Esteron 99C, Weedone LV4). Rate: 1.5 to 4quart/acre. Use where cover of small brush, including oaks and maples, is uniform. Apply uniformly over foliage during June and July. Grass cover is not affected, although many broadleaf weeds are controlled.

2,4-D plus dicamba (Super Brush Killer, BK 800). Rate: 0.5 to 2 gal/acre. Use over a uniform distribution of small brush, including oaks and maples. Provides post-emergent control of annual and perennial broadleaf weeds. Grasses are not affected. Apply uniformly over foliage during late spring and summer before foliage is fully developed. Do not plant conifers within three to four weeks of application.

Dicamba (Banvel, Trooper). Rate: 1 to 2 gal/acre. Use over a fairly uniform distribution of small brush,including maples and oaks. Provides pre- and post-emergent control of annual and perennial broadleaf weeds. Grasscover is not affected. Apply as a foliar spray or inject into larger individual trees. Apply to foliage after leaves are fully developed but three weeks before the first frost. Injections and frill treatments are effective on most species year round. Do not plant conifers within 6 months of application.

Fosamine (Krenite). Rate: 1.5 to 3 gal/acre. Use to control brush. Will not control broadleaf weeds and grasses. Apply to fully developed foliage within 2 months of leaf coloration; thoroughly wet foliage to ensure complete suppression.

Glyphosate (Roundup, Accord). Rate: 1 to 2 quart/acre.Controls broadleaf weeds, grasses, sedges, woody perennials and broadleaf tree species. Apply to foliage of actively growing plants in late summer. Use the highest recommended rates when oaks and maples are present. Use full strength for injections and frill treatments.

Hexazinone (Velpar L, Pronone 10G). Rate: 0.5 to 1 gal/acre, 5 to 15 pound/acre. Controls hardwood brush and grasses, broadleaf weeds and woody perennials as well. Use only on areas where Scotch pine will be planted. For best results, apply when soil moisture is ample and both temperature and relativehumidity are high.

Picloram plus 2,4-D (Pathway), ready-to-use formulation. Apply solution to cut stumps to control sprouting, or use as a frill or girdle treatment on individual hardwood stems. Both treatments are effective in any season.

Triclopyr (Redeem). Rate: 1.3 to 2.7 pints/acre.Controls hardwood brush and broadleaf weeds. Does not control grasses. Conifers planted sooner than two months

after treatment may be injured. Use in year prior to planting. For best results, add an agricultural surfactant to the spray mix.

Grass and herbaceous growth

Fluazifop-butyl (Fusilade 2000). Rate: 2 to 3 pints/acre. Controls annual and perennial grasses but not broadleaf weeds or sedges. Effective in late spring and early summer when grasses are actively growing but before they exceed recommended growth stages. Effectively controls quackgrass when applied before grass exceeds 10 inches. For maximum effectiveness, apply with a non-ionic surfactant in two applications at half the recommended rate.

Glyphosate (Roundup, Accord). Rate: 1 to 2 quart/acre.Effectively controls annual and perennial grasses, sedges and broadleaf weeds. Apply to actively growing vegetation. Late summer and fall applications will control bracken fern and other late-season perennial grasses and broadleaf weeds. Do not apply within six hours of rainfall.

Hexazinone (Velpar L, Pronone 10G). Rate: 0.5 to 1 gallon/acre, 5 to 15 pound/acre. Effectively controls annual and perennial forbs andgrasses. Slightly effective on bracken fern. For bestresults, apply in early spring before herbaceous growth is well established. Use only in areas that will be planted with Scotch pine.

Sulfosate (Touchdown). Rate: 0.67 to 5.3 pints/acre. Effectively controls annual and perennial grasses, sedges and broadleaf weeds. Apply to actively growing vegetation. Do not apply within six hours of rainfall.

NEW PLANTATIONS

Tilled, clean soil

Metolachlor (trade name: Pennant L, Pennant 5G). Rate: 2 to 4 quarts/acre or 40 to 80 pounds/acre. Exerts pre-emergent control of annual grasses and certain broadleaf weeds when applied in early spring before weeds begin to grow and trees are dormant. At the highest rates Pennant will also control annual and yellow nutsedge. Does not control woody vegetation or established weeds.

Oxyfluorfen (Goal). Rate: 5 to 10 pints/acre.Provides pre-emergent control of grasses and broadleafweeds. Apply in early spring before weed growth begins and while trees are dormant. Oxyfluorfen can controlestablished weeds less than 4 inches high.

Pendimethalin (Stomp). Rate: 2 to 4 quarts/acre.Provides pre-emergent control of grasses and broadleafweeds. Apply in early spring before weed growth begins and while trees are dormant.

Simazine (Princep Liquid). Rate: 0.5 to 1 gal/acre.Exerts pre-emergent control over most broadleaf weeds and grasses. Apply in late fall or in spring before weed seeds germinate. Does not control woody vegetation. Do not apply to transplants less than 3 years old. Does not controllate-season annual grasses or perennials. Use higher rates on soils with high silt, clay or organic matter content.

NEW PLANTATIONS

Herbaceous growth is present

Atrazine (Aatrex, Atrazine 4L) and simazine (Princep Liquid). Rates: 1 to 1.5 quarts/acre and 1 to 3 quarts/acre, respectively. Controls both grasses and broadleaf weeds and providessummer-long control of actively growing grasses andbroadleaf weeds. Does not affect late-season annual grasses and broadleaf weeds. Apply using a directed spray if trees have begun to grow.

Glyphosate (Roundup, Accord) and simazine (Princep Liquid). Rates: 2 quarts/acre and 2 to 4 quarts/acre, respectively. Used for control of actively growing grasses and broadleaf weeds. Does not affect late-season annual grasses and broadleaf weeds. Apply using a directed spray.

Hexazinone (Velpar L, Pronone 10G). Rate: 0.5 to 1 gallon/acre, 5 to 15 pounds/acre, respectively. Provides contact and residual control of annual andperennial weeds and grasses. Apply in spring when growth is less than 2 inches. Use only on Scotch pine plantations that have been planted for at least 2 months and have received sufficient rainfall to ensure soil settling. Increase the rate to 1 to 2 pound ai/acre when applying to medium- and fine-textured soils.

Oxyfluorfen (Goal). Rate: 5 to 10 pints/acre.Provides pre- and post-emergent control of grasses andbroadleaf weeds. Apply in early spring before weed growth exceeds 4 inches and while trees are dormant.

Sulfosate (Touchdown) and simazine (Princep Liquid). Rates: 0.67 to 5.3 pints/acre and 2 to 4 quarts/acre, respectively. Effectively controls annual and perennial grasses, sedges and broadleaf weeds. Apply as a directed spray to actively growing vegetation. Do not apply within six hours of rainfall.

ESTABLISHED PLANTATIONS

Directed spray application with dormant trees:

Bentazon (trade name: Basagran T/O). Rate: 1.5 to 2pints/acre. Apply a post-emergent directed spray in early summer to control a variety of broadleaf herbaceous weeds and sedges when applied before susceptible plants exceed recommended growth stages.

Glyphosate (Roundup, Accord) and simazine (Princep Liquid). Rates: 1 to 2 quarts/acre and 1 to 3 quarts/acre, respectively. Provides existing and residual control of grass andbroadleaf weed competition. Does not affect late-season annual grasses and broadleaf weeds. Apply in late spring and early summer. Avoid spraying Christmas tree foliage. Do not apply within six hours of rainfall.

Sulfosate (Touchdown) and simazine (Princep Liquid). Rates: 0.67 to 5.3 pints/acre and 2 to 4 quarts/acre, respectively. Effectively controls annual and perennial grasses, sedges and broadleaf weeds. Apply as a directed spray to actively

growing vegetation. Apply in late spring and early summer. Avoid spraying Christmas tree foliage. Do not apply within six hours of rainfall.

Triclopyr (Redeem). Rate: 1.3 to 2.7 pints/acre.Apply using a directed spray to control a wide variety of broadleaf weeds, as well as brambles, poison ivy, sumac and other similar woody perennials. Use on Christmas trees that were planted at least three full years before application.

ESTABLISHED PLANTATIONS

Over-the-top application with dormant trees:

Atrazine (Aatrex, Atrazine 4L) and simazine (Princep Liquid). Rates: 1 to 2 quarts/acre and 1 to 3 gallons/acre, respectively. Controls existing grasses and broadleaf weeds and provides summer-long control of herbaceous vegetation. Apply inearly spring when vegetation is less than 2 inches high and before tree growth begins.

Pronamide (Kerb). Rate: 1 to 2 pounds/acre. Controls many broadleaf weeds and grasses, especially quackgrass. Apply in late fall before soil freezes up, when air temperatures are below 55 degrees F. Treatment is not completely effective on soils with high organic matter content. Rainfall following application is necessary for chemical activation.

Atrazine (Aatrex, Atrazine 4L), simazine (Princep Liquid) and oryzalin (Surflan A.S.). Rates: 1 to 2 quarts/acre, 1 to 3 quarts/acre and 0.5 to 1.5 quarts/acre, respectively.

Use for season-long control of annual and perennial grasses and broadleaf weeds. Apply in early spring when herbaceous vegetation is less than 2 inches high and Christmas trees are still dormant.

Glyphosate (Roundup, Accord). Rate: 1 quart/acre. Apply in late summer or early fall after Christmas trees have gone dormant. Use 5 to 10 gallons of carrier per acre and apply at 40 psi. Glyphosate can be used over the tops of all Christmas tree species if they are dormant. This practice is not recommended by the manufacturer and may injure or kill trees that are not dormant. Douglas-fir are very susceptible to damage because they do not hardened off until late fall if weather conditions are favorable for growth.

Oxyfluorfen (Goal). Rate. 5 to 10 pints/acre.Provides pre- and post-emergent control of grasses andbroadleaf weeds. Apply in early spring before weed growth exceeds 4 inches and while trees are dormant.

ESTABLISHED PLANTATIONS

Over-the-top application when trees are growing:

Fluazifop-butyl (Fusilade 2000). Rate: 2 to 3 pint/acre. Controls annual and perennial grasses but not broadleaf weeds or sedges. Effective in late spring and early summer when grasses are actively growing but before they exceed recommended growth stages. Effectively controls quackgrass when applied before growth exceeds 10 inches. For maximum effectiveness, apply with a non-ionic surfactant in two applications at half the recommended rate. A directed spray is recommended for Fraser fir.

Hexazinone (Velpar L, Pronone 10G). Rate: 0.5 to 1 gallon/acre, 5 to 15 pound/acre. Use only on established (at least 1 year) Scotch pine plantations. Apply when herbaceous vegetation is less than 2 inches high. For best results, apply when soil moisture is ample and both temperature and relative humidity are high.

Sethoxydim (Vantage). Rate: 1.5 to 3.25 pints/acre.Effectively controls quackgrass and late-season annualgrasses. Apply anytime herbaceous vegetation is present, regardless of Christmas tree dormancy. The spray mixture requires a non-phytotoxic oil concentrate at a rate of 2 pints/acre.

Clopyralid (trade name: Stinger). Rate: 0.25 to 0.67 pint/acre. Applied in early summer it controls a number of herbaceous broadleaf weeds such as alfalfa, sweet and red clover, horseweed, sowthistle, Canada thistle and vetch. Applications must be made before susceptible plants exceed recommended growth stages.

SPECIAL SITUATIONS

Bracken fern

Asulam (Asulox). Rate: 1 gal/acre. Apply to actively growing bracken fern after budbreak and hardening of new tree growth. Do not disturb treated ferns after application. Shows control in the year followingapplication and lasts for two or more years. Do not use a wetting agent.

Sedges

Bentazon (trade name: Basagran T/O). Rate: 1.5 to 2pints/acre. Apply a post-emergent directed spray in early summer when plants are 6 to 8 inches tall. If needed make a second application at the same rate 7 to 10 days later. Add an oil concentrate to the spray mixture.

Metolachlor (trade name: Pennant L, Pennant 5G). Rate: 2 quarts/acre or 80 pounds/acre.Applied as an over-the-top pre-emergent in early spring before sedges emerge. One-half inch of rainfall is necessary within seven days to activate the herbicide.

Nursery seedling production

Dichlobenil (Casoron 4G, Norosac 4G). Rate: 100 to 150pounds/acre. Inhibits the germination of grass and broadleaf weed seeds but does not control established vegetation. Apply in late fall or early spring. Generally used to sterilize nursery soils.

Oxadiazon (Ronstar G, Ronstar 50WP). Rate: 100 to 200 pound/acre or 4 to 8 pounds/acre.Controls a variety of annual broadleaf weeds and grasses in seedbeds or tree nurseries. Apply anytime before weed seed germination. May be used on newly transplanted or established container stock, as well as field-grown plants. Remove all existing weed growth prior to application.

Oxyfluorfen (Goal). Rate: 5 to 10 pints/acre.In conifer seedbeds, oxyfluorfen exerts pre- and post-emergent control of annual grasses and broadleaf weeds. For pre-emergent control, apply in early spring after conifer seeds have been sown but before they germinate. For postemergent control, apply in the spring when vegetation is less than 4 inches high but at least 5 weeks after conifer seeds have germinated. In established plantations, apply before budbreak or after new growth has hardened off.

If you have questions or would like additional information, please contact
Dr. Karen Potter-Witter, Professor, MSU Department of Forestry