Herbicides for shelterbelt weed control

The success of prairie shelterbelt planting is dependent upon many variables, some of which can be controlled or influenced. Weed competition is one such variable.

Shelterbelt weed control begins with site preparation. The elimination of annual weeds is important and much easier to accomplish prior to planting. The planting area should be tilled to control annual weeds, the perennial weeds should then be left to grow until they reach the correct stage for effective glyphosate (Roundup, Touchdown) treatment. Tillage should not be conducted for 10 days follow-ing glyphosate application. The site can then be maintained through tillage until it is time to apply and incorporate a preplant herbicide treatment.

For preplant treatment, two options exist: either the application of trifluralin (Treflan, Rival) or a mixture of trifluralin (Treflan, Rival) plus metribuzin (Sencor). Both treatments require tillage for incorporation and can be applied in the fall or in the spring, prior to planting. The treatment chosen will depend on the tree species to be planted.

For continued maintenance, several herbicide options are available: sethoxydim (Poast Ultra) can be applied for control of annual grasses and suppression of quack grass. Paraquat (Gramoxone) and glyphosate (Roundup Original) can be applied as directed sprays (avoiding contact with tree leaves or green, immature bark). Roundup gives control of annual and perennial weeds; Gramoxone gives control of annual weeds and top growth control of perennial weeds.

Three herbicides are available to provide residual weed control (control of germinating weeds) through soil application. Application in the fall of the first year or the early spring of the second year should be restricted to linuron (Linuron, Lorox, Afolan). In the year after planting and in subsequent years, fall linuron application can be continued or simazine (Simazine, Princep) or dichlobenil (Casoron) can be used instead. For these soil applied herbicides, selection should be based on the weed species to be controlled, the soil texture and the tree species. Linuron, simazine and dichlobenil should be applied to a trash fee soil surface and in some cases may require some form of precipitation to activate the chemical.

Important:

Safety precautions should be taken to protect yourself, others and the environment from careless use of herbicides. Always use protective equipment and consult the product label for instructions on proper use, storage, handling and disposal of herbicides. Avoid spray drift to non-target plants.

Glyphosate
(Roundup Original, Wrangler, Laredo, Renegade, Victor, Touchdown)

• Glyphosate's ability to move throughout the plant, following absorption, make it capable of con-trolling perennial weeds as well as annuals. This characteristic makes it useful for site prepara-tion as well as maintenance. It can be used to clean up perennial weeds such as Canada thistle and quack grass.
• When spraying around trees, glyphosate application should be restricted to a directed or shielded spray as contact with the tree foliage or green, immature bark will result in significant damage or death of a tree. Conifers (spruce and pine) present an exception to this rule. They are sensitive to glyphosate only during the period of active growth (ie. April - August). Contact from glyphosate application after September 1^st is tolerated by these species. Use caution!
• The range of application rates for glyphosate is quite broad, depending on the species of weed to be controlled. For annual weeds, the rate is 1.3 - 2.5 L/hectare for liquid formulations of Roundup Original, Wrangler, Laredo, Renegade, Victor or Touchdown or 0.7 - 1.3 kg/hectare for Roundup Dry. For perennial weeds the rate is 5 - 7 L/hectare for liquid formulations or 2.7 -3.7 kg/hectare for Roundup Dry. The product information, provided with each container, should be consulted for application rates for specific weed species. For preparation of a solution for handgun application, a general recommendation is 20 mL of product to each litre of water.
• Water hardness and volume can have a bearing on the effectiveness of Roundup application. Water hardness can reduce glyphosate effectiveness as can the use of high water volumes. Lower water volumes generally result in a greater degree of weed control. The common recom-mendation for water volumes is 50 - 100 L/hectare.

Linuron
(Linuron, Lorox, Afolan)

• Linuron interferes with the photo synthetic process in susceptible plants, resulting in their death. For shelterbelt application, the best times for treatment are late fall or early spring. At these times of the year the trees are dormant, there are very few weeds present and those species that are present (most often winter annuals of the mustard family, ie. stinkweed, flixweed, shep- herd's-purse) are susceptible to linuron.
• Following preemergence linuron application (application before the weeds have emerged) rain-fall or sprinkler irrigation, within 10 days, is necessary to provide incorporation of the herbicide into the germination zone of the soil. Do not till the soil after linuron application as this disrupts herbicide activity.
• Postemergence application (application to existing weeds) must be conducted when the weeds are small to be effective. If application takes place when the trees are actively growing (have broken bud or are leafed out) spray must be directed away from the growth to avoid injury to the trees.
• The first linuron application can take place in the fall of the year the trees are planted. Annual application in either spring or fall will reduce the need for other weed control measures during the growing season.
• The rate for shelterbelt application is 2.8 L/acre for the flowable (suspension) products and 2.7 kg/acre for the dry flowable (wettable granule) products. The water volume should be a mini-mum of 100 L/acre.
• The weed species controlled include: goosefoot spp., common groundsel, common chickweed, prostrate knotweed, lamb's-quarters, pigweed spp., purslane, ragweed, shepherd's-purse, stinkweed, wild buckwheat, mustard spp., green smartweed and lady's-thumb. Established perennial weeds are not controlled.
• Tree species for which linuron is registered include: caragana, green ash, Siberian elm, American elm, Manitoba maple, choke cherry, saskatoon berry, poplar, willow, Colorado spruce, white spruce and Scots pine.

Metribuzin
(Sencor 75 DF)

• Metribuzin is readily absorbed by plant roots and moved upward into the shoots and leaves. In susceptible plants it inhibits photosynthesis and causes leaky cells which dry up and disinte- grate. Susceptible weed seedlings emerge through the treated soil but become chlorotic then turn brown and dry up, usually within 2 to 5 days in sunlight. This often occurs before the weeds are large enough to be noticeable.
  Tank Mix:
  For shelterbelt use, it is recommended that Sencor be tank mixed with Treflan and applied prior to planting. This tank mix should be incorporated into the soil to an 8 cm depth within 24 hours of application. For incorporation, a disc type implement or field cultivator with mounted harrows should be used (not a chisel plow or deep tillage cultivator). If available, a rotovator will also work well.
• Rates of application for this tank mix are 160 g per acre Sencor 75 DF plus 2.1 litres per acre Treflan 480 EC in a minimum of 50 litres water.
• The weed species controlled by this treatment include green foxtail, redroot pigweed, Russian thistle, wild oats, wild buckwheat, witch grass, stinkweed, barnyard grass, wild mustard, lamb's-quarters, purslane, Persian darnel, prostrate pigweed and shepherd's-purse.
• It is registered for use prior to planting caragana, green ash, choke cherry, villosa lilac, rooted poplar, saskatoon berry and sea-buckthorn.

Trifluralin
(Rival, Treflan, Bonanza)

• Trifluralin is primarily absorbed by emerging plant shoots, secondarily by seedling roots. It inhibits cell division and cell formation. In grass plants the area affected is the node from which the first leaf is developed. In broadleaf plants the area of the stem below the cotyledons (seed halves) or just above them is the area affected.
• For effective weed control, trifluralin needs to be incorporated into the upper layer of soil (the germination zone). This need for incorporation makes it difficult to use trifluralin around existing trees. Therefore, most applications associated with shelterbelts are for site preparation prior to planting.
• Recommended rates of application are dependent on soil texture and range from 1.8 to 3.6 L/acre for 480 g/L and 500 g/L EC formulations and 2.2 to 4.5 L/acre for 400 g/L EC formulations. The lower application rates should be used on lighter soils with less than 6% organic matter; the higher rates should be used on soils with 6 - 15% organic matter and of loam to clay texture. Water volume for applications should be at least 45 L/acre.
• Within 24 hours of application, trifluralin should be incorporated to an 8 cm depth. This is best accomplished by the use of a disc type implement or field cultivator with mounted harrows (not a chisel plow or deep tillage cultivator). If available, a rotovator will also work well.
• Weeds controlled by trifluralin include wild oats, foxtail spp., barnyard grass, Persian darnel, bromegrass, pigweed spp., lamb's-quarters, purslane, wild buckwheat, Russian thistle, chick-weed, knotweed, cow cockle and goosefoot. Refer to Sencor tank mix for control of weeds in the mustard family.
• Shelterbelt species for which trifluralin is registered include American elm, caragana, green ash, Scots pine and Siberian elm.
• Note: You can not plant unrooted poplar and willow cuttings in Treflan, Rival or Bonanza treated soil.
• Granular Treflan and Heritage should be applied at a rate of 18 kg/acre and Rival at a rate of 9kg/acre.

Simazine
(Simazine, Pricep)

• Simazine is absorbed through plant roots and translocated to the shoots where it interferes with photosynthesis, resulting in the herbicidal effect. Very limited foliar absorption occurs following postemergence simazine application.
• Applied preemergence, simazine works similar to linuron; however, it is more persistent, providing a longer period of control. The usual time of application would be late fall or early spring, to a relatively weed free soil surface with limited trash cover. Weeds present at the time of appli-cation will not be controlled.
• For shelterbelt use, the recommended application rate is 1.5 kg/acre for the wettable granule formulation (ie. Princep Nine-T), 1.7 kg/acre for the wettable powder formulation (ie. Simazine 80W) and 2.7 L/acre for the suspension formulation (ie. Simazine Flowable). Careful attention should be given to label precautions regarding the texture of the soil to be treated. Do not use on course-textured soils.
• Water volumes for application is a minimum of 100 L/acre. Continuous agitation is required in the sprayer tank during mixing and application.
• The weed species controlled include: lady's-thumb, lamb's-quarters, purslane, ragweed, wild buckwheat, smartweed, barnyard grass, wild oats, green foxtail, witch grass, chickweed, common groundsel, mustard spp., nightshade spp., pigweed spp., shepherd's-purse and speedwell spp.
• Simazine can be used for weed control in plantings of the following tree species: cedar, apple, cotoneaster, dogwood, rose, juniper, Colorado spruce, Norway spruce, white spruce, mugho pine, caragana, green ash, Siberian elm, American elm and Manitoba maple. Application is not recommended until the trees have been established for at least one year. Do not use on poplar or lilac.

Sethoxydim
(Poast, Poast Ultra)

• Sethoxydim is a contact and systemic (moves through the plant system) herbicide. It is rapidly absorbed by plant leaves and is rainfast 1 hour after application. Once absorbed, it causes growth to stop by blocking the production of new membranes. Leaves become chlorotic, then necrotic (dried up). The leaf color change, during this process, is generally yellow to purple or red before they become necrotic. The process takes anywhere from one to three weeks for completion.
• Rates for shelterbelt or woody ornamental application are 0.4 to 1.1 litres of Poast or 0.16 to 0.45 litres of Poast Ultra per acre with Merge adjuvant added at a rate of at least 1% of the water volume used. Water volume should be 40 - 80 litres per acre. The maximum application rate is for quackgrass suppression. The optimum growth stage for application for quackgrass suppression is 1 - 3 leaves. For control of annual grasses and volunteer cereals, application should be made at the 1 - 6 leaf stage with application at the 2 - 3 leaf stage providing optimum control.
• Weed grasses controlled by sethoxydim include green foxtail, barnyard grass, witch grass, Persian darnel, wild oats, volunteer wheat, oats and barley and quackgrass.
• Sethoxydim is registered for use on the following tree species: white spruce, Colorado spruce, Scots pine, Douglas fir, cedar, juniper, caragana, green ash, lilac, saskatoon berry, buffaloberry, sea-buckthorn, potentilla and spirea.

Dichlobenil
(Casoron)

• Following soil application, susceptible weed seeds do not emerge as dichlobenil inhibits germi-nation and cell division. It is readily absorbed by roots and leaves. Due to the nature (ie. granular) and application of the product (soil applied) foliar uptake is not a factor in the tolerance of tree and shrub species to this herbicide.
• Dichlobenil is a volatile herbicide, which can be lost in the form of vapours following application to warm, moist soil. Therefore, it is recommended that application take place in late fall or, if application is delayed until spring, that shallow tillage be conducted to provide incorporation following application. If vapours do form following spring application, they can cause considerable damage to trees and shrubs if absorbed by opening buds or new leaves.
• The rates of application for shelterbelt and ornamental use range from 45 - 70 kg/acre (11 g - 17 g per sq. metre). For site preparation, 18 months prior to planting, application rates range from 90 - 110 kg/acre (22 - 27 g per sq. metre). The site preparation treatment is particularly useful for control of quackgrass, perennial thistles, dandelion and bindweed. Careful attention should be given to label precautions regarding the texture of the soil to be treated. Do not use on course textured soils.
• Several weed species are controlled by dichlobenil, including annual bluegrass, artemisia, bind-weed, blue aster, Canada thistle, chickweed, crabgrass, quackgrass, dandelion, foxtail spp., common groundsel, field horsetail, prostrate knotweed, kochia, lamb's-quarters, mustard spp., pigweed spp., plantain, purslane, sheep sorrel, shepherd's-purse, smartweed, sow- thistle, spurge, vetch wild buckwheat, wild barley, witch grass, evening primrose, goosefoot spp., ragweed, wild carrot, yellow wood-sorrel and yellow rocket.
• Tree species for which dichlobenil is registered include: arborvitae, green ash, birch, caragana, cedar, crabapple, elm, honeysuckle, juniper, lilac, linden, maple, rose, spirea, willow, yew, ap-ple, cherry and saskatoon berry. Application is not recommended until the trees are at least one-year-old. Not recommended for spruce or pine.

Paraquat
(Gramoxone)

• Paraquat is a rapidly absorbed contact herbicide that is rainfast within 1 hour of application. Under normal conditions it remains in the leaf tissue of treated plants. It is non-selective, meaning that crop plants, including trees, will be damaged if improper application occurs. Upon absorption by the plant leaves, a chain reaction begins whereby cell membranes are destroyed resulting in wilting, browning and death of the leaves and other green tissue.
• For shelterbelt weed control, paraquat is most useful for control of relatively small annual weeds and seedling perennial weeds. Large, well established annual weeds may generate new top growth. In the case of established perennial weeds, paraquat has to be applied repeatedly to provide control, eventually depleting the weed's root system causing the plant to die.
• When applying paraquat along shelterbelts, spray must not be allowed to come in contact with tree foliage, green buds or green immature bark. This can be achieved through the use of a directed spray and/or some form of shielded spray equipment.
• Rates of application range from 2.2 - 4.4 litres of product per acre, based on weed population density. As paraquat's effectiveness is dependent on thorough weed coverage, high water volumes ranging from 100 - 400 litres per acre are recommended. For high volume handgun application, a solution consisting of 70 ml of product for every 10 L of water is recommended.
• Due to the toxic nature of this herbicide, it is important that you do not get it on your skin, in your eyes or on your clothing. Do not inhale fumes or spray mist. Wash splashes from skin and eyes immediately. Remove and wash contaminated clothing. Wear eye protection, respirator, rubber gloves, coveralls and waterproof footwear when handling concentrate.