ORNAMENTALS NORTHWEST ARCHIVES

Transcription

1 ORNAMENTALS NORTHWEST ARCHIVES Sept.-Oct Vol.11, Issue 2 Pages Richard Regan OSU Extension Horticulture Agent Salem WEED ALERT & HERBICIDE UPDATE Annual and perennial grass weed control is a particular concern during the fall, winter, and early spring. Preemergence herbicides used in weed control programs are often applied at this time of year. Preemergence herbicides are those products that are effective in controlling weeds before they emerge or break through the soil surf ace. Three major considerations when selecting a herbicide are: 1) what grasses need to be controlled, 2) which herbicide can be used on certain conifers, and 3) how to use the herbicide properly. Table I shows the effectiveness of 14 different preemergence herbicides on certain annual and perennial grasses. Where available, information from the Pacific Northwest was used. Conifer crop tolerance to these herbicides is presented in Table 2. While species are listed as indicated on the label, specific cultivars are not. If a label only used the common name of a genus, such as "Pine", it is listed on the table as any species within that genus (i.e. Pinus spp). Some preemergence herbicides have postemergence activity, others do not and must. be applied before weeds emerge. The herbicide descriptions will help you select herbicides for a weed control program but should not be used alone. Consult manufacturers' labels for specific uses and precautions. Preemergence herbicide descriptions 1. ALACHLOR (Lasso) 4E, 15G DANGER Controls most annual grasses and a few broadleaf weeds. Apply anytime to weed-free soil and irrigate within 1 hour after treatment to minimize possible injury. Applications made when temperatures are above 90 degrees may cause injury. Persists in the soil for 6 to 10 weeks. Do not exceed 3 applications per year allowing at least 21 days between treatments. 2. ATRAZINE (AAtrex, Atrazine, AAtrex Nine-0) 80W, 9OWDG, 4L CAUTION Atrazine is a selective triazine herbicide used for preemergence and early postemergence weed control in conifers. Apply October through March when trees are dormant as a broadcast spray over-the-top of foliage. Can be applied post-emergence to small weeds. Requires rainfall or irrigation for activation. Apply only one time per year because it has long residual effectiveness.

2 3. CHLOROPROPHAM (urloe, Chloro-IPC) 4E 20G CAUTION Chloropropham is a selective preemergence herbicide for field-grown, dormant nursery stock. Apply to weed-free soil from late-fall through early-spring before new growth begins. Residual life of 1 to 6 months depending on soil temperature. Lost from the soil rapidly above 85 degrees. Do not apply to nursery stock that will be transplanted within 1 month after treatment. The granular formulation is safer for ornamentals. Thuja spp. may be sensitive to chloropropham treatments. 4. DCPA (Dacthal) 75W, 5G - CAUTION Pre-emergence control of annual grasses and certain broadleafs when applied to the soil surface before weed seeds germinate. Shallow mechanical cultivation (less than 2 inches) followed by rainfall or irrigation increases activity. DCPA provides up to 3 months of control if applied properly during the growing season and must be reapplied for longer control. This material is safe to use on many herbaceous and woody ornamentals. 5. HEAZINONE (Velpar) 25WDL DANGER Hexazinone is a highly water soluable triazine compound used as a selective, preemergence and postemergence herbicide. Apply in spring before budbreak. Requires rainfall or irrigation (0.5 to 1.0 inches) for activation but can cause damage to conifers or reduced weed control if heavy rainfall occurs after treatment. oliar application to weeds is most effective under conditions of high temperature (80 degrees ), high humidity, and good soil moisture. Necrotic spotting of Picea pungens and severe damage to Sequoiadendron giganteum and Thuja occidentalis have been observed (not registered uses). 6. METOLACHLOR (Pennant, Dual) 5G, 8E WARNING Metolachlor is a selective pre-emergence material for control of most annual grasses, yellow nutsedge, and a limited number of broadleaf weeds. Apply to weedfree soils at least 5 days after transplanting, but do not apply granules to wet foliage. Provides approximately 60 days of control, less under excessively wet conditions. Use the higher rates on fine-textured soils, in container media, and where yellow nutsedge and heavy grass infestations are expected. Do not use on seedbeds or on unrooted cuttings, or in greenhouses, and do not make more than two applications per year. 7. NAPROPAMIDE (Devrinol) 50W, 2G, 5G CAUTION Apply napropamide anytime to weed-free containers and irrigate immediately with 1 to 2 inches of water. or field-grown stock, apply in winter (November to ebruary) to weed free soil and irrigate if no rainfall occurs within 2 or 3 days or apply March through October and irrigate within 24 hours to wet soil 2 to 4 inches deep. It is a long lasting compound (up to 9 months under certain conditions) which will give season long control of susceptible weeds. However, under conditions of high sunlight intensity, there is fairly rapid loss by photodecomposition.

3 8. ORYZALIN (Surflan A.S.) 4A.S. CAUTION Recommended as a directed or over-the-top spray. Apply anytime to weed-free soil or containers and irrigate immediately with 0.5 inches of water. Should be applied to established plants; rooted liners established in containers 2 weeks prior to treatment. Provides weed control for 2 to 6 months depending on the rate used. Do not repeat treatment within 90 days. Shallow cultivation (1 to 2 inches) will not reduce herbicide effectiveness. Plant only ornamental species on label into soil treated the previous season with oryzalin or injury may occur. 9. OADIAZON (Ronstar, Chipco Ronstar) 2G, 50W WARNING Oxadiazon can be used for newly transplanted or established ornamentals. Apply to weed-free soil anytime of year. Rainfall or irrigation after application will improve weed control activity and reduce crop damage. The 50W formulation should be applied as a directed spray and has postemergence activity except on grasses which are generally resistant. Cultivation of treated soil will reduce weed control which normally varies from 3 to 6 months. Oxyfluorfen is a preemergence herbicide with some postemergence activity. Apply to dormant conifers (prior to budbreak or after the foliage has had a chance to harden-off) in containers or fields after transplanting and irrigate with 0.5 to 0.75 inches of water. Applications should be made to seedbeds after sowing, but prior to conifer germination, or 5 weeks after emergence of the conifer seedling. Do not apply to young seedlings if cloudy weather has persisted because the waxy cuticle that protects the plant does not develop properly as it does with sunny conditions. Postemergence applications can control susceptible broadleaf weeds up to 4 inches tall. Cedrus spp. was observed to be damaged by this material (not a registered use). 10. OYLUOREN (Goal) 1.6E -WARNING Oxyfluorfen is a preemergence herbicide with some postemergence activity. Apply to dormant conifers (prior to budbreak or after the foliage has had a chance to harden-off) in containers or fields after transplanting and irrigate with 0.5 to 0.75 inches of water. Applications should be made to seedbeds after sowing, but prior to conifer germination, or 5 weeks after emergence of the conifer seedling. Do not apply to young seedlings if cloudy weather has persisted because the waxy cuticle that protects the plant does not develop properly as it does with sunny conditions. Postemergence applications can control susceptible broadleaf weeds up to 4 inches tall. Cedrus spp. was observed to be damaged by this material (not a registered use). 11. PRONAMIDE (Kerb) 50W CAUTION Pronamide is a selective preemergence and early postemergence compound for control of annual and perennial grasses and a few broadleaf weeds. Root uptake is necessary (no foliar activity) for control thus adequate rainfall or irrigation must follow treatment to move it into the root zone. Apply in fall or early-winter when soil temperatures are below 55 degrees but before the soil freezes up. The product is rapidly decomposed by soil microorganisms at higher soil temperatures. Like other root-active herbicides, make sure the soil is well settled and the new transplants are well rooted prior to treatment. Do not apply to container-grown conifers or to plants less than one year old or to fall transplants planted less than one year, or to spring transplants planted less than 6 months.

4 12. SIMAZINE (Simazine, Princep) 80W, 4G, 4, 90WDG CAUTION Simazine is a selective triazine compound used as a preemergence herbicide for field-grown conifers. Apply at least 1 year after transplanting nursery stock and activate with rain or sprinkler irrigation. all and spring applications provide for longer control of susceptible weeds. Under dry soil conditions shallow cultivation often improves activity. Do not apply to Christmas tree transplants less than 3 years of age (California, Oregon, and Washington, 1 year after transplanting). Do not apply more than 4.0 lbs A.I. of simazine per acre per year. 13. ORNAMENTAL HERBICIDE 2 3G (oxyfluorfen 2% + pendimethalin 1%) - CAUTION Ornamental Herbicide 2 is a premixed combination of oxyfluorfen (Goal) and pendimethalin (Prowl) providing preemergence weed control in container and field-grown conifers. Apply to weed-free soil or containers and irrigate immediately with 0.25 inch of water. or containers, apply immediately after transplanting potted liners or 2 to 3 weeks after transplanting bare-root liners. Apply to field-grown stock any time to weed-free soil. This product provides weed control for a maximum of 3 months. Do not use Ornamental Herbicide 2 in greenhouses or enclosed areas. 14. ROUT (oxyfluorfen 2% + oryzalin 1%) 3G - CAUTION A premixed combination of oxyfluorfen (Goal) and oryzalin (Surflan) for preemergence weed control in container and field-grown conifers. Apply to containers after 0.5 inches or irrigation has settled media for potted liners and 2 weeks after planting bare-root liners. Apply to fieldgrown stock immediately after planting or in spring to weed-free, slightly loosened soil. ollow treatment with 0.5 inches of sprinkler irrigation. Weed control can be expected for a maximum of 3 months. Newly forming leaves are particularly sensitive to this product. Do not use this product in greenhouses or enclosed areas.

5 Table 1. Grass Weed Species ound in Conifer Crops and Their Susceptibilities to Herbicides.* GRASSES PREEMERGENCE HERBICIDES Alachlor Atrazine Chlorpropham DCPA Hexazinone Metolachlor Napropamide Oryzalin Oxadiazon Oxyfluorfen Pronamide Simazine OH2 Rout Annual Bluegrass G G G G G G G G G Annual Ryegrass G G G N G G Barnyardgrass G G G G G G G G G G Bromegrasses G G G G G Bentgrass G P G Crabgrasses G G G G G G G G all Panicum G G G G G G G oxtails G G G G G G G G Johnsongrass (sdlg) P G G N G Orchardgrass N P G P Quackgrass P G P P P Perennial P P G N P P Ryegrass Tall escue N G G N Velvetgrass N G R G N Volunteer Grains (barley, oats, rye, wheat) Wild Oats N *Information based on manufacturers' labels. Consult label for specific use. **KEY TO HERBICIDE REGISTRATION: = IELD GROWN D = IELD GROWN, DORMANT C = CONTAINER GROWN = IELD OR CONTAINER GROWN S = SEEDBED, IELD, OR CONTAINER GROWN BLANK= NOT ON LABEL

6 Table 2. Herbicide Registrations or Conifers (Narrowleaf Evergreens).* CONIER PREEMERGENCE Alachlor Atrazine Chlorpropham DCPA Hexazinone Metolachlor Napropmamide Oryzalin Oxadiazon Oxyfluorfen Pronamide Simazine OC2 Rout Abies spp. D Abies balsamea D Abies concolor D Abies fraseri S Abies grandis D D S Abies lasiocarpa Abies procera D D S Abies veitchii Cedrus spp. D Cedrus atlantica C Chamaecyparis spp. Chamaecyparis lawsoniana C Chamaecyparis thyoides Cryptomeria japonica Cupressus spp. Cupressus macrocarpa C Cupressus sempervirens Juniperus spp. D Juniperus chinensis Juniperus conferta C Juniperus excelsa C Juniperus horizontalis Juniperus procumbens C Juniperus sabina Juniperus scopulorum C Juniperus squamata Juniperus virginiana Larix kaempferi Picea spp. D Picea abies S Picea engelmannii Picea glauca S Picea omorika Picea pungens D S Picea rubens Picea sitchensis D D S *Information based on manufacturers' labels. Consult label for specific use. **KEY TO HERBICIDE REGISTRATION: = IELD GROWN D = IELD GROWN, DORMANT C = CONTAINER GROWN = IELD OR CONTAINER GROWN S = SEEDBED, IELD, OR CONTAINER GROWN BLANK= NOT ON LABEL

7 Pesticide Use - Due to constantly changing laws and regulations, no liability for the suggested use of chemicals in this Newsletter is assumed by the ONW Newsletter. Pesticides should be applied according to label directions on the pesticide container. Permission to Reprint material appearing in the ONW Newsletter is granted with the request that you credit the source: Ornamentals Northwest Newsletter, date, volume, issue, page numbers. Do not excerpt or reprint in such a manner as to imply the author's endorsement or criticism of a product or concept. Nondiscrimination - The information in the Ornamentals Northwest Newsletter is provided with the understanding that no discrimination is intended and that listing of commercial products implies no endorsement by the authors. Criticism of products or equipment is neither intended nor implied.