SUNFLOWERS INTRODUCTION

Transcription

1 SUNFLOWERS INTRODUCTION Weed management is an important component of successful sunflower production. Because sunflower is usually planted at low densities and grows slowly during the first several weeks, weeds which emerge and become established during this time can be very competitive and reduce sunflower yield potential. Sunflower is a strong competitor with weeds that emerge 3 or more weeks after sunflower, therefore, maintaining a weed-free sunflower crop for the first 3 to 4 weeks will minimize weed competition and maximize yields. It is essential that sunflower be planted into a seedbed free of growing weeds. Weed control before planting can be accomplished with tillage, herbicides, or a combination of both. If tillage is the predominate method of weed control, implements such as the V-blade, tandem disc or field cultivator are effective. These implements warm and dry the surface but maintain moisture below the sunflower seed, which encourages rapid sunflower development and may delay weed seed germination. The use of nonselective herbicides such as glyphosate (numerous names) and Gramoxone Max provide an alternative to preplant tillage for weed control. These foliar-applied herbicides can control seedling broadleaf weeds and grasses; however, they must be applied prior to sunflower emergence to avoid severe crop injury. Edited by: Dr. Steve Miller Plant Sciences University of Wyoming Laramie, WY sdmiller@uwyo.edu 176

2 WEED RESPONSE TO SUNFLOWER HERBICIDES Preplant/Preemergence Postemergence Weeds Dual Magnum Eptam Glyphosate Gramoxone Max Grasses barnyardgrass F-G E E G E E F E E E E crabgrass F-G G E F F-G F-G F F F-G G-E E foxtails E E E G G-E E F-G E E E E volunteer grain F G E F-G F-G G P P-F F-G G-EE E sandbur P G-E E G F-G G P G F-G E E Broadleaves bindweed, field N N P-F P P P P P N N N buckwheat, wild N F P-F F P-F P-F F P-F P N N cocklebur N P G-E F-G N P F N G-E N N knotweed N P F-G F P P P P P-F N N kochia P F G-E F-G G-E G-E E G-E G-E N N lambsquarters, common F F G-E E E E E G-E F-G N N mallow, common P P G F-G P P P-F P G N N mustard, spp. P P G-E G N N P N E N N nightshade, spp. F-G F-G F-G G-E P F E P E N N pigweed, redroot G G G-E E E E E E E N N thistle, Canada N N N G N N P N P N N thistle, Russian P-F P G F-G G G-E F G G N N Control: E = Excellent, G = Good, F = Fair, P = Poor, N = No Control, - = Insufficient Regional Data Response of weeds to any of the listed herbicides may be altered by growing conditions, weed populations, genetic variation, application time and rate. Ratings may vary from season to season and over geographic areas. Prowl Sonalan Spartan Treflan Beyond Poast Select 177

3 SUNFLOWER Herbicide Application and Remarks PREPLANT/PREEMERGENT Dual Magnum, (7.62EC) Rate: 1 to 2 pt/a S-metolachlor Time: Preplant or preemergence. Incorporation improves consistency. Adjust rates based on soil type. Dry weather following application reduces effectiveness. Cultivate if weeds develop. Eptam (7E) Rate: 2.5 to 3.5 pt product/a EPTC Time: Apply and incorporate just before planting. Use lower rate on coarse textured soil. Must be incorporated immediately and thoroughly in the top 3 inches of soil. Soil should not be wet at the time of application. Glyphosate Rate: Product amount/a 0.39 ae 75 ae ae numerous brands 3.0 lb ae (4 lb ai) 16 fl oz 32 fl oz 48 fl oz 3.7 lb ae (5 lb ai) 13 fl oz 26 fl oz 40 fl oz 4.0 lb ae (5.4 lb ai) 12 fl oz 24 fl oz 36 fl oz 4.5 lb ae (5.5 lb ai) 11 fl oz 22 fl oz 32 fl oz Time: Preplant or anytime prior to crop emergence, but postemergence to the weeds. Use the low rate for small annuals. Ammonium sulfate at 8.5 to 17 lb/ 100 gal will improve consistency especially with hard water, cool weather or if weeds are under moisture stress. Apply all treatments before crop emerges or crop injury will result. Gramoxone Max (3SL) Rate: 1.75 to 2.7 pt product/a paraquat Time: Preplant or anytime prior to crop emergence, but postemergence to the weeds. Apply with a nonionic surfactant at 0.12 to 0.25% v/v. Good plant coverage is essential. RESTRICTED USE HERBICIDE. Apply all treatments before crop emerges or crop injury will result. Prowl (3.3EC) Rate: 1.8 to 3.6 pt (3.3 EC)/A or 16 to 3.2 pt (3.8 EC)/A Prowl H 2 O (3.8 EC) pendimethalin Time: PPI up to 30 days prior to planting or preemergence. 178

4 SUNFLOWER - continued Herbicide Application and Remarks Preemergence applications most effective in controlling weeds when adequate rainfall or irrigation is received within 7 days following application. Weed control will be reduced if incorporated too shallowly when top soil is dry. Sonalan (3EC) Rate: 1.5 to 3.0 pt product/a ethalfluralin Time: PPI - for best results immediately incorporate. Shallow incorporation prior to planting with field cultivators or narrow blade plows with or without mulch treaders are recommended. Read label for carryover precautions. Sensitive crops may be injured the following year. Spartan (75DF) Rate: 2 to 4 oz product/a sulfentrazone Time: May be applied in the fall, up to 30 days prior to planting or preemergence. Adjust rates based on soil type. Requires moisture for activation. Provide adequate furrow closure and soil covering at planting. Crop injury may occur on coarse textured soils with low organic matter and soil ph greater than 8.0, especially on calcareous outcroppings. Poor growing conditions at and following sunflower emergence (such as cold temperatures and soil compaction) may result in sunflower injury. Treflan M.T.F. (4EC) Rate: 1 to 2 pt product/a various brands 4EC, 5EC Time: PPI - for best results immediately incorporate. 80DF trifluralin Shallow incorporation with a tandem disc with small blades or field cultivator equipped with three or four rows of sweeps spaced no more than 7 inches apart is recommended. POSTEMERGENCE Read label for carryover precautions. Use lower rates under 20 inches of rainfall. Poast (1.5EC) Rate: 1 to 1.5 pt product/a sethoxydim Time: Postemergence when grasses are 2 to 4 inches tall. Requires an oil additive. Ammonium sulfate 2.5 lb/a or UAN (1 gal/a) may be added to improve control of volunteer cereal. Do not cultivate 5 days before or 7 days after application. 179

5 SUNFLOWER - continued Herbicide Application and Remarks Select (2EC) Rate: 6 to 8 fl oz/a Time: Postemergence to grasses up to 6 inches tall. Apply with an oil adjustment. UAN or AMS may improve control of certain species. Allow a 70 day interval between application and harvest. Do not graze or forage stalks. HERBICIDE RESISTANT SUNFLOWER Beyond Rate: 4 fl oz imazamox Time: Sunflower 2 to 8 leaves, grasses less than 5 leaves and broadleaf weeds less than 3 inches tall. Apply with NIS and UAN. MSO and oil adjuvants are not prohibited but may increase sunflower injury. Use only on Clearfield sunflower varieties. Refer to label for crop rotation restrictions. HARVEST AID Gramoxone Max (3SL) Rate: 1 to 1.3 pt product/a paraquat Time: Back side of sunflower heads yellow and bracts turning brown. Seed moisture content under 35%. For oilseed varieties only. Use a nonionic surfactant. RESTRICTED USE HERBICIDE. Do not graze treated areas or feed forage to livestock. Allow 7-day interval between application and harvest. Defol 6 (6LC) Rate: 1 to 2 gal product/a sodium chlorate Time: Apply 7 or more days before harvest when seed heads are fully mature. Caution For use on confectionery and oilseed varieties. Thorough coverage of plant is essential. Do not allow grazing of treated fields or feed treated forage. 180