With the cool spring, plant growth has been delayed, but farmers and applicators particularly in the Southern half of PA are considering burndown options for corn. Remember that environmental conditions and the size of the weeds can greatly affect the activity of burndown herbicides and weed control. Daytime temperatures above 55 F and nights above freezing with sunny days help improve herbicide activity. After a cold spell, wait for a few days of warm, sunny weather before applying herbicides and remember that herbicides work slower under cool conditions. Increasing the rate of the burndown herbicide may be necessary if weeds are stressed by cold conditions or are larger in size. Scout fields prior to spraying to ensure you use the correct herbicide program for the problem. For corn, some common burndown herbicides include the following:
Broad-spectrum foundation products
Glyphosate - Generally applied at 0.75 to 1.125 lb ae per acre (32 to 48 fl. oz of a 41% product). Use the 1.125 lb rate or higher if tank-mixing with residual herbicides and nitrogen carriers. Do not use with suspension type liquid fertilizers. Add 2-4 lb/acre ammonium sulfate (AMS) or a similar product for improved performance. Typically applied in 10 to 20 gallons of liquid carrier per acre. May be applied in clear liquid nitrogen fertilizer or clear liquid complete analysis fertilizers but may be less effective on certain annual and perennial weeds.
Gramoxone SL (Syngenta) - This product contains paraquat and is applied at 2-4 pt per acre for control of emerged weeds. Paraquat is the main alternative to glyphosate for nonselective burndown. Since it is a contact herbicide, apply in 20 gallons of liquid carrier or more and do not use flood jet tips for best results. Be sure to include an appropriate nonionic surfactant. Add a triazine herbicide (atrazine, metribuzin, etc.) to Gramoxone to increase burndown activity. Using UAN as a partial carrier will also increase the activity.
Liberty (glufosinate) - This active ingredient has been labeled postemergence in Liberty Link corn and soybean, but is also labeled for burndown in conventional corn and soybean. We have not really considered this much of a burndown herbicide simply because its strength is small annual weeds and it is not very effective on larger winter annuals, perennials, or burndown of cover crops. However, it is labeled for burndown application up to 36 fl. oz per acre, and can now be used sequentially in both Liberty Link corn and soybean (burndown followed by post). Most of the fit for this is for soybean and not corn. It has gained some traction in the Mid-Atlantic for burndown control of marestail in particular. Remember, Liberty is most effective on small actively growing weeds under warm temperatures, with bright sunlight, include AMS and use sufficient carrier volume and spray tips to get thorough coverage of the weeds.
Broadleaf only products
2,4-D ester - A PGR herbicide that can be applied at 1 pint 7 to 14 days before planting or 3 - 5 days after planting for greater crop safety. Plant corn at least 1.5 inches deep. Use the ester formulations of 2,4-D, instead of the amine. Esters (LV4) are usually more effective under cool conditions, are less water soluble and better on perennial weeds. Also, esters usually penetrate the waxy leaf surface (cuticle) better than amines. 2,4-D will help control a number of emerged winter annuals including marestail.
Dicamba (Clarity/Banvel) - A PGR herbicide that can be applied at up to 1 pint per acre on medium and fine textured soils with at least 2.5% organic matter. It can be tank-mixed with 2,4-D, and like 2,4-D, direct contact with corn seeds must be avoided. So plant corn at least 1.5 inches deep and apply 7 to 14 days ahead of planting or delay application until corn is emerging. Dicamba is often necessary for successful alfalfa and/or clover burndown.
Control of small emerged broadleaves (and maybe grasses depending on the product)
Atrazine - apply 1 to 2 lb per acre preplant or preemergence to corn (rate may depend on tillage system). Controls small emerged annual broadleaf weeds and will suppress annual grasses (as well as provide residual control). Can be applied in UAN for improved burndown activity.
Balance Flexx and Corvus (Bayer Crop Science) - Balance Flexx and Corvus contain the herbicide isoxaflutole. Corvus also includes an herbicide called thiencarbazone. Both products include a corn safener for the isoxaflutole component. Isoxaflutole in combination with atrazine can provide control of small emerged annual weeds. The thiencarbazone component will improve foliar and residual grass control. Tank mix with other herbicides including 2,4-D, Gramoxone, or glyphosate for broader spectrum activity. For greater crop safety, plant corn at least 1.5 inches deep and make sure the seed is well covered.
Basis Blend (Dupont) is a mixture of rimsulfuron and thifensulfuron (Harmony) and can be applied preplant or preemergence to corn. The typical Basis Blend rate is 1.25 to 1.5 oz per acre. Plant corn 1.5 inches deep and apply 7 or more days before corn planting for greater crop safely. Typically tank-mixed with atrazine and/or 2,4-D LVE to increase the spectrum of activity. Resolve (rimsulfuron) and Resolve Q (rimsulfuron plus thifensulfuron plus safener) have similar use labels.
Clopyralid (Component of Hornet and Surestart - Dow AgroSciences or TripleFLEX - Monsanto) - A PGR herbicide that can provide burndown and residual control of selected annual broadleaf weeds. The 5 oz rate of Hornet contains 0.195 lb or 6.7 fl oz of Stinger. The 1.75 pt rate of Surestart or TripleFLEXX contains 0.063 lb clopyralid or 2.8 fl oz (3 pt rate contains 0.108 lb or about 5 oz of Stinger). It is particularly effective on the ragweeds, can help control clover and alfalfa, and will suppress emerged Canada thistle.
Harmony 50 SG (thifensulfuron - Dupont) -Applied at 0.45 to 0.90 oz per acre preplant or at planting to corn (or soybean). Thifensulfuron will help control wild garlic and provide some suppression of certain winter annual weed species. Include an appropriate surfactant. It is not as broad spectrum at Harmony Extra and is typically tank-mixed with glyphosate and/or other herbicides.
Harmony Extra 50 SG (thifensulfuron plus tribenuron - Dupont) - Applied at 0.45 to 0.90 oz per acre. Allow at least 14 days between application and planting of corn. (7 days for soybeans). For improved control of wild garlic and some winter annual weeds. Include an appropriate surfactant. Typically tank-mixed with glyphosate and/or other herbicides.
Panoflex 50 SG (thifensulfuron plus tribenuron - Dupont) is labeled at 0.3 to 0.6 oz per acre for spring burndown prior to several crops. Panoflex contains the same active ingredients as Harmony Extra, but has more tribenuron and less thifensulfuron than Harmony Extra. It is active on winter annual broadleaves. Tank-mix with 2,4-D ester or glyphosate to broaden the spectrum of activity.
Instigate (Dupont) is a mixture of rimsulfuron (Resolve) plus mesotrione. Apply Instigate at 5.25 to 7 oz per acre (normal rate is 6 oz). It may be applied up to 14 days prior to corn planting. The addition of COC or MSO is recommended for burndown of labeled weeds 3 inches or less in height. For larger weeds, tankmix with paraquat, glyphosate or other burndown herbicides for additional activity.
Lumax/Lexar (Syngenta) - Lumax and Lexar contain Dual II Magnum, atrazine, and mesotrione (Callisto). The atrazine and mesotrione components can provide substantial burndown and control of small annual broadleaf weeds. Mesotrione is also quite effective for suppression of dandelion.
Metribuzin (formerly Sencor 75DF) - This product was labeled preemergence at up to 5.3 oz per acre on medium textured soils with greater than 2% organic matter as part of the burndown program. There are a number of metribuzin products (Metribuzin, TriCor, Dimetric, Glory, etc.) with different labels, so check with your local supplier for details. It can be tank-mixed with glyphosate, Gramoxone, 2,4-D or other preemergence products.
Prequel 45 WG (Dupont) is a mixture of isoxaflutole plus rimsulfuron that is generally applied at 1.66 oz per acre (up to 2.5 oz). Prequel can provide some control of small emerged annual weeds and can be tank-mixed with 2,4-D, atrazine and other herbicides to increase the spectrum of activity. For greater crop safety, plant corn at least 1.5 inches deep and make sure the seed is well covered.
Sharpen 2.85 SC (saflufenacil - BASF). The product is a contact type herbicide and can be applied at 1 to 3 oz per acre up to 14 days ahead of corn planting. Include MSO in the tank to maximize burndown activity on emerged broadleaf weeds including glyphosate resistant marestail (horseweed). The active ingredient saflufenacil is also found in the premix Verdict which contains saflufenacil and the grass herbicide found in Outlook. At the higher rate, Sharpen also provides residual control on annual broadleaf weeds.
Valor 51 WDG (fumioxazin- Valent) (not Valor XLT) is a contact type herbicide and may be included in the corn burndown program to enhance the speed of burndown and provide residual control of annual broadleaves. Corn may be planted 7 days after application at the 2 oz per acre rate (requires minimum of 25% surface residue and 0.25 inch of rainfall between application and planting). May be applied at up to 3 oz per acre 14 to 30 days prior to corn planting.