Burndown: Hot Topics to Consider This Spring

As we deal with another spring filled with extreme weather conditions and as the window tightens between spraying burndown herbicides and crop planting, there are certain relevant issues that need to be considered.

Wait periods between burndown herbicides and crop planting.

With the zeal to get crops planted soon, some are forgetting about the necessary wait periods. Here are some guidelines to be aware of:

• 2,4-D ester (LVE) — When applied at 1 pint/acre, there is a 7-day waiting period for soybean. This is also the safest use in corn. If you apply 1 quart, wait at least 15 days to plant soybean. However, if you are running behind and plant corn before spraying a burndown, then wait at least 3 to 5 days after crop safety to spray 2,4-D 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 or 6) 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. Also keep in mind that in Enlist E3 soybeans, 2,4-D products (i.e., not Enlist One or Duo) can be used as burndown but must be applied 7-14 days before planting depending on rate. (Despite the fact that these 2,4-D formulations might not technically injury E3 varieties when sprayed at burndown, according to the label they cannot be applied immediately at planting or postemergence.)
• Basis Blend — Apply at 0.825-2.5 oz/acre in burndown programs before corn emergence; corn injury may occur under cool, wet conditions, so 1.5 oz rate is a good compromise. In soybean, apply 0.825 oz at least 15 days before planting; tankmix to enhance control. It provides some weedy grass control and fair to good burndown activity on several key broadleaves.
• Dicamba (Clarity, others) — In corn, it 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. Therefore, 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 can be used burndown before soybeans but must wait 14 days for 8 fl oz per acre or less or 28 days for 16 fl oz before planting any variety of soybean including XtendFlex plus at least 1-inch of rainfall must occur during that timeframe before planting. Dicamba is often necessary for successful alfalfa and/or clover burndown.
• Elevore — Either corn or soybean can be planted 14 days after application when applied at 1 fl oz/acre. However, corn can be planted after 3 days if seed is planted at least 1.5 inches deep and completely covered. Provides control of glyphosate-resistant marestail.
• Enlist One/Duo — Can be used in a burndown program before field corn or soybean. Enlist E3 soybeans or any kind of field corn can be planted immediately. However, non-Enlist soybeans must follow similar planting restrictions as 2,4-D.
• Glyphosate — There is no wait period between spraying and planting corn or soybean. This can be used in the burndown and POST in glyphosate-resistant crops. Increase the rate to 1.5 lb ae/acre for larger weeds.
• Gramoxone 3.0 SL/paraquat 3 lb/gal — There is no wait period between spraying and planting corn or soybean. You can increase the rate up to 2.7 pt/acre for larger weeds. Can tank-mix with metribuzin plus 2,4-D and still be able to plant corn or soybean. This mixture provides better burndown activity than paraquat alone.
• Harmony/Extra, Audit 1:1, and other thifensulfuron + tribenuron mixes — Can be added to the 2,4-D and/or glyphosate burndown at 0.45 to 0.90 oz/acre for both corn and soybeans. You must wait 7 days to plant soybeans and 14 days for corn. It provides burndown of several winter annuals such as chickweed, deadnettle, henbit, and mustards. Without glyphosate, it provides average (70-80%) control on many key broadleaves and no grass control; with glyphosate, it improves control of curly/broadleaf dock, wild garlic, common groundsel, field pansy, and Canada thistle.
• Liberty 280 (and other glufosinate products) — Labeled up to 43 fl oz/acre in the burndown application. Liberty is most effective on small, actively growing weeds under warm temperatures. Use sufficient carrier volume (minimum 15 GPA, 20 GPA is better) and spray nozzles to get thorough droplet coverage of the weeds. Liberty Ultra can also be used but adjust rates and make sure to follow drift mitigation strategies recommended on the label.
• Reviton — Can be used in a burndown program before field corn or soybean. Corn can be planted immediately after application; wait 7 days to plant soybean if using 2-3 fl oz (0 days at 1 fl oz). It has a low use rate (1 to 3 fl oz/A) and can be tankmixed with other herbicides, especially glyphosate. MSO or COC plus AMS must be added to the spray solution. Reviton is similar to Sharpen and is less active on marestail but has better activity on field pansy/violet, primrose, and some grasses compared to Sharpen.
• Sharpen — Labeled for both corn and soybean. Use only the 1 fl oz/acre in soybean for burndown if planting soybean immediately. Higher rates can be used, but be aware of planting restrictions for soybeans. Corn can be planted immediately at any labeled rate. Always add MSO and AMS as the adjuvants to the spray tank for optimal weed control.

Burndown herbicides, drift, and vineyards.

Some vineyard owners are reporting that grapes are starting to break buds. It is likely that herbicides can cause extensive damage to grapevines between bud break and fruit set. Therefore, lately, we have received calls asking for burndown herbicide suggestions for fields adjacent to sensitive crops such as vineyards or specialty crops. Most broadleaf plants (e.g., grapes, vegetables, fruit crops, ornamentals, certain trees, non-tolerant soybeans, tobacco, etc.) are extremely sensitive to plant growth regulator (PGR) herbicides. PGR herbicides include phenoxy, benzoic, and pyridine classes of compounds. The most common PGR herbicides used are those containing 2, 4–D or dicamba. But others that have been documented as causing injury include picloram (e.g., Tordon), triclopyr (e.g., Garlon), and clopyralid (e.g., Stinger). All the PGR herbicides should be considered as potentially injurious to non-target sensitive plants as a result of spray drift. Herbicide formulations and vapor pressure are primary factors associated with the volatility of most PGR herbicides. In general, the higher the vapor pressure of a pesticide, the greater its tendency to volatilize. Unfortunately, it is difficult to simply use their vapor pressure values to determine how much volatility will occur and thus cause off-target movement and injury. Many factors, including environmental issues play a part in the overall potential for herbicides to volatilize. Temperature and relative humidity are important for volatility – high temperatures and very low relative humidity usually cause much more volatility. Though volatility is important, off-target movement of herbicides is also due to small spray droplet drift and/or temperature inversions.

Alternative burndown herbicide options and drift reduction.

Historically, many of the standard burndown herbicide programs have included 2,4-D, primarily to control glyphosate/ALS-resistant marestail and other weeds such as dandelion and winter annuals. However, if crop production fields are near sensitive crops or areas, auxin herbicides have the potential to cause problems even early in the season if grapes or sensitive trees are starting to bud or break dormancy. Choline salt formulations of 2,4-D (Enlist One and Freelexx) and triclopyr (Vastlan in pasture or other settings) might possibly have a fit to reduce volatility but small droplet drift is still a concern. Furthermore, glyphosate drift can cause problems in these settings, and glyphosate-resistant weed species will not be controlled. In cases like this, some alternative herbicides for burndown include paraquat (e.g., Gramoxone), glufosinate (e.g., Liberty 280/Ultra), saflufenacil (e.g., Sharpen), and tiafenacil (Reviton). And depending on the type of weeds being controlled, other herbicide options (or their generic alternatives) such as Basis Blend, Harmony Extra, Canopy DF, metribuzin, Lorox, or others can provide some burndown activity. To improve the effectiveness of these products, especially during early spring conditions, make sure to use higher rates, include necessary adjuvants, use higher spray volumes (≥15 gpa), spray when weeds are small (3-5” tall) and actively growing; and apply during sunny days and warm temperatures (>50F daytime). Most of the soil-applied residual herbicides that are tank-mixed with burndown herbicides are not volatile and usually don’t cause problems to sensitive crops (unless severe drift occurs). However, no matter what herbicide is being applied, it is best to reduce drift and keep the spray in the target area. Some drift-reducing suggestions include – use low-drift nozzles and specially developed drift control adjuvants, increase carrier spray volumes (e.g., 20 gpa), reduce spray rig ground speed, use wide angle nozzles that allow lower boom heights, spray in low wind conditions, and apply when the wind directions are away from the sensitive area.

Communication is key to help reduce the chances of herbicide drift.

DriftWatch by FieldWatch is now available to use in Pennsylvania. It is a free, online Voluntary Specialty Crops Registry designed to alert applicators about locations of sensitive areas. The stewardship tool allows for improved communication and collaboration between producers of specialty crops and pesticide applicators using a technology platform where producers can map their sites and provide contact information to pesticide applicators through an online mapping system. More details and to register. Please consider using this new tool to help reduce the issues with drift. It is not a regulator tactic but simply a means to be a better neighbor.