Planning is the bedrock of farming, but—as often is the case—farmers should consider what happens when things don’t go according to plan. This is particularly true with the farm weed management plan (WMP). A wet spring or fall can impact a farmer’s ability to use tillage or apply a herbicide prior to planting. However, there are several herbicide products that can be applied PRE and POST in corn to overcome this challenge. Although there is some flexibility in timing, applying these herbicides as soon as possible after planting may decrease the risk of poor herbicide performance. When a weed control tactic is delayed, weeds will continue to grow, and application rates may need to be increased to provide satisfactory weed control. Rotational crop interval restrictions must also be kept in mind with later-than-normal applications. As with all pesticides, read and understand the label for each product prior to application.
Q. I planned to use tillage to take out existing weeds before I planted, but it was too wet. What are some options?
A. A burndown herbicide program can help reduce weeds prior to planting. DiFlexx® herbicide, DiFlexx® DUO herbicide, Roundup PowerMAX® herbicide, or XtendiMax® herbicide with VaporGrip® Technology (a Restricted Use Pesticide, RUP) are products that can be used or included in a tank mix prior to planting. Consult each product label to determine use requirements and possible tank mix options. Each field should be scouted to determine weed species and size prior to selecting the best product. While not optimal, late burndown in corn is not catastrophic. Because of the residual activity of some corn herbicides (e.g., atrazine) on weeds that have emerged, XtendiMax® herbicide with VaporGrip® Technology (RUP) and DiFlexx® herbicide can be used for control of emerged weeds around the time of planting and after the crop has emerged.
Q. Is there a flexible burndown or residual program that lets me plant corn or soybean?
A. While there are products that will work with corn or soybean, it is important to keep in mind that application rates and wait periods may differ for each crop. Also keep in mind that tank mixes with other products may increase the efficacy of the herbicide.
• Some burndown herbicides that can be used in corn or soybean include:
» 2,4-D LVE
» BASIS® Blend
» Elevore™ Herbicide
» glyphosate
» Gramoxone® SL 3.0 herbicide/paraquat 3 lb per gallon
» Harmony® Extra SG herbicide
» Audit® 1:1 Herbicide
» Liberty® 280 Herbicide
» Reviton® herbicide
» Sharpen® Herbicide
• Some residual broadleaf herbicides that can be used in corn or soybean include:
» Lorox® L
» metribuzin
» Python® Herbicide
» Valor® EZ Herbicide
• Some residual grass/broadleaf herbicides that can be used in corn or soybean include:
» Verdict® Powered by Kixor® Herbicide
» Zidua® SC herbicide
» Anthem® MAXX herbicide
» Anthem® Flex herbicide
» Fierce® Herbicide
Q. I planned to use a burndown product to take out weeds before I planted, but did not. What are some options?
A. If you have selected a corn product with Roundup Ready® 2 Technology, Roundup PowerMAX® herbicide can be used PRE through the V8 growth stage or until corn plant height reaches 30 inches, whichever comes first. Additional burndown choices that can be used after planting any field corn seed product include XtendiMax® herbicide with VaporGrip® Technology (a Restricted Use Pesticide, RUP), DiFlexx® herbicide, Diflexx® DUO herbicide, and Laudis® Herbicide (applied up to the V8 growth stage) which can be applied to emerged corn.
If weeds are 3 inches tall or less, Capreno® herbicide can be used as a burndown and provide early season residual control. It is recommended that the product be applied as soon as possible after planting to control emerged weeds. Using a product or tank mixing with a product that provides early residual control can also be beneficial if a planned burndown could not be used before planting. Products like Capreno® herbicide and Harness® MAX Herbicide can help extend residual activity when tank mixed with your other herbicide options. Capreno® herbicide can be used for foliar and residual control of grass and broadleaf weeds, while Harness® MAX can be used for foliar control of broadleaf weeds and residual control of both grass and broadleaf weeds. Laudis® Herbicide is another option that can add foliar control and a short-term residual on grass and broadleaf weeds.
Q. I want to add a residual product with my burndown prior to planting. What are some options?
A. Including atrazine can help provide control of many broadleaf weeds and some grass species. Balance® Flexx herbicide can help provide control of both grass and broadleaf weeds. These herbicides—in combination with a premix acetochlor brand such as Degree Xtra® Herbicide, Harness® Xtra Herbicide, or Harness® Xtra 5.6L Herbicide—can provide good control with multiple effective sites of action for weed control. Corvus® herbicide is a premium in-can mixture for full spectrum weed control that is recommended for use with atrazine for season long residual control. TripleFLEX® Herbicide and Harness® MAX Herbicide provide residual control of grass and broadleaf weeds, and can be used outside of areas where there are atrazine or isoxaflutole (the active ingredients in Corvus® herbicide and Balance® Flexx herbicide) restrictions. Check labels and consult locally with experts for a local, tailored solution.
Q. What herbicide can I apply after corn has emerged when both a burndown and residual control are needed for early season weeds?
A. For control of emerged weeds, Roundup PowerMAX® herbicide can be used PRE through the V8 stage or until corn plant height reaches 30 inches, whichever comes first, on field corn products with Roundup Ready 2 Technology®. Laudis® herbicide can be tank mixed with glyphosate products for enhanced control of broadleaf weeds, some grasses, and glyphosate-tolerant weeds. Additionally, when glyphosate-tolerant weeds are a concern, DiFlexx herbicide, which is a dicamba product, or DiFlexx® DUO herbicide, which contains dicamba and tembotrione, can be broadcast applied to corn up to the V7 stage or 36 inches crop height, whichever comes first. Both of these products include a safener.
Q. What are some overall general recommendations when weed control is delayed?
A. Some general recommendations when the weed management plan (WMP) is delayed are:
• Increase glyphosate rates to at least 1.5 lb acid equivalent/A. Note, usually this will not provide control of marestail but it should on other weeds.
• Use 2,4-D ester in the mix, even if it means waiting another 7 days to plant soybean.
• Consider having the burndown custom applied if labor or time is short.
• Add a saflufenacil herbicide to improve control with glyphosate/2,4-D; as long as the residual herbicides in the mix do include flumioxazin, sulfentrazone, or fomesafen if the application is made within 14 days of soybean planting.
• Consider substituting Gramoxone® or glufosinate for glyphosate. Either one should ideally be applied with metribuzin and 2,4-D. Use the higher, labeled rates and a spray volume of 15 to 20 gpa for best results. However, in a no-till production system with large weeds, high rates of glyphosate may be more effective then Gramoxone® or glufosinate as long as glyphosate-resistant weeds are not present.
• It is possible to substitute tillage for burndown herbicides. Make sure that the tillage is deep and thorough enough to completely uproot weeds. If weeds re-grow after tillage, they will be very difficult to control later in the season.
