Adjusting Soybean No-till Burndown Programs for Later Planting

Weed growth has been somewhat slow this year due to the cold weather in late winter, but the current warm and wet weather should change this.  Those fields not treated with burndown herbicides yet may present some challenges by the time fields are dry enough for traffic again, especially if they were not treated last fall.  Wet weather and delayed planting can have several effects on no-till burndown programs, especially in soybeans.   First, the weeds get bigger and what is a relatively tame burndown situation in April can become pretty hairy by the first two weeks of May.  Second, in the rush to plant when it finally dries out, it can be difficult to keep 2,4-D in the burndown mix and wait yet another 7 days to plant soybeans.  A review of the soybean burndown options for this situation follows.

1.  In all mixtures containing glyphosate, increase rate to the equivalent of 1.5 to 2.2 lb ae/A.  This will help with many weeds, but obviously not with glyphosate-resistant marestail or ragweeds.

2.  One option is to just omit the 2,4-D ester and rely on glyphosate for the burndown.  This is probably the worst choice on this list, but it can work in some fields.  This is not an option in fields with marestail, or glyphosate-resistant ragweeds.  Use a glyphosate rate of 1.5 to 2.2 lbs ae/A.  We recommend applying with a residual herbicide that contains chlorimuron (Canopy/Cloak, Valor XLT, Envive, Authority XL) to improve control of dandelions and many summer and winter annual broadleaf weeds (but not ALS-resistant marestail or ragweeds).  The mixture of glyphosate and chlorimuron or cloransulam is likely to be variable for control of even ALS-sensitive marestail by the time we can get into fields.

3.  Keep 2,4-D ester in the mix with glyphosate and wait another 7 days to plant.  Plant the corn acres first and come back to soybeans to allow time for this.  Have the burndown treatment custom-applied if labor or time is short.

4.  Apply a combination of glyphosate, Sharpen (or other saflufenacil product), and MSO.  Major drawback to this is that saflufenacil cannot be used in combination with residual products that contain flumioxazin (Valor) or sulfentrazone (Authority/Spartan) less than 14 days before planting.  Best options for residual herbicide in this mixture, especially where marestail are present – metribuzin or Canopy/Cloak DF + metribuzin, making sure that the metribuzin rate is at least 0.38 lbs ai/A.  A spray volume of at least 15 gpa should be used and it is essential to use MSO as the adjuvant.

5.  Use Liberty (36 oz/A) for burndown.  This should be applied with a metribuzin-containing herbicide.  One benefit of this compared with option 4 is that Liberty can be applied with any residual herbicide.   However, Liberty can struggle with burndown of some weedy situations, and is best suited for fields that were treated last fall.  A spray volume of at least 15 gpa should be used.  Avoid use of nozzles that produce primarily large droplets.

6.  Substitute tillage for burndown herbicides.  Make sure that the tillage is deep and thorough enough to completely uproot weeds.  Weeds that regrow after being “beat up” by tillage are often impossible to control for the rest of the season.  There can be a benefit to treating fields with glyphosate prior to tillage, where weeds are dense and large, to ensure a weed-free seedbed.

7.  Gramoxone usually works well in late spring only when combined with both 2,4-D ester and metribuzin, especially when weeds have much size.  Use the high Gramoxone rate and crop oil concentrate, and a spray volume of 15 to 20 gpa, depending upon nozzle type.

8.  Some things that probably will not work.  We have not had much success with combinations of glyphosate and 2,4-DB, although high rates of 2,4-DB can help control certain weeds. Valor and Authority do not have enough foliar activity to help control emerged weeds, although they do cause contact herbicide symptomology on weed leaves (and can actually cause antagonism in mixtures with systemic herbicides).  Metribuzin does help control emerged weeds, although this is expressed best in mixtures with Liberty, Sharpen, or Gramoxone.

9.  The cost of several of these options can be about twice the cost of a typical glyphosate/2,4-D mixture.  This is not really the situation to balk at spending a few extra dollars.  Failing to effectively control weeds at the time of no-till soybean planting creates problems for the rest of the growing season.

10.  Late-spring burndown tends to be less of an issue in corn, due to the contribution of atrazine and mesotrione (in Lumax/Lexar) to burndown, and the ability to use dicamba.  Labels for 2,4-D products vary with regard to preemergence use in corn.  Some recommend avoiding application between 7 days before and 3 to 5 days after planting, while others are less restrictive. 

Crop Observation and Recommendation Network

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.