UPDATED CONTENT: Dicamba and 2,4-D Plantback Restrictions

NOTE:  There has been some confusion about plantback restrictions listed in this post from earlier today.  The plantback restrictions discussed in this post are for ester formulations of 2,4-D.  Please see updated content in this post and new blog post for use of 2,4-D as a burndown herbicide. 

With the cold, wet weather prevalent from January until now in Mississippi, many burndown herbicide applications were delayed.  In some situations, growers are ready to plant, but the field requires a burndown.  This has led to a multitude of questions on plantback restrictions for 2,4-D and dicamba prior to planting corn and soybeans.

Auxinic herbicide injury characteristic of dicamba on soybean (Photo: Dr. Tom Eubank)

Labels for different formulations of dicamba (Clarity, Banvel, etc.) are pretty consistent on plantback restrictions.  Dicamba may be applied to fields that will be planted to corn any time preplant until planting.  Once corn is planted, dicamba should not be applied again until after corn emergence; therefore, do not spray dicamba behind the planter.  In fields that will be planted to soybean, the dicamba plantback restriction is strict.  For example, the Clarity label states, “following application of Clarity and a minimum accumulation of one inch of rainfall or overhead irrigation, a waiting interval of 14 days is required for 8 fluid ounces per acre, and 28 days is required for 16 ounces per acre.  These intervals must be observed or crop injury will occur.”  The key point is the rainfall total is required before the clock begins between dicamba application and soybean planting.  Cotton may be planted 21 days after dicamba, and grain sorghum and rice may be planted 15 days following dicamba. The 2014 Weed Control Guidelines for Mississippi (MSU-ES Publication 1532) lists 63 formulations of 2,4-D that are labeled for application in the state.  Many of these are only labeled for application to turf, ornamentals, forages, etc.  However, there are a multitude of 2,4-D formulations labeled for application to agricultural fields.  2,4-D was discovered in 1941 and was first tested as a herbicide in 1944.  Because of its broad range of use patterns and the length of time that 2,4-D formulations have been commercially available, there are many labels to read. Even though all 2,4-D labels do not contain the same wording, there is continuity concerning plantback restrictions among the labels for 2,4-D products commonly sold this time of year by the corporate distributors in the Mississippi Delta.  These plantback restrictions are summarized in Table 1.

If 2,4-D is applied preplant, corn planting must be delayed 7 to 14 days after the application, depending on application rate.  However, in contrast to dicamba, 2,4-D may be applied preemergence following corn planting but before corn emerges.  Keep in mind that any burndown application of glyphosate plus 2,4-D and/or dicamba will work slowly, even with the warmer weather.  If burndown has been delayed and the field is ready to plant, consider changing the burndown to a paraquat-based application. The Weed Control Guidelines for Mississippi (MSU-ES Publication 1532) was updated for 2014 and all tables listing Rotational Crop Restrictions were merged into a single table that can be found on pages 21 to 23.  The Weed Control Guidelines and publications specific to managing herbicide-resistant weeds in Mississippi may be accessed at http://msucares.com/crops/weeds/index.html.  These publications also contain specific information on herbicide mixtures, application rates, or alternative burndown herbicide options.