From the Field-Agronomy Notes: Vol. 2, Num. 10

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May 12th, 2017

With the massive rainstorm of April 24th/25th well behind us, many growers have shifted their focus from fertilizer leaching adjustments to weed management (in case you missed the conversation about fertility management you can see previous articles Volume 2, Number 8 and Volume 2, Number 9). With an increased focus to weed management in tobacco, growers are right to ask these questions. Below are some of the more common questions we’ve heard and our attempt to provide logical explanations.

1. What happened to the Spartan and Command that I applied? 

First and foremost, it is difficult to estimate how much herbicide may have been leached or completely removed from fields. Our best guess is that some was likely leached or washed off of fields; however, it is probable that not all is lost. Time will certainly tell, so field monitoring is absolutely critical to ensure that appropriate corrections are made in a timely manner.

2. Do I need to reapply either of these materials (Spartan and Command)?

The short answer to this one is NO. Both herbicide labels only allow for ONE application per growing season and, therefore, strongly discourage re-application. Some of this information is a little tricky to find on the label, but if you’d like to see for yourself the labels are below. See “Replanting Instructions” on page 7 of the Spartan 4F label, and “Tobacco Replanting Instructions” on page 15 of the Command 3ME label. One other reason I feel good about not reapplying Spartan and Command is that I’m seeing very good weed suppression from both materials in weed control experiments this season. A handful of our trials were established one to two weeks before the big rainfall event, and recent evaluations are showing very good suppression at this point. Also, keep in mind that these two herbicides are being referenced as a matter of convenience. Both materials are the two most commonly used herbicides in North Carolina tobacco production and they are the ones that I’m getting the most questions about.

3. I applied Spartan and Command, and now need to re-bed a few spots because they were washed out. Will this hurt anything?

This is another shot in the dark, but I firmly believe that this re-bedding in this situation is probably okay. It’s has to be done to re-establish the rows that were destroyed by flooding, so we really don’t have much of an option. Either way, I feel much better about PRE-T applications of Spartan and Command than PPI. I think that PRE-T applications + high rainfall + re-disking/re-bedding = a PPI application. That might be a bit of a stretch, but I don’t think it’s too far out there. If producers are considering the possibility of re-bedding, it is strongly suggested that they disk fields to knock down those beds and then re-bed in a normal fashion. I worry that by not knocking down the beds and starting from scratch, that re-bedding might bring more treated soil into the row middle and increase the Spartan concentration to a level where stunting is strong possibility. Another way to look at it is that disking what might be left of beds will mix/dilute the herbicide and that re-bedding will bring it back into the row ridge where it needs to be, but at a safer concentration.

4. I have not transplanted and used Spartan and Command PRE, should I apply another herbicide?

The million dollar question…I would certainly keep this one in the back of mind. We’ve already established that Spartan (4F and Charge) and Command 3ME are off the table, so that basically leaves Prowl and Devrinol as the only materials offering residual weed control (assuming neither of these were already applied). Given that Prowl must be incorporated, it could be a little more hassle to successfully apply the material. Even greater concern comes into play if Spartan has already been applied, as we do not recommend that both herbicides be applied PPI when used together. The standard recommendation in this program is that Prowl be applied PPI and Spartan that be applied PRE-T. This fact may push growers to use Devrinol (2XT or 50 DF) as both formulations can only be applied PRE-T. Devrinol can also be applied overtop of seedlings immediately after transplanting, so there is some flexibility in that. One other option, albeit a temporary one, is Poast for postemergence grass control. This material will do an excellent job cleaning up grasses that may have escaped and might buy a little time until something can be applied at layby.

5. Speaking of layby, give serious thought to a layby herbicide application. Survey data from Cooperative Extension Agents indicates that 15-20% of the tobacco acreage receives a layby herbicide application on an annual basis. This number can be greatly improved, and I believe that 2017 will be the season to give it a serious look. What are your options for layby herbicides?

  • Prowl H2O or 3.3ECband applied to row middles, must be kept off of tobacco leaves due to residue concerns. Apply after layby cultivation.
  • Devrinol 50DF or 2XT-band applied to row middles, apply after layby cultivation. Rates are 2-4 lbs a.i./acre, use higher rates to provide longer residual control but be aware that carryover to small grains is a concern.
  • Aim EC-must be applied with a shielded sprayer at layby or post-directed under the canopy after first harvest. The most important comment regarding Aim application is to keep the material off of tobacco to prevent serious injury. Aim is a post-emergence material and does not offer residual control. Furthermore, if Palmer amaranth or other Pigweed species are greater than four inches tall, control will be very poor. I’d expect decent control of morningglory though.
  • Poast-has a 42 day pre-harvest interval (PHI), so we’ll be bumping that interval at layby but in most seasons we’re likely okay to make this application.

Ultimately, all is not lost in terms weed control and we have some flexibility in what can be done at this point to manage weed populations. Given the concern placed upon weed seed contamination in tobacco exports, it is critical that an extra focus is placed upon weed management at all stages of the 2017 crop. North Carolina producers have made great strides in reducing the weed related issues expressed by tobacco customers and cannot afford to lose ANY ground.