From the Field – Agronomy Notes: Vol. 5, Num. 2

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March 16th-

Things on the tobacco front have been rather quiet over the last few weeks, aside from major news about the USDA Quality Loss Adjustment Program signup and the easing of EU tariffs on US ag commodities. Frankly, we’ve not had this much good news in a long time – particularly not all at once.

Switching gears a bit, tobacco greenhouses are looking great at the moment. I’m very impressed with our plant stand, specifically as I think back to the weather we had around seeding in mid/late-February (cloudy/poor sunlight). Unless things go off the rails over the next three to four weeks (fingers crossed that they don’t), I anticipate that we’ll have a good supply of plants  – though it may be a little tight given the big increase in acres this year. If you have or need extra plants, be sure to contact your local County Agent as we get into the transplanting season.

The weather has also been absolutely beautiful over the last couple of weeks and we’re seeing a lot of field work take place. This is another good sign, considering how wet and cool February was. As growers begin the shift to field preparation, questions about weed control programs are starting to pop up. These conversations have been pointed, timely, and are very important as we start the 2021 tobacco season. Weed control in 2021 is likely to be a much larger talking point than it was in 2020 – and not necessarily for reasons that are extremely obvious.

Readers will remember that we predicted above average weed pressure for the 2021 growing season in our county meetings this past January. This outlook stems from the poor growing conditions in 2020 and the weed escapes we observed in our rotational crops. Here it is important to note that we have some really good herbicide programs available for tobacco producers, but we’re very limited with those options – particularly relative to programs available in other crops. More specifically, some of our grower base has been told they cannot apply pendimethalin (Prowl or other generic formulations), not even preplant incorporated. That is a blow to us because it was a useful herbicide that offered good to excellent residual control of pigweed and most annual grasses, and it was relatively cheap. Personally, I really liked pendimethalin as a layby option for growers because it gave us an increase in weed control compared to relying completely on PRE applications of sulfentrazone (Spartan 4F or others) and clomazone (Command 3ME or others). In the absence of pendimethalin, growers really need to look at Devrinol (napropamide) as a substitute. Devrinol can be applied over tobacco immediately after transplanting and/or band applied to row middles at layby. Of course, it can also be applied PRE-T so growers should consider their weed species, population densities, previous experience with weed escapes, and rotational crops as they choose when/how to apply these products. The points here are that we have to remember that pendimethalin may not be something we can recommend across the board anymore (growers will know if they can/cannot use it) but we do have another option that works just as well in Devrinol.

One of the other reasons we need to think a bit more thoroughly about weed management relates to weed seed contamination in cured tobacco. For those that have been around as long as me, you probably remember the weed seed discussions we had at Winter Meetings back in 2013/2014. For those unfamiliar with this topic, there are tobacco customers that have the authority to reject shipments of tobacco that are found to contain noxious weed seeds. Certainly, the term noxious is relative but those end users don’t want to import things like crabgrass and pigweed. This particular issue has not been discussed over the last few years because of changes with marketing. However, tobacco agronomists in the flue-cured belt spent significant time working with USDA-APHIS in 2021 to put a damper on this exact topic. Bottomline, there appear to be some big moves on the tobacco buying front and we need to try to help make these things happen as best we can. Reducing weed seed has to be a high priority and it will only be accomplished with exceptional weed control.

With such a strong focus on tobacco weed management in 2021, it’s rather timely that we have a new production tool to offer our tobacco clientele. During the off-season, we had the pleasure of working with Greg Buol and David Jordan here in the Crop and Soil Sciences Department to create a Tobacco Weed Risk Assessment Tool. This tool is designed to help a farmer identify specific weed management practices, their cost, and the impact they might have to weed development. Admittedly, the risk of weed escapes in tobacco production is very low because of our herbicide programs, secondary cultivation, and hand weeding efforts. However, one of the most valuable aspects of this tool is the fact that a grower can select a number of weed management options and then create a useful budget for each of the programs. We hope that guidance from the budget aspect will be useful as we continue to look at further integration of other herbicides and hand weeding efforts. Greg and I have included instructions on how to use the tool on the Tobacco Portal. It’s fairly intuitive, but feel free to reach out if you have any questions.

The final comment I’ll make pertains to recommended herbicide programs. We are still recommending PRE applications of Spartan (4F, Charge, or other labeled formulations) and Command (3ME or other labeled formulations). These products can be tank mixed and applied PPI or PRE-T. For the last few years, we’ve shared the philosophy that layby herbicide applications should be considered and that applying something at layby is better than applying nothing. If we look back on tobacco herbicide trials from the last decade, we can definitively say that layby herbicides increase end of season weed control by 8-50% depending on weed species, active ingredient, application rate, growing conditions, etc. Not once have we observed injury/stunting (when labels are followed and we’re not sloppy) nor have we failed to significantly improved weed control in end of season ratings. Given the strain and cost associated with labor for hand weeding, adding a residual layby product (such as Devrinol or Prowl) to the mix might be worthwhile for growers not already using one.

As always, please feel free to reach out if you have any questions or concerns!!

Post Authored by:

Dr. Matthew Vann, Tobacco Extension Specialist

Dr. Charlie Cahoon, Extension Weed Specialist