From the Field – Agronomy Notes: Vol. 4., Num. 2

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March 26, 2020-

The world has changed dramatically since our last posting. We hope that you, your families, and farming enterprises are staying safe during this time of great uncertainty.

While things are changing rapidly around the world, the ag community remains as determined as ever to produce the food, feed, and fiber for society. Speaking as someone who lives in (very) urban area of the North Carolina, I find great comfort in knowing that our basic need for food will be met thanks to the American farmer and those involved in the shipping/transport industry.

So, how does tobacco fit into all of this? Tobacco is certainly not a food crop, nor is it used to any large degree for feed or fiber. That point may raise a few eyebrows regarding its significance in our current climate. However, I think that one would be remiss not to see the bigger picture regarding our tobacco farmers and the role that tobacco plays as a centerpiece in the family farming operations of our state. For example, certification numbers from grower training events in 2019 tell us that there were more than 1,500 tobacco farmers in North Carolina alone. If you look at the entire tobacco belt (Fig. 1), that number increases to more than 6,500. In today’s ag economy very few, if any, of these farmers grow tobacco exclusively. These farmers also grow crops such as corn, cotton, peanuts, soybeans, sweet potatoes, and other produce. They are also involved in dairy, pork, beef, and poultry production. The positive impact our tobacco farmers have on their local, regional, and state communities is astronomical, so they are essential in times like these.

Tobacco Growing Regions chart

Figure 1. The Tobacco Growing Regions of the United States. (photo courtesy of Tobacco Associates, Inc.)

As we approach the transplanting season, where do our tobacco farmers currently stand? Our greenhouse season is well underway, and has been since mid-February. We have had a fairly good greenhouse season that has largely been absent of any widespread issues. I anticipate that we’ll have a good supply of high quality transplants. Should you have extra plants that you’d like to get rid of or if you need extra plants for the farm, contact your local Extension Agent. We’ve setup a distribution list within Extension that will help move seedlings as needed.

With the greenhouse season winding down for most of our farmers, our next focus becomes field preparation. From my perspective, a large piece of field preparation involves decisions about weed management. For the most part, those decisions are fairly straightforward since we have so few herbicide options for tobacco production. However, there are certain aspects of application methods and rates that are worth diving into.

For most of our tobacco farmers (60 – 65%), base herbicide programs consist of applications of sulfentrazone and clomazone, applied in a tankmix either before or right after bedding. These two active ingredients are popular because they offer excellent control of our most troublesome weed species (Pigweed, nutsedge, morningglory, annual grasses, and common ragweed). Farmers also have access to pendimethalin (where approved for use by contracting tobacco companies) and napropamide. We generally see the use of these products at lower frequencies (≈10%) in PRE applications. My team put together a post in 2017 that outlines some of the considerations one might make regarding pre or post-bedding applications of these active ingredients. Feel free to give that article a look as a refresher.

The major focus of this Agronomy Note addresses the question of what should be done at layby. For years now we’ve strongly encouraged producers to consider making a layby herbicide application. Our rule of thumb in these discussions is that something is better than nothing in nearly every case. As it stands today we have four active ingredients than can be used at layby (napropamide, pendimethalin, sethoxydim, and carfentrazone).

When thinking through production scenarios, we have to realize that there’s really not a “one size fits all” approach and that these decisions should be handled on a case by case basis. Within the recommendations I offer each season, the following considerations are made: 1.) what weed species are in my fields, 2.) are they already emerged or is control acceptable for now, and 3.) what might I be planting after tobacco. It’s important to know what the weed complex is in each field because we see vast differences in control among the different materials. For example, sethoxydim only control grass that has emerged while carfentrazone only controls some broadleaf weeds that have emerged. When we compare napropamide and pendimethalin, the former will control ragweed a little better than the latter. A full overview of expected weed control can be found in the 2020 NC Ag Chemical Manual (pg. 301). Just as important is weed emergence because only two of the four herbicides labeled for layby have residual activity, napropamide and pendimethalin. If weed emergence isn’t a major issue at the time of application, then carfentrazone and sethoxydim are completely out of consideration. Finally, you must pay attention to each chemical label and understand the implications for herbicide applications and plant back periods. Each label should be reviewed individually because they are not all the same.

Why have we made major pushes for layby applications in recent years? The answer is simple – it improves our chances of staying ahead of late-season weed flushes, particularly those occurring after first harvest. Since 2016, my team has made significant investments in evaluating layby herbicide programs. In each of these trials, our goal was to look at herbicides not currently approved for use in tobacco production by comparing them to our current standards of napropamide and pendimethalin. Results from one of those trials can be found in Table 1. First and foremost, the most apparent thing we see in Table 1 is the importance of sulfentrazone in managing Palmer amaranth. We rely very heavily on PPO herbicides (Spartan, Aim, Valor, Reflex, Cobra, Ultra Blazer, etc.) in MANY crops and it is imperative that we are able to continue the use of this group of herbicides. Second, if we look within each PRE program, we find that suppression of annual grasses and nutsedge is improved following a layby herbicide. The same programs did not have a major impact on Palmer amaranth control because the bulk of the heavy lifting was accomplished by the sulfentrazone applied PRE.

Table 1. Palmer amaranth, yellow nutsedge, and annual grass control 12 weeks after transplanting in response to herbicide programs at Kinston and Rocky Mount in 2018.a 
Treatmentb Palmer Amaranth Annual Grassc Yellow Nutsedge
Kinston Rocky Mount Kinston Rocky Mount Pooled Locations
Clom. + Sulf. 100 a 91 a 90 c 88 b 88 bc
Clom. + Sulf. fb. Prod. X 100 a 95 a 99 a 96 a 98 a
Clom. + Sulf. fb. Pendi. 100 a 96 a 98 ab 96 a 96 ab
Clom. + Sulf. fb. Naprop. 98 a 92 a 98 ab 93 ab 96 ab
Clom. 28 d 20 c 93 bc 87 b 24 d
Clom. fb. Prod. X 46 bc 47 b 99 a 96 a 93 a-c
Clom. fb. Pendi. 51 b 45 b 94 a-c 96 a 86 a-c
Clom. fb. Naprop. 37 cd 30 bc 95 a-c 96 a 89 bc

aTreatment means followed by the same letter within the same column are not significantly different according to Tukey-Kramer at ≤ 0.05.

bAbbreviations: +, tankmix; fb, followed by application 6 weeks after transplanting; Clom., clomazone (2 pt/a); Sulf., sulfentrazone (5 Fl oz/a); Prod. X., experimental product (2 oz/a); Pendi., pendimethalin (2 pt/a); Naprop., napropamide (3 qt/a). Clom. + Sulf. and Clom. treatments applied PRE-T.

cAnnual grass consisted of large crabgrass, goosegrass, and Broadleaf signalgrass.

In summary, we encourage growers to remain steadfast in their management programs. We’ve made great progress since 2013 in the battle against weeds, but we CANNOT let up. If you’d like more information about weed management systems, give our new publication a look! Dr. David Jordan led a team here at NC State that put together a decade worth of research in a variety of crops and cropping systems. Hat’s off to Dr. Jordan for his efforts!

As always, if you have questions about this information (or anything else), give your local Extension Agent a call! We’re here to serve!

Until next time, keep that pride in tobacco (and keep the weeds under control)!

Post Authored By:

Dr. Matthew C. Vann, Tobacco Extension Specialist, Dept. of Crop and Soil Science, NC State University

Dr. Matt D. Inman, Extension Tobacco Specialist, Plant and Environmental Sciences Dept., Clemson University