From the Field – Agronomy Notes: Vol. 4, Num. 7

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June 25, 2020-
The 2020 tobacco season continues to be one marked by unique challenges. Though these issues are diverse, and quite extreme, the major problem continues to be excessive rain. Estimates between our last crop update and this one average more than five inches in most of the Coastal Plain. I particularly think about the northern area of Sampson County which reported 8 to 10 inches last Friday night alone (June 19). Table 1 gives us a general idea of just how wet it’s been. While tobacco was not in the ground for the entire month of April in most of the locations represented, this table is a good indicator of how hard the past three months were for field preparation, transplanting, CPA applications, etc.
In addition to the rainfall, the odd temperature patterns need to be included in the conversation as well. When I got home from work last Tuesday afternoon (June 16) the dash of my truck read 58 degrees. In my almost 34 years, I don’t know that I’ve seen that on an afternoon in mid-June. When you pair the cool temperature and damp conditions, you can absolutely bet that tobacco root structure is going to be affected. Root architecture is going to play a big role in what we see happen moving forward with this crop.
Table 1. Monthly and Cumulative Rainfall for Select Tobacco Growing Locations in North Carolina. Data Provided by the North Carolina State Climate Office. 
Location April May June Total Avg
Border Belt (Whiteville) 3.82 10.02 6.70 20.54 11.75
Cunningham (Kinston) 4.77 6.01 4.63 15.41 11.90
Upper Coastal (Rocky Mount) 5.79 4.71 5.83 16.33 11.17
Central Crops (Clayton) 4.56 3.49 5.97 13.95 10.33
Oxford Tobacco (Oxford) 7.26 6.31 8.08 21.65 10.71
Upper Piedmont (Reidsville) 4.05 8.28 2.56 14.89 11.66
Mountain (Waynesville) 6.78 4.02 1.57 12.37 12.07
Upper Mountain (Laurel Springs) 9.14 13.04 2.67 24.85 12.81

-June 1 to 20

-Cumulative average represent the period of April 1 to June 20 from 1981 to 2010.

Nitrogen Management
The most immediate thought I have about the 2020 crop is fertilizer management. What we know about leaching adjustments is very short-term and doesn’t really take into account what happens later in the season or after multiple leaching rainfalls. It almost goes without saying that we’re approaching uncharted territory. What I’m leaning on is the experience we gained during the 2013 season when it seemed to rain every single day (at Border Belt Research Station the seasonal average was 100% above normal!). At the time we were in the midst of a rather involved nitrogen application trial, from which the following two points were gleaned:
1.) Downstalk applications of liquid nitrogen solutions (that mimic sucker control applications) can green up tobacco for about 7-10 days, thus buying some additional time before harvest. Yield is not improved with this application when we are focused on greening up tobacco for holdingability; however, in our current situation we might see some improvements – particularly in areas where tobacco is thin with a washed-out appearance.
2.) Soil applications of liquid nitrogen solutions can increase cured leaf yield when applied just after topping. These applications need to be applied at the high volumes required for downstalk applications to ensure sufficient wash-in if rainfall is limiting.
I think that these two points are worth considering for our grower base. Many have already asked what can be done to turn around a crop that is going to ripen very, very fast and that appears to be extremely yellow in color and thin bodied. Should you decide to use the downstalk approach, it is absolutely critical that you do not apply the liquid nitrogen solution before topping. This crop is going to be too tender before to make this happen without substantial injury. We recommend no more than three gallons of UAN be mixed with water at a solution volume of at least 50 gallons/acre (in this case, 47 gallons of water would be mixed with 3 gallons of UAN). This will supply almost 10 lbs of nitrogen per acre. One other tip is that growers should apply this solution when dew is still present as that will help dilute salts and promote leaf runoff. If a grower wants to apply more than 10 lbs of nitrogen, they should do it in more than one application just to be safe. I also would not apply this solution when air temperature climbs above 90 degrees as the injury potential will increase with added heat stress. My final point for the downstalk application is that they should not add ANYTHING to the liquid nitrogen and water solution. That includes pesticides, contact, surfactants, etc. These additives will only increase the risk of crop injury. We are currently dealing with a very tender crop and the added stress of salts and chemicals might be too much for plants to handle. As a side note, I have seen and have had at least one phone call about sunscald. This current observation simply reinforces our tender crop scenario – thus bolstering the concern I have about injury potential.
In contrast, the soil application is much safer but can be a little more difficult to do because we need to get the nitrogen as close to the base of the plant as possible without getting it on the leaves. Under current conditions, lugs are probably going to deteriorate very fast, so waiting to do this after de-lugging or first harvest might make this an easier task to accomplish. Where we have done this in the past, I’ve encouraged growers to use a moderate solution volume to ensure sufficient wash-in (30-40 gallons per acre). If someone is lucky enough to time this before a good rain, then a lower volume might work well (20-25 gallons per acre). If a concentrated band close to the base of the plant isn’t possible, then we might suggest trying to spray the side of the bed in a slightly wider spray pattern. If neither of these are possible, then a dropline application to the row middles with a wide angle spray nozzle may be the only practical application. With current conditions, a minimum of 10 lbs N/acre is where I would start with my adjustments if I were in the heart of the Eastern growing belt. However, 15-20 lbs N/acre is not unreasonable in some situations and might be advisable if the application is made to the row middles because some of the nitrogen will likely not be used by plants.
The final point I’ll make about these two nitrogen application methods is that they are not part of our standard recommendations. If you’d like to talk about these a bit more, please give contact your local Extension agent for more information.
Topping & Sucker Control
My next thoughts shift from fertilizer management to topping and sucker control. The best advice I can offer at the moment is for growers to top plants in the early button stage. We know that early topping will increase root mass by about 30% relative to late topping. Given the rainfall and cool soil temperatures that we’ve experienced, I think that early topping will help us scavenge some of the fertilizer that was leached from our soils or some that was applied as a leaching adjustment. At present, our crop is very up and down in size, so we encourage farmers to top fields multiple times and not wait for everything to come into flower. We lose one percent of our total yield potential everyday that a plant is in full flower. As variable our plant size is at the moment, a delay in topping for the sake of efficiency will cost us dearly in terms of yield and quality.
Sucker control will be much harder if the crop is up and down as I just described. Regardless, we suggest that first contact applications be made in advance of the 50% button stage. Inevitably, we are most likely going to see some chemical topping this season – and that’s okay – as we’ll have made our first application in a timely manner to address the first flush of suckers. We typically start our contact applications at a 4% solution concentration (v/v) when using our C8-C10 alcohol products, and we increase that concentration to 5% (v/v) in the second contact application (which follows 3-5 days later). We want to follow those recommendations this season, but growers should really pay attention to boom height and operating pressure. Low boom height and high pressure will increase the chance of injury from contact solutions on a tender crop like the one we have. We also remind growers that contact materials are formulated to burn parts of the tobacco plant (suckers) without injuring the leaves. When we add other products to the solution (foliar fertilizers, surfactants, pesticides, etc) we only increase our chances for injury. Ultimately, growers need to be smart and cautious.
Where a crop is extremely up and down, growers will more than likely be forced to spot spray areas with larger tobacco. In some extreme cases they may have to dropline sucker control solutions. It’s been a few years since we discussed dropline applications but as a rule of thumb, growers should use the same solution concentrations that are used for over-the-top applications. They should also target 0.5 to 1.0 fl oz of solution per plant (15 to 30 mL, respectively). I’ll argue that total output per plant does not matter as long as all leaf axils on the plant are filled with solution. Producers should also pay special attention to chemical labels to ensure that proper PPE is used by applicators.
Before closing, the tobacco team will be posting a series of video presentations pertaining to current topics of interest. These videos will be available on July 13 and will be followed by a webinar on July 16. Additional information and the registration link can be found in a previous article we hope that you’ll consider joining us!
As always, best of luck as we make a big push to get to topping. Please feel free to give us a call if you have any questions or concerns about the crop!