From the Field – Agronomy Notes: Vol. 4, Num. 6
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June 12, 2020-
Our spring season (almost summer) continues to be one for the record books, and not in a way that we had hoped for. Most, if not all, of the tobacco area in North Carolina received an abundance of rain during the last two weeks of May. The highest total we have been made aware of is 14 inches down in the Border Belt area. The rest of the tobacco belt has probably received one-half to one-third of that total. June seems to have changed the tone of 2020 quite a bit as last week brought temperatures in the mid-90’s and we finally dried out to a large degree. Certainly, there were some pop-up showers, but nothing close to what happened in May. In many of the places I have recently traveled, a small rain shower would do a lot of good, and it appears that was delivered Wednesday evening (June 10th) and during some of Thursday (June 11th).
During the period of dry, warm weather we began to see the effects of a cool, damp May. What we are seeing is tobacco that is extremely nitrogen deficient and overdue for a leaching adjustment. Decisions pertaining to fertilizer leaching adjustments are the hardest of all agronomic choices to make, in my opinion. If we apply too little, then we never regain some of the yield that has been lost and we produce a light-colored leaf. In contrast, if we over shoot on the recommendations, we can delay the onset of ripening and have great difficulty curing the crop. As we start to navigate these situations, Page 71 of the 2020 Flue-Cured Production Guide is a great starting point. Below are a few comments about fertilizer considerations and other areas of crop management that are worth considering.
Nitrogen decisions will be the most important for leaching adjustments in nearly all of the situations around our state. As a rule of thumb when using the leaching adjustment table that I just mentioned, growers might consider shaving off 5-10% of the recommendation printed in the book. This guidance was developed a few decades ago with older varieties that do not have the root mass or nitrogen use efficiency of modern varieties. Perhaps in slight contrast to that statement, growers should not be scared of the recommendations suggested in the production guide (once the 5-10% is accounted for). We still have ample time to use the nitrogen that is now being applied and we should have ample curing space this year.
In some of the tobacco that I have seen in person, most of what we would consider to be lower-stalk tobacco is almost banana yellow (Figure 1). This is indicative of severe nitrogen deficiency. We need to keep in mind that a nitrogen leaching adjustment will probably do very little to help these severely deficient leaves, as there is still going to be a high demand for nitrogen as the upper-stalk continues to develop. In this situation the demand for nitrogen in the newly developing upper-stalk leaves greatly outweighs the need for nitrogen in the older, lower-stalk leaves. The bottom line here is that when we see a nitrogen deficiency at this stage of growth, it’s almost too late for the older leaves to rebound.
I also encourage you to remember that green up from a nitrogen application is not immediate under the conditions that we had at the beginning of the week (hot and dry). We need rain or irrigation (soil moisture) to facilitate nitrogen movement from the soil solution into the root zone for uptake. We should also be mindful of how we are applying nitrogen. If a crop has not yet reached the layby stage, then growers should use conventional practices to deliver nitrogen. If the crop is bigger than layby stage, then high clearance sprayers should be used to apply liquid nitrogen materials that have been mixed with water to ensure a high delivery volume. A high solution volume will help facilitate wash in to the root zone. In contrast, if a grower is lucky enough to time an application before a rain then a lower output solution may be acceptable. In my opinion, a high solution volume is 40-50 gal/acre, and a moderate volume is 20-30. Growers should also make an effort to place the fertilizer in a band as close to the base of the plant as possible without having direct contact with leaves. At higher solution volumes, direct contact with leaves may not be as big of a concern relative to the lower solution volumes because of dilution – however, great care should be taken in order to reduce the potential for leaf injury from fertilizer salts. These applications are not easy, but are likely necessary in some cases.
If potassium is needed our options are less flexible, as granular products (K-Mag and Sulfate of Potash) are probably going to be the only practical options. Applications with a high clearance sprayer are virtually impossible with these dry products, but broadcast applications with a high clearance spreader might be considered. In past situations, growers have purchased custom blends of nitrogen and potassium to apply in this manner in a single pass. This is a gamble because we know it’s not the most efficient application of fertilizer and we have a risk of fertilizer salts injury if granules adhere to the leaves or bud of plants. Should a grower decide to make this application, they should do so when the tobacco is dry. We are sometimes asked about liquid potassium products and their performance. I don’t really know of any liquid products that have been tested in tobacco, and some that I’ve found contain language expressing compatibility issues with UAN materials. As a reminder, we encourage producers to apply potassium at a 1:1 ratio with nitrogen in coarse soil textures.
Obviously, Spartan and Command are off the table so that leaves us with Prowl, Devrinol, and Poast as our best options. I strongly encourage growers to consider these products given how much rain we’ve had, as we simply don’t know where pre-transplanting herbicides are – all we know is that they probably aren’t where we want them to be. Growers are going to have to be proactive with Prowl and Devrinol because they do not have any kind of POST emergence control. But they do need to wait for grass to emerge before spraying Poast since it has no PRE emergence control. If using Poast, be mindful of the inclusion of a Crop Oil Concentrate. We need the Crop Oil for good weed control, but we are worried that some of this crop could be extra tender and the Crop Oil could cause some burn so do not mix it at a rate higher than recommended by the label. If growers are making band applications of Prowl or Devrinol, they shouldn’t be stingy. There are plant back concerns, but I foresee weed pressure being very heavy in this tobacco crop so we need to take full advantage of any chemical help we can get. That means that 3 qt of Devrinol or even 1.5 to 2 pt of Prowl are reasonable to me, but growers will have to take into account previous applications of the materials and should follow the labels.
Aim can be considered if weeds (pigweed and morningglory) are small at layby. The biggest drawback to Aim is that it has POST emergence control only, and weeds must be small (Pigweed <4 inches) in order to achieve good control. In addition, layby applications require hooded or shielded sprayers to keep the product off of the tobacco. The next crop stage for application is after first harvest, where it can be POST-directed under the canopy. If someone elects to use Aim, they must remember to thoroughly clean out the ENTIRE sprayer. Aim is notorious for adhering to all the little nooks and crannies in spraying systems, only to be drawn out by other pesticides at less than opportune times.
Virtual Field Day:
Our annual field day was originally scheduled for July 16 in Kinston at the Cunningham Research Station. We have canceled the in-person event, but plan to post video recordings of our field trials here on the Tobacco Portal for viewing at your leisure. Videos will be posted by July 13 and we will then have a live webinar on the morning of July 16. Dr. Blake Brown will deliver a tobacco situation update, with the rest of the faculty joining afterwards for a live question and answer segment. More information will be posted as we get closer to July.
As always, your local Extension agent is here to help navigate decisions during these trying times. This has been a very trying season, so please do not hesitate to reach out for assistance!
Post Authored By:
Dr. Matthew C. Vann, Tobacco Extension Specialist, Dept. of Crop & Soil Sciences
Dr. Charlie Cahoon, Extension Weed Specialist, Dept. of Crop & Soil Sciences
Steve Killette, Field Crop Agent, N.C. Cooperative Extension of Lenoir County