From the Field – Agronomy Notes: Vol. 5, Num. 1

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February 9, 2021-

The start of the 2021 tobacco season begins with high hopes in uncertain times!

Just last week, Extension agents wrapped up the winter tobacco meeting season. In spite of an all-virtual meeting schedule, we estimate that more than 500 people with tobacco interests tuned in to hear the latest and greatest Extension information. This was a far cry from the 1,300+ that we met with in 2020 but all things considered, we’re proud of what was accomplished. While it’s difficult to gauge the mood and outlook of participants through a computer, most would agree that hope sprang abundant. We ended 2020 very strong, even as we faced a pandemic and some of the strangest weather patterns in recent history. For me, that’s really a testament to the good folks working hard to grow this crop and those providing up-to-date production information (…County Extension agents!!).

The close of the winter meeting season (for tobacco folks) marks the beginning of greenhouse season. As we start to seed over the next few weeks, it’s important to think about the recommendations set in place to help you achieve success. I also think back to some of the common problems we documented in 2020, so it’s also a great time for a few gentle reminders. Below are three agronomic points to consider this greenhouse season:

1.) Seeding Date: we only need 50-60 days to produce a field ready transplant, so unless your goal is to transplant the first or second week of April, there’s no major rush to fill a greenhouse just yet. It’s also worth noting that we strongly recommend seeding when the weather forecast predicts five consecutive days of good sunlight. That just doesn’t look very promising for the week ahead, at least in the Triangle. I know that it’s generally been difficult to find a stretch of sunny days in 2021, so sometimes we do what we have to – but the point is we’re likely to have quicker and more uniform seed germination when sunlight is at its maximum. Cloudy days (in my opinion) were the number one issue we faced in the early part of the greenhouse season in 2020, and there were isolated cases where it created variable growth because of the variable germination. Remember, we can control temperature, nutrients, pests, water chemistry, etc., but we cannot control the sunlight! From a more practical standpoint, the forecast for this week (Feb. 7th  – 13th) has a chance of showers almost every day. In contrast, next week is supposed to be bitterly cold thanks to the blast of arctic air that is rolling across the US at the moment. The next three weeks are generally the peak of seeding for most greenhouse operations in North Carolina, so we may have to pick and choose what’s best from a combination of weather, labor availability, and targeted transplanting date.

Seeding tobacco float trays

Figure 1. Seeding tobacco float trays in an on-farm test in 2015. These trays were seeded on March 5, 2015, and were field ready on April 24, 2015.

2.) Temperature Management: tobacco greenhouses should be maintained between 68 and 86°F during germination (roughly two weeks after seeding/floating). Once maximum germination is obtained, then growers may lower the minimum temperature to as low as 55°F. As you think about temperature management, remember a few things: I.) do not let temperatures in the greenhouse climb above 90°F, II.) cooler greenhouses (<68°F) will slow down or delay germination, and III.) a constant temperature will slow down or delay germination (hence the recommendation for fluctuation between 68 and 86°F!!). It’s also worth commenting that thermometer placement is also important in the greenhouse. We sometimes find temperature variability across a greenhouse (side-to-side, up and down, and end-to-end); therefore, having an accurate reading of the air temperature closest to the plant is in our best interest.

Greenhouse thermometers on trays

Figure 2. Proper placement of greenhouse thermometers is critical to temperature management. NC State Extension recommends thermometers be placed on top of trays during germination.

3.) Nutrient Management: A good nutrient management plan begins with a source water sample/analysis. Once you know the water chemistry amendments that are needed for tobacco seedling production, you can start to think about the application of NPK fertilizer sources. Fortunately, there are a number of good, reputable tobacco greenhouse fertilizer sources available. However, the methods in which you use them must be very precise. For example, we DO NOT recommend pre-charging floatbeds with NPK materials, as that action greatly increases the potential for soluble salts injury in newly emerged seedlings. As a work around, we recommend that the first application of NPK fertilizer be incorporated into the float water about 7 – 10 days after trays are floated. Typically, this allows for sufficient seed germination (and a small amount of seedling growth) just before the influx of fertilizer salts reaches the upper one-third of the cells in each tray. It’s also important that commercial transplant producers do not wait more than about 10 days to fertilize seedlings for the first time, as growth differences may develop among trays when this is delayed. To go along with this application timing recommendation, NC State Extension recommends that growers target a float water concentration of no more than 150 ppm N. We know that flue-cured tobacco seedlings need a total of 250 ppm N to reach a “field ready” size, so the remaining 100 ppm should be applied three to four weeks later. Thus, we are “split-applying” our nutrients, in just the same manner that we do in the field! Remember that N is generally our target nutrient when we calculate NPK greenhouse fertilizers because these tobacco blended products are developed to ensure that sufficient P and K are likewise applied in appropriate rates. Certainly, growers must also consider secondary (Ca, Mg, and S) and micronutrients (B); however, tobacco greenhouse fertilizers usually have a sufficient charge of these nutrients, but we have products that can be used later in the greenhouse season, IF NEEDED. For further information about secondary and micronutrients, see the transplant production chapter of the 2021 Tobacco Production Guide, the new NC State Extension Tobacco Greenhouse Production Poster, or contact your local Extension agent.

As always, we wish you a safe and successful 2021 growing season! Be sure to check back with us periodically for important crop updates.

Until next time, keep that pride in tobacco!!