Palmer amaranth (Amaranthus palmeri S. Wats.) is a highly competitive weed that can be difficult to manage in many cropping systems. Research to date has not quantified the growth and development of A. palmeri in a manner that allows direct comparisons across cropping systems. Research was conducted to compare the growth, development, and seed production of A. palmeri when competing with corn (Zea mays L.), cotton (Gossypium hirsutum L.), peanut (Arachis hypogaea L.), and soybean [Glycine max (L.) Merr.] when emerging with crops or emerging three weeks after crops emerge. Regardless of when A. palmeri emerged, seed production was greatest and similar in cotton and peanut and exceeded that of corn and soybean; seed production in soybean exceeded that of corn. However, seed production was approximately 10-fold greater when A. palmeri emerged with crops compared with emergence three weeks later. These results illustrate the importance of controlling weeds during the first three weeks of the season relative to contributions of A. palmeri to the weed seed bank and is the first report comparing seed production in presence of these crops in a manner allowing a statistical comparison of seed production and highlighting the importance of crop sequence for seed bank management.

Proposed regulations mandating lower nicotine concentrations in tobacco (Nicotiana tabacum L.) products will likely require changes in tobacco production to reduce nicotine while maintaining yield and quality. The agronomic practices used for tobacco production have a significant impact on the synthesis and accumulation of nicotine in flue‐cured tobacco. Nicotine is the primary alkaloid in flue‐cured tobacco and is one of the main reasons for its commercial production. Most agronomic practices that improve plant health and yield have a positive effect on nicotine production and accumulation. Some of the most important factors that affect nicotine concentrations are N fertilization, planting density, topping practices, sucker control, and harvesting practices. The amount of N available to the plant has a substantial effect on nicotine, as N is a primary component of the nicotine molecule. Factors leading to higher N uptake lead to higher nicotine concentrations. Plant and leaf densities within the field also have a significant effect on nicotine, where increasing densities leads to lower nicotine concentrations. Flowering and sucker production are both significant sinks of energy and other resources. Eliminating the inflorescence via topping and controlling suckers lead to higher nicotine concentrations. In fact, substantial nicotine synthesis and accumulation occurs in the days and weeks following topping. This comprehensive review discusses the agronomic factors affecting alkaloid production in flue‐cured tobacco, and how these factors can be adjusted to manipulate the ultimate nicotine concentration. Core Ideas Proposed regulations may require lower tobacco nicotine concentrations. Production practices and timing significantly influence nicotine and leaf quality. Nitrogen fertility, crop density, growth regulation, and harvesting are paramount. Low density, high N, and increased maturity enhance nicotine accumulation. Flowers and axillary shoots are sinks that limit foliar nicotine concentrations.

Palmer amaranth (Amaranthus palmeri S. Watson) populations resistant to acetolactate synthase-inhibiting (ALS) herbicides and glyphosate are fairly common throughout the state of North Carolina (NC). This has led farm managers to rely more heavily on herbicides with other sites of action (SOA) for A. palmeri control, especially protoporphyrinogen oxidase- and glutamine synthetase inhibitors. In the fall of 2016, seeds from A. palmeri populations were collected from the NC Coastal Plain, the state’s most prominent agricultural region. In separate experiments, plants with 2 to 4 leaves from the 110 populations were treated with field use rates of glyphosate, glufosinate-ammonium, fomesafen, mesotrione, or thifensulfuron-methyl. Percent visible control and survival were evaluated three weeks after treatment. Survival frequencies were highest following glyphosate (99%) or thifensulfuron-methyl (96%) treatment. Known mutations conferring resistance to ALS inhibitors were found in populations surviving thifensulfuron-methyl application (A122S, P197S, W574L, and/or S653N) in addition to a new mutation (A282D) which requires further investigation. Forty-two populations had survivors after mesotrione application with one population having 17% survival. Four populations survived fomesafen treatment, while none survived glufosinate. Dose-response studies showed an increase in fomesafen needed to kill 50% of two populations (LD50); however, these rates were far below the field use rate (less than 5 g ha-1). In two populations following mesotrione dose-response studies, a 2.4- to 3.3-fold increase was noted with LD90 values approaching the field use rate (72.8 and 89.8 g ha-1). Screening of the progeny of individuals surviving mesotrione confirmed the presence of resistance alleles as a higher number of survivors at the 1X rate compared to the parent population, confirming resistance to mesotrione. These data suggest A. palmeri resistant to chemistries other than glyphosate and thifensulfuron-methyl are present in NC, which highlights the need for weed management approaches to mitigate the evolution and spread of herbicide-resistant populations.

Research was conducted at 5 locations between 2012 and 2013 to determine the effect of nitrogen application rate and timing on yield, quality, and leaf chemistry of flue-cured tobacco. Urea-ammonium-nitrate was applied at 75, 100, and 125% of the recommended nitrogen rate for each specific field condition. All treatments were applied at differing intervals beginning at transplanting and concluding prior to or at topping. Yield data were collected postharvest, and leaf quality was determined according to U.S. Department of Agriculture grade. Crop value per hectare was quantified by a combination of yield and quality. Tissue samples were collected at layby and topping to evaluate total leaf nitrogen content at the respective growth stages. In addition, SPAD meter readings were collected at topping. Composite cured leaf tissue samples from all 4 stalk positions were analyzed for total alkaloid and reducing-sugar content. Data were subjected to analysis of variance (ANOVA) with the use of the PROC GLM procedure in SAS ver. 9.4. Treatment means were separated with the use of Fisher's protected LSD at P # 0.05. Crop yield, quality, and value were not affected by treatments across all locations, thus leading to the conclusion that all nitrogen application rates and timings were suitable under the observed growing conditions. Leaf nitrogen content at layby and topping, total alkaloids, reducing sugars, and SPAD readings were affected by application rate and timing. In general, as rate of applied nitrogen increased, alkaloid levels increased and reducing sugars decreased. Leaf nitrogen content at topping and SPAD measurements were highest in plots receiving a nitrogen application later in the season. Excessive rainfall in both seasons likely played a significant role in observed results. Based on current knowledge and information gained from this research, lateseason nitrogen application is a useable tool but should be performed with caution to prevent reduction in leaf quality.

Core Ideas Lower‐leaf removal will reduce cured leaf yield but can reduce the portion of lower‐demand stalk positionsNitrogen application after leaf removal is of limited value and is currently discouragedIf these programs are to find commercial success, a higher selling price should be offered by leaf purchasers With a current global over‐supply of flue‐cured tobacco (Nicotiana tabacum L.), tobacco producers in North Carolina have been encouraged to remove the lowermost leaves prior to harvest due to their low value in manufactured products. The objective of this research was to compare lower‐leaf removal programs. Research was conducted in 2016 and 2017 to quantify the agronomic effects of three lower‐leaf removal programs (0, 4, and 8 leaves plant−1) and the subsequent delivery of four N application rates (0, 5.6, 11.2, and 16.9 kg N ha−1 above base recommendation). All treatments combinations were applied during the early flowering stage of growth (8–10 wk after transplanting), when plants were approximately 120 cm tall. Programs absent of leaf removal generally produced the highest cured leaf yield. The addition of 16.9 kg N ha−1 increased yield when compared to lower N application rates within the 4‐leaf removal program. Nitrogen application did not affect yield in the 8‐leaf removal program. Cured leaf value was greatest in the 0‐leaf removal program (USD $10,131 ha−1) and was reduced in the 4‐ and 8‐leaf programs by $1611 and $2645 ha−1, respectively. Lower‐stalk positions were nearly eliminated in the 8‐leaf removal program, while the 4‐leaf removal program reduced their presence by more than 50%. Ultimately, if these programs are to be encouraged or required by industry, the removal of four leaves per plant proved to be more practical when paired with additional N, due to moderate yield reduction and lower‐stalk leaf production.

Core Ideas Poultry feather meal is acceptable in organic flue‐cured tobacco production. Application rates of organic N should reflect those in conventional production. Soil moisture is critical for N mineralization and assimilation. Information on N management in organic flue‐cured tobacco production is limited. Research was conducted from 2012–2013 to determine the effects of two certified organic N sources applied at three rates on the yield, quality, and chemical constituents of flue‐cured tobacco. These organic N sources included Nature Safe 13–0–0 (NS) and Nutrimax 12–1–0 (NM), both of which consisted of hydrolyzed poultry feather meal. Application rates for both fertilizer sources were 17 kg N ha−1 above recommendation (B+), at recommendation (B), and 17 kg N ha−1 below recommendation (B–). A conventional control containing urea‐ammonium‐nitrate (UAN) was applied at the B application rate. Tobacco yield and quality were similar among conventional and organic N programs. Leaf N concentration, SPAD measurements at flowering, and total alkaloid concentration of cured leaves responded positively to increased N application rates, regardless of organic fertilizer source. The largest increases in nitrogenous‐based leaf constituents were observed in this study where B+ treatments were applied; however, those increases did not translate into increased leaf yield or quality and could delay the initiation of leaf senescence in growing seasons with low soil moisture. Results from this study demonstrate the acceptability of poultry feather meal sources for organic tobacco production, and confirm that application rates of organic N sources should follow conventional recommendations.

Core Ideas Recognizing micronutrient disorders is important for commercial production. Unique, previously unobserved nutrient disorder symptoms were observed. Foliar nutrient concentrations were identified for burley and flue‐cured tobacco. Symptoms and critical values were compared with published results. Nutrient disorders often manifest unique symptoms and vary in critical nutrient ranges where visual symptoms appear depending on plant species and type. Understanding and recognizing nutrient disorders for different types of tobacco is important for maintaining yield and quality. Burley and flue‐cured tobacco (Nicotiana tabacum L.) account for over 90% of all tobacco produced in the United States, and thus, were grown in this study to investigate the effects of micronutrient disorders. Tobacco plants were grown in silica sand culture, and control plants received a complete modified Hoagland's all‐nitrate solution, whereas nutrient‐deficient treatments were induced with a complete nutrient formula withholding a single nutrient. Boron toxicity was also induced by increasing the element tenfold higher than the complete nutrient formula. Plants were automatically irrigated, and the leached solution was captured for reuse. A complete replacement of nutrient solutions was done weekly. Plants were monitored daily to document and photograph symptoms as they developed. A description of nutrient disorder symptomology and critical tissue concentrations associated with symptomology are presented.

Deriving crop information from remotely sensed data is an important strategy for precision agriculture. Small unmanned aerial systems (UAS) have emerged in recent years as a versatile remote sensing tool that can provide precisely-timed, fine-grained data for informing management responses to intra-field crop variability (e.g., nutrient status and pest damage). UAS sensors with high spectral resolution used to compute informative vegetation indices, however, are practically limited by high cost and data dimensionality. This research extends spectral analysis for remote crop monitoring to investigate the relationship between crop health and 3D canopy structure using low-cost UAS equipped with consumer-grade RGB cameras. We used flue-cured tobacco as a case study due to its known sensitivity to fertility variation and nutrient-specific symptomology. Fertilizer treatments were applied to induce plant health variability in a 0.5 ha field of flue-cured tobacco. Multi-view stereo images from three UAS surveys collected during crop development were processed into orthoimages used to compute a visible band spectral index and photogrammetric point clouds using Structure from Motion (SfM). Plant structural metrics were then computed from detailed high resolution canopy surface models (0.05 m resolution) interpolated from the photogrammetric point clouds. The UAS surveys were complimented by nutrient status measurements obtained from plant tissues. The relationships between foliar nitrogen (N), phosphorus (P), potassium (K), and boron (B) concentrations and the UAS-derived metrics were assessed using multiple linear regression. Symptoms of N and K deficiencies were well captured and differentiated by the structural metrics. The strongest relationship observed was between canopy shape and N foliar concentration (adj. r2 = 0.59, increasing to adj. r2 = 0.81 when combined with the spectral index). B foliar concentration was consistently better predicted by canopy structure with a maximum adj. r2 = 0.41 observed at the latest growth stage surveyed. Overall, combining information about canopy structure and spectral reflectance increased model fit for all measured nutrients compared to spectral alone. These results suggest that an important relationship exists between relative canopy shape and crop health that can be leveraged to improve the usefulness of low cost UAS for precision agriculture.