Mark W. Shankle

Efficacy and Tolerance of Flumioxazin on Sweetpotato (Ipomoea batatas)1

Experiments were conducted at three locations in Louisiana in 2002 and 2003 to evaluate flumioxazin (36, 72, or 109 g ai/ha) applied pretransplant (PRE) or post-transplant (POST) to sweetpotato. All treatments were applied immediately before or after sweetpotato transplanting to weed-free beds. PRE applications caused 4% or less injury with any rate of flumioxazin at 9 or 18 d after transplanting (DATr) compared with 18 to 20% injury at 9 DATr and 6 to 14% at 18 DATr with 72 or 109 g/ha POST, respectively. Injury from PRE applications of flumioxazin were not different from injury with clomazone (840 g ai/ha) applied POST. Injury at Chase, LA, in 2002 was 8% and less with flumioxazin PRE, but 35 to 83% with flumioxazin POST and appeared to be due to the use of greenhouse-grown cuttings instead of field-grown cuttings, which were used in the other two experiments. There was no interaction between experiments for sweetpotato yield. Plots treated with flumioxazin PRE or 36 g/ha POST yielded greater than sweetpotato treated with clomazone for U.S. No. 1 and 2 grade yield as well as total marketable yield. No differences were observed in yellow nutsedge control with any rate of flumioxazin. At 34 or 50 DATr, flumioxazin controlled yellow nutsedge 73 to 85% with 72 or 109 g/ha applied PRE or POST. Flumioxazin, regardless of application timing or rate, controlled carpetweed and spiny amaranth at least 86%. A similar experiment in Mississippi evaluated tank-mixes of flumioxazin (36, 72, or 109 g/ha) and clomazone (840 g/ha) applied PRE or POST. No sweetpotato injury was observed with flumioxazin PRE. However, injury from flumioxazin POST increased with increased rates (18 to 50% at 18 DATr and 16 to 93% at 25 DATr). Weed control was greater than 80% with all treatments. Nomenclature: Clomazone; flumioxazin; broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash #3 BRAPP; carpetweed, Mollugo verticillata L. # MOLVE; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray # IPOHE; pitted morningglory, Ipomoea lacunosa L. # IPOLA; redroot pigweed Amaranthus retroflexus L. # AMARE; spiny amaranth, Amaranthus spinosus # AMASP; yellow nutsedge, Cyperus rotundus L. # CYPES; sweetpotato, Ipomoea batatas (L.) Lam. ‘Beauregard’. Additional index words: Clomazone, Amaranthus retroflexus, Amaranthus spinosus, Brachiaria platyphylla, Cyperus rotundus, Ipomoea hederacea var. integriuscula, Ipomoea lacunosa, Mollugo verticillata, AMARE, AMASP BRAPP, CYPES, IPOHE, IPOLA, MOLVE. Abbreviations: DATr, days after transplanting; PRE, pretransplant; POST, post-transplant.

Confirmation of an Enzyme-Linked Immunosorbent Assay to Detect Fluometuron in Soil1

Research was conducted to compare the results of an enzyme-linked immunosorbent assay (ELISA) to high-performance liquid chromatography (HPLC) for detecting fluometuron in the environment. A linear relationship for HPLC (R2 > 0.90) and ELISA (R2 > 0.66) analysis was observed between the natural logarithm of the detected fluometuron concentrations regressed against time in soil collected from a cropped area, a grass filter strip, and a riparian forest. Both methods detected the same initial fluometuron concentration (y-intercept) for two of the three soils evaluated. The ELISA and HPLC measurements of fluometuron concentrations compared favorably with r values from 0.83 to 0.98. Predicted fluometuron half-lives determined from HPLC and ELISA measurements were: 110 and 112 d in the cropped watershed, 28 and 29 d in the riparian area, and 11 and 11 d in the grass filter strip, respectively. Results from both techniques indicated shorter half-lives in soil from the grass filter strip and riparian area than in cropped area soil. There was an inverse correlation between predicted half-lives and soil organic matter, pH, clay, and cation exchange capacity. Additional index word: Herbicide degradation. Abbreviations: BMPs, best management practices; CEC, cation-exchange capacity; DAT, days after treatment; DT50, 50% disappearance time; ELISA, enzyme-linked immunosorbent assay; HPLC, high-performance liquid chromatography; IC50, analyte concentration that decreases chromogen activity by 50%; LDD, least detectable dose; MD-MSEA, Mississippi Delta Management Systems Evaluation Area; OM, organic matter.

Runoff quality from no-till cotton fertilized with broiler litter in subsurface bands.

Surface broadcast of broiler litter to no-till row crops exposes the litter and its nutrients to risks of loss in runoff water and volatilization and may limit the potential benefit of litter to the crops. Subsurface banding of litter could alleviate these risks. A field study was conducted in 2008 and 2009 on an upland Falkner silt loam soil to determine the effect of broiler litter placement on runoff nutrient losses from no-till cotton ( L.). Treatments included surface broadcast broiler litter applied manually, subsurface-banded litter applied by tractor-drawn equipment, and no broiler litter, all in combination with or without winter wheat ( L.) cover crop residue. Broiler litter rate was 5.6 Mg ha. The experimental design was a randomized complete block with a split-plot arrangement of treatments replicated three times. In 2008, simulated rainfall was used to generate runoff 27 d after litter application. Subsurface-banded litter reduced runoff total C, N, P, NH, NO, Cu, Zn and water-soluble P (WP) concentrations by 72, 64, 51, 49, 70, 36, 65, and 77%, respectively, compared with surface broadcast. The reductions were greater in 2009 where runoff occurred 1 d after litter application. Bacterial runoff was decreased by one log with subsurface-banded litter compared to surface broadcast. Except for C, NH, N, and WP, the presence of winter cover crop residue did not affect the load or runoff nutrient concentrations in either year. The results indicate that subsurface banding litter to no-till cotton substantially reduces nutrient and bacterial losses in runoff compared with surface broadcasting.

Effects of Subsurface Banding and Broadcast of Poultry Litter and Cover Crop on Soil Microbial Populations

Agronomic management is aimed at managing the crop environment to maximize crop yield, but soil biology is often ignored. This study aimed to compare the application of poultry litter via broadcast and subsurface banding versus standard inorganic fertilizer to cotton ( L.) and their effects on soil bacterial populations and fecal indicator bacteria. The study comprised a randomized complete block design, with fertilizer and time of application as treatment effects and cover crop as a main effect. Soil cores were collected and analyzed from 2008 to 2014. Fecal indicator bacteria were at detection limits for all treatments, where the integron 1 gene was significantly elevated in litter plots. There were few differences between litter application approaches, but both significantly increased key biogeochemical genes over control plots, whereas a cover crop only increased soil moisture and urease C. Data suggested a positive residual effect of litter application with 16S, phosphatase A, and urease C genes elevated over controls, but similar to standard fertilizer plots. High-throughput 16S ribosomal RNA analysis suggested increased diversity and enrichment indices in litter and standard fertilizer over untreated control plots. Litter and standard fertilizer effects persisted 4 and 2 yr after application, respectively, as evidenced by residual library community structures. This study demonstrated the positive effects of litter application on the soil bacterial community when compared with untreated control plots. Some differences between standard fertilization and litter practices were noted and suggest that there is a positive residual effect on soil microbial populations associated with both practices.

An Evaluation of Pre-emergence Metam-Potassium and S-metolachlor for Yellow Nutsedge (Cyperus esculentus) Management in Sweetpotato

Field studies were conducted in 2014 and 2015 at Pontotoc, MS to evaluate combinations of metam-potassium and S-metolachlor for yellow nutsedge control and sweetpotato crop response. Treatments consisted of a factorial of five metam-potassium rates (0, 149, 261, 372, and 484 kg ha-1) by three S-metolachlor rates (0, 0.80, and 1.34 kg ha-1). Additionally, a hand-weeded check was included for comparison. Crop injury was limited to ≤4% at 4 weeks after transplanting (WAP) and was transient. At 2 WAP yellow nutsedge control was 58, 74, and 76% in plots treated with S-metolachlor at 0, 0.80, and 1.34 kg ha-1, respectively. Nutsedge control in all treatments decreased from 2 to 15 WAP. At 15 WAP, S-metolachlor at 0, 0.80, and 1.34 kg ha-1 provided 35, 68, and 70% yellow nutsedge control, respectively. Metam-potassium rate did not influence yellow nutsedge control after transplanting. Sweetpotato yields in the hand-weeded check were 4,640; 22,180; 7,180; 34,000; and 1,360 kg ha-1 for jumbo, no. 1, canner, marketable, and cull grades, respectively. S-metolachlor applied at either 0.80 or 1.34 kg ha -1 provided jumbo, no. 1, and marketable sweetpotato yields equivalent to the hand-weeded check. Canner and cull yields were not influenced by S-metolachlor rate. Metam-potassium rates used in the present study resulted in yields equal to or greater than the hand-weeded check. Nomenclature: Metam-potassium; S-metolachlor; yellow nutsedge, Cyperus esculentus L.; sweetpotato, Ipomoea batatas L. Lam.

Effects of Metribuzin Applied Lay-by on Weed Control and Sweetpotato Crop Response

Field studies were conducted at the Pontotoc Ridge-Flatwoods Branch Experiment Station in Pontotoc, MS in 2015 and 2016 to determine the influence of lay-by metribuzin application on weed control and sweetpotato crop response. With the exception of weedy and hand-weeded checks, all plots received flumioxazin at 107 g ai ha-1 pre-transplanting followed by (fb) clomazone at 1,120 g ai ha-1 immediately after transplanting. Lay-by treatments consisted of S-metolachlor (800 g ai ha-1), metribuzin (210 or 315 g ai ha-1), metribuzin (210 g ha-1) plus napropamide (1,120 g ai ha-1), and metribuzin (210 g ha-1) plus S-metolachlor (800 g ha-1). At 4 weeks after transplanting, sweetpotato crop injury was 3 to 15%, but was transient and not evident after 6 (2015) to 8 weeks after transplanting (2016). Season-long weed control was excellent (≥98%) for all herbicide treatments used in the study. Hand-weeded check plots yielded 4,600; 18,350; 28,770; and 1,520 kg ha-1 of jumbo, No. 1, marketable, and cull grades, respectively. Jumbo, No. 1, and marketable yields from all herbicide-containing treatments in the study were greater than the weedy check and similar to the hand-weeded check. For all treatments, the portion of yield graded as cull was similar to the hand-weeded check. Canner yield response differed between years. In general, canner yield was greater in 2016 (8,460 to 10,670 kg ha-1) than 2015 (1,570 to 3,570 kg ha-1). In both years, canner yield in all treatments was similar to the hand-weeded check with one exception: in 2015 sweetpotato receiving metribuzin plus napropamide yielded more canners (3,570 kg ha-1) than the hand-weeded check (2,300 kg ha-1). Nomenclature: Metribuzin; sweetpotato, Ipomoea batatas (L.) Lam.

Development of a Mechanical Undercutting System to Minimize Sweetpotato Skinning during Harvest

Abstract. Sweetpotatoes have been an important high-value crop in Mississippi and future growth is expected. Industry growth has created the need for a continuous supply of sweetpotatoes throughout the year. Therefore, managing the harvest process and postharvest storage environment is critical to maintaining a year-round supply of quality sweetpotato roots. This has been a challenge in Mississippi and growers have been experiencing post-harvest losses due to excessive root shrinkage (weight loss) and bacterial and fungal rots. Studies indicate that 20% to 25% of sweetpotatoes are lost to moisture loss and decay during postharvest storage. This is directly related to skinning at harvest procedures that cause cuts and abrasions (skinning) to the delicate skin of the sweetpotato root is. These wounds provide a way-of-entry for diseases to infect the root, as well as moisture loss that results in root shrinkage. De-vining sweetpotatoes prior to harvest is a commonly used method to halt root growth and to begin toughening the skin. This method is viable for producers using manually-assisted harvesting for the fresh market. Producers using bulk harvesting prefer to leave vines on to reduce the amount of foreign material going into storage. A new method of halting plant growth and allowing the root to cure in the ground prior to harvest is needed. The objective of this study was to design and test a mechanical root pruning blade to halt plant growth and initiate skin set prior to harvest of sweetpotatoes and to quantify the effects of undercutting sweetpotatoes on skin strength relative to de-vining. It was hypothesized that cutting the deep root of the sweetpotato plant would allow this process to begin. Therefore, two different undercutting implements were designed and fabricated. One was assembled from currently available off-the-shelf components and the other was a modified commercially available sweetpotato digger. These implements were tested in experimental plots and the skin strength was directly measured. Root skin strength was measured at three days and six days after treatment. There was a significant rainfall event on the fifth day after treatment, meaning that no comparison between the time periods can be made. One of the tested varieties responded to undercutting. Results indicated that at three days after treatment, undercutting had no significant effect on skin strength for both vine conditions (vine-on and de-vined). At six days after treatment, undercutting with the newly developed implement significantly increased skin strength for roots in which the vine had been left on. There was no difference between using the modified digger and no treatment. Additionally, there was no treatment effect on roots which were de-vined. These results indicate that in a bulk harvesting system, undercutting with the new implement will increase skin strength after the roots have cured in the ground.