Progress 09/01/23 to 08/31/24
Outputs
Target Audience:The target audience for this project includes researchers in crop pest management, especially those who study weeds and weed management techniques in vegetable crop production. The target audience also includes agricultural professionals and vegetable crop producers, especially those in the western United States. Changes/Problems:The continued absence of soil-borne diseases in our field studies have prevented conclusions regarding barley and mustard cover crop effects on soil-borne diseases impacting chile pepper. Attempts to address this problem included increases in field plot size and a greenhouse study using soil inoculated with disease-causing organisms. Unfortunately, neither of these possible corrections generated enough chile pepper plants with disease symptoms for statistical analysis. The unexpected occurrence of adult leafhoppers on barley plants in the field compelled a controlled-environment experiment on feeding preferences and reproductive behavior of beet leafhopper on barley and mustard cover crops. Although this study was not in the original proposal, this study was critical because it clarified possibilities for a weed-suppressive cover crop to support an insect pest that transmits a viral disease to chile pepper. Such knowledge supports prudent recommendations for use of cover crops as weed management tactics. The original proposal called for economic cost-benefit analysis based on 2024 data collected from two sites, Leyendecker and Los Lunas. The unusually high amount of cover crop biomass combined with a specific type of mechanical seeder at Los Lunas led to a poor stand of chile pepper. Accordingly, we currently do not have two site-years of data for the proposed economic analysis. To generate the needed data, we will repeat the field study at Leyendecker only in 2024-25. What opportunities for training and professional development has the project provided?This project is supporting one PhD student and two undergraduate research assistants. How have the results been disseminated to communities of interest?Framing concepts and results from this study were presented to farmers, agricultural professionals, and researchers attending the 42nd Annual New Mexico Chile Conference in Las Cruces, NM on February 6, 2024. Project results were presented to practitioners attending field day events at the New Mexico State University Leyendecker Plant Science Research Center (May 22, 2024), and the New Mexico State University, Agricultural Science Center at Los Lunas (October 19, 2024). Project concepts and results were disseminated to the scientific research community through a presentation at the 77th Annual Meeting of the Western Society of Weed Science in Denver, CO on March 6, 2024, as well as a field presentation to the Western IPM Center Advisory Committee on June 11, 2024. Results from field and controlled environment studies pertaining to weed suppression abilities of barley and mustard cover crops have been published in a peer-reviewed article in Weed Science. What do you plan to do during the next reporting period to accomplish the goals?We will repeat the field study under Objective 4 at Leyendecker only. This field study will provide two years of data on possibilities for replacing, or enhancing, napropamide with a barley cover crop. Further, data from the second and first years will allow us to conduct cost-benefit analyses to indicate expected economic gains from reduced hand hoeing. We will disseminate results from this study by providing presentations at the Annual Meeting of the Western Society of Weed Science in March 2025. We will also prepare manuscripts for submission to peer-reviewed scientific journals such as Weed Science and Economic Entomology. Results of this study will be presented to agricultural scientists and professionals attending the 2025 New Mexico Chile Conference, the 2025 Leyendecker Plant Science Center Field Day, and the 2025 Los Lunas Agricultural Science Center Field Day.
Impacts
What was accomplished under these goals?
Objective 1: Identify cover crops that do not cause large migrations of beet leafhoppers out of the cover crop and into the surrounding vegetation Adult beet leafhoppers were found on all cover crops grown in fields during winter 2023. This was unexpected because literature suggested beet leafhoppers are not typically found in grass stands. To determine if the weed-suppressive barley cover crops host beet leafhoppers, we conducted a controlled environment study involving barley and brown mustard cover crops to evaluate feeding preferences and reproductive behaviours of beet leafhoppers. Specifically, we determined the feeding preference of adult beet leafhoppers infected with beet curly top virus (BCTV) with dual choice tests performed with brown mustard ('Caliente Rojo') and two barley cultivars ('Stockford' and 'Valor'). In a subsequent no-choice test, adult beet leafhoppers were caged onto individual leaves of barley and brown mustard, and the plant tissue was stained and examined for the presence of beet leafhopper sheaths, punctures, and eggs. Results from the dual choice feeding experiment indicated beet leafhoppers exhibited a nine-times greater preference for brown mustard than either barley cultivar. In no-choice tests, adult leafhoppers fed on barley, but no eggs were laid on either barley cultivar. Brown mustard supported both leafhopper feeding and oviposition. This research indicated that barley cover crops may serve as food sources for beet leafhoppers, but barley is less likely than brown mustard to sustain beet leafhopper that have the capacity to transmit BCTV to chile pepper. Objective 2: Identify cover crops and cover crop termination times that maximize weed and disease suppression in chile pepper Field studies conducted in 2021-22 and 2022-23 determined that a barley cover crop is more effective than brown mustard for early-season weed control in chile pepper. Barley-induced suppression of weeds occurred when barley was terminated 16 to 21 days before chile pepper seeding. In 2023-24, we conducted a field study to determine production profitability responses to a barley cover crop grown for weed suppression in chile pepper. Procedures and results from this field study are described under Objective 4. Similar to the first two years of this study, the general absence of soil-borne disease in chile pepper fields prevented conclusions on cover crop suppression of soil-borne diseases. A greenhouse study with field soil also failed to generate soil-borne disease on chile pepper. Objective 3: Identify cover crops and cover crop termination times that support vigorous development of chile pepper plants Field studies conducted in 2021-22 and 2022-23 determined that barley and mustard cover crops did not reduce chile pepper stands or chile pepper fruit yield. As noted above, a field study in 2023-24 was conducted in support of economic cost-benefit analyses (Objective 4). Objective 4: Conduct cost-benefit analyses by determining barley cover crop effects on weed infestation severity, hand hoeing requirements, and chile pepper yield. In 2023-2024, we conducted a field study at the following two New Mexico State University research farms: Leyendecker Plant Science Research Center (herein, "Leyendecker"), and Los Lunas Agricultural Science Center (herein "Los Lunas"). Experimental units were plots measuring 19.81 m by 4.05 m at Leyendecker, 19.81 m by 3.05 m at Los Lunas. Treatments included, but were not limited to, a noncover control and a barley cover crop. Treatments also included a soil residual herbicide commonly applied at chile pepper seeding, napropamide. Accordingly, the full complement of treatments were: 1) barley cover crop with napropamide, 2) barley cover crop without napropamide, 3) noncover control with napropamide, and 4) barley cover crop without napropamide. The barley cultivar in this study was 'Stockford' at Leyendecker, 'Valor' at Los Lunas. At Leyendecker, barley was seeded in a field with clay loam soil on October 24, 2023. At Los Lunas, barley was seeded in a field with sandy loam soil on October 6, 2023. From seeding to termination, cover crops were flood irrigated three times at Leyendecker, and four times at Los Lunas. At Leyendecker, the barley cover crop was terminated on April 6, 2024. At Los Lunas, the barley cover crop was terminated on April 16, 2024. Termination involved mowing, disking, listing rows, and flood-furrow irrigation. At the time of termination, the mean aboveground dry biomass for barley at Leyendecker was 11,599 kg ha-1; 8,873 kg ha-1 at Los Lunas. Chile pepper was direct seeded on April 25, 2024, at Leyendecker, April 30, 2024, at Los Lunas. Immediately after seeding, preemergence applications of napropamide were made using a CO2 backpack sprayer. At Leyendecker, the napropamide rate was 2.24 kg ha-1. At Los Lunas, the napropamide rate was 1.12 kg ha-1. Weed densities and hand hoeing times were determined at 4 and 8 weeks after chile pepper seeding (WAS). At green fruit maturity, marketable fruits were hand harvested and weighed in the field to determine crop yield fresh weight. Results from Leyendecker indicated weed densities at 4 and 8 WAS were lowest for chile pepper that followed the barley cover crop and was treated with napropamide. Weed densities were similar between the treatment that included the barley cover crop without napropamide and the treatment lacking the barley cover crop but with napropamide. Weed densities in chile pepper were greatest in plots lacking both the barley cover crop and napropamide. The combination of the barley cover crop and napropamide reduced hand hoeing time 26 to 50% compared to the treatment lacking both the barley cover crop and napropamide. Percentage reductions in hoeing time, relative to the treatment lacking both barley and napropamide, ranged from 0 to 33% for treatments featuring barley without napropamide and napropamide without barley. There were no differences among treatments in chile pepper fruit yield. At Los Lunas in 2024, the amount of barley biomass at termination was 380x greater than previous years at this site. This led to seedbeds containing high amounts of barley residue at the time of chile pepper seeding. In addition to directly interfering with chile pepper seeding, the large amount of barley residue on the soil-surface precluded a site-specific field operation that removes soil from seedbeds after crop seeding - "decapping". The high amount of barley residue at Los Lunas led to severe reductions in chile pepper stands and fruit yields, as well as increases in both weed density and hand hoeing time, compared to treatments lacking barley cover crops. It should be noted that study sites differ in both mechanical seeder (Leyendecker, MaxEmerge Plus; John Deere; Los Lunas, Cole Planet Jr.; Cole Planter Company) and conventional use of "decapping" (Leyendecker, no; Los Lunas, yes). One-year results from this field study suggest a barley cover crop that is mowed and incorporated into the soil controls early season weeds in chile pepper to the same degree as a preemergence herbicide conventionally applied at chile pepper seeding. Further, the results from this field study suggest the combination of barley cover crop and preemergence herbicide improves weed control outcomes relative to either tactic used alone.
Publications
- Type:
Peer Reviewed Journal Articles
Status:
Accepted
Year Published:
2024
Citation:
Toth CR, Schutte BJ. Barley cover crops outperform brown mustard for early-season weed control in New Mexico chile pepper. Weed Science. Published online 2024:1-30. doi:10.1017/wsc.2024.81
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2024
Citation:
Toth CR, Schutte BJ. 2024. Suitability of a barley cover crop to suppress weeds of chile pepper in southern New Mexico. Proceedings of the 77th Annual Meeting of the Western Society of Weed Science 77:133
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2024
Citation:
Toth CR, Schutte BJ. 2024. Barley cover crops outperform brown mustard for early-season weed control in chile pepper. Poster Presentation at the 2024 New Mexico Chile Conference.
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Progress 09/01/22 to 08/31/23
Outputs
Target Audience:The target audience for this project include researchers in crop pest management, especially those who study weeds and soil-borne dieases in vegetable crops. The target audience is also agricultural professionals and vegetable producers in the western United States. Changes/Problems:Adult beet leafhoppers were found in barley in 2023. This unexpected result from the field study has compelled new controlled environment studies to clarify beet leafhopper preferences for barley. Similar to the first-year of this study, the general absence of soil-borne disease in chile pepper fields prevented conclusions on cover crop suppression of soil-borne diseases. Cover crop effects on soil-borne diseases will be clarified through a series greenhouse studies. What opportunities for training and professional development has the project provided?This project is supporting one PhD student and two undergraduate research assistants. How have the results been disseminated to communities of interest?Framing concepts and early results from this study were presented to farmers, agricultural professionals, and researchers attending the 25th International Pepper Conference in Tucson, AZ on September 27, 2022, as well as a field day at the New Mexico State University, Agricultural Science Center at Los Lunas on August 8, 2023. Over 300 members of the local agricultural community attended the field day at the Los Lunas Agricultural Science Center. Early results were also communicated as a presentation at the Annual Meeting of the Western Society of Weed Science in Boise, ID on March 1, 2023. What do you plan to do during the next reporting period to accomplish the goals?We will conclude and repeat greenhouse studies clarifying cover crop effects on chile plant susceptibility to disease from Phytophthora capsici and Verticillium dahliae, and cover crop effects on the growth and survival of Phytophthora capsici and Verticillium dahliae in soil. The field study comparing cover crop treatments (barley, mustard, barley-mustard combination, and non-covered control) for weed suppression in chile pepper has indicated that barley is the optimum cover crop at both study sites. In the upcoming year, a two-site field study (Leyendecker and Los Lunas), will clarify economic costs and benefits of barley cover crops for weed suppression in chile pepper. Specifically, this field study will determine if barley cover crops replace, enhance or inhibit a pre-emergence herbicide conventionally used in chile pepper, and will conduct cost-benefit analyses to indicate expected economic gains from reduced hand hoeing. We have determined concentrations sinigrin in tissues of mustard cover crops. We will continue quantification of biopesticidal compounds by determining concentrations of hordenine and gramine in barley tissues. This information, combined with measurements of cover crop biomass at termination, will allow us to determine amounts of allelopathic chemicals added to soil by the terminated cover crops. We will conduct controlled environment experiments to clarify feeding preferences for beet leafhoppers (Circulifer tenellus). Specifically, we will determine if beet leafhoppers feed and survive on barley, and we will determine the degree to which beet leafhoppers prefer to feed on mustard cover crops, barley and winter annual weeds that are known to host beet leafhoppers. Results from these experiments are expected to help explain will provide Results of this study will be presented to agricultural scientists and professionals attending the 2024 New Mexico Chile Conference, the 2024 Leyendecker Plant Science Center Field Day, and the 2024 Los Lunas Agricultural Science Center Field Day. Results will be shared with the scientific community at the 2024 Annual Meeting of the Western Society of Weed Science and through a manuscript submitted to a peer-reviewed, scientific journal.
Impacts
What was accomplished under these goals?
Objective 1: Identify cover crops that do not cause large migrations of beet leafhoppers out of the cover crop and into the surrounding vegetation In 2022-2023, we conducted a field study at two New Mexico State University (NMSU) research farms: the NMSU Los Lunas Agricultural Science Center (herein "Los Lunas"), and the NMSU Leyendecker Plant Science Research Center (herein, "Leyendecker"). Los Lunas is located in central New Mexico, whereas Leyendecker is located in south-central New Mexico. Cover crops in this study include barley (Hordeum vulgare), mustard (Brassica juncea) and a combination of barley and mustard. At Leyendecker, the barley cultivar was 'Stockford', which was previously determined to grow well in southern New Mexico and suppress weeds in the subsequent chile pepper crop. At Los Lunas, the barley cultivar was 'Valor'. This cultivar was selected because: 1) previous research determined 'Valor' exhibited relatively high levels of cold tolerance, and 2) cold damage to barley was a short-coming in 2021-2022. The mustard cultivar at both study sites was 'Caliente rojo'. At Leyendecker, cover crops were seeded in a field with clay loam soil on October 21, 2022. At Los Lunas, cover crops were seeded in a field with sandy loam soil on October September 19, 2022. From seeding to termination, cover crops were flood irrigated three times at Leyendecker, four times at Los Lunas. Beginning in January 2023, cover crop plots were vacuum-sampled for beet leafhoppers (Circulifer tenellus). Adult leafhoppers were found in all cover crop treatments, including barley monocultures. At Leyendecker, adult leafhoppers tended to be most abundant in the mustard cover crop, and adult beet leafhopper abundance declined from January to mid-March. At Los Lunas, the mustard cover crop tended to have the fewest adult leafhoppers because the mustard cover crop did not survive the winter at Los Lunas. Adult leafhoppers were collected from the barley cover crop at Los Lunas. Cover crops were terminated with the following sequence of field operations: mowing, disking, listing rows, and flood-furrow irrigation. At Leyendecker, cover crops were terminated on April 6, 2023. Cover crops at Los Lunas were terminated on April 11, 2023. At the time of termination, mean aboveground dry biomass for cover crops at Leyendecker was as follows: barley, 8367 kg ha-1; mustard, 6064 kg ha-1; barley-mustard combination, 6719 kg ha-1. For Los Lunas, mean aboveground dry biomass for cover crops at termination was as follows: barley, 1821 kg ha-1; mustard, 0 kg ha-1; barley-mustard combination (combination treatment), 1691 kg ha-1. Seventy one percent of the biomass in the combination treatment was barley. This high percentage of barley biomass in the combination treatment, combined with poor mustard survival in the monoculture treatment, suggest that a cold-tolerant cultivar of barley is better suited as a winter cover crop in central New Mexico than the mustard species used in this study. Just prior to termination, yellow sticky traps were positioned on the perimeters of cover crop plots. Shortly after cover crops were mowed, yellow sticky traps were recovered and brought to the laboratory. In the laboratory, traps were inspected for beet leafhoppers in adult form. Adult leafhoppers were not found on yellow sticky traps. The absence of beet leafhoppers on yellow sticky traps suggests that cover crop terminations in this study did not cause large migrations of beet leafhoppers out of the cover crop and into the surrounding vegetation. Objective 2: Identify cover crops and cover crop termination times that maximize weed and disease suppression in chile pepper Chile pepper 'Sandia' was seeded April 27, 2023 at Leyendecker and Los Lunas. At four weeks after chile pepper seeding at Leyendecker, plots that were formerly barley had fewer weeds than plots that did not have a cover crop (non-cover control). Barley-induced suppression of weeds in chile pepper was only observed at four weeks after chile pepper seeding. Neither the mustard cover crop treatment nor the barley-mustard combination cover crop treatment reduced weed densities in chile pepper at Leyendecker. At both study sites, the barley cover crop treatment reduced the amount of time required to hand hoe weeds in chile pepper plots at four weeks after crop seeding. These results are generally consistent with first-year results in this study and suggest a barley cover crop that is incorporated in soil suppresses early season weeds in chile pepper. To substantiate evidence from the field study, a complementary study to assess weed suppressive properties of field soil from barley plots was conducted under controlled conditions. To do this, seeds of Amaranthus palmeri were incubated in soil collected from barley and non-cover control plots after barley was mowed and disked. Following incubation, seeds were subjected to germination assays under temperatures and photoperiods conducive to A. palmeri germination. Time-integrated measures of barley germination indicated that A. palmeri seed germination was inhibited by soil from barley plots. These results corroborate field study results as they indicate barley created soils that suppress germination of a common weed species. However, soil from barley plots did not adversely affect seedling survival or seedling development under controlled conditions. Repeated surveys of chile pepper plots found no chile pepper plants exhibiting symptoms of wilt disease caused by either Phytophthora capsici and Verticillium dahliae. Greenhouse studies determining cover crop effects on the susceptibility of chile pepper plants to soilborne diseases failed to identify differences among cover crop treatments. The primary pesticidal compound in the mustard cover crop biomass is sinigrin. High-performance liquid chromatography (HPLC) analyses indicated that sinigrin contents in aboveground biomass for mustard cover crops in this study were as follows: 17.8 μmol g fresh weight-1 for mustard grown with barley at Leyendecker, 15.2 μmol g fresh weight-1 for mustard grown without barley at Leyendecker 21.3 μmol g fresh weight-1 for mustard grown with barley at Los Lunas, 30.9 μmol g fresh weight-1 for mustard grown without barley at Los Lunas. Pesticidal compounds in barley biomass include gramine and hordenine. HPLC analyses for determining gramine and hordenine contents in barley biomass are currently in progress. Objective 3: Identify cover crops and cover crop termination times that support vigorous development of chile pepper plants At both study sites, cover crops (barley, mustard, combination of barley and mustard) did not reduce chile pepper stands or chile pepper fruit yield.
Publications
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2023
Citation:
Schutte, B. J., A. Bajagain, A. Nagila, C. Toth. 2023. Cover crops for pest suppression in chile pepper. Proceedings of the 76th Annual Meeting of the Western Society of Weed Science 76:121
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2023
Citation:
Schutte, B. J. 2022. Developing chemical and cultural tactics to reduce weeds and hand hoeing in chile pepper. 25th International Pepper Conference. Tucson, AZ
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Progress 09/01/21 to 08/31/22
Outputs
Target Audience:Concepts underlying this project were shared with agricultural professionals, extension agents, farmers, and agricultural scientists attending the following two regional conferences: 1) New Mexico Chile Conference (February 1, 2022), and 2) New Mexico Agriculture Sustainability Workshop (June 28, 2022). Changes/Problems:Cover crops seeded at Leyendecker on September 22, 2021 failed to produce consistent, dense stands. This was likely due to soil compaction caused by an additional tractor pass through the field. The cover crops at Leyendecker were reseeded on October 20, 2021; however, the need for a new field and the lack of space at the research farm caused us to reduce the physical size of the study by eliminating a cover crop termination time treatment. The termination time treatment was also eliminated at Los Lunas because cover crops were dormant and not actively growing in March, which was when first cover crop terminations were originally planned. We terminated all cover crop treatments at Los Lunas in early April because we believed that this was latest termination time that would allow for chile pepper harvest before the first frost in fall. Despite not including a termination time treatment in this project, we identified a cover crop treatment (barley) and termination time (3 weeks before chile pepper seeding) that suppressed weeds in chile pepper and did not reduce chile pepper stands. Further, this cover crop treatment did not harbor beet leafhoppers, which are potential vectors for the curtovirus that causes curly top disease in chile pepper. In 2022-23, we will repeat the study as it was conducted in 2021-22, with two modifications. The reason for repeating the study as conducted in 2021-22 is that we need to obtain evidence that further supports, or counters, the promising results for barley observed in 2021-22. We will modify the study in 2022-23 by planting a barley variety better suited for cold at Los Lunas compared to the variety planted at Los Lunas in 2021-22. At Leyendecker, the barley variety planted in 2022 will be the same as the barley variety planted in 2021. The second modification for 2022-23 is delayed cover crop termination at Los Lunas. Specifically, we will terminate cover crops at Los Lunas in late April, which will allow for more cover crop biomass at termination compared to 2021-22. Following cover crop termination, chile pepper will be seeded in mid-May at Los Lunas. Discussions farm managers who work in the Los Lunas area indicated that seeding in mid-May will provide the chile pepper crop enough time to produce a robust yield. What opportunities for training and professional development has the project provided?This project is supporting one PhD student and one undergraduate research assistant. How have the results been disseminated to communities of interest?Concepts of this study were presented to farmers and agricultural professionals attending the New Mexico Chile Conference on February 1, 2022, as well as the New Mexico Agriculture Sustainability Workshop on June 28, 2022. What do you plan to do during the next reporting period to accomplish the goals?We will conclude and repeat growth chamber studies that are clarifying cover crop effects on weed seed viability and weed seedling vigor. We will also conclude and repeat greenhouse studies that are clarifying cover crop effects on chile plant susceptibility to disease from Phytophthora capsici and Verticillium dahliae, and cover crop effects on the growth and survival of Phytophthora capsici and Verticillium dahliae in soil. The field study comparing cover crop treatments (barley, mustard, barley-mustard combination, and non-covered control) for weed and disease suppression in chile pepper will be repeated at two study sites (Leyendecker and Los Lunas). These field studies will again include repeated measurements on beet leafhopper population densities in cover crops, repeated measurements on cover crop biomass, repeated measurements on weed infestation densities in chile pepper, repeated measurements on hand hoeing requirements in chile pepper, repeated measurements on disease incidence in chile pepper, and chile pepper stand count and yield. We will employ the HPLC procedures developed in the first year of this study to determine allelopathic chemical concentrations in both barley and mustard. This information, combined with measurements of cover crop biomass at termination, will allow us to determine amounts of allelopathic chemicals added to soil by the terminated cover crops. First-year results of this study will be presented to agricultural scientists and professionals attending the International Pepper Conference (September 26-28, 2022) and the Annual Meeting of the Western Society of Weed Science (February 27-March 2, 2023). Results of this study will also be presented to agricultural professionals and farmers attending the 2023 New Mexico Chile Conference, the 2023 Leyendecker Plant Science Center Field Day, and the 2023 Los Lunas Agricultural Science Center Field Day. First and second-year results on beet leafhopper preferences for cover crop species will be presented at the 2023 Meeting of WERA 1007, Curly Top Virus Biology, Transmission, Ecology and Management.
Impacts
What was accomplished under these goals?
Objective 1: Identify cover crops and cover crop termination times that do not cause large migrations of beet leafhoppers out of the cover crop and into the surrounding vegetation This study includes field sites at two New Mexico State University (NMSU) research farms: the NMSU Los Lunas Agricultural Science Center (herein "Los Lunas"), and the NMSU Leyendecker Plant Science Research Center (herein, "Leyendecker"). Los Lunas is located in central New Mexico, whereas Leyendecker is located in south-central New Mexico. Cover crops in this study include barley (Hordeum vulgare 'Stockford') , mustard (Brassica juncea 'Caliente rojo') and a combination of barley and mustard. These cover crops were seeded in a field with sandy loam soil at Los Lunas on September 14, 2021. At Leyendecker, cover crops were seeded in a field with clay loam soil on September 22, 2021. However, because cover crops seeded at Leyendecker on September 22, 2021 failed to produce a sufficient stand, cover crops at this study site were re-seeded on October 20, 2021. Aboveground biomass of cover crops was harvested at biweekly intervals beginning at cover crop seeding. Results indicated that cover crop biomass accumulated in a sigmoidal pattern over time, with rapid increases in cover crop biomass during fall and late spring, and more subtle increases in cover crop biomass in winter. Beginning in January 2022, cover crop plots were sampled for beet leafhoppers (Circulifer tenellus). Adult leafhoppers were found in two cover crop treatments: mustard and a combination of barley and mustard. Adult beet leafhoppers were not found in the barley cover crop. Comparisons between mustard and the barley-mustard combination indicated that adult leafhoppers were more abundant in the mustard cover crop at both study sites. For both mustard and barley-mustard cover crops, beet leafhoppers abundance declined from January to mid-March. Cover crops were terminated with the following sequence of field operations: mowing, disking, listing rows, and flood-furrow irrigation. At Leyendecker, cover crops were terminated on March 22, 2022. Cover crops at Los Lunas were terminated on April 7, 2022. At the time of termination, mean aboveground dry biomass for cover crops at Leyendecker was as follows: barley, 507 g m-2; mustard, 162 g m-2; barley-mustard combination, 384 g m-2. For Los Lunas, mean aboveground dry biomass for cover crops at termination was as follows: barley, 134 g m-2; mustard, 122 g m-2; barley-mustard combination, 130 g m-2. Just prior to termination, yellow sticky traps and pots with plants of Bassia scoparia (summer annual weed that hosts beet leafhoppers) were positioned on the perimeters of cover crop plots. Shortly after cover crops were mowed, yellow sticky traps and B. scoparia plants were recovered and brought to the laboratory. In the laboratory, plants and traps were inspected for beet leafhoppers in adult form. Adult leafhoppers were not found on B. scoparia plants, and only two leafhoppers were found on yellow sticky traps. The absence of beet leafhoppers on B. scoparia plants, and the low number of beet leafhoppers on yellow sticky traps, is consistent with the observation of relatively few beet leafhoppers on cover crop plants shortly before cover crop termination. These first-year results suggest that cover crop terminations in this study did not cause large migrations of beet leafhoppers out of the cover crop and into the surrounding vegetation. First-year results also indicate that a mustard cover crop is a potential overwinter host for beet leafhoppers, whereas a barley cover crop is not a host for beet leafhopper. Objective 2: Identify cover crops and cover crop termination times that maximize weed and disease suppression in chile pepper Chile pepper 'Sandea' was seeded April 15, 2022 at Leyendecker, April 28, 2022 at Los Lunas. Chile pepper seedlings were first observed approximately three weeks after chile pepper seeding. Beginning at four weeks after chile pepper seeding, weed densities were determined every two weeks. At four weeks after chile pepper seeding at Leyendecker, plots that were formerly barley had fewer weeds than plots that did not have a cover crop (non-cover control). Barley-induced suppression of weeds in chile pepper was only observed at four weeks after chile pepper seeding. Neither the mustard cover crop treatment nor the barley-mustard combination cover crop treatment reduced weed densities in chile pepper at Leyendecker. Cover crops did not affect weed densities in chile pepper at Los Lunas. At both study sites, cover crop treatments did not reduce the amount of time required to hand hoe chile pepper plots. These results, combined with the results on cover crop biomass, suggest a barley cover crop that is incorporated in soil suppresses early season weeds in chile pepper, provided the barley cover crop has sufficient biomass. To determine the effects of terminated cover crops on the viability of weed seeds, mesh packets containing seeds of Amarnathus palmeri, Anoda cristata, or Echinochloa crus-galli were buried in soil after cover crops were mowed and disked. Buried seed packets were recovered just before chile pepper seeding, which was approximately three weeks after cover crop termination. Recovered weed seeds were tested for viability using tetrazolium staining assays. Results indicated that terminated cover crops did not reduce percentages of viable weed seeds compared to non-cover control treatments. At Los Lunas, the barley-mustard combination treatment may have promoted seed longevity of Amaranthus palmeri and Echinochloa colona. For these species, percentages of viable seeds were greater in the barley-mustard combination treatment than the noncover control. Growth chamber studies clarifying cover crop effects on weed seedling vigor and weed seedling emergence are currently in progress. Repeated surveys of chile pepper plots found no chile pepper plants exhibiting symptoms of wilt disease caused by either Phytophthora capsici and Verticillium dahliae. Greenhouse studies determining cover crop effects on the susceptibility of chile pepper plants to soilborne diseases are currently in progress. A greenhouse study determining cover crop effects on the growth and survival of Phytophthora capsici and Verticillium dahliae in soil is in progress. To isolate and quantify allelopathic chemicals from barley and mustard plant tissues, we have evaluated and refined high-performance liquid chromatography (HPLC) procedures published in literature. For barley, HPLC procedures were developed for gramine and hordenine. For mustard, HPLC procedures were developed for glucosinolates including sinigrin. The secondary metabolites assessed in our HPLC procedures are considered the primary allelopathic chemicals in our cover crop species. Objective 3: Identify cover crops and cover crop termination times that support vigorous development of chile pepper plants At both study sites, cover crops (barley, mustard, combination of barley and mustard) did not reduce chile pepper stands. Data on chile pepper yield are currently being collected.
Publications
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