Source: NEW MEXICO STATE UNIVERSITY submitted to
ALLELOPATHIC COVERS CROPS FOR PEST SUPPRESSION IN CHILE PEPPER IN THE SOUTHWEST
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
NEW
Funding Source
Reporting Frequency
Annual
Accession No.
1026918
Grant No.
2021-70006-35307
Project No.
NM2021COVER
Proposal No.
2021-04877
Multistate No.
(N/A)
Program Code
ARDP
Project Start Date
Sep 1, 2021
Project End Date
Aug 31, 2024
Grant Year
2021
Project Director
Schutte, B.
Recipient Organization
NEW MEXICO STATE UNIVERSITY
1620 STANDLEY DR ACADEMIC RESH A RM 110
LAS CRUCES,NM 88003-1239
Performing Department
EPPWS
Non Technical Summary
High costs for weed control and yield loss from soil-borne diseases are severe threats to chile pepper production in the United States Southwest. To address these threats to chile pepper, we will develop ecologically-based tactics that target both weeds and soil-borne pathogens. Specifically, we will establish optimum management practices for barley and mustard cover crops that are incorporated into soil shortly before chile pepper seeding. Based on our preliminary studies and reports in literature, we expect that optimally managed mustard and barley cover crops will suppress weed emergence, reduce requirements for hand hoeing, and accelerate mortality in weed seedbanks. We also anticipate that optimally managed mustard and barley cover crops will suppress propagule persistence and growth of soil-borne pathogens, and inhibit infection on chile pepper plants by soil-borne pathogens. In addition to determining the extent of cover crop-induced reductions in weeds and soil-borne diseases, we will conduct cost-benefit analyses that will clarify the economic benefits of mustard and barley cover crops. These cost-benefit analyses will be presented to farmers during outreach events. With knowledge gained from this study, farmers will be able to effectively utilize an integrated pest management tactic that improves profitability by diminishing pesticide and hand labor requirements in chile pepper.
Animal Health Component
0%
Research Effort Categories
Basic
20%
Applied
80%
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
2160199114040%
2160199110230%
2160199107015%
2160199113015%
Goals / Objectives
This project will develop best practice guidelines for mustard and barley cover crops grown for suppressing pests in chile pepper. To do this, we will first determine cover crop termination times that (1) do not cause large migrations of beet leafhoppers out of the cover crop and into the surrounding vegetation, (2) maximize weed and disease suppression in chile pepper, and (3) support vigorous development of chile pepper plants. With this knowledge, we will conduct cost-benefit analyses by determining mustard and barley cover crop effects on weed infestation severity, hand hoeing requirements, soil-borne disease incidence, and chile pepper yield. We will also determine cover crop effects on the survival of weed seeds and pathogen propagules in soil. This will clarify the abilities of the cover crops to provide long-term pest suppression. If mustard and/or barley cover crops produce pest-suppressive soil without contributing to regional leafhopper problems, and if these cover crops improve profitability of chile pepper production, we will have developed an ecologically based pest management tactic appropriate for a crop that is central to the agricultural economy of the Southwest.
Project Methods
Objective 1. Determine optimum termination times for barley and mustard cover crops that are grown as green manures for weed and disease suppression in chile pepper. Study sites and field study design. We will conduct field studies at two New Mexico State University (NMSU) research farms: Leyendecker Plant Science Research Center near Las Cruces, NM and the Agricultural Science Center at Los Lunas, NM. Treatments will be factorial combinations of cover crop species (barley, mustard, mixture of barley and mustard) and cover crop termination date (30, 20, and 15 days before chile seeding). The experiment will also include a non-cover crop control. Treatments will be arranged in randomized complete block design with four replications.Field operations. At both study sites, cover crops will be grown on flat ground and flood-irrigated as needed. Plots without cover crops will not be irrigated because applying water to fallow land is not a typical practice in New Mexico.Beginning at the second week of March, we will implement treatments for cover crop termination time. Each termination event will include the following sequence of operations: mowing, discing, listing rows, and flood-furrow irrigation. During the second week of April, we will seed chile pepper. Herbicides and fungicides will not be applied at seeding. Chile peppers will be grown with furrow irrigation. Throughout chile pepper growing seasons, we will control weeds as needed using cultivation, hand hoeing and herbicides. Site-specific weed control problems will maintain weed-free conditions as best as possible. Prior to each weed control intervention, we will collect data on weed infestation severity (details below). Chile pepper fruits will be harvested once per site-year in early September.Data collection. At 2-week intervals beginning in January, beet leafhoppers in mustard cover crop subplots will be sampled using two collection methods. When mustard plants are rosettes, leafhoppers will be sampled using a cordless vacuum described in and with sweep nets. When mustard plants are bolting, leafhoppers will be sampled using the funnel bucket method and sweep nets.Just before mustard cover crop terminations, yellow sticky traps and pots with bolting plants of Sisymbrium irio (winter annual weed that hosts beet leafhoppers) will be positioned at cardinal and intercardinal points along the perimeters of mustard cover crop plots. Prior to deployment, S. irio plants will be grown in a greenhouse that is kept free of leafhoppers. One day after cover crop termination, yellow sticky cards will be retrieved and London rocket plants sampled for beet leafhopper using the funnel bucket method. For each sample, the numbers of nymphs, adult females and adult males will be determined.Just prior to cover crop termination, we will collect aboveground biomass. Biomass will be sorted to cover crop and winter weeds and biomass will be dried and weighed. For mustard cover crop plots, we will collect whole plants to measure biomass and sinigrin concentrations for both roots and shoots. Sinigrin will be extracted from biomass and analyzed with HPLC. For barley cover crop plots, we will collect whole plants to measure biomass, hordenine and gramine concentrations for both roots and shoots. Data on secondary metabolite concentrations will be combined with data on biomass, incorporation depth and soil bulk density to estimate the amount of biopesticide delivered to the soil.After incorporation of cover crops, but prior to irrigation, we will bury mesh packets in each plot. Mesh packets will differ by content and contain one of the following: (1) weed seeds, (2) microsclerotia from a pathogenic isolate of V. dahliae, (3) oospores from a pathogenic isolate of P. capsici, (4) rice grains colonized by V. dahliae mycelium, or (5) rice grains colonized by P. capsici mycelium (details on biological materials below). Packets will be exposed to cover crop residues by burial to the 20-cm depth in centers of raised beds. We will recover packets immediately prior to chile pepper seeding and immediately after chile pepper harvest. Recovered packets will be brought to the laboratory where we will determine germination rates for weed seeds, microsclerotia and oospores, as well as mycelium survival.At 14-day intervals beginning at crop seeding and continuing to harvest, we will systemically survey chile pepper plants for symptoms of infection by Phytophthora capsici and Verticillium dahliae. For each pathogen, disease incidence will be determined as the percentage of plants infected out of the total number of plants examined in four 10-m transects per plot. For symptomatic plants, disease severity will be scored using a rating system. Isolations will be made from symptomatic plants to confirm the involvement of P. capsici or V. dahliae in the symptoms.We will also conduct greenhouse evaluations that will determine the ability of field soil to suppress the growth of the pathogens and subsequent plant infection. Soil for the greenhouse evaluations will be collected before chile pepper seeding. Soil will be placed in pots and inoculated with mycelium-colonized rice grains to create the following pathogen treatments: soil with P. capsici, soil with V. dahliae, and a non-inoculated control. We will then plant one chile pepper in the center of each pot. Pots will be arranged on a greenhouse bench in a randomized complete block design. Site-years will be assessed separately. Soil in pots will be maintained at high moisture levels with daily watering. We will measure chile pepper plant height and evaluate plants for disease symptoms at 7, 14 and 21 days after planting. Disease incidence and severity will be assessed. At 21 days after planting, plants will be harvested, dried and weighed to determine root and shoot dry weights.At 14-day intervals beginning at crop seeding and continuing to harvest, we will identify to species, count and remove weeds occurring in permanent quadrats. We will also identify, count and remove weeds from quadrats immediately prior to each weed control intervention. The time required for one individual to hoe 8-m2 sections will be determined for each hoeing event. To determine cover crop termination time effects on chile plant development, we will record chile plant heights at 14-day intervals beginning at crop seeding and continuing to harvest. Chile plant densities in 4-m sections of row will be determined 28 days and 42 days after crop seeding. We will harvest fruits by hand from 4-m sections of crop row.Objective 2. Determine chile pepper profitability responses to barley and mustard cover crops that are seeded in fall, terminated in spring and subsequently incorporated into soil.We will use results from objective 1 to identify the cover crop-specific termination time that (1) does not cause large migrations of beet leafhoppers, (2) maximizes weed and disease suppression, and (3) supports vigorous development of chile pepper plants. The optimum termination times will be further assessed in a field study conducted at two university research farms (sites described above). Procedures for establishing and terminating cover crops, as well as procedures for growing chile pepper be identical to those in objective 1. The experimental design will be a randomized complete block design with four replications. Treatments will be factorial combinations of cover crop species (barley, mustard, barley-mustard mixture, no cover crop control) and the following two pesticide treatments: (1) no synthetic pesticides, and (2) a pre-emergence herbicide (napropamide) and a systemic fungicide (methoxyacetyl) applied following label guidelines. Experimental units (plots) will be 30 m long, four beds wide. We will conduct cost-benefit analyses separately for sites. Our general approach will be to integrate data from this study with expenditure and return estimates published in NMSU Crop Enterprise Budgets.

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.

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