We are determining the real-world potential and limitations of two promising techniques for reducing hand hoeing costs and decreasing incidences of soil-borne disease in chile pepper (herein “chile”). Specifically, our previous studies indicated that: (1) weed densities and hoeing times in chile were reduced by stale seedbeds implemented during the summer prior to chile planting, and (2) soil-borne diseases were less prevalent when a Brassicaceae cover crop (BCC) or mustard seed meal (MSM) was amended to soil. In this project, we hypothesize that fallow season stale seedbeds and BCC can be combined to produce a single, integrated tactic for improved pest management in chile production. Further, we hypothesize that MSM applications after crop emergence do not reduce chile fruit yield, and therefore, post-emergence applications of MSM are non-herbicidal methods for controlling mid-season weeds in chile. To test our first hypothesis, we are conducting field studies to determine the effects of stale seedbeds, with and without BCC, on the management and severity of weeds and soil-borne diseases in chile. Field study results are being used in economic analyses that evaluate the costs of stale seedbeds and BCC relative to the economic gains in subsequent chile production. To test our second hypothesis, we are conducting greenhouse studies to evaluate crop safety of different MSM application strategies, and field studies to determine chile fruit yield responses to post-emergence applications of MSM. These studies are necessary because prior to this project, there was little technical guidance for MSM applications after crop emergence. Rain prevented implementation of fallow-season stale seedbeds at some study sites, but results from one site suggest that a BCC is not compatible with fallow-season stale seedbeds because these late-summer stale seedbeds do not provide sufficient time for BCC growth before frost. Additional results indicated that a BCC has potential to suppress weeds in chile; however, this weed suppressive potential is not fully realized because of a lack of knowledge on best management practices for the BCC. Most notably, farmers growing a BCC must consider the possibilities for the BCC to harbor insects that are damaging to chile. Results from MSM studies indicated that post-emergence applications of MSM must be incorporated in soil, do not cause visual injury on chile, do not reduce chile fruit yield and provide pre-emergence control of weeds. Our educational outreach program is ongoing; however, early results suggest success and farmer adoption of the some tactics. As a result of our outreach, we are expecting that farmers and agricultural professionals will understand the benefits and limitations of fallow season stale seedbeds, Brassicaceae cover crops and post-emergence applications of mustard seed meal.
- Through on-farm research, determine the effects of fallow-season stale seedbeds with and without a Brassicaceae cover crop on chile production factors including incidence of soil-borne disease, weed infestation severity, weed management requirements, weed seedbank density, and chile yield.
- Develop safe and effective strategies for using mustard seed meal to control mid-season weeds in chile pepper.
- Communicate the potential and limitations of fallow season stale seedbeds, Brassicaceae cover crops and mustard seed meal for weed and disease control in chile pepper.
- Under real-world conditions, fallow-season stale seedbeds and Brassicaceae cover crops can be combined to reduce incidence of soil-borne disease and weed infestation severity in chile pepper.
- Under real-world conditions, a Brassicaceae cover crop improves pest management programs for chile pepper by inhibiting weeds and reducing incidence of soil-borne disease.
- Mustard seed meal applications after chile pepper emergence provide pre-emergence control of weeds but do not cause either crop injury or reductions in crop yield.
In 2018-19, we conducted two replicated field experiments on three farms in southern New Mexico. We also conducted a non-replicated, on-farm field experiment. For these experiments, farmers contributed to the development of strategies that (1) addressed their specific weed and disease problems, and (2) considered the constraints of their farm operation. Also in 2018-19, we conducted a series of greenhouse experiments that guided our field studies, and we conducted replicated field experiments at university research farms. Research farm experiments contributed to our understanding of Brassicaceae biofumigation and served as focal points for educational activities during university field days in summer 2019.
On-farm, Replicated Experiment 1. Brassicaceae cover crop effects on weeds and disease in chile pepper. A Brassicaceae cover crop (herein abbreviated “BCC”) mixture of Caliente ‘Rojo’ (Brassica juncea cv ‘rojo’) and arugula (Eruca sativa) was seeded at farms near Columbus, NM (31°47.649’ N, 107°51.483’ W); Deming, NM (32°14.714’ N, 107°51.464’ W); and Las Uvas, NM (32°35.317’ N, 107°22.008’ W). The nearest two study sites were separated by 52 linear km (32 miles). The BCC was seeded following preparatory procedures that included discing, and at Columbus shaping raised beds. The BCC was seeded at approximately 8 kg ha-1 (6 to 9 lb acre-1) on September 29, 2018 at Deming; November 10, 2018 at Columbus; and October 29, 2018 at Las Uvas. After seeding, fields were irrigated as needed with subsurface drip.
The BCC was compared against bare ground, and a site-specific cover crop alternative. The three treatments (BCC, bare ground, site-specific alternative) were arranged in a randomized complete block design with three replications. Cover crop alternatives included barley (Hordeum vulgare) at Las Uvas and Columbus, BCC with wheat (Triticum aestivum) at Deming.
In addition to on-farm study sites, this experiment included a study site at a university research farm near Las Cruces, NM (NMSU Leyendecker Plant Science Research Center; 32° 12.131′ N, 106° 44.771′ W; herein “Leyendecker”). At this site, BCC and bare ground plots were arranged in a randomized complete block design with three replications. BCC was seeded at Leyendecker on October 11, 2018.
At each site, data on weed biomass, BCC biomass and BCC glucosinolate content were collected at cover crop termination. Cover crops were terminated on February 22, 2019 at Deming; February 14, 2019 at Columbus; March 5, 2019 at Las Uvas; March 15, 2019 at Leyendecker. Additional data on cover crop effects on weeds and soil-borne diseases were collected during the 2019 chile pepper growing season. Measurements of BCC effects on weeds included, but were not limited to, the survival and germinability of Palmer amaranth seeds buried in soil immediately after BCC termination.
Implementation costs for BCC were determined with New Mexico State University Crop Enterprise Budgets (http://costsandreturns.nmsu.edu) and in consultation with participating farmers. We intended to assess benefits derived from BCC by considering BCC effects on hand-hoeing and chile pepper fruit yield. However, results indicated that the BCC did not affect hand hoeing costs or chile pepper fruit yield.
On-farm, Replicated Experiment 2. Mustard seed meal for control of mid-season weeds in chile pepper. Farmers participating in this study expressed interest in side-dress applications of mustard seed meal (herein abbreviated “MSM”) during middle phases of the chile pepper growing season. However, prior to this project, there was little technical guidance for MSM applications after crop emergence. To address this knowledge gap, we conducted: 1) a series of greenhouse experiments that determined optimal application methods for post-emergence applications of MSM in chile pepper, and 2) field experiments to evaluate the potential for crop injury and yield loss from post-emergence applications of MSM.
Greenhouse experiments. The objective of the first greenhouse experiment was to determine the effects of soil-surface MSM applications (without incorporation) on chile plants at different stages of development. Treatments were factorial combination of MSM rate (0, 2200, and 4400 kg ha-1) and stages of chile plant development (germination, 2-leaf, 4-leaf, and 6-leaf stage). Treatments were arranged on a greenhouse bench in a randomized complete block design with four replications. Experimental units were pots containing field soil (Belen silt loam) and chile seeds buried to the 2-cm depth. Chile stage treatments were initiated at different times so that all MSM was applied on one day. Response variables included, but were not limited to, dry weights of chile plant aboveground biomass at 21 days after MSM application.
The objective of the second greenhouse experiment was to determine whether incorporating MSM in soil protects chile plants from MSM-induced injury. Treatments were factorial combination of MSM rate (0, 2200, and 4400 kg ha-1) and MSM location (MSM buried, MSM on soil surface). Experimental units were plastic bins with field soil containing a single row of chile plants. At the time of application, chile plants had 6 to 8 leaves — equivalent to the developmental stage when chile pepper crop is typically thinned. MSM-induced injury was assessed with response variables including repeated measured of chile plant photosynthesis, as well as plant fresh weight, dry weight, height and leaf area at 14 days after MSM application.
Field experiment. This experiment was conducted at collaborator farms near Deming, NM and Las Uvas, NM, as well as university research farms including Leyendecker and the NMSU Agricultural Science Center at Los Lunas, NM (herein “Los Lunas”). At each site, two MSM rates (4400 kg ha-1, 2200 kg ha-1) were each applied to four plots paired with non-treated control plots. At the time of application, chile plants were 36 to 42 cm tall. Based on insights obtained from our greenhouse studies, MSM was applied and incorporated in soil between neighboring chile rows (Figure 1). Immediately following MSM incorporation, all plots were watered by hand with sprinkling canisters. The irrigation volume was 15 L plot-1, which was sufficient to saturate the upper 3 cm of soil.
To ensure that the MSM rates were sufficient for weed control, we measured weed responses to MSM with two response variables: 1) ambient weed emergence from 0.25 m2 quadrats centrally located in study plots, and 2) Palmer amaranth emergence from PVC pipes positioned in study plots after MSM application, but prior to irrigation. Each PVC pipe contained 50 Palmer amaranth seeds buried 1-3 cm from the soil surface. Response variables also included visual assessments of MSM injury to chile at 14 and 28 days after application, as well as chile pepper yield.
On-farm, Non-replicated Experiment. A fallow-season stale seedbed was implemented at the farm near Las Uvas, NM. Unseasonal rain precluded fallow-season stale seedbeds at the farms near Columbus, NM and Deming, NM. The fallow-season stale seedbed was initiated with a sequence of preparatory procedures that included tilling, laser leveling, listing and shaping raised beds into rows. Raised beds were irrigated on September 17, 2018. Weed seedlings were identified to species and counted on October 1, 2018. Weed seedlings were terminated with a broad-spectrum herbicide (glyphosate) on October 9, 2018. On October 29, 2018; cover crops were seeded following procedures described above please see (“On-farm, Replicated Experiment 1”).
On-farm, Replicated Experiment 1. Brassicaceae cover crop effects on weeds and disease in chile pepper.
BCC establishment differed among study sites. In early December 2018, BCC stands were robust at Deming (106 ± 5 BCC plants m-2, 85 ± s.e. 1.6 % cover) and Leyendecker (241 ± 14 plants m-2, 89 ± s.e. 2.1 % cover), moderately robust at Columbus (85 ± 14 plants m-2, 50 ± 6.7 % cover) and weak at Las Uvas (85 ± 14 plants m-2, < 5% cover; all data are means ± standard errors).
Site-to-site differences in BCC stand vigor in December persisted to spring. For three sites (Columbus, Deming and Leyendecker), BCC aboveground biomass at termination ranged from 463 to 597 g m-2 (Table 1), which was comparable to published reports of BCC biomass in other regions of the US (Weed Science 53:695-701; Agronomy Journal 108:151–161; Agronomy Journal 107:1235–1249), but less than maximum levels of BCC biomass reported in the SARE publication “Managing Cover Crops Profitably, 3rd edition” (approximately 900 g m-2). At Columbus, BCC biomass at termination was greater than the biomass for the site-specific alternative (barley), and at Deming BCC biomass was equivalent to the biomass of the site-specific alternative (BCC with wheat).
Low biomass for BCC at Las Uvas was caused by a frost shortly after seeding. This frost was not entirely unexpected considering the typical time for first frost at Las Uvas (Table 1). Although disappointing, the Las Uvas results indicate the need to seed BCC well before the expected first frost. Because BCC seeding at Las Uvas was delayed by the stale seedbed operation, Las Uvas results suggest that late-summer stale seedbeds do not provide sufficient time for BCC seeding.
In general, BCCs at termination suppressed winter weeds (Table 1) and contained sinigrin — its primary pesticidal compound — at concentrations consistent with previous reports (Table 2). At sites where BCC established (Columbus, Deming, Leyendecker), incorporated BCC residues reduced the number of Palmer amaranth seeds in soil (Figure 2). Palmer amaranth seeds that persisted in BCC residue were less germinable than seeds retrieved from soil without the BCC, suggesting that BCC residues induced secondary dormancy in Palmer amaranth seeds.
At Columbus, the effects of BCC on weeds and disease in chile was not determined because all chile plants were intentionally terminated shortly after emergence. Chile seedlings were terminated because the farmer collaborator determined that the stand was not sufficient for strong yield, which was consistent with statewide reports of relatively few acres of chile in excellent condition (Figure 3). The farmer collaborator did not attribute poor chile performance to a specific cover crop, as demonstrated by the termination of chile across the entire field. Following chile termination, the field at Columbus was seeded in cotton that was managed conventionally. For this cotton crop, early season weeds and soil-borne diseases were not affected by cover crop treatment.
At Deming, cover crop treatment did not affect the following variables in the chile pepper growing season: chile stand density at 3 weeks after emergence; weed densities at 3, 6, and 9 weeks after chile emergence; hoe times at 3, 6, and 9 weeks after chile emergence; disease incidence at 13, 15, and 16 weeks after emergence; and chile fruit yield collected at 19 weeks after chile emergence. Similarly, weed densities, hoe times, or disease incidence were not affected by cover crop treatment at Las Uvas.
Although the BCC did not affect the response variables considered in this study, BCC may still have influenced chile pepper production. The farmer collaborator in Deming indicated that the BCC likely harbored insects that were damaging to the chile crop. Most notably, the farmer collaborator suspects that beet leafhoppers (Circulifer tenellus) in BCC persisted after cover crop termination and transmitted a curtovirus to cause curly top disease in chile. Such an occurrence would be consistent with previous research indicating that Brassicaceae plants in the U.S. Southwest are hosts for both beat leafhoppers and the beet curly top virus (Southwestern Entomologist 28:117-182; Plant Disease 89:480-486). In our study, we were not able to detect BCC-induced curly top in chile because the viral disease, which is transmitted by leaf hoppers, was prevalent across the entire field and not confined to BCC plots. However, additional data collected supports the farmer’s hypothesis. Specifically, at 16 weeks after emergence in the BCC field, chile stand density (8.6 plants 10-m row-1) was lower and more variable (coefficient of variation, 53.6%) than chile stand density in a nearby field that did not follow a BCC (16 plants 10-m row-1; coefficient of variation, 13.4%). Further, the farmer collaborator indicated that the chile pepper yield in the BCC field was 40% lower than nearby chile pepper fields without the BCC.
Initial economic analyses indicated that the cost of growing and terminating the BCC ranged from $104 to $158 acre-1. This was considerably more expensive than cover crop production costs presented in the SARE Technical Bulletin “Cover Crop Cover Crop Economics: Opportunities to Improve Your Bottom Line in Row Crops.” In this study, the maximum cost for cover crop production occurred at Columbus where the cost for BCC termination was $121 acre-1. The high cost for BCC termination at Columbus was caused by the sequence of tillage operations needed to terminate BCC on raised beds. At Deming, where BCC was not grown on raised beds, the cost for BCC termination and subsequent soil preparation for chile was $51 acre-1. These results reveal the difficulty in terminating the BCC on raised beds.
Lessons to date from the on-farm study investigating BCC for weed and disease suppression in chile pepper:
- A BCC mixture of Caliente ‘Rojo’ (Brassica juncea cv ‘rojo’) and arugula (Eruca sativa) has the potential to suppress weeds in chile; however, this weed suppressive potential might not be fully realized because of a lack of knowledge on best management practices for the BCC.
- A BCC should be seeded several weeks before the expected date for first frost. This means that a BCC may not be compatible with stale seedbeds performed in late summer or early fall.
- A BCC on raised beds is difficult and expensive to terminate. Growing a BCC on flat ground is recommended.
- Farmers growing a BCC must consider the possibilities for these cover crops to harbor insects that are damaging to chile pepper.
We are currently writing an extension article that presents these lessons and their underlying data. We have also initiated experiments to clarify BCC management practices that minimize risk of insect damage to chile pepper crops.
On-farm, Replicated Experiment 2. Mustard seed meal for control of mid-season weeds in chile pepper.
Greenhouse experiments. Results from the first greenhouse experiment indicated that chile plants from the 2-leaf to 6-leaf stages were severely injured by MSM applications to the soil surface (Figure 4). Ninety-two percent of the 2-to-6-leaf stage plants were terminated by MSM at 4400 kg ha-1. MSM at 2200 kg ha-1 killed 67% of chile plants from the 2-leaf to 6-leaf stages. Severe crop injury from MSM without incorporation was consistent with previous research that determined the biofumigation properties of MSM were attributed to volatile compounds that are toxic to many plant species.
Results from the second greenhouse study indicated that MSM injury on chile was reduced or eliminated by incorporating MSM in soil. Specifically, greenhouse study results indicated that MSM at 4400 kg ha-1 on the soil surface caused lasting reductions in chile plant photosynthesis; but, photosynthetic rates recovered from initial injury when MSM at 4400 kg ha-1 was buried (Figure 5). For MSM at 2200 kg ha-1, surface applications initially reduced photosynthesis, whereas buried applications generally did not affect photosynthetic rates in chile plants. Reductions in photosynthesis caused by MSM on the soil surface resulted in diminished plants at 14 days after application (Figure 6). Together, the greenhouse experiments indicated that burying MSM protects chile plants from damage that can occur from post-emergence applications of MSM. We applied this knowledge to our field study where we evaluated the potential for crop injury and yield loss from post-emergence applications of MSM.
Field experiment. Post-emergence applications of MSM provided varying degrees of weed control, with weed control generally higher for MSM at 4400 kg ha-1 (Table 3) compared to MSM at 2200 kg ha-1 (Table 4). For both rates and at all sites, post-emergence applications of MSM did not cause visual injury and did not reduce chile pepper yield (Table 3,Table 4). These results are promising because (1) this represents one of the first reports of safe, effective application of MSM after crop emergence, (2) if not controlled, weeds that emerge during the middle phases of the chile pepper season severely reduce both yield and harvest efficiency, and (3) farmer collaborators on this project specifically asked us (i.e., researchers) to develop a strategy for applying MSM after chile pepper emergence. We are currently writing an extension and scientific articles that present the information from this experiment on post-emergence applications of mustard seed meal.
On-farm, Non-replicated Experiment. The fallow-season stale seedbed successfully reduced seedbanks of weed species that hinder chile pepper production at the farm near Las Uvas. Most notably, the stale seedbed initiated by irrigation on September 17 caused considerable emergence of black nightshade (Solanum americanum) — a summer annual species that is the primary weed management challenge at this study site. Species-specific plant densities at 22 days after irrigation were as follows (mean ± standard error): black nightshade, 395 ± 31 plants m-2; yellow nutsedge (Cyperus esculentus), 9 ± 2 plants m-2; common lambsquarters (Chenopodium album), 2 ± 1 plants m-2; spurred anoda (Anoda cristata), 1 ± 1 plants m-2; morningglory species (Ipomoea spp.), 1 ± 1 plants m-2; pigweed species (Amaranthus spp.), 1 ± 1 plants m-2; yellow woodsorrel (Oxalis stricta), 1 ± 1 plants m-2. Emerged weeds were terminated prior to flowering. Thus, emerged weeds represent reductions in weed pressure for chile pepper grown in 2019, especially for resident weed species with annual lifecycles (black nightshade, common lambsquarters, spurred anoda, pigweed and morningglory species, yellow woodsorrel). The farmer was pleased with the initial results of the fallow-season stale seedbed and plans to use the tactic again in the future.
Changes in awareness and knowledge are determined at field days and stakeholder meetings. This is done with anonymous, written, pre-then-post-tests. Post-tests also contain questions regarding the probability of implementing or recommending fallow-season stale seedbeds and/or Brassicaceae biofumigation techniques. Test format and language will closely follow the “Western Region Sustainable Agriculture Research & Education Program Outreach Survey” provided on the Western SARE website (https://wsaregrants.usu.edu/grants/docs/AppendE.pdf).
Educational & Outreach Activities
Project concepts were presented to farmers and agricultural professionals at the 2018 Sustainable Agriculture Field Day held at the NMSU Leyendecker Plant Science Research Center in June 2018. The presentation included demonstration plots showing mustard seed meal effects on weeds in chile pepper.
Project concepts and early results were presented at a public open house hosted by the NMSU College of Agricultural, Consumer and Environmental Sciences in April 2019. Early results were also presented at the 2019 Sustainable Agriculture Field Day held at the NMSU Fabian Garcia Science Center. This presentation featured a lecture and poster (Figure 7) presentation. This poster was also presented at a field day held at the NMSU Agricultural Science Center at Los Lunas in August 2019. The field day at Los Lunas also featured a field tour, handout (Figure 8), and a request for additional farmer collaborators. Seven farmers provided contact information and expressed interest in hosting on-farm evaluations of MSM as a pest management tool for chile pepper. Attendance at field days ranged from 55 to 75 people.
Of all field day events, the most comprehensive program on Brassicaceae biofumigation was presented at the 2019 Sustainable Agriculture Field Day. Surveys indicated that, prior to this field day program, 68% of attendees had a poor understanding of Brassicaceae cover crops, 11% had a good understanding of BCC and 0% had an excellent understanding of BCC. After the field day program, 47% had a good understanding of BCC and 42% had an excellent understanding of BCC. Unfortunately, field day attendees did not provide information on their likelihood of adopting or recommending BCC.
Outreach activities scheduled for 2020 include field days for which demonstration plots have already been initiated. In addition, we will develop and distribute print and electronic materials presenting principles and practices of MSM and BCC biofumigation for chile pepper production in New Mexico, and we will give presentations at grower group meetings including the New Mexico Chile Conference in February 2020.
Results have been shared with the scientific community through an abstract and poster presentation at the 2019 annual meeting of the American Society of Agronomy, the Crop Science Society of America, and the Soil Science Society of America. Additional results will be presented through a poster and presentation at the joint annual meeting of the Weed Science Society of American and the Western Society of Weed Science in March 2020.
- Benefits and drawbacks for Brassicaceae cover crops, mustard seed meal soil amendments and fallow-season stale seedbeds for chile pepper production in New Mexico
Educational activities are ongoing. At this time, farmers have indicated increased knowledge on the limits and potential for Brassicaceae cover crops, mustard seed meal and fallow-season stale seedbeds.
Personal conversations indicated farmer adoption of fallow-season stale seedbeds.