Cowpea, Vigna unguiculata Walp., is an important source of protein and vitamins that is widely grown in the Southern U.S primarily for fresh market consumption and freezing. Cowpea is very attractive to honey bees and other bee species and this has in part been attributed to its nectariferous nature. Bees are an important component of productivity and sustainable agroecosystem. Currently, bee populations are in decline ostensibly due to loss in habitats (which results in reduction in floral resources and nesting sites) as well as the use of pesticides especially neonicotinoids. One of the project objectives is to identify cowpea cultivars with resistance to pests and diseases, high pollinator activity and good nodulation efficiency. From our results the most common pollinators recorded on cowpeas were honey bees, carpenter and bumble bees. During the five-week sampling period, 57% of the pollinators recorded were honey bees followed by bumble bees (30%). Bee populations varied among the different cowpea varieties and over time. Dixielee, Penny Riley, Whippoorwill Steel Black, Whippoorwill and CT Pink eye Purple Hull were the most attractive cowpea varieties to pollinators. Iron and Clay, Tohono O’odham and Red Bisbee recorded the least number of pollinators. Brown marmorated stink bug (BMSB) populations were highest in Dixielee, Penny Riley, Whippoorwill Steel Black, Whippoorwill, Mayo Colima and CT Pink eye Purple Hull the same varieties attracted to pollinators. Carrapichio, California Blackeye #5, Cream 40, Iron and Caly, Lady, Purple hull Bigboy, running Conch, and Tohono O’odham recorded the least BMSB.
The overall goal of the proposed study is to increase crop production and sustainability through intercropping cowpea cultivars that are highly attractive to pollinators while at the same time resistant to insect pests and diseases in a vegetable cropping system. These cultivars would also increase soil health by their ability to nodulate with the existing rhizobia. The project goal will be met by the following three objectives that systematically address the problem the project seeks to solve.
Objective 1. Identify cowpea cultivars with resistance to pests and diseases (including nematodes), high pollinator activity and good nodulation efficiency.
Objective 2. Evaluate the effect of two best cowpea cultivars with pest and disease resistance, high nodulation and high pollinator attractiveness (from objective #1) on overall yield of vegetable crops in two cropping systems with/without cowpea (mono and intercropping).
Objective 3. Assess system profitability from Best Production Practices (BPPs) used in objective #2 by growers through collaborative farmer-managed on-farm demonstration.
Objective 1. Identify cowpea cultivars for resistance to pests and diseases and pollinator activity and nodulation efficiency. Experimental plots were established at the NC A&T research farm, Greensboro, NC. Twenty-four cowpea varieties were grown, each treatment was planted in 2 rows, each 5 m long with 1m inter-row spacing and replicated 4 times in a Randomized Complete Block Design (RCBD). No insecticide and fertilizer were applied.
Evaluation of pollinators using pan trap: Pollinators were sampled within each treatment using pan traps. Traps were made from 16oz. squat polypropylene deli bowls painted with UV-bright fluorescent blue or yellow paint and unpainted 12oz. white styrofoam bowls. The bowls were individually glued onto a 36” plant prop using adhesive and one of each color bowl were placed between the 2 rows within each cowpea variety during the sampling period. Each bowl was filled with approximately 250mL of soapy water solution (2.5mL of detergent in 1-gallon water). Traps were set out early in the morning (8:00 -10:00 am) and collected after 24 hours weekly for 5 weeks. Traps were collected in the order they were placed to ensure that all traps were available to insects for the same amount of time. After 24 hours each pan trap was removed and drained and content removed and placed into vials containing 70% ethanol and stored for later identification.
Evaluation of pollinators using sticky trap: For all treatments, sticky traps (Sticky Strips, Olson Products, Medina, OH 44358; 15-by-15-cm yellow cardboard sticky-coated on both surfaces) were impaled on plant stakes and placed between the two 5m rows. Traps were left exposed for 24 hours. Samples were collected weekly for five weeks.
Visual observation of pollinators and brown marmorated stink bug: For each cowpea variety, the two 5m rows were observed for 2 minutes each for pollinators (bees, carpenter bees, bumble bees, and lepidoptera) and brown marmorated stinkbug. Observations were conducted weekly for five weeks and data was recorded on the number of pollinators and BMSB.
Evaluation of nodulation efficiency: Two plants from each cowpea variety were dug up at flowering and placed in bags after the loose soil was carefully shaken off and labelled as needed. These were transported to the laboratory and assessed for fresh weight, nodule count and viability (by opening 5 nodules/plant).
Determination of chlorophyll content in situ: Chlorophyll readings were taken weekly using a chlorophyll meter (Konica SPAD-502Plus). For each cowpea treatment, five random plants were selected and measurements taken from one leaf (highest) of each plant. This method was chosen since height varied among the cowpea varieties. Individual SPAD readings were averaged for each treatment. Data was collected weekly for five weeks.
Evaluation of agronomic performance: At the fresh pod stage, twenty five fresh pods were harvested from each cowpea variety and weighed. The pods were opened, seeds counted and separated into damaged and undamaged seeds. The number of damaged and undamaged seeds were recorded. At the dry pod stage, twenty five dry pods were randomly selected from each cowpea variety and weighed. The pods were opened and seeds counted and separated into damaged and undamaged seeds and recorded.
From visual observations, honey bees, carpenter bees and bumble bees and wasps were noticeable pollinators on the research plots. Overall, during the five weeks sampling period, more honey bees were observed followed by bumble bees (Fig. 1).
During the first three weeks of visual sampling, there was a steady increase in the total number of pollinators observed followed by a decline (Fig. 2). This increase can be attributed to the presence of more honey bees observed during this time compared to the other pollinators (Fig. 2). Later in the season, the population of honey bees declined but carpenter bee and wasp populations were on the increase (Fig. 2).
More honey bees were observed during the first week and our data during this sampling period show most of the honey bees (21, 22 and 25) were recorded on Early Scarlet, Dixielee and CT pinkeye purple Hull cowpeas respectively (Fig. 3).
In the second week honey bees were still the major pollinator observed in the presence of some bumble bees and a few carpenter bees (Fig. 4). The distribution of honey bees varied among the twenty-four cowpea varieties with >30 honey bees observed on Mississippi Silver, whippoorwill Steel Black and whippoorwill; >40 observed on Perking black and Rouge et noir; >60 on CT Pinkeye purple Hull and Dixielee (Fig. 4).
In week three more honey bees and bumble bees were observed on most of the cowpea varieties except for Red Bisbee which had no bumble bees. Most of the pollinators were observed on CT Pinkeye purple Hull, Dixielee, Penny Rile and Whippoorwill, Whippoorwill Steel Black (Fig. 5).
In week four and five, the population of bumble bees observed had declined and that of carpenter bees and wasps had increased with more pollinators observed on CT Pinkeye purple Hull, Penny Rile and Whippoorwill and Iron and Clay, Red Bisbee and Tohono O’odham recording the least pollinators (Figs. 6 and 7). Results from sticky cards indicate that the number of pollinators was highest during the third week of sampling, similar to results from visual observations.
The number of brown marmorated stink bug (BMSB) observed on the twenty-four cowpea varieties was different among the varieties with the least BMSB observed on Carrapichio, California Black Eye5, Cream 40, Iron and Clay, Lady, Running Conch, Purple Hull Bigboy and Tohono O’odham (Fig. 8). More BMSB were observed on CT Pinkeye purple Hull, Whippoorwill and Dixielee (Fig. 8) the same varieties on which more pollinators were observed.
During the five weeks of visual observations, the number of brown marmorated stink bug varied over the weeks and among the varieties (Figs. 9-13).
A number of cowpea cultivars were efficient at producing a large number of nodules with ingenious rhizobia (Mixed Iron and Clay, Rouge et noir, Carrapichio and Whippoorwill) and low mean number of nodule were recorded in Black Crowder, Running Conch, CT Pinkeye Purple Hull and Early Scarlet (Fig. 14).
Our results indicate that the chlorophyll content was not different among the different cowpea cultivar (Table 1). Results from yield data indicate that most of the cowpea varieties produced more pods except Iron and Clay and Tohono O’odham which were vegetative throughout the season. The least fresh pod weight was recorded for Cream 40, Lady and Penny Rile (Table 2). From the fresh seeds, Big boy had the most (51%)damaged fresh seeds and Whippoorwill had the least (27%) damaged dry seeds (Table 2).
|Table 1. Chlorophyll content (SPAD Units) of 24 cowpea varieties|
|Varieties||Mean (±SE) Chlorophyll content|
|Week 1||Week 2||Week 3||Week 4||Week 5||Mean|
|Big Boy||57.3 ±1.7||61.5±1.5||66.1±1.7||67.8±1.5||63.5±1.8||63.2±1.8|
|Big red ripper||53.8 ±1.7||58.4±2.0||64.4±1.6||58.9±1.5||60.3±1.6||59.1±1.7|
|Black crowder||56.3± 2.8||60.2±1.5||62.9±1.4||64.5±1.6||63.3±1.6||61.4±1.5|
|CT Pinkeye Purple Hull||65.7±1.2||65.1±2.1||68.8±1.1||69.5±1.6||67.1±1.2||67.2±0.9|
|Iron & clay||50.2±2.2||61.3±1.3||61.4±1.6||58.0±1.5||62.7±1.3||58.7±2.3|
|Peking black||56.4 ±1.5||60.6±1.1||64.0±1.6||65.4±1.3||61.3±1.2||61.5±1.5|
|Purple hull Bigboy||60.8±1.6||58.7±1.4||66.9±1.3||65.5±1.0||66.8±1.9||63.7±1.7|
|Rouge et nior||62.1±1.0||60.4±1.2||66.8±1.0||64.5±1.5||60.9±1.4||62.9±1.2|
|Tohono O’odham||56.0 ±1.5||60.3±1.0||58.8±1.6||56.0±1.6||56.5±1.4||57.5±0.9|
|Vietnamese black||55.6 ±1.7||64.3±1.3||63.2±2.1||63.9±1.3||63.0±1.7||62.0±1.6|
|Whippoorwill Steel Black||55.4 ±1.3||57.6±2.2||62.6±1.5||63.7±1.3||65.0±2.1||60.9±1.6|
|Zipper cream||60.4 ±2.6||62.0±1.2||69.6±1.0||63.7±1.2||62.3±1.5||63.6±1.2|
Table 2. Fresh and dry seed yield and percentage damage of 24 cowpea varieties
|Varieties||Fresh pod Weight (g)||Dry pod Weight (g)||% Fresh seed damaged||% Fresh seed undamaged||% Dry seed damaged||% Dry seed undamaged|
|Big Red Ripper||261.5||61.3||26.6||73.4||58.4||41.6|
|CT Pinkeye Purple Hull||184.8||41.8||19.3||80.7||66.8||33.2|
|Iron & Clay||Vegetative||Vegetative||Vegetative||Vegetative||Vegetative||Vegetative|
|Purple Hull Big boy||208.4||46.8||33.4||66.6||71.7||28.3|
|Rouge et Noir||292.1||46.1||29.7||70.3||64.4||35.6|
|Whippoorwill Steel Black||125.1||43.3||31.9||68.1||27.3||72.7|
Educational & Outreach Activities
Presentation of our findings for this first year will be presented at the next Entomological Society of America meeting. Demonstration plots (companion cropping of cowpea and cucurbits/other crops) will be setup during the Small farm day with the hypothesis that inclusion of cowpeas in a mixed vegetable cropping system will increase pollinator and beneficial arthropod activity as well as soil (N) health, crop yield and farm profitability. During this second year of the project participating farmers will be intercropping selected cowpea varieties (based on results from year one) with other vegetable crops they grow (mostly cucurbits).
N/A for this reporting period.