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Commercial Horticulture > Comm Hort Blog > Posts > Challenges to Cowpea Curculio Management in Alabama

Cowpeas or southern peas (Vigna unguiculata) are a popular vegetable crop in the southern U.S. due to its high heat tolerance and rapid growth. In Alabama, southern peas frequently get a multitude of insect pests that include chewing insects such as the cowpea curculio and caterpillars (various species), and sucking insect pests like stink bugs, leaffooted bugs, aphids, and thrips. Currently, conventional insecticides and cultural control practices used by producers are helpful to manage a majority of the listed pests, except the cowpea curculio (Chalcodermus aeneus Boheman, Fig. 1). Cowpea curculio is notorious for its resistance or tolerance to popular insecticides, such as the synthetic pyrethroids. Entomologists at the University of Georgia have been studying the cowpea curculio for many years, but the challenge continues. Crop damage from the curculio and other pests can quickly reduce yields by 50% or more if pests are not controlled in a timely manner. This article focuses on a review of literature and results from two years of cowpea curculio management studies completed by the Commercial Horticulture Extension team. This article provides some preliminary information about integrated pest management (IPM) strategies. Mention of product names and companies does not mean endorsement. Insecticide product names have been mentioned as examples only; producers should check insecticide labels and compare products. The Southeastern U.S. Vegetable Crop Handbook is a key resource for producers in Alabama and it is available in various formats. An educational video summarizing cowpea curculio information from Alabama along with links to other resources is available as a ‘Learning Module’ on Alabama Vegetable IPM website.   

cowpea curculio 2015-fig1.JPG 

 
Curculio life cycle: There are several useful Extension publications on cowpea curculio biology from the University of Georgia (Extension Circular 1038) and the University of Florida (Publication EENY-223). This insect overwinters in the adult stage and begins emerging in April or May depending on the availability of suitable host plants. Adults are known to feed on cowpeas, snap beans, lima beans, and peas along with weedy hosts such as evening primrose, moss verbena, wild bean and sicklepod among others. Adults are known to infest cowpeas and weeds simultaneously. Adults feed directly on various plant parts and cause the most damage to the pods with chewing mouthparts. Females create small feeding holes on pods and lay eggs inside the pod which protects the larval stages. One pod can have numerous feeding holes or stings with numerous eggs hatching into larvae – this may result in high crop damage and contamination even at low population levels. The larvae are pale yellow and legless since they spend all their time feeding and living inside the pea pods. After completing four larval instars, larvae drop to the ground and develop a pupal cell. Adult curculios emerge after 10 days of pupation.
 
Key identification characters: Adults are very active in the morning and evening hours – they avoid the hot afternoons and may drop to the base of the plant for shade. Adults are black oval, very similar in shape to the cotton boll weevil and plum curculio. There are numerous Adults feed directly on various plant parts and their chewing mouthparts cause the most damage to the pods. Adults feign death when approached making it challenging to scout. Adult emergence (first generation) can be sudden with a second generation that develops in a month – this creates tremendous pest pressure in the southern pea-producing areas of Alabama.  
 
Curculio behavior: Adults prefer to walk from plant to plant and spread rapidly through the field. There can be an edge-effect where curculios may be first seen on field edges. Due to their feigning behavior, crop scouts must look at the bottom of the plant for true insect counts. Adults can fly and appear to be able to infest new production areas (as seen in Alabama where curculios are spreading westward).
 
Scouting and monitoring: Direct crop scouting at weekly intervals or sooner during production season is the best way to estimate population levels. Scout and keep a record of curculio populations before and after insecticide applications to document successes and challenges. Entomologists at the University of Georgia have developed a yellow pyramid trap that looks similar to and functions like the plum curculio trap (modified Tedder’s trap). The pyramid trap was effective in the first detection of cowpea curculios in South Georgia.  During production season, it is a good idea to check southern pea plants directly along with weeds (e.g., sicklepod) along the field edges. Use of a white beat sheet at the plant base and shaking plants may also be an effective way for scouting for adults. Scouting may become challenging if aphids and other sucking pests make the plants sticky. Caterpillars also feed directly on peas and leave small round holes on developing pods. Keep a record of all insect pests seen in the field and consult with a regional Extension agent for developing a site-specific IPM plan. Scouting accuracy improves with sampling size.
 
Lessons from insecticide test plots: Results reported herein should be considered preliminary as our studies are ongoing. In Alabama, the cowpea curculio seems to be most damaging south of Interstate 85 where most of the southern peas are grown and winters are warmer than northern parts of the state. It may take several years for curculio populations to develop in a new production area, so remember to rotate crops and avoid monoculture with the same variety of southern peas. The first year of our small plot tests at the Wiregrass Research and Extension Center (Headland, AL, 2014) was challenged by the sudden detection of a large number of curculios in this new field. In 2015, we observed a more gradual emergence of adults with two overlapping generations. Five foliar insecticides were evaluated in an attempt to prevent pod damage with early treatments. All insecticides were applied five times using a back-pack sprayer. Test materials included a new insecticide premix (Besiege), synthetic pyrethroid (bifenthrin), synergist (PBO-8), microbial insecticide (Botanigard), and a tank-mix (Botanigard + bifenthrin). Untreated check plots did not receive any insecticide applications. Test plots with southern pea variety Elite were scouted once every week and pod samples were collected for assessing external and internal pod damage. Weekly insecticide applications in July (at flowering stage) appeared to delay curculio establishment with the greatest benefit accrued from several bifenthrin and synergist applications (Fig. 2). Microbial insecticides may be effective in suppressing adults (Fig.2) but are slow acting and require complete plant coverage with routine spray.
curculio counts headland 2015 -fig2.jpg 
 
Seed damage assessments suggested a sudden increase in pod feeding in 7 days as a result of control failure. An average of 40 feeding holes or stings on pods was associated with 86% internal seed damage in the test plots (Fig.3). Since larval feeding inside the seed is difficult to control with insecticides, adult curculios appear to be the only target to prevent crop losses. Repeated insecticide applications in test plots controlled most of the other chewing and sucking insect pests, except aphids (results not shown). Insecticide tests in Georgia have suggested significant reduction in stings on Purple Hull and Cream Eight with Besiege and cyfluthrin (Baythroid) after nine applications. Cowpea curculio research in Alabama will continue to expand with collaborative input from producers and researchers.   
 
 curculio seed damage headland 2015 - fig3.jpg  
 
Overall IPM recommendations: Here are some IPM suggestions based on field experiences and research data available from Alabama and Georgia. Producers should keep in touch with Extension agents for latest IPM information. A cowpea curculio management video is available on the IPM website.
·    Plant southern peas carefully in relation to other crops. White Acres pea variety seems to be more resistant to curculio than Pinkeye Purple Hull (UGA observation).
·    Fall tillage and field sanitation may be helpful to slow down population buildup (pupae live in soil), although we have not evaluated these methods in Alabama. Keep weeds under check at all times.
·    Start insecticide treatments ahead of pod formation, preferably targeting the first generation of adults. Apply insecticides frequently at 3-5 day intervals, depending on the insecticide label.
·    Addition of synergist (at the high rate) with synthetic pyrethroid insecticides may improve control. Watch for spider mite outbreaks that can be induced by pyrethroids.
·    Don’t quit spraying too soon – second and overlapping generations of curculios can be devastating to the maturing crop.
·    Avoid overusing insecticides – it is not good for the environment and not good for your farm. Check the insecticide label and follow the recommendations since label is the law.
 
Alabama Extension IPM resources:
·    Cowpea curculio IPM video:  http://www.aces.edu/anr/ipm/Vegetable/cowpeacurculio.php
·    Cowpea curculio PowerPoint presentation:  http://goo.gl/WCrnuK
·    Alternative Vegetable IPM Slide Chart for small producers: https://store.aces.edu/itemdetail.aspx?ProductID=18412
·    Facebook page:  Alabama Vegetable IPM
·    Alabama IPM Communicator e-newsletter:  www.aces.edu/ipmcommunicator
·    2015 Southeastern U.S. Vegetable Crop Handbook:  http://goo.gl/RL8BkI    (remember to download newest version)
 
References:
·    Riley, D. G. 2014. Cowpea curculio in southern pea. University of Georgia Extension. Circular 1038.
·    Riley, D., and J. Kicklighter. 2012. Cowpea curculio management in southern peas and snap beans.
·    Capinera, J. L. 2009. Cowpea curculio. University of Florida. Publication number EENY-223.
·    Griffin, R. P. and J. Williamson. 2009. Bean and southern pea insect pests. Clemson Cooperative Extension. Publication number HGIC 2201.
 
Ayanava Majumdar, Ext. Entomologist
Neil Kelly, Regional Ext. Agent
Larry Well, Director, Wiregrass Research and Ext. Center

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