Barbara Shew

Research Assistant Professor and Extension Specialist

• B.S., Colorado State University
• M.S., (Plant Pathology), N. C. State University
• Ph.D., (Plant Pathology), N. C. State University

Research Interests

Program goal: reduce damage caused by peanut diseases through use of host resistance, fungicides applied according to disease advisories, and innovative cultural practices.

Host resistance

Planting disease resistant cultivars is the most valuable strategy for reducing or eliminating pesticide applications while maintaining crop health and yield. Although partial resistance has been found for several peanut pathogens, high levels of resistance to major diseases are not available in commercial cultivars.

We work closely with NCSU peanut breeder Dr. Tom Isleib to identify and characterize resistance to leaf spots, Sclerotinia blight, Cylindrocladium black rot, and other important diseases in advanced peanut breeding lines. We also work with Drs. Tom Stalker and Shyamlrau Tallury to identify useful sources of disease resistance in wild Arachis spp and in wild species-derived lines.

Disease advisories

Disease advisories are widely used in North Carolina and Virginia for timely application of fungicides for peanut disease control. Using a disease advisory can save one to three leaf spot sprays in a typical growing season compared to calendar-based sprays. Eliminating unnecessary leaf spot sprays also reduces the likelihood of spider mite outbreaks during dry periods.

Advisories are used to time fungicide applications for control of Sclerotinia blight. Currently, weather-based disease advisories assume that all cultivars are equally susceptible to disease. However, moderately resistant cultivars such as Perry and VA 98R, and new lines with higher levels of resistance, often need fewer fungicide applications than susceptible cultivars. Research is testing a new advisory developed by Dr. Damon Smith (former graduate student) that accounts for cultivar resistance.

We also have initiated studies to determine how leaf spot advisories should be adjusted for new leaf spot resistant lines. Improving delivery of advisories through the use of modeled or networked weather data is another program goal.

Cultural practices

Integrated management of peanut diseases
A multi-disciplinary, multi-state project with Drs. Gail Wilkerson (PI), David Jordan, Rick Brandenberg, and Ph.D. student Bridget Robinson seeks to develop integrated approaches to pest management, and to weigh pest control practices as they impact all aspects of crop health. Results of these studies are being used to develop an Internet based Peanut Risk Management tool for growers.

Weed infection and diversity of Sclerotinia minor

We have found that many annual weeds commonly found in peanut fields during winter fallow are hosts of Sclerotinia minor, causal agent of Sclerotinia blight. It is possible that fungal populations are maintained on these weeds in the absence of a cultivated host. In addition to harboring peanut pathogens, weed hosts may help to maintain diversity in field populations of S. minor and TSWV. Our aim is to gain a better understanding the diversity of populations of S. minor found in peanut production areas.

Organic production
There is growing demand for organic peanuts, but the potential for production of virginia-type peanut for the organic market has received little attention. We are investigating foliar disease management based on host resistance and application of approved fungicides. Stand establishment and seedling diseases have emerged as major impediments to organic production. Several biological agents and cultural methods are being investigated by graduate student Sarah Ruark for use in organic production systems.

Project Personnel

• Joyce Hollowell - Agricultural Research Specialist. Program support, biology of Sclerotinia minor

• Sarah Ruark – Graduate Student. Improving peanut seed and seedling health in organic production systems

• Damon Smith – Ph.D., 2007. Currently Assistant Professor, Department of Entomolgy and Plant Pathology, Oklahoma State University.

Cooperators

NC State University:

• Dr. Tom Isleib, Crop Science
• Dr. Tom Stalker, Crop Science
• Dr. David Jordan, Crop Science
• Dr. Shyamlrau Tallury, Crop Science
• Dr. Gail Wilkerson, Crop Science
• Dr. Ryan Boyles, State Climate Office

Herbert Green Agroecology:

• Dr. Mark Boudreau

Virginia Tech:

• Dr. Pat Phipps

Extension

As part of a team that includes Dr. David Jordan in Crop Science, Dr. Rick Brandenburg in Entomology, and county extension personnel, I have extension responsibilities for peanut diseases. We prepare educational materials, conduct field testing, and participate in grower meetings, demonstrations and field days. I also work with the North Carolina Plant Disease and Insect Clinic to diagnose peanut diseases.         

• 2007 Peanut Information
• Agricultural Chemicals Manual
• Peanut Risk Management
• Peanut Disease Information Notes
• Tomato Spotted Wilt Index
• Peanut Disease Advisories -click on this link to view today's weather based disease advisories.
• Peanut Scouting Manual - IPM Center
• Field Trial Reports (all .pdf files)
• Evaluation of Foliar Fungicides for the Control of Peanut Diseases in North Carolina, 2006
• Application time and sequence of fungicide treatments for controlling Sclerotinia blight of peanut, 2006
• Evaluation of Foliar Fungicides for the Control of Peanut Diseases in North Carolina, 2005
• Application time and sequence of fungicide treatments for controlling Sclerotinia blight of peanut, 2005

Teaching

PP 506 (Epidemiology and Disease Control): Offered annually in the spring. The class is co-taught with Drs. Mike Benson (coordinator; cultural practices, biocontrol) and Turner Sutton (fungicides). Lecture topics include disease progress curves and models of disease progress, disease assessment, spatial pattern of disease, sampling, disease gradients, design of epidemiological experiments, host resistance, and disease forecasting.

Recent Publications

• Isleib, T.G., P.W. Rice, S.C. Copeland, R.W. Mozingo II, J.B. Graber, B. Shew, D.L. Smith, H. Melouk, and H.T. Stalker. 2006. Registration of N96076L peanut germplasm. Crop Sci. 46: 2329
• Smith, D.L., J.E. Hollowell, T.G. Isleib, and B.B. Shew. 2006. Analysis of factors that influence the epidemiology of Sclerotinia minor on peanut. Plant Dis. 90:1425-1432.
• D.L. Smith, J.E. Hollowell, T.G. Isleib, and B.B. Shew. 2007. A Site-specific, Weather-based Disease Model for Sclerotinia blight of Peanut. Plant Disease (in press).
• J. E. Hollowell, T. G. Isleib, S. P. Tallury, S. C. Copeland, and B. B. Shew. 2007. Screening of Virginia-Type Peanut Breeding Lines for Resistance to Cylindrocladium Black Rot and Sclerotinia Blight in the Greenhouse. Peanut Science (in press).
• Hollowell, J.E. and B.B. Shew. 2005.  First Report of Sclerotinia minor on Allium vineale in North Carolina. Plant Dis. 89:908. Published on-line as DOI: 10.1094/PD-89-0908C.
• Hollowell, J.E. and B. B. Shew. 2005. First Report of Sclerotinia minor on Sida spinosa in North Carolina. Plant Dis. 89:1128. Published on-line as DOI: 10.1094/PD-89-1128A.
• Shew, B.B. and F.Waliyar. 2005. Peanut diseases, ecology and control. In: Encyclopedia of Pest Management, D. Pimentel (ed). Published on-line as DOI: 10.1081/E-EPM-120041160 
• Hollowell, J.E., B.B. Shew, M.A. Cubeta, and J.W. Wilcut. 2003. Weed species as hosts of Sclerotinia minor in peanut fields. Plant Disease 87:198-199.
• Hollowell, J.E., B.B. Shew, and T.G. Isleib. 2003. Evaluating isolate aggressiveness and host resistance from peanut leaflet inoculations with Sclerotinia minor. Plant Disease 87:402-406.
• Lemay, A.V., J.E. Bailey, and B.B. Shew. 2002. Resistance of peanut to Sclerotinia blight and the effect of acibenzolar‑S‑methyl and fluazinam on disease incidence. Plant Disease 86: 1315‑1317.
• Stalker, H.T., M.K. Beute, B.B. Shew, and K.R. Barker. 2002. Registration of two root-knot nematode-resistant peanut germplasm lines. Crop Sci. 42:312-313.
• Stalker, H. T., M. K. Beute, B. B. Shew, and T. G. Isleib. 2002. Registration of five leaf spot-resistant peanut germplasm lines. Crop Sci. 42:314-316.

Contact Information

Email: barbara_shew@ncsu.edu