Applied Research On Field Crop Disease Control 2005

Author: P.M. Phipps, Plant Pathologist, Tidewater Agricultural Research & Extension Center, Suffolk; Virginia Tech

Publication Number: 450-564, posted February 2006

ACKNOWLEDGMENTS

The author wishes to thank the Virginia Agricultural Experiment Station and the many cooperators and contributors who provided the resources needed for conducting this applied research program. Dr. Darcy Partridge, Post-doctoral Research Associate, joined our team in March 2005 and provided leadership in testing new transgenic lines of peanut for resistance to Sclerotinia blight. Dr. Partridge also provided professional help in making disease assessments in the field and presenting results during tours attended by growers, county agents, university faculty, workers in private industry, and commodity group leaders. Special recognition is extended to Barron Keeling, Steve Byrum and Ed Hobbs for technical skills to operate the Peanut/Cotton InfoNet, maintain four weather stations, manage 37 field trials, collect accurate records, process data, and help in preparing this report. The assistance of Dr. Benjy Cline at Virginia Tech in updating programs for the Peanut/Cotton InfoNet was greatly appreciated. Dr. Dave Walker also deserves recognition for running climatological models and issuing frost advisories for peanut on the Peanut/Cotton InfoNet. Carolyn Daughtrey, Brenda Kennedy, and Linda Harrell are recognized for assistance in stand counts, flower counts, growth measurements, and harvesting transgenic peanuts with a stationary picker. Dr. John Eisenback and Diane Reaver of the Department of Plant Pathology, Physiology & Weed Science contributed to this research by processing and identifying nematode populations in soil samples from cotton, soybean and peanut trials.

LIST OF COOPERATORS AND CONTRIBUTORS

Virginia Polytechnic Institute and State University, and Virginia Agricultural Experiment Station
Mr. R. D. Ashburn, Farm Manager, Tidewater Agricultural Research & Extension Center
Dr. Benjy Cline, Department of Entomology
Dr. Dennis L. Coker, Tidewater Agricultural Research & Extension Center
Dr. Jon D. Eisenback, Dept. of Plant Pathology, Physiology, and Weed Science
Dr. Joel Faircloth, Tidewater Agricultural Research & Extension Center
Dr. Elizabeth A. Grabau, Dept. of Plant Pathology, Physiology, and Weed Science
Dr. D. Ames Herbert, Jr., Tidewater Agricultural Research & Extension Center

Faculty at other Universities
Dr. Bill Branch, Peanut Breeder, Univ. Georgia
Dr. Dan Gorbet, Peanut Breeder, Univ. Florida
Dr. Tom Islieb, Peanut Breeder, NC State Univ.

County Extension Agents
Wes Alexander, Southampton, County, VA
Glenn F. Chappell, II, Prince George County, VA
Rex Cotten, City of Suffolk, VA
Glenn Rountree, Isle of Wight County, VA

Growers and/or land owners
Kenny Edwards, Branchville, VA .........................................Cotton test
M. L. Everett, Joyner, VA......................................................Weather station
Glenn H. Hawkins, Skippers, VA..........................................Weather station, Soybean test
Rick Morgan, Corapeake, NC................................................Cotton test
Glenn Chappell, Sr., Dinwiddie County ................................Soybean test

Commodity Groups and Organizations
Cotton Incorporated
Cotton Foundation, Seedling Disease and Nematode Control Committee
National Cottonseed Treatment Program
Virginia Cotton Board
Virginia Peanut Board
National Peanut Board
Virginia Agricultural Council
Virginia IPM Program

Private Companies
Amvac Chemical Corp, Newport Beach, CA
BASF Corp., Raleigh, NC
Bayer CropScience, Kansas City, MO
Birdsong Peanuts, Franklin, VA
Cerexagri, Inc., King of Prussia, PA
Crompton Crop Protection, Williamstown, N.J.
Sipcam Agro, Inc., Roswell, GA
Syngenta Crop Protection, Wilmington, DE
Tessenderlo Kerley, Inc., Eufaula, AL
Valent U.S.A. Corp., Cary, NC

POLICY FOR ACCEPTANCE OF PESTICIDES FOR TESTING

Research on synthesis and exploration of agricultural chemicals and biotechnology for use in pest control continues to provide new materials for field evaluation. Compounds are being made available by private companies and universities for local research in a variety of ways; ranging from a sample with a code number to a thoroughly-tested material, with secure patents, technical data sheets, and comprehensive resumes of results of laboratory and field trials. Unfortunately, it is not possible for a scientist to include all materials and use patterns in a field research demonstration program. Therefore, materials are selected according to (i) overall need for a product in a particular crop or problem area, and (ii) overall promise of the material to improve crop management at the local level.

Before a material can be accepted for testing, the following descriptive information is required: (i) a list of the spectrum of biological activity, (ii) data on phytotoxicity and suggested rates of application, (iii) methods of application, (iv) formulations available, (v) mammalian toxicity (LD50), (vi) possible health hazards, and (vii) possible hazards to the environment. Additional information that would be desirable includes: (i) identity of the active ingredient(s) and inert materials, (ii) physical properties (solubility, MP, VP, stability, etc.), (iii) residue information, (iv) residual soil life, (v) EPA residue tolerance (if any) and registration status, (vi) patent status, and (vii) unit cost in commercial markets.

Upon completion of field applications, it is the responsibility of the sponsor to dispose of all unused test materials. Because of limited space in controlled pesticide storage facilities and expenses associated with shipping and disposal, all sponsors are encouraged to ship not more than 1.5 times the anticipated quantity needed to complete a test.

INTRODUCTION

Rainfall in May and Oct was 0.95 and 2.22 in. above normal and in Apr, Jun, Jul, Aug, and Sep was 0.92, 1.61, 0.71, 1.25, and 1.38 in. below normal, respectively. Rainfall during the period totaled 28.25 in. which was 2.7 in. below normal (Appendix Tables 128, 129). Minimum air temperatures averaged near normal (±1°F) in Apr and May, 2°F above normal in Jun, 3°F above normal in Sep, 4°F above normal in Jul and Aug, and 6°F above normal in Oct. Maximum air temperatures were near normal (±1°F) in Apr, Jun and Oct, 2°F below normal in May, 3°F above normal in Aug, 4°F above normal in Jul and 5°F above normal in Sep according to records from a NOAA station at the Tidewater AREC in Suffolk (Appendix tables 126, 127). Cool temperatures and frequent rainfall in May slowed the speed of emergence in field crops. However, most crops were planted in a timely manner and showed good emergence by two to three weeks after planting throughout Eastern Virginia. Seasonal heat units for peanut from May 1 to October 31 totaled 2932 in Suffolk, which was well above the 2500 to 2600 needed for maturity (Table 1). Cotton degree-days (DD60) in the same period totaled 2297 which was 116 above the average for 1995 to 2004. As the harvest season approached, many fields exhibited normal maturity and good yield potential. No frost damage was observed in peanuts, since the first killing frost did not occur until the end of October.

Peanut yields in 2005 are projected to average 2900 lb/A (Table 2). Excesses of moisture in May were favorable for Cylindrocladium black rot (CBR), which was the most destructive disease of peanut in 2005 (Table 3). The second most damaging disease in peanut was northern root knot nematode. Early leaf spot and late leaf spot caused some defoliation in late September and early October, but the incidence of web blotch was generally low due to above normal temperatures from Jul through October. The incidence of tomato spotted wilt virus (TSWV) was considered low in 2005 and similar to levels seen in 2004. Southern stem rot appeared to be higher than in previous years, which may be attributed to warmer than normal temperatures in 2005. Certainly, the warmer temperatures helped in suppression of losses to Sclerotinia blight. Overall, the continued reduction in peanut acreage has resulted in many acres of peanut being planted at 4-year intervals after 3 years of cotton. This cropping system is likely to benefit peanut by reducing the incidence and severity of disease and yield losses caused by CBR, nematodes, leaf spots, and Sclerotinia blight.

Cotton yields in 2005 are projected to average 835 lb or 1.74 bales/A. Only a few diseases caused significant damage in cotton production. Rhizoctonia damping-off and other seedling diseases caused minor losses of stand and no impact on yield. Poor stands were often associated with soil compaction by heavy rainfall immediately after planting and/or planting seed too deep (deeper than 0.75 in.). The optimum depth of planting is usually 0.25 to 0.5 in. Crop damage by southern root-knot nematode, Meloidogyne incognita, accounted for the heaviest loss of yield in fields planted continuously to cotton for 5 years or longer. No significant losses to reniform nematode, Rotylenchulus reniformis, were detected in 2005. Instances of yield losses to stubby root were found, but overall were less destructive than southern root knot. Sting nematode continues to be highly damaging to cotton, but occurrences are usually confined to small portions of fields. As in previous years, the Columbia lance nematode was not detected in the region in 2005. Below normal rainfall in 2005 was thought to suppress development of hardlock in cotton since disease incidence was not observed to exceed one or only a few locules in up to 10% of open bolls.

Powdery mildew, Stagonospora leaf blotch, and tan spot were the most common diseases of wheat in southeastern Virginia. Leaf blotch and tan spot accounted for the greatest reductions of yield in the region. Stripe rust was widely scattered throughout southeastern Virginia, and only a few fields exhibited heavy disease pressure near the end of the growing season. Occurrences of scab on heads were minimal in 2005 and had little or no impact on yield.

Corn yields are forecast to be 124 bu/A or 22 bushels below the record set in 2000. Dry weather stress was likely the single most important factor that depressed yields in 2005. The widespread occurrence of stubby root nematode and isolated patches of sting nematode were thought to account for most of the yield losses to disease in corn. Stalk rots and foliar diseases caused minor damage in the Tidewater area in 2005.

The December forecast for soybean yield in 2005 was 29 bu/A with an expected harvest of 520,000 acres in Virginia. Nematodes were thought to have the greatest impact on yield of all soybean diseases in 2005 (Table 4). Soybean cyst, southern and northern root-knot and stubby root nematodes probably accounted for the greatest losses of yield. Frogeye leaf spot, anthracnose, and Cercospora blight appeared to be the most common foliar diseases of soybean. Frogeye leaf spot was the most aggressive and widespread during pod filling through the R5 stage of reproductive growth, but leaves appeared to be able to tolerate high numbers of lesions with minimal defoliation. Thereafter, Cercospora blight appeared to be the most aggressive disease in the final four weeks of the growing season. Laboratory examinations of more than 350 leaf samples of soybeans from June through October in eastern Virginia failed to detect soybean rust in 2005. In addition, several samples of Kudzu were examined and none exhibited soybean rust.

The research described in this book was designed to evaluate strategies for improving disease control and the overall efficiency of crop production in Virginia. Commercial products are named for informational purposes only. Virginia Cooperative Extension, Virginia Polytechnic Institute and State University, and Virginia State University do not advocate or warrant those products named nor do they intend or imply discrimination against those not named.

The primary purpose of this book is to provide a summary of research for cooperators and contributors in various projects. Nineteen chapters from this book have been prepared for publication by the American Phytopathological Society in Fungicide & Nematicide Tests, and Biological & Cultural Tests in 2006. Reprints of these publications are available upon request.

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