Source: UNIVERSITY OF ARKANSAS submitted to
MANAGEMENT OF SOILBORNE PLANT PATHOGENS BY CULTURAL PRACTICES, HOST RESISTANCE AND DECISION AIDS FOR THE USE OF FUNGICIDES
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
TERMINATED
Funding Source
Reporting Frequency
Annual
Accession No.
0186088
Grant No.
(N/A)
Project No.
ARK01861
Proposal No.
(N/A)
Multistate No.
(N/A)
Program Code
(N/A)
Project Start Date
Oct 1, 2000
Project End Date
Sep 30, 2006
Grant Year
(N/A)
Project Director
Rothrock, C. S.
Recipient Organization
UNIVERSITY OF ARKANSAS
(N/A)
FAYETTEVILLE,AR 72703
Performing Department
PLANT PATHOLOGY
Non Technical Summary
This project is designed to elucidate factors that impact losses from soilborne pathogens on major row crops in Arkansas i.e. cotton, soybean, and rice including soil environmental factors, root exudates, and the use of cover crops. A decision aid for the use of in furrow fungicides will be developed and validated in grower fields. This research has the potential to reduce fungicide use and address new strategies to control important soilborne pathogens.
Animal Health Component
70%
Research Effort Categories
Basic
30%
Applied
70%
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
2162410116020%
2121710116020%
2162410102020%
2121710107010%
2124020110210%
2121530116010%
2121820116010%
Goals / Objectives
The proposed research emphasizes soilborne diseases of row crops because they are a major constraint to initial stand establishment and growth throughout the season. Objectives include. 1. Elucidating the role of abiotic factors, such as soil temperature, water, and oxygen, on pathogen survival and disease development. 2. Characterizing the role of exudates from plants on spore germination and growth of soilborne plant pathogens. 3. Developing a decision aid for the use of in furrow fungicides for the seedling disease complex on cotton. 4. Quantifying the impact of cover crops as green manures on pathogen survival and disease development. 5. Identifying and characterizing host resistance to select soilborne plant pathogens in soybean and cotton. The costs of registering fungicides, public environmental concerns, and the trend toward more sustainable production systems with fewer purchased inputs necessitate increased understanding of the ecology of these pathogens and managing diseases through more judicious use of fungicides and less disease conducive production systems. Results from these investigations will be integrated into pest management systems to minimize the risks of specific pathogens causing diseases and improving profitability and environmental quality.
Project Methods
This project is designed to elucidate critical factors that impact losses from soilborne pathogens on major row crops in Arkansas, including cotton Gossypium hirsutum, soybean Glycine max, and rice Oryza sativa. In many cases, these pathogens are widespread and have a wide host range and thus are common to many crops. However, control approaches differ depending on the crop and pathogen. The proposed research emphasizes soilborne diseases of row crops because they are a major constraint to initial stand establishment and growth throughout the season. The role of soil edaphic factors including water potential, oxygen diffusion rate, soil temperature, and illumination flux on soilborne diseases will be examined in controlled environmental and field studies. Studies will focus on early season diseases of cotton, soybean and rice. Controlled environmental studies will focus on Pythium root rot of soybean and rice and use pasteurized noninfested and artificially infested soils. Field studies with natural populations of pathogens also will examine the role of soil environmental factors on seedling diseases for cotton and soybean. The role of root exudates in susceptibility of soybean cultivars to Pythium species and role of exudates in germination and survival of T. basicola chlamydospores will be characterized. Numerous organic compounds found in root exudates, i.e. sugars, amino acids and vitamins, will be examined for their ability to stimulate germination of chlamydospores of T. basicola. The profile of exudates that stimulate spore germination will allow the selection of candidate nonhost plant species that may impact survival of the pathogen. The susceptibility of the soybean cultivars Hutcheson and Archer, as well as other cultivars characterized as flood tolerant, will be quantified in controlled environmental studies using artificially infested soils. Seed and root exudates will be characterized from cultivars which differ in susceptibility. The development of a decision aid for growers for the application of in furrow fungicides will be developed by collating and analyzing data that is available from fungicide evaluation tests from Arkansas. Validation of the model and decision aid will be conducted on grower fields. The ability of cover crops incorporated as green manures for the suppression of soilborne plant pathogens will be examined in new and established field studies. These studies will focus initially on the seedling disease complex of cotton. Winter cover crops will include hairy vetch and canola and Indian mustard selected specifically for high levels of glucosinolates. This research has the potential to address new strategies to control important soilborne pathogens of numerous crops. Other benefits include the characterization of the role of specific exudates in initiation of pre infection events for soilborne pathogens and examining the use of nonchemical control practices for the management of soilborne pathogens.

Progress 10/01/00 to 09/30/06

Outputs
The value of hopper-box (custom seed) and in-furrow fungicides was examined using cottonseed treated with standard fungicide seed treatments by assessing stand and yield response from over 100 replicated trials. These fungicides do not improve stand over the base fungicide seed treatment consistently and stand response is environmentally dependent indicating the use of these products should be targeted for when seedling disease pressure is greatest. Environmental factors that increased seedling disease pressure and thus warrant the use of additional fungicides are minimal soil temperatures below 20 C and to a lesser extent heavy rainfall the first few days after planting. Using data from the National Cottonseed Treatment Program from 1993-2004, a total of 214 trials, fungicides improved stand over the nontreated control 56% of the time. This indicates the value of fungicide seed treatments across the Cottonbelt. Seedling disease pressure was determined by comparing the stand for the nontreated control and the standard fungicide treatment. Stands were generally improved by 10% to 25% with the use of fungicides. Some of the more recent seed treatment fungicide changes have included the shift in control of Rhizoctonia solani from PCNB to Triazoles and Azoxystrobin. Treatments including these new chemistries have improved stands over PCNB when examining treatments over all sites and years. Research on the root-knot nematode/T. basicola interaction was examined over a range nocturnal temperatures. Plant height and fresh top weight increased with an increase in nocturnal temperatures. There were significant reductions in plant growth and development with T. basicola, but not M. incognita at these nocturnal temperatures, but decreases in plant height and weight was seen where both pathogens were present in comparison with either pathogen alone, indicating that the interaction between T. basicola and M. incognita occurs even at soil temperatures below the minimum temperature which has been reported as necessary for damage from M. incognita. Paired plots in growers' fields have found that areas of the field affected by this disease complex averaged 25% lower yields compared to nonaffected areas. Research on nematode/fungal pathogen interaction was expanded with work on the reniform nematode and T. basicola using paired plots in growers' fields. Yield reductions of 20% or more were found for areas of the field affected by this disease complex compared to nonaffected areas. One of the primary factors in stand establishment in Arkansas rice fields are seedling diseases caused by Pythium spp., which significantly reduce stands and growth of rice especially under cool soil temperatures. Rice genotypes with a range of reported cold tolerance were evaluated for susceptibility to Pythium spp. in the growth chamber and selected genotypes also were evaluated in the field to confirm their cold tolerance and Pythium resistance and validate the screening procedure. Only 8% of the genotypes screened had stand counts in the infested treatment comparable to or better than those of the resistant control, indicating at least moderate resistance.

Impacts
Data from a series of in-furrow and custom seed treatment fungicide tests on cotton have identified the environmental conditions when seedling diseases are severe enough to warrant fungicide applications and should increase profitability of cotton production through reducing unnecessary cash inputs while maintaining the sustainability of the production system. Data from a series of seed treatment tests validated the value of seed treatment fungicides for the control of seedling diseases on cotton and identified the most efficacious compounds and most important pathogens.There were significant reductions in plant growth and development with T. basicola, but not M. incognita at typical nocturnal temperatures at planting, but decreases in plant height and weight was seen where both pathogens were present in comparison with either pathogen alone. The interaction between T. basicola and M. incognita occurs even at soil temperatures below the minimum temperature which has been reported as necessary for damage from M. incognita. Seedling disease studies on rice have identified specific genotypes with cold tolerance and Pythium resistance holding the promise for more reliable stand establishment by controlling seedling diseases.

Publications

  • Monfort, W. S., Kirkpatrick, T. L., and Rothrock, C. S. 2006. Effects of nocturnal soil temperatures and Meloidogyne incognita densities on cotton seedling growth and the interaction with Thielaviopsis basicola. Plant Dis. 90:519-522.
  • Davis, R. M., Colyer, P., Rothrock, C. S., and Kochman, J. 2006. Fusarium wilt of cotton: Population diversity and implications for management. Plant Dis. 90:692-703.
  • Buchanan, M. L., and Rothrock, C. S. 2006. Value of the use of in-furrow fungicides for cotton. Page 65 in: Proceedings of the 2006 Beltwide Cotton Conferences http://www.cotton.org/beltwide/proceedings.
  • Winter, S. A., and Rothrock, C. S. 2006. Results from the national cottonseed treatment program for 2005. Pages 72-79 in: Proceedings of the 2006 Beltwide Cotton Conferences http://www.cotton.org/beltwide/proceedings.
  • Bates, G. D., and Rothrock, C. S. 2006. Efficacy of a high-glucosinolate Indian mustard cover crop for biofumigation of soil to control reniform nematode on cotton. Pages 135-139 in: Summaries of Arkansas Cotton Research 2005. D. M. Oosterhuis, ed. Arkansas Agricultural Experiment Station Research Series 543.


Progress 01/01/05 to 12/31/05

Outputs
The value of hopper-box (custom seed) and in-furrow fungicides was examined using cottonseed treated with standard fungicide seed treatments by assessing stand and yield response from over 100 replicated trials. In-furrow or hopper-box fungicides do not improve stand over the base fungicide seed treatment consistently and stand response is environmentally dependent indicating the use of these products should be targeted for when seedling disease pressure is greatest. Environmental factors that increased seedling disease pressure and thus warrant the use of additional fungicides are minimal soil temperatures below 20 C and to a lesser extent heavy rainfall the first few days after planting. Research on root-knot nematode/T. basicola interactions was examined over a range nocturnal temperatures typical of field conditions from 2001 to 2003. Plant height and fresh top weight increased with an increase in nocturnal temperatures. There were significant reductions in plant growth and development with T. basicola, but not M. incognita at these nocturnal temperatures, but decreases in plant height and weight was seen where both pathogens were present in comparison with either pathogen alone. Trends of increased disease associated with T. basicola were observed with increasing inoculum rates of M. incognita, indicating that the interaction between T. basicola and M. incognita occurs even at soil temperatures below the minimum temperature which has been reported as necessary for damage from M. incognita. Stand problems also cause significant production losses and management problems in Arkansas rice fields. One of the primary factors in stand establishment early are seedling diseases caused by Pythium spp., which significantly reduce stands and growth of rice especially under cool soil temperatures. Rice genotypes with a range of reported cold tolerance were evaluated for susceptibility to Pythium spp. in the growth chamber and selected genotypes also were evaluated in the field to confirm their cold tolerance and Pythium resistance and validate the screening procedure. Only 8% of the genotypes screened had stand counts in the infested treatment comparable to or better than those of the resistant control, indicating at least moderate resistance. Analyses of stand from 8 field sites in 2005 suggest stand for the untreated seed and the relative stand for the fungicide/untreated seed treatments support results from the controlled environmental studies, which is that cold-tolerant Pythium resistant cultivars have the greatest stands for the untreated seed and demonstrate little improvement with the use of fungicides.

Impacts
Data from a series of in-furrow fungicide tests on cotton have identified the environmental conditions when seedling diseases are severe enough to warrant fungicide applications. There were significant reductions in plant growth and development with T. basicola, but not M. incognita at typical nocturnal temperatures at planting, but decreases in plant height and weight was seen where both pathogens were present in comparison with either pathogen alone. The interaction between T. basicola and M. incognita occurs even at soil temperatures below the minimum temperature which has been reported as necessary for damage from M. incognita. Seedling disease studies on rice have identified specific genotypes with cold tolerance and Pythium resistance holding the promise for more reliable stand establishment by controlling seedling diseases.

Publications

  • Monfort, W. S., Kirkpatrick, T. L., and Rothrock, C. S. 2006. Effects of nocturnal soil temperatures and Meloidogyne incognita densities on cotton seedling growth and the interaction with Thielaviopsis basicola. Plant Disease (In press).
  • Schulz, M. L., and Rothrock, C. S. 2005. Role of field history in developing a decision-aid for the use of in-furrow fungicides. Page 146 in: Proceedings of the 2005 Beltwide Cotton Conferences http://www.cotton.org/beltwide/proceedings.
  • Rothrock, C. S., Winters, S. A. 2005. Report of the cottonseed treatment committee for 2004. Pages 249-256 in: Proceedings of the 2005 Beltwide Cotton Conferences http://www.cotton.org/beltwide/proceedings.
  • Schulz, M., Rothrock, C., Colyer, P., Gbur, E., and Kirkpatrick, T. 2005. The importance of soil conduciveness, cropping history and edaphic factors on cotton seedling diseases. Phytopathology 95:S94.
  • Rothrock, C. S., and Winter, S. A. 2005. The value of fungicide seed treatments and seed treatment chemistries for cotton stand establishment:Twelve years of results from the cotton disease council's national cottonseed treatment trials. Page 118 in: Proceedings of the 2005 Beltwide Cotton Conferences http://www.cotton.org/beltwide/proceedings.
  • Monfort, W. S., Kirkpatrick, T. L., and Rothrock, C. S. 2005. Effects of increasing Meloidogyne incognita densities on the interaction with Thielaviopsis basicola under early-season environmental conditions. Pages 210-216 in: Summaries of Arkansas Cotton Research 2004. D. M. Oosterhuis, ed. Arkansas Agricultural Experiment Station Research Series 533.
  • Rothrock, C. S., Sealy, R. L., Lee, F. N., Anders, M. M. and Cartwright, R. D. 2005. Reaction of cold-tolerant adapted rice genotypes to seedling disease caused by Pythium species. Pages 120-124 in: Rice Research Studies 2004. R. J. Norman, J. F. Meullenet, and K. A. K. Moldenhauer, eds. Arkansas Agricultural Experiment Station Research Series 529.


Progress 01/01/04 to 12/30/04

Outputs
Fungicides are now universally sold on cottonseed to control a number of seed-borne and soilborne fungi that affect the germination of seed and the emergence, survival and vigor of seedlings. By using a series of experiments in the National Cottonseed Treatment Program organized by the Cotton Disease Council, the value of fungicide seed treatments, improvements in seed treatments, and the value of hopper-box (custom seed) and in-furrow applications versus seed treatments were examined. The National Cottonseed Treatment Program has 15 to 20 trials annually in which industry nominates a number of seed treatment combinations for evaluation. A standard fungicide treatment, Vitavax-PCNB + Allegiance, and a nontreated control are included to assess efficacy of the nominations and seedling disease pressure. In addition, the fungicide treatments Allegiance or PCNB are included to aid in determining the importance of Pythium spp. or Rhizoctonia solani, respectively. Disease ratings and pathogen isolations for seedlings and soil populations of selected soilborne fungi are conducted by collecting seedlings and soil from the nontreated control plots at each location. Soil temperature and water data also are collected for the sites. From 1993-2004, a total of 214 trials were conducted by cooperators, with fungicides improving stand over the nontreated control in 120 trials or 56% of the time. This indicates the value of fungicide seed treatments across the Cottonbelt. For states with a response, fungicides improved stand in 17% to 80% of the trials in those states. Seedling disease pressure was determined by comparing the stand for the nontreated control and the standard fungicide treatment. Stands were generally improved by 10% to 25% with the use of fungicides. The fungicides and fungicide combinations used for treating cottonseed are constantly changing as new chemistries become available and with a greater understanding of disease causing agents. Some of the more recent changes have included the shift in control of Rhizoctonia solani from PCNB to Triazoles (Baytan, Nu-Flow M, and Systhane) and Azoxystrobin (Dynasty and Protege). Treatments including these new chemistries have improved stands over PCNB when examining treatments over all sites and years, confirming that advances are being made in controlling this pathogen. These tests have also given us information on seedling diseases of cotton. Isolation of Thielaviopsis basicola, Rhizoctonia solani and Pythium species was correlated with their soil populations. Hypocotyl disease severity was correlated with Rhiozctonia solani and Thielaviopsis basicola isolation and root disease severity with Thielaviopsis basicola isolation. In-furrow or hopper-box fungicides do not improve stand over the base fungicide seed treatment as consistently as the seed treatment and stand response is environmentally dependent indicating the use of these products should be targeted for when seedling disease pressure is greatest.

Impacts
Data from a series of seed treatment tests validated the value of seed treatment fungicides for the control of seedling diseases on cotton and identified the most efficacious compounds and most important pathogens.

Publications

  • Monfort, W. S, Kirkpatrick, T. L. and Rothrock, C. S. 2004. Effects of nocturnal soil temperatures and Meloidogyne incognita densities on cotton seedling growth and the interaction with Thielaviopsis basicola. Phytopathology 94: (6) S72.
  • Rothrock, C. S., Schulz, M. L., Colyer, P. D., Gbur, E. E., and Kirkpatrick, T. L. 2004. Value of environmental factors in predicting cotton seedling desease severity. Phytopathology 94: (6) S89.
  • Monfort, S. Rothrock, C., Mauromoustakos, A. and Kirkpatrick, T. 2004. Potential usefulness of newly available statisticial methods for modeling Meloidogyne incognita, Thielaviopsis basicola and influential soil factors on yield. Page 354 in: Proceedings of the Beltwide Cotton Conferences. http://www.cotton.org/beltwide/proceedings.
  • Gomaa, N. M., Rothrock, C. S. 2004. Influence of different environmental conditions on the epidemiology of the cotton seedling disease complex. Page 369 in: Proceedings of the Beltwide Cotton Conferences. http://www.cotton.org/beltwide/proceedings.
  • Rothrock, C. S., Schulz, M. L., Gbur, E. E., Kirkpatrick, T. L., and Colyer, P. D. 2004. Developing a decision-aid for the use of in-furrow fungicides. Page 327 in: Proceedings of the Beltwide Cotton Conferences. http://www.cotton.org/beltwide/proceedings.
  • Williams, K. R., Kirkpatrick, T.and Rothrock, C. 2004. Vapam (Sodium methyldithiocarbamate) and Telone II (1,3-dichloropropene) for control of root-knot nematode (Meloidogyne incognita) in cotton in Ashley County, Arkansas, Page 386-388 In: Proceedings of the Beltwide Cotton Conferences. http://www.cotton.org/beltwide/proceedings.
  • Rothrock, C. S., Monfort, W. S., Kirkpatrick, T. L., and Williams, K. R. 2004. Losses associated with the reniform nematode and black root rot in producers fields in 2003. Page 411 In: Proceedings of the Beltwide Cotton Conferences. http://www.cotton.org/beltwide/proceedings.
  • Rothrock, C. S., and Winters, S. A. 2004. Report of the National Cottonseed Treatment Committee for 2003. Pages 452-458 In: Proceedings of the Beltwide Cotton Conferences. http://www.cotton.org/beltwide/proceedings.
  • Rothrock, C. S., Monfort, W. S., Kirkpatrick, T. L., and Williams, K. R. 2004. Interaction between the reniform nematode and Thielaviopsis basicola on cotton. Pages 187-189 in: Summaries of Arkansas Cotton Research 2003. D. M. Oosterhuis, ed. Arkansas Agricultural Experiment Station Research Series 521.


Progress 01/01/03 to 12/31/03

Outputs
Seedling diseases are one of the major constraints to stand establishment in cotton. Growers frequently are faced with the decision of whether to spend additional cash for in-furrow fungicides to provide additional protection against seedling pathogens. In-furrow fungicides are a significant cash input, $10-$15 per acre, and are applied as insurance against possible greater cash inputs in replanting or losses in yield. A decision-aid is being developed using existing research and environmental data. In 2002 and 2003, six sites were located in growers' fields each year, with additional sites on the Delta Branch Experiment Station. From the results, it is clear that seedling diseases occur over all environments, however, they are most important as temperature decreases. Rainfall did increase disease but this was less important than soil temperature at planting. The model for the 98 studies in the data base from Arkansas and Louisiana indicate that environment, soil temperature and rainfall, can be used to predict whether in-furrow fungicides are good insurance or whether the grower should save his money. The model indicated that below a minimal temperature at planting of about 60oF in-furrow fungicides consistently increased stands. Rainfall had a more complex response on stand, with fields having little or no rainfall or heavy rainfall (>2 inches) after planting increasing the likelihood of in-furrow fungicides improving stands. The decision-aid developed will; 1)help producers make planting decisions to increase the likelihood of a uniform stand, and 2) provide assistance for the economic use of in-furrow and hopper-box fungicides. A synergistic interaction between Thielaviopsis basicola, the fungus that causes black root rot, and the root-knot nematode (Meloidogyne incognita), which causes root galling, has been demonstrated on cotton which expands the range of temperatures at which disease symptoms are expressed and increases the severity of disease. Research on nematode/fungal pathogen interaction was expanded with work on the reniform nematode and T. basicola in 2003 using paired plots in growers' fields. Yield reductions of 20% or more were found for areas of the field affected by this disease complex compared to nonaffected areas. GPS is being used to examine the distribution of cotton pathogens in the field as related to yield, fertility, and texture.

Impacts
The goal of research on these pathogens and developing a decision-aid for the use of in-furrow fungicides to control the seedling disease complex is to increase profitability of cotton production through reducing unnecessary cash inputs while maintaining the sustainability of the production system.

Publications

  • Rothrock, C. S., Kirkpatrick, T. L., Walker, N. R., and Monfort W. S. 2003. Estimating yield losses associated with the interaction between Thielaviopsis basicola and the root-knot nematode on cotton. Proceedings of the 3rd World Cotton Research Conference.
  • Rothrock, C. S., Kirkpatrick. T. L., Williams, K. R., and Winters, S. A. 2003 Importance of the interaction between Thielaviopsis basicola and Meloidogyne incognita on cotton. Proceedings of the 8th International Congress of Plant Pathology 2:330.
  • Rothrock, C. S., and Winters, S. A. 2003. Report of the National Cottonseed Treatment Committee for 2002. Proceedings of the Beltwide Cotton Conferences.
  • Gomaa, N. M., and Rothrock, C. S. 2003. Changes in colonization of cotton by the cotton seedling disease complex pathogens Rhizoctonia solani, Pythium spp., and Thielaviopsis basicola over time and soil environmental conditions. Page 239 in: Proceedings of the Beltwide Cotton Conferences.
  • Williams, K. R., Kirkpatrick, T., and Rothrock, C. 2003. Telone II (1,3-dichloropropene) vs. Vapam (sodium methyldithiocarbamate) for control of root knot nematode (Meloidogyne incognita) in cotton in Ashley County, Arkansas. Pages 279-281 in: Proceedings of the Beltwide Cotton Conferences.


Progress 01/01/02 to 12/31/02

Outputs
Research effort has focused on the characterization of soilborne pathogens and pathogen distribution and prevalence as it relates to seedling diseases on cotton and other crops. Several tests in 2002 examined the time of infection of cotton by seedling disease pathogens and the influence of the environment on colonization. Rhizoctonia solani and Pythium spp. infected cottonseed within 24 hours of planting. Thielaviopsis basicola was not isolated until four days after planting and then increased dramatically with time after planting. R. solani colonization was favored by drier than wetter soils. T. basicola isolation was favored by wetter than drier soils. The effect of treatment response on isolation of seedling disease pathogens from plants was greatest within four days of planting. A synergistic interaction between T. basicola, the fungus that causes black root rot, and the root-knot nematode (Meloidogyne incognita), which causes root galling, has been demonstrated on cotton in cooperation with Dr. T. Kirkpatrick. This interaction expands the range of temperatures at which disease symptoms are expressed and increases the severity of disease. Paired plots in growers' fields have found that areas of the field affected by this disease complex averaged 25% lower yields compared to nonaffected areas. Now that the widespread occurrence of these pathogens has been determined and potential yield losses quantified, strategies to manage these pathogens are being investigated. In 2002, Vapam and Telone II were used in strips to examine the ability of these treatments to control one or both pathogens. Telone II was also examined in a field using GPS to examine distribution of each pathogen in the field as related to yield, fertility, and texture. Recent research has concentrated on developing decision-aids for the application of in-furrow fungicides to help growers determine if spending additional cash for in-furrow fungicides will provide additional protection against seedling diseases and increase yields. Currently approximately 50 field studies/sites have been placed in the database for the decision-aid. The database will help define the conditions under which a response was found with the use of in-furrow fungicides for parameters such as soil temperature, soil water, and weather forecast. Six validation trials were established in growers' fields in three counties in 2002. In three of these six studies, stand was improved by the use of in-furrow fungicides. These stand improvements occurred in drier soils, near field capacity.

Impacts
The widespread occurrence of Thielaviopsis basicola and the root-knot nematode (Meloidogyne incognita) has been demonstrated along with the potential yield losses from their interaction. Fumigation is being examined to reduce losses from this interaction. The goal of research on these pathogens and developing a decision-aid for the use of in-furrow fungicides to control the seedling disease complex is to increase profitability of cotton production through reducing unnecessary cash inputs, while maintaining the sustainability of the production system.

Publications

  • Wrather, J. A., Phipps, B., and Rothrock, C. S. 2002. Fungi associated with postemergence cotton seedling disease in Missouri. Online. Plant Health Progress doi:10.1094/PHP-2002-0722-01-RS.
  • Gomaa, N. G. and Rothrock, C. S. 2002. Influence of time of planting on the isolation frequency of Pythium spp., Thielaviopsis basicola and Rhizoctonia solani on cotton. Phytopathology 92:S30.
  • Rothrock, C. S. 2002. Report of the Cottonseed Treatment Committee for 2001. Proceedings of the Beltwide Cotton Conferences.
  • Rothrock, C. S., and Kirkpatrick, T. L. 2002. Estimating the importance of the interactions between Thielaviopsis basicola and the root-knot nematode on cotton using paired plots in growers' fields. Proceedings of the Beltwide Cotton Conferences.
  • Rothrock, C. S., Kirkpatrick, T. L., and Williams, K. R. 2002. Prevalence of Thielaviopsis basicola in Arkansas; association with abiotic and biotic soil factors. Proceedings of the Beltwide Cotton Conferences.


Progress 01/01/01 to 12/31/01

Outputs
A synergistic interaction between Thielaviopsis basicola, the fungus that causes black root rot, and the root-knot nematode (Meloidogyne incognita), which causes root galling, has been demonstrated on cotton which expands the range of temperatures at which disease symptoms are expressed and increases the severity of disease. To examine the importance of this disease complex a total of 455 cotton fields (558 samples) in Ashley County, Arkansas were sampled in the fall for fertility, nematode, and fungal analyses to determine the prevalence of Thielaviopsis basicola and Meloidogyne incognita and their association with one another and soil fertility factors. Thielaviopsis basicola was detected in 75% of these cotton fields, 32% of fields had over 100 propagules per gram of soil. Meloidogyne incognita was detected in 54% of these cotton fields. From this extensive sampling, it was found that as the population of Thielaviopsis basicola increased, population of the root-knot nematode also increased, increasing the likelihood that the disease complex will be important. Paired plots in growers' fields have found that areas of the field affected by this disease complex averaged 25% lower yields compared to nonaffected areas. Recent research has concentrated on developing decision-aids for the application of in-furrow fungicides to help growers determine if spending additional cash for in-furrow fungicides will provide additional protection against seedling diseases and increase yields. Currently 36 field studies/sites have been placed in the database for the decision-aid. Of these 36 sites, 8 sites had stand responses as a result of the use of in-furrow fungicides. The database will help define the conditions under which a response was found with the use of in-furrow fungicides for parameters such as soil temperature, soil water, and weather forecast. A series of validation trials are being established in growers' fields in three counties in 2002 to help growers use in-furrow fungicides efficiently and refine the decision-aid.

Impacts
Now that the widespread occurrence of Thielaviopsis basicola and the root-knot nematode (Meloidogyne incognita) has been determined and potential yield losses quantified, strategies to manage these pathogens are being investigated. The goal of research on these pathogens and developing a decision-aid for the use of in-furrow fungicides to control the seedling disease complex is to increase profitability of cotton production through reducing unnecessary cash inputs while maintaining the sustainability of the production system.

Publications

  • Kirkpatrick, T. L. and Rothrock, C. S. (eds.). 2001. Compendium of Cotton Diseases, 2nd edition. APS Press.
  • Rothrock, C. S. 2001. Rhizoctonia solani. Pages 15-16 In: Compendium of Cotton Diseases, 2nd edition. T. L. Kirkpatrick and C. S. Rothrock, eds. APS Press.
  • DeVay, J. E., and Rothrock, C. S. 2001. Control of Seedling diseases. Pages 19-20 In: Compendium of Cotton Diseases, 2nd edition. T. L. Kirkpatrick and C. S. Rothrock, eds. APS Press.
  • Rothrock, C. S., and Kirkpatrick, T. L. 2001. Bronze wilt. Page 56 In: Compendium of Cotton Diseases, 2nd edition. T. L. Kirkpatrick and C. S. Rothrock, eds. APS Press.
  • Rothrock, C. S. 2001. Report of the Cottonseed Treatment Committee for 2000. Pages 89-93 In: 2001 Beltwide Cotton Production Conferences. National Cotton Council, Memphis.
  • Rothrock, C. S., Sealy, R. L., Kluepfel, D. A., and Yan, Z. 2001. Association of Agrobacterium tumefaciens with cottonseed. Page 116 In: 2001 Beltwide Cotton Production Conferences. National Cotton Council, Memphis.
  • Rothrock, C. S., Winters, S. A., Bonnoua S. and Nehl D. B. 2001. Role of host exudates in the development of black root rot. Page 130 In: 2001 Beltwide Cotton Production Conferences. National Cotton Council, Memphis.