Technical Summary: 

Plant-parasitic nematodes are a serious economic threat to cotton production in Mississippi.  The two major species are the root-knot nematode and more recently the reniform nematode These two nematodes have been found in over 34 % of the Mississippi cotton producing acreage. Disease loss studies have estimated that these two nematodes reduce Mississippi cotton yields by 22 % annually in infested soils. Specific symptoms are not always associated with these nematodes therefore intensive soil sampling is required to accurately detect these pests. No cotton varieties with resistance to these nematodes are available to our producers, therefore the application of nematicides are the most frequently utilized means of nematode management.  The spatial distribution of plant-parasitic nematodes is in a scattered pattern across an infested field. Areas exist in the field where no there are no nematodes present. Other areas of the field may seem uniformly infested with the nematode but the population levels will vary. This is an ideal situation for site-specific applications of nematicides using variable rate technology. The objectives of this study are to compare conventional uniform field applications of nematicides to site specific applications for nematode management in a cotton production system. Another factor that must be examined will be the optimum grid sampling size to best represent the spatial distribution of plant-parasitic nematodes in the field. It is anticipated that the results from this study will show that a cotton producer can take a portion of the soil sampled for fertility or other precision agricultural practices and develop nematode contour maps that will be representative of the nematode distribution in the field. Nematicide prescription maps can then be created to target nematode numbers unique for a specific field situation. Variable rate applications will reduced the total amount of pesticides that are applied thus optimizing nematicide use to target locations resulting in a savings to the cotton grower without loss in cotton yields. 

Objectives: 

Objectives from original proposal - 2001: 

1. Determine the appropriate grid size when sampling nematodes for use with variable rate nematicide applications.

2. Examine the utility of nematode distribution data sets for variable rate nematicide applications.

Objectives for 2002 proposal:

1. Determine if the grid sampling size currently used in Mississippi precision agriculture is on a scale accurate enough to determine nematodes spatial distribution for use in variable rate nematicide applications.

2.  Evaluate conventional nematicide applications with variable rate applications for nematode management in Mississippi cotton production.

Procedures:

Objective 1: Cotton fields naturally infested with the reniform or root-knot nematodes will be selected for the study. Large plots will be established by dividing the field into 25  acre blocks. Each block will be mapped and georeferenced on 10, 7.5, 5, and 1 acre subplots. Four additional randomly chosen 1 acre subplots will be further subdivided and plotted on 1/2, 1/4, 1/16 and 1/64 acre  grids. Nematode samples will be collected at each grid intersect. Four, 2.5-cm dia. X 20-cm deep soil cores will be collected from an area within 3 feet of each reference point. Nematodes will be separate from the soil using the gravity screening and sucrose centrifugation techniques. Data will be subjected to analysis for spatial dependence and for the sampling design using the appropriate analysis. Results from this part of the study will determine the best grid sample size to most accurately determine the spatial distribution of the nematode. Results will also help determine the most accurate pixel size or resolution from aerial images when used in nematode number estimations.  

Objective 2: Variable rate technology for nematicide application will be employed in cotton fields naturally infested with the reniform nematode. Nematode contour maps will be generated from nematode counts collected from georeferenced sample points. Nematicide prescription maps will then be developed with the range of nematode numbers and taking into account  current nematode damage thresholds. Variable rates and conventional technologies will be compared for nematicide applications for nematode management.  Plot size will consist of 12 rows,  spaced 38 inches apart that run the length of the field. Plots will be arranged in a complete randomized design with five replications.  Treatments will consist of either variable rate nematicide applications or conventional single rate applications.   Measured biological data including nematode populations, plant stress, soil analysis and yields will be combined in a database.  Analysis of variance will be conducted on the variable rate and conventional technology effects on cotton yield.  The profitability of the variable rate and conventional technologies will be examined.  This process is cyclic and continuous using the previous years data analysis to determine next seasons inputs.

Justification: 

Nematode Control

Cotton is a critical cash crop to Mississippi economy producing more than 1.81 bales per acre on over 1.1 million acres in 1999. Cotton production is highly dependent on pesticides including herbicides, insecticides, and nematicides to produce economical yields.  New technologies   including transgenic varieties have enabled growers to reduce herbicide and insecticide applications and continue to cultivate plentiful yields.  Producers have taken advantage of the new technologies and have incorporated transgenic varieties into their production practices.  Plant-parasitic nematodes are a major economic concern to cotton production. However, neither host resistant nor transgenic cotton varieties are available as alternatives to replace nematicides for nematode management in cotton production.   With the acceptance of precision agriculture and  availability of the new technologies of  remote sensing,  spectral images with global positioning systems (GPS), and geographical information systems (GIS), cotton production could be improved by adjusting nematicide applications to the spatial distribution of  in-field nematode population levels using variable rate technology (VRT) .  This would result in optimized production with a minimum input of nematicides  and   corresponding reduced impact of pesticides on the environment. 

Plant-parasitic nematodes are a major economic pest to cotton production.  Nematodes are responsible for yield losses grater than 762,520 bales of cotton across the cotton belt last year.  The two most prevalent nematode species include the root-knot (Meloidogyne incognita) and reniform (Rotylenchulus reniformis).   The root-knot is well established and found in all cotton producing states.  The reniform, however, is a newly emerging nematode species that is spreading rapidly across the southeast and is becoming the major nematode pest.  

The reniform nematode was first described as a pathogen of cotton in 1940 in Georgia.  It was later identified in cotton in Alabama in 1959 and in Mississippi in 1980. In 1985, the reniform nematode was known to infest only 8 percent of the cotton acreage in Mississippi.  However, in 1999, over 34.6 percent of the cotton acreage is now infested. It is currently the most economic reducing pest associated with cotton production in Mississippi.  In 2001, yield losses greater than 20% were attributed to this nematode resulting in losses greater than 145 lbs per acre in a nematode infested field. It has been estimated that this nematode will become the most serious nematode threat to cotton in the southeast U. S.  if it continues to spread at the present rate. 

The reniform nematode has a debilitating effect on the growth and yield of the cotton plant which varies according to the population density and length of the time that a field has been infested.  Fields in which the nematode has been introduced relatively recently may display areas of uneven plant growth or stunting giving the field an irregular appearance.  Nematode numbers will generally be higher in areas of poor plant growth.  After a field has been infested for several years the population density would become more distributed throughout the field and resulting in the areas of uneven growth which are not as obvious. A continual decline in cotton yields may be the only indication to the producer that a problem may exist in the field. The absence of easily distinguished visible symptoms requires extensive soil sampling to determine the accurate detection of this nematode.  There are currently no commercially available cotton cultivars with resistance to the reniform nematode.  Therefore the application of chemical nematicides are the most frequently utilized method of management.  These chemicals may provide economic nematode control during a single season but they do not provide long-term management and must be used annually.  Additionally, the nematicides are applied at a predetermined rate uniformly across the field without regard to the spatial distribution of the in-field nematode population levels. 

 Literature Review: 

Nematode Control

Agriculture today is encountering an infinite number of new technologies to improve production and at the same time reduce environmental pollution. The use of spectral imaging and variable rate technology (VRT) incorporated with geographical information systems (GIS) and global positioning systems (GPS) integrate the developing technologies. The use these new technologies have only received limited use but now are becoming more practical and available to the cotton producer.   These technologies have been used to identify soil type and surface conditions (Everitt et al., 1989, 1994; Nixon et al., 1987), insect infestations (Everitt et al., 1994, Weisz et al., 1995), weed infestations (Brown et al., 1994, Nixon et al., 1985), and   virus disease development (Nelson, 1994).   However, in the area of nematology the use of these new technologies have been limited to infrared remote sensing to detect plant injury due to nematodes in cotton (Heald et al., 1972).  Studies designed to detect and determine nematode population densities and the development of corresponding yield maps to these populations have not been conducted.  

This proposed research is a core research project designed to detect and determine variation in crop growth resulting from parasitism due to the reniform nematode.  Additionally, using  hyperspectral imagery if feasible to discriminate between nematode population levels within an established cotton production system.  The results of this core research will then be integrated in cooperation with scientist that have previously created yield maps.  This in turn will be used to develop site-specific nematode population maps for use in variable rate management.

References: 

Everett, J. H.,  D. E. Escobar, M. A. Alaniz and M. R. Davis. 1989. Using multi spectral video imagery for detecting soil surface conditions.  Photogrammetric Engineering and Remote Sensing 55(4):467-471. 

Everitt, J. H., D. E. Escobar, K. R. Sunny and M. R. Davis. 1994.  Using airborne video global positioning systems and geographical information system technology for detecting and mapping citrus blackfly infestations. Southwestern Entomologist Vol. 19 No. 2: 129-138. 

Giles, K. 2000. Variable Rate Technology (VRT) for Site-Specific Agriculture,  University of California, Davis. 

Heald, C. M.,  W. H. Thames and C. L. Wiegand. 1972. Detection of Rotylenchulus reniformis Infestations by Aerial Infrared Photography.  Journal of Nematology   Vol. 4, No. 4:298-300. 

Lass, L. and R. Callihan, 1993. GPS and GIS for weed surveys and management.  Weed Technol. 7:249-254. 

Lawrence,  G.W.  and K.S. McLean.  1999.  Reniform nematodes.  Pp 42-44. In T. Kirkpatrick and C. Rothrock, eds.  Compendium of Cotton Diseases.  APS Press, St. Paul, Minnesota. 

Lawrence, G.W.,  K.S.  McLean and A.J. Diaz.  1998.  Nematode management investigations in Mississippi, 1997.  Mississippi Agricultural and Forestry Experiment Station Bulletin 1076. 

Lawrence, G.W.,  K.S. McLean and A.J. Diaz.  1999.  Nematode management investigations in Mississippi, 1998.  Mississippi Agricultural and Forestry Experiment Station Bulletin (In Press). 

Nixon, P. R.,  D. E. Escobar and R. M. Menges. 1985. A  mulitband video system for quick assessment of vegetal condition and discrimination of plant species.  Remote Sens. Environ. 17:203-208. 

Nelson, M. R., R. Felix-Gastelum, T. V. Orum, L. J. Stowell and D. E. Myers. 1994. Geographic Information Systems and Geostatistics in the Design and Validation of Regional Plant Virus Management Programs. Phytopathology 84:898-905.
 

Solie, J.B.  2000. The Impact of Precision Farming Strategies on Profitability, Agricultural Outlook Forum, Feb. 24, 2000 

Sorley, R.  and  D. W. Dickson 1991.  Determining consistency of spatial dispersion of nematodes in small plots.  Journal of Nematology 23:65-72. 

Strickland, R. M.,  D. R. Ess and S. D. Parsons.  1998. Precision Farming and Precision Pest Management: The Power of New Crop Production Technologies.  Journal of Nematology 30(4): 431-435. 

Usery, L., S. Pocknee, and B. Boydell. 1995. Precision farming data management using geographic information systems.  Photogrammetric Engineering & Remote Sensing 61(11): 1383-1391. 

Varsa, E. C., S.A. Ebelhar, S.K. Chong, S.J. Indorante, and T.D. Wyciskalla, 1998. Evaluation of Variable Rate Technology as a Management Tool for Potassium Fertilization of Grain Crops, University of Illinois NRCS. 

Weisz, R., S. Fleiseher and Z. Smilowitz. 1995. Site-specific integrated pest management for high value crops: sample units for map generation using the Colorado potato beetle (Coleoptera: Chrysomelidae) as the model system. J.  Econ. Entomol. 88: 1069-1080.

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