Principal Investigator:

Terry Wheeler
TAES
RT. 3, Box 219
Lubbock, TX 79403
E-mail: ta-wheeler@tamu.edu

Cooperators:

Dana Porter
Steve Searcy
Mike Schubert
Harold Kaufman
Clyde Crumley

Primary Research Location: Denver City

Project Title: The influence of soil moisture and variable rate fungicide application on management of pod rot of peanut.

Reporting Period: September 1, 1999 to August 31, 2000

Objectives:

1. Determine variation in soil moisture in peanut fields

2. Relate peanut pod rot or other diseases to soil moisture

3. Develop recommendations to treat peanut for pod rot based on soil moisture.

4. (Not stated in original proposal) determine the relationship between peanut foliar
browning (unknown cause) and site-specific factors in the field.

A. Summary of Progress:

1) Soil moisture was measured across the Western Peanut Growers circle during July - September. During much of July, a Thetaprobe and MSTR probe, which are tools that would be readily accessible to producers were used. From late July through middle of September, neutron probe readings were taken at 89 locations within the peanut part of the circle, and approximately 90 locations in the cotton part of the circle. Only the readings for the peanut part of the circle will be used in evaluations. Soil moisture was not uniform across the circle as can be seen with Fig. 1 of two of the evaluation periods at 30 and 61 cm depths. Readings were taken down to 90 cm, but differed little from the 61 cm depth. A soil moisture release curve was developed to relate neutron probe readings to % moisture (gravimetric) and then to pressure. This curve shows an usually steep decline in moisture with very small changes in pressure (Fig. 2) for this site.
The Thetaprobe, which only measures surface water, was more reliable in laboratory testing to relate readings to % moisture than the MSTR probe, and will be the instrument utilized during the 2001 growing season in a producer's field. Aerial color infrared photographs were taken at three times during the growing season. These images can show soil texture differences and water stress in many fields. However, for the test circle, soil texture appeared similar across the circle in June (Fig. 3). There appeared to be an area with slightly different soil texture in the photograph taken in August (Fig. 4). An image taken in September (Fig. 5) did demonstrate differences in plant growth that may be related to water treatments and a foliar necrosis problem which is discussed later.

Figure 2.

2) The peanut acreage at the Western Peanut Grower's circle near Denver City had low levels of Pythium pod rot at various locations (Fig. 6). Each point in the map is a spot where at least two pods were found with Pythium like symptoms, but there were no spots found with more than 5 pods rotted (out of 100's), so no locations were identified with more than low levels of disease. The soil moisture readings were converted to bars for the peanut acreage and then a map was created through ARCVIEW surface analysis extension to predict soil pressure for the entire peanut area (Fig. 6). The points where soil moisture was measured are marked in black and the spots with pod rot are marked in red (Fig. 6). For each date that neutron probe readings were taken (27 July, 2 August, 12 August, 16 August, 25 August, 5 September, and 14 September), the area in the peanut acreage that was 0 to -0.1 bars; -0.101 to -0.20 bars; -0.201 to -0.30 bars; -0.301 to -0.40 bars; -0.401 to -0.60 bars; and -0.601 to -1.1 bars was calculated. The percent of pod rot (out of the total number of pod rot locations) that occurred in each of these soil moisture pressure categories was also calculated. The percent of pod rot measurements was generally similar to the percentage of area each soil moisture pressure class covered (Table 1). However, on 25 August, the 0 to -0.1 category accounted for 30 % of the peanut acreage and 48 % of the pod rot spots. This was the only time period when this wettest category of soil had more than 3 % of the overall peanut acreage.

3) The overall goal of this project is to improve the profitability of fungicide management for pod rot. The fungicide metalaxyl (Ridomil) is the most common fungicide recommended for control of Pythium pod rot. Pod rots can also be caused by other fungi in Texas, with Rhizoctonia solani being the most common problem in the High Plains of Texas. To reduce the acreage treated with one or more fungicides (if both Pythium and R. solani are present) it was necessary to develop a variable rate application system capable of putting out several different combinations of materials or rates. Dr. Steve Searcy oversaw the development of a variable rate applicator (Fig. 7). A variable rate sprayer with a direct injection pump (precision peristaltic injection pump), carrier pump, and control valves that meter the carrier and active ingredient were provided by Dr. Searcy as well as a Mid-Tech 6300 Total Application Sprayer Control (TASC). The Mid-Tech TASC 6300 console controls desired rates by sensing changes in ground speed or active boom width and adjusting the rate of carrier and injection of chemical into the carrier accordingly. The components of a TASC system are radar, flow meter, flow control valve, boom interface, chemical injection pump, chemical container, and TASC control console. A WAG vision system is the "brain" that provides application rates to the TASC 6300. The project purchased a VCD from WAG Corp., but it is still awaiting delivery. Dr. Steve Searcy provided a WAG VCD so the system could be tested. The testing was conducted at College Station as part of a student's (Chris Hundley) precision agriculture project. The Wag unit reads data from a prescription file, and based on the location of the sprayer in the field, identification of the proper application rates for that location are determined and sent to the TASC console to be executed. A differential global positioning receiver is used to determine location within a field. The target application rates for a specific location in the field are sent through a serial port to the variable rate control interface (VRCI) which then exit the VRCI and enter the TASC console. The actual rates applied are sent from the TASC back through the VRCI to the WAG unit and are displayed as an "applied" field. An overview of the application apparatus is seen in Fig. 8, and the components for the variable rate system are in Fig. 9. The field area boundaries are developed through a software package called PC-GPS (Microtechnology, Corvallis, OR), and then exported as a shape file to SSToolBox. This software package is used to create the application map. The system tested in College Station included carrier and active ingredient (ai) rate parameters. In the tests (Fig. 10), where the carrier was designated as 0 or ai as 0, the system should have been off (grey areas), and when the carrier was 15 (blue areas) and ai > 0 (red areas) the system should have been on. For the most part this did occur, though in the northwestern most blue square, the system turned off partway through (Fig. 10). In a second test, the system failed to turn off in one grid (northwest most grid) and the rates applied were slightly higher than desired for one pass (western grid in red, in the middle) (Fig. 11). The system will be operating at the Western Peanut Grower's circle during 2001 and will need more testing as to reliability. For the 2001 growing season, fungicide applications will be made based on the area in which the soil is near saturation (0 to -0.1 bar).

4) A light colored browning symptom has plagued peanuts grown in the west Texas area. Often large parts of a field will die prematurely, with the primary symptom being leaf edge burning which quickly progresses to all above ground parts. Though a number of People have investigated causal agents (Thielaviopsis basicola, and salt concentrations), no satisfactory explanation has been found. The Western Peanut Grower's circle demonstrated this problem during the 2000 growing season during September. A map was created based on the intensity of symptoms (Fig. 12), and soil samples were taken from a number of locations, which were georeferenced, and analyzed for conductivity of the 0-3" and 4-6" depths. The intensity of symptoms was negatively related to salt concentration in the soil, but salt levels did not exceed levels damaging to peanut (Table 2). However, the pattern of browning was related to the irrigation treatments. Those receiving LEPA did not show browning symptoms and those in a "spray mode" showed the most severe symptoms. The irrigation systems which applied the same amount of water as the LEPA and spray systems, but were intermediate in the type of application (i.e. not as concentrated an amount of water as LEPA or as much a droplet as the spray mode) showed symptoms closer to the severity of the spray mode than the LEPA system. The amount of water was varied within some of the LEPA treatments, however, that did not appear to be related to the browning symptom. So, the "cure" for the browning symptom was discovered (i.e. use LEPA), but the causal agent is still unknown. It does appear that efforts should be concentrated on the above ground plant instead of soil factors.

B. Education/technology transfer:
Since this work is preliminary, it has not yet been shared with others outside of the project. All the data collected will be rechecked for errors during the winter, before a firm conclusion will be reached. The peanut field season only terminated a week prior to this report being due, so the analysis is preliminary. Using remote sensing to detect soil texture changes however has been well documented in previous projects. Two sessions were used to present remote sensing information to county agents and producers during a precision agriculture meeting held in Ropesville, TX in August. Participants included T. Wheeler, H. Kaufman, and S. Searcy.
As a response to the meeting with the precision agriculture committee during the past summer, Harold Kaufman flew fields for 11 producers who were working with Scott Orr, Water Use, Conservation and Compliance Director with the High Plains Underground Water District #1. Terry Wheeler processed the images into vigor classes so the producers could more easily interpret the images. There has been no feed back from Scott Orr as to the response of the producers to the images.

C. Milestones achieved: Pod rot, though minor during 2000, was spatially correlated with near saturated conditions in the field in late August.

D. Publications: None have yet been produced based on this project, though precision agriculture type publications are listed on other projects (see Bronson for on-farm research (Wheeler and Kaufman), and Lascano for the research cotton project (Searcy).

E. Precision agriculture proposals:
Testing the reliability of remote sensing directed scouting for integrated pest management, submitted to the Southern Regional IPM program, by Wheeler, Kaufman, and K. Siders.

Comparison of conventional IPM scouting versus remote sensing directed IPM scouting. K. Siders, T. Wheeler, and H. Kaufman. Funded for $15,000 from 1/00 - 12/00. This project has been resubmitted to Texas Dept. of Agriculture for the 2001 growing season.

F. Precision Agriculture meetings attended/papers presented: none at precision agriculture meetings, however, precision agriculture presentations are listed below for 1999 - 2000.

12/6/00: Remote Sensing, A Practical Diagnostic Tool for Cotton Problems, 2000 Plant Protection Conference, College Station, TX. Kaufman

9/20/00: Precision Agriculture, presented in Saltillo, Mexico, as a keynote speaker for an agricultural symposium. Wheeler

8/14/00: Can Remote Sensing be used to create Variable Rate Nematicide Application Maps?, American Phytopathology Society Annual Meeting, New Orleans, LA. Wheeler

1/8-9/00: Remote Sensing and Agriculture (poster, joint with representatives from Mississippi State, Utah, and Penn State), Farm Bureau National Meeting, Houston, TX. Wheeler

1/7/00: The relationship between incidence of Verticillium wilt and reflectance in a wilt nursery, National Cotton Annual meeting, San Antonio, TX. Wheeler

G. Other developments: