Untitled Document


Principal Investigator:  Terry Wheeler, TAES, Rt. 3, Box 219, Lubbock, TX 79403; telephone 806-746-4014; email ta-wheeler@tamu.edu

Cooperators:  Vijay Kumar Choppakatla (West Texas A&M Univ.), Dana Porter (TAEX/TAES, Lubbock), Mike Schubert (TAES, Lubbock), Jerry Warren (TAEX, Terry county), Mr. Lenard (Terry county), Mr. Ronnie Floyd (Terry county), Mr. Alton Shipley (Gaines county).

Primary Research Location:  Western Peanut Growers Field in Gaines, County

Project Title: The Effect of Soil Moisture on Pod Rot

Project Objectives:

1)      determine variation in soil moisture in peanut fields;

2)      relate peanut pod rot or other peanut diseases to soil moisture;

3)      develop recommendations to treat peanut pod rot based on soil moisture.

Reporting Period:  January 1, 2001 to December 31, 2001

Summary of Progress

 

Research at the Western Peanut Growers Field (Objectives 1 and 2)

     Soil moisture was measured at the research site located in Gaines county using a neutron probe in aluminum access tubes to a depth of 1, 2, and 3’.  The first two spans of the circle are in continuous peanut (two consecutive years).  This area in 2000 was left to natural variation for soil moisture, but in 2001 was manipulated to create a zone of 100, 75, and 50 % water replacement as measured by evapotranspiration (ET) (Figure 1).  The circle is divided into six equally spaced sections.  Sections 1, 2, 5, and 6 were in cotton, except the first two spans of the circle, and sections 3 and 4 were in peanut  (Figure 1).  Forty-two points were established for each ET rate under the first two spans to measure soil moisture and disease. The rest of the circle which was in peanut (pies 3 and 4) had different types of irrigation nozzles (wobbler [span 5], wobblers and bubblers [span 6], LEPA [spans 3,4,7,8, and 9]) and rates (span 8), which may have impacted moisture content of the soil.  However, altitude also had an impact on average soil moisture measurements (Figure 2).  The locations that soil moisture was measured for everything but the first two spans, were at points which had been originally sampled in spring of 2000 and were assayed for soil physical and chemical properties


Figure 1


 

Figure 2
 

 


      Pythium sp. was the primary pathogen causing pod rot in 2001.  Isolations from roots sampled on 10 July, established the presence of Pythium on 10 % of the roots and Rhizoctonia on 17 % of the roots.  There was no relationship between isolation frequency of these pathogens and ET treatment, measured soil moisture or subsequent pod rot.   In 2000, there was < 1 % incidence of pod rot at any location under this circle.  In 2001, in spans 3-9 where peanuts were rotated with cotton, there was a similarly low incidence of pod rot.  However, in the first two spans where peanuts were grown for two consecutive years, pod rot increased substantially, especially in the areas with higher ET replacement (Table 1, Figure 3).  When ANOVA was used to relate ET, location (pie) and their interaction to pod rot, there was a significant impact of both ET, and location (Table 2).  The highest incidence of pod rot at harvest (both with counting pods and visual assessment) were in pies 5 and 6, which actually received less water than pies 3 and 4, because the pivot was speeded up or completely skipped those pies which were planted in cotton (pies 1, 2, 5, and 6) as compared with peanut (pies 3 and 4).  Altitude generally is the lowest in the south and highest in the north. Pod rot as measured in midAugust was correlated (P < 0.05) with only 1 of 6 sets of soil moisture measurements taken before pod sampling.  Pod rot as measured at harvest was correlated with only 3 of 12 sets of soil moisture measurements.  Neither set of pod rot measurements was correlated with the average soil moisture measurements taken over the growing season (2 July to 14 September). 

Table 1. Pod rot incidence as affected by irrigation treatment (ET is replacement of water which was removed through evapotranspiration)

            % Pod Rot from sampling at

% ET   August              Harvest

50        0                      3

75        3                      8

100      7                      9

Table 2. Pod rot incidence as affected by position of the peanuts in the field

            location            % of Pod rot from sampling at

Pie       in field              August              Harvest

1          Northwest        0                      7

2          North               1                      2

3          Northeast         5                      3

4          Southeast         3                      6

5          South               3                      10

6          Southwest        7                      13

Figure 3: Visual rating of pod rot across the entire test area (individual ratings and average across pies).
Western Peanut Growers Field (Objective 3)

      Nineteen locations at this field in the first two spans were selected for fungicide applications, based on incidence of pod rot, during August sampling.   A six foot of row was treated with Ridomil Gold EC (1/2 pt/acre) on 2 September at a distance of two rows to the south of each selected point, while an equal length of row was left untreated  to the north of each selected point.  These areas were dug prior to the field being harvested, weighed and graded to estimate a $/acre value.  No areas were selected in the 50 % ET plots, since there was no pod rot in August found in this part of the field. 

     Peanuts that are sold at quota prices ($610/ton) would have paid for the fungicide application (valued at approximately $50/acre) under the 100 %ET treatment, but not under the 75 % ET treatment (Table 3).  Nonquota peanuts ($325/ton in this example) would not have covered the cost of the fungicide treatment under either ET scenario. The value of peanuts is dependent on a proportion of the (sound mature kernels + sound split kernels) and other kernal (which include rotted kernels). The percentage of pod rot in August was a significant predictor of the percentage of other  kernels for both fungicide treated (P = 0.02) and non treated (P = 0.0001) plots.  An equation derived from the fungicide work, predicted an average value of $783.94/acre if there was no pod rot (quota prices), and a decrease of $12.04/acre for each percentage of pod rot observed in August.  Assuming a fungicide cost of $50/acre, then there needed to be at least 4.2 % pod rot in August to pay for a fungicide application.  Only the 100 % ET treatment averaged over 4 % pod rot at that time. The percentage of pod rot at harvest was significantly correlated with value of the crop in the nontreated plots (P = 0.03), but not in the fungicide treated plots (P = 0.43).  This is another indicator that the fungicide treatments did impact subsequent pod rot and crop value, which occurred after the first sampling date in midAugust.  Since fungicide treatments will be most valuable if they go out before pod rot develops, it is unfortunate that the isolation frequency of Pythium  from roots in July was not related to any measured variables. 

Table 3. Value of harvested crop for two irrigation treatments (ET is replacement of water which was removed through evapotranspiration)

            $/acre for quotaa peanuts                      $/acre for nonquotaa peanuts

% ET   No fungicide     Fungicideb                           No fungicide               Fungicide

75             544.29                       464.31                                       289.94                       247.34

100           590.31                       667.57                                       314.46                       355.62

aQuota peanuts were worth $610/ton, while nonquota peanuts were estimated at $325/ton.

bThis cost does not include the  chemical or application costs for Ridomil Gold EC.  That was estimated at $50/acre.

Producer’s Fields (Objective 1-2)

     In response to comments made during the 2001 evaluation of PA projects, three producers fields were monitored for soil moisture and pod rot in 2001.  One goal was to determine how to measure soil moisture in a manner  which could be realistically used by producers (i.e. not a neutron probe).  Methods that were tested included gravimetric, tensiometers, and a theta probe.  The theta probe, if it does not break during the season, was the easiest method to use.  However, due to the fragile nature of this tool, more work with probes that are less accurate will also be tested in the future.  Of greater concern than finding a reliable tool, was when and where to measure soil moisture.  Most measurements only provided information on how recent the pivot had been there, not on relative differences within the field.  Near the end of the season, a method was tried in which the theta probe was used to measure surface moisture at a set distance from the pivot, and then the same locations were measured at 24 and 48 hrs after the pivot passed.    In 2002, this method will be used exclusively and measurements will be taken at monthly intervals. 

     The three producer’s fields were selected because of their history of pod rot (Rhizoctonia according to their descriptions), though these fields had all been out of  peanut production at least 2 years.  While there was some pod rot at the Floyd and Lenard fields in August, very little was found at harvest.  However, at the Shipley field, a great deal of pod rot was found at harvest, though this field only had six positive sites for pod rot in August (out of 87 sites examined).  The pod rot (caused by Pythium) apparently came on in September, after Mr. Shipley increased his irrigation in the field.  The entire field was visually rated for pod rot after digging (Figure 4).  There was no correlation between the moisture levels (determined gravimetrically at one day in time) and pod rot.  However, there was more pod rot in the southern part of the field than the northern part (Figure 4).  It should be possible to test for differences in soil moisture in this same field next year (2002 growing season), using the “improved methodology” by measuring over time at a set distance from the pivot. 

     Areas were also selected in August to treat with fungicide as was done at the Western Peanut Growers field.  However, each of these fields were treated with Folicur, which is active on Rhizoctonia solani.  Since only the Shipley field had significant pod rot at harvest, and the wrong fungicide was applied, no yield data will be presented.   

     The first year working with producers was time intensive, yet yielded little in the way of positive results.  However, if areas where water drains at different rates can be identified before pod rot begins, then a better sampling scheme for pod rot can be initiated.  A great deal of time was spent sampling roots to determine if that was a predictor for pod rot.  Since it was not, that activity will be eliminated during 2002.  More effort will be made also to spray small plots with fungicide in 2002.  It will be necessary to scout the fields more frequently in 2002 to acquire more complete information on the temporal dynamics of pod rot and when to apply fungicides.


Figure 4.  Visual rating of Alton Shipley’s peanut field for pod rot after digging (individual evaluations and average across larger blocks).
 


Education/technology transfer:

      The pod rot project was discussed with the Terry county agricultural extension agent during 2001.  He was very helpful in selection of producers.  The producers on the project were also made more aware of the importance of water and pod rot.  Particularly Mr. Shipley who had such a terrible experience when he overwatered his field.  The Gaines county agricultural extension and IPM agents have been replaced during 2001, so these new agents will also be invited to participate and learn from the project during 2002.

Milestones achieved:

1)      Both 75 and 100 % ET achieved similar levels of pod rot at harvest.  It was assumed at the initiation of this project, that the higher water treatment would have more pod rot.  This is significant, because while 100 % ET may be considered “over watering”, 75 % would not.  One point of caution, at the site this work was conducted, the field manager began overwatering all target ET levels in September. 

2)      Isolation of Pythium or Rhizoctonia solani from roots prior to pod formation, was not a predictor of pod rot severity.

3)      A treatment threshold at 4.2 % pod rot has been identified and will be tested in future studies.

4)      Soil moisture can be best monitored using a set distance from the pivot for all initial observations and then a second observation at  48 hours later.

5)      The most accurate instrumentation (neutron probe) measurements averaged for 12 times during the season, could not be highly correlated with %ET (R2 = 0.04).  All soil moisture measurements must be made in relation to the pivot position!!!

Publications:  No peer-reviewed publications from this project in 2001.  The portion of this report which dealt with work conducted at the Western Peanut Growers site in 2001 was included in the Annual Report for the Western Peanut Growers Association.

Precision agriculture proposals:

1)      Use of an Aerial Hyperspectral Sensor to Identify Stresses which Limit Cotton Production by T. Wheeler, S. Armstrong, R. Boman, J. Bordovsky, K. Bronson, T. Doederlein, H. Kaufman, W. Keeling, S. Maas, D. Porter, S. Russell, and K. Siders. Submitted to Cotton Incorporated at their request in June 2001.  Funded at $17,500 for 2001.

2)      Use of an Aerial Hyperspectral Sensor to Identify Stresses which Limit Cotton Production by T. Wheeler, S. Armstrong, R. Boman, J. Bordovsky, K. Bronson, T. Doederlein, H. Kaufman, W. Keeling, S. Maas, D. Porter, S. Russell, and K. Siders. Submitted to Cotton Incorporated for 2002.  Funded at $14,500 for 2002.

3)      Use of an Aerial Hyperspectral Sensor to Identify Stresses which Limit Cotton Production by T. Wheeler, S. Armstrong, R. Boman, J. Bordovsky, K. Bronson, T. Doederlein, H. Kaufman, W. Keeling, S. Maas, D. Porter, S. Russell, and K. Siders. Submitted to Cotton Incorporated for $17,500 for 2003. Pending.

4)      Narrow band Spectral Imagery for Detection of Parasitic Nematodes on Cotton. By K. S. McLean (Auburn), G. W. Lawarence (Mississippi State), and T. A. Wheeler (Texas A&M).  Submitted to IFAFS.  The Texas subcontract for direct costs was $61,797.  Not funded.

5)      Prediction and Management of Peanut Pod Rot as a Function of Soil Moisture and Field History. By T. A. Wheeler, D. Porter, and A. M. Schubert. Submitted to the Center for Integrated Pest Management (located at North Carolina State University) for $24,000.  Not funded.

6)      Management of cotton based on remote sensing and GIS technologies. Dr. Steve Maas was the lead investigator.  My role was to handle the pest (disease, insect, weed) data collection from remotely sensed fields.  Submitted to IFAFS. Not funded.

Precision Agricultural meetings attended/papers (posters) presented:

1)      Cotton Beltwide (Atlanta, GA) panel discussion for the production section: presented “The success and failures of precision agriculture and nematology”. Jan. 2002. Approximately 300 people attended.

2)      Cotton Beltwide (Atlanta, GA) poster at the nematology workshop: Precision Agriculture and Nematology (included four posters (4’ x 8’)). Jan. 2002. Approximately 200 people attended.

3)      American Phytopathology Society (Salt Lake City, UT) Annual Meeting:  presentation  (Optimizing time of year for remote sensing based nematode sampling in cotton).    Aug. 2001. Approximately 50 people attended.

4)      Friona, TX county meeting:  Use of remote sensing and global positioning systems in farming. 1/24/01. Approximately 10 people attended.

5)      Muleshoe, TX county meeting:  Use of remote sensing and global positioning systems in farming. 1/25/01.  Approximately 100 people attended.

6)      Lubbock, TX  Texas Agronomy Annual Meeting:  Precision agriculture and cotton production. 2/26/01.  Approximately 40 people attended.

7)      Gaines co., TX. Western Peanut Growers Field Day. 9/21/01.  The use of Remote Sensing to Detect Water Stress. Approximately 50 people attended.