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Management of Asian Soybean Rust, Nematode/Rust Interactions and Cotton Nematodes

Mueller, John
Clemson University
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End date
  1. Document the occurrence and distribution of Asian Soybean Rust in South Carolina.
  2. Determine the effects of planting date and soybean cultivar maturity group on ASR development, ASR-induced yield losses, and fungicide efficacy against ASR.
  3. Determine the length of efficacy of commonly used fungicides for ASR control.
  4. Determine whether naturally occurring biological stresses such as soybean cyst nematode will affect the development and severity of Asian Soybean Rust and subsequent yield losses.
  5. Determine the viability of the GPS/SEC based - variable rate nematicide application system developed at Clemson University in managing Columbia lance, reniform and root-knot nematodes on cotton.
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NON-TECHNICAL SUMMARY: Asian soybean rust poses a new threat to sobyean production in the in the Southeastern united States. Management will depend upon spraying when disease incidence and severity are very low. Growers will not have detected the disease in their field when it is time to spray and do not know which fungicides are most efficious or what effects other major diseases such as soybean cyst nematode will have on management practices. This project will identify when rust has arrived in a given geographic area via the use of monitoring plots. Growers will receive a 7 to 14 warning prior to the needed spray date. This research will evaluate the efficacy of common fungicides and the effects of soybean cyst nematode on management decisions.

APPROACH: Sentinel plots will be established at 15 sites to document the occurrence of Soybean Rust. Maturity Group (MG) 4 and 7 cultivars will be planted 3 weeks prior to the normal planting date. At each sample date 50 leaves will be collected from each plot and examined under a dissecting scope. Data collected will be used to determine the rate of development of ASR using AUDPC. Objective 2: Two experiments will be conducted to determine the effects of soybean MG and planting date on ASR development. In the first experiment MG 5, 6, 7, and 8 cultivars will be grown with cultivar as main plots and fungicide sprays as subplots. Tebuconazole will be applied at R2 and R4. Beginning at R1 plots will be sampled and data used to determine the rate of development of ASR using AUDPC. In the second experiment MG 7 and 8 cultivars will be planted on May 5th and June 5th with cultivar as main plots, planting dates as subplots, and sprayed vs nonsprayed as sub-subplots. Plots will be treated at R2 and 14 days later with tebuconazole. Beginning at R1 plots will be sampled on a weekly basis and rust severity determined as described previously. Objective 3: Residual efficacy of six commercially available fungicides will be determined. Each fungicide will be applied once either at R1 or when ASR is first detected in the area. Beginning at R1 plots will be sampled and rust severity determined and data analyzed as described in Objective 1. Objective 4: The effects of soybean cyst nematode (SCN) on the development of ASR will be determined. This experiment will consist of 2 levels of SCN resistance (resistant & susceptible), 2 levels of fungicide (sprayed & unsprayed), and 2 levels of 1,3-dichloropropene (treated & nontreated). Nematode densities will be determined at-planting, 30-days-after planting, and at harvest. Percentage yield loss will be determined. The relative effects of SCN resistance on ASR development will be monitored as described in Objectives 2 and 3. The effects of ASR on SCN population development will also be evaluated. Objective 5: Three fields that are representative of cotton production systems will be selected which are infested with either Columbia lance, reniform or Southern root-knot nematodes. Each 5 to 10 acre field will first be mapped for soil type using a soil electrical conductivity meter. Nematode samples will be collected at the initiation of these studies by grid sampling each field in 0.5 acre or smaller increments. A soil texture map with four categories of percentage sand will be developed. Six nematicide regimes will be evaluated including: 1). nontreated control; 2). 0.34 kg/ha aldicarb in-furrow at-planting (ifap); 3). 0.68 kg/ha aldicarb ifap; and 4). 1.02 kg/ha aldicarb ifap; 5). 27 liters/ha 1,3-dichloropropene (1,3-D) applied i.f. preplant; and 6). 36 liters/ha 1,3-D applied i.f. preplant. Experimental units will consist of a specific combination of soil type X nematicide regime X nematode density. Yield and nematode data will be combined to develop crop damage functions and practical action thresholds for each nematode species over a range of initial nematode population densities and soil textures.

PROGRESS: 2008/01 TO 2008/12
OUTPUTS: OUTPUTS: Asian Soybean Rust (ASR) monitoring plots were established in Aiken, Allendale, Anderson, Bamberg, Barnwell, Berkeley, Calhoun, Colleton, Darlington, Dorchester, Florence, Hampton, Horry, Lee, Lexington, Marlboro, Newberry, Orangeburg, and Sumter Counties. Sites were sampled biweekly prior to flowering and weekly after flowering. Incidence and severity of ASR were determined using a dissecting microscope. Results were disseminated to agents, growers, and agricultural industry personnel via the USDA ASR PIPE website and the "South Carolina ASR Newsletter". All first finds for individual counties were disseminated within 12 hours. Suggested ASR management practices were included in each announcement based on the location, incidence and severity of the ASR find and the projected weather conditions. Three fungicide trials were conducted at the Edisto Research and Education Center in Barnwell County to evaluate the efficacy of various fungicides in controlling ASR. The first test compared the efficacy of applications at R-3 of Topguard at either 7 or 14 fl oz/acre to the efficacy of combinations of Topguard (7.0 or 14.0 fl. oz./acre)at R-3 + either 7.0 fl. oz./acre of Topguard, 6.0 fl. oz./acre of Headline, or 4.0 fl. oz./acre of Folicur at R-5. The second test compared the efficacy of single applications of 7 fungicides applied at R4/R5 to a nontreated check. Fungicides included 10.0 fl oz/acre of Stratego; 4.0 fl. oz./acre of Folicur; 7.0 fl. oz./acre of Provost; 6.0 fl. oz./acre of Headline; 5.0 fl. oz./acre of Domark, 10.0 fl. oz./acre of Stratego + 1 fl. oz./acre of Proline; and 8.0 oz./acre of Topsin M + 4 fl. oz./acre of Tebuconazole. The third test compared the efficacy of single sprays of 11 fungicides to a nontreated check. Fungicides included: 4.0 fl. oz./acre Quadris Xtra; 4.0 fl. oz./acre Alto; 14 fl. oz./acre Quilt; 7.0 fl. oz./acre Stratego; 5.0 fl. oz./acre Domark; 4.0 fl. oz./acre Loredo; 4.0 fl. oz/acre Folicur; 6.0 fl. oz./acre Headline; 4.0 fl. oz./acre Punch; 7.0 fl. oz/acre Topguard; and a combination of 16.0 oz./acre of Topsin M + 4 fl. oz./acre of Tebuconazole In all tests incidence and severity of ASR was recorded prior to treatment and at biweekly intervals afterward until harvest. Yields were recorded.
PARTICIPANTS: PARTICIPANTS: County Agricultural Agents collected soybean rust leaf samples every week in June, July, August, September and October. These individuals and their counties were: Marion Barnes, Allendale/Colleton; Vic Bethea, Dillon/Marlboro; Jonathan Croft, Berkeley/Dorchester; Randy Cubbage, Lee; Charles Davis, Calhoun/Orangeburg; Trish DeHond, Darlington; Greg Harvey, Sumter; Bruce Johnson, Horry; John Oxner, Aiken/Lexington; Joe Varn, Bamberg/Barnwell, and Tommy Walker, Hampton; Mark Malsik, Meteorologist at South Carolina Department of Natural Resources who provided weekly weather reports for the Rust Newsletter. Partner organizations include: South Carolina Soybean Promotion Board who provided funding for the rust projects. South Carolina Department of Natural Resources who allowed Mark Malsick to provide weekly weather updates. Training and Professional Development opportunities: Twenty county agents participated in the rust monitoring project and received training in rust detection and management as part of thier participation. Results from all surveys and tests have been presented at the Edisto REC Fall Field Day and at county and state level grower meetings as presented by all individuals working on the project.
TARGET AUDIENCES: Target audiences include the county agricultural agents, cotton growers, soybean growers, and peanut growers in South Carolina and neighboring states for both the rust projects and the nematode management projects.

IMPACT: 2008/01 TO 2008/12
In 2008 Asian Soybean Rust (ASR) was first detected on leaf samples collected from Hampton County on September 15. Eventually ASR was detected in 16 of the 20+ counties surveyed in South Carolina. Counties in which rust was detected included Allendale, Anderson, Bamberg, Barnwell, Berkeley, Calhoun, Colleton, Darlington, Dillon, Dorchester, Florence, Hampton, Horry, Lexington, Marlboro, and Orangeburg. In most of these counties rust was present only at very low levels of severity, usually less than 5%. These low levels of rust arrived relatively late in the growing season. Therefore very few fields had levels of rust capable of causing yield losses prior to growth stage R-6. Spray advisories were issued primarily for soybeans planted in late May and June in the southern half of the state and for late-planted soybeans in the northern portion of the state. This resulted in approximately half of the soybean acres being sprayed at least once. Without these advisories the projected spray pattern would have been 2 sprays on every acre at $10 per spray per acre. For 540,000 acres this would equal $10,800,000 in total costs. Instead, only 270,000 acres were sprayed once for a cost $2,700,000 or a savings of $8,100,000 for the state. This reduced spraying also helped to avoid exerting pressure on rust and other fungal pathogens to develop resistance to the strobilurin fungicides being used. The results from the 3 ASR fungicide trials demonstrated that the yield losses to soybean under the conditions present in 2008 were minimal. In each test results showed that disease levels and accompanying yield losses did not warrant spraying. This shows that the spray recommendations provided were appropriate.

Funding Source
Nat'l. Inst. of Food and Agriculture
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