Latent Infection, Fungicide Efficacy and the Need for Predictive Models

Transcription

1 Latent Infection, Fungicide Efficacy and the Need for Predictive Models Raymond W. Schneider Nicole A. Ward Clark L. Robertson E. Paul Mumma Department of Plant Pathology & Crop Physiology Louisiana State University Agricultural Center

2 Fungicide Evaluations

3 Evidence for Extended Latent Infection, 2008 Single applications First symptoms at R6

4 Observations and Working Hypotheses Spores are deposited on leaf surfaces and latent infection occurs up to several weeks before visible symptoms. Protective fungicides would be more efficacious if applied before latent infection. Residual activity would affect time of disease onset and rate of disease development. Must be able to monitor spore deposition and latent infection.

5 Field Experiments Multiple planting dates, including MG s s IV, V and VI, thus assuring different times of infection. Multiple dates and number of applications of triazoles, strobilurins and chlorothalonil Assessment of latent infection with qpcr. Monitor spore deposition with electrostatic spore sampler.

6 Assessment of Time of Infection Time of Application V3, V7, R1, R3, R5, and R6 V3, V7, R1, R3, and R5 V3, V7, R1, and R3 V3, V7, and R1 V3 and V7 V3 R6 R5 and R6 R3, R5, and R6 R1, R3, R5, and R6 V7, R1, R3, R5, and R6 Fungicides Topguard Stratego Quadris Headline Domark Echo and Rates 7 oz/a 10 oz/a 15.5 oz/a 12 oz/a 5 oz/a 16 oz/a

7 Latent Infection I Jul 19 V4 Sept 6 R5 49 days qpcr negative qpcr positive Symptoms Cotton was interplanted to account for spores on leaf surface. Inoculum was present at time of planting.

8 Latent Infection II and III Planted mid-may July 23 R2 36 days Aug 28 R6 Planted mid-july Aug 20 V4 64 days Sep 25 R5 qpcr negative qpcr positive Symptoms

9 Latent Infection II Latent Infection II Disease Severity (%) qpcr R2 Symptoms R6 V3 V7 R1 R3 R5 V3, V7 V3, V7, R1 V3, V7, R1, R3 Nontreated Control

10 Latent Infection III Latent Infection III Disease Severity (%) qpcr V4 Symptoms R5 V6 R1 R3 R5 Nontreated Control

11 Field Views of Fungicide Treatments Nonsprayed control Topguard, 7 oz, R1

12

13 Multistate Project on Spore Trapping and Deposition Scott Isard Les Szabo Glen Hartman Jim Marois John Mueller Ray Schneider Major unknown: Wet vs. dry deposition

14

15 Monitoring Spore Deposition with Electrostatic Sampler qpcr protocol developed by James Haudenshield (Hartman lab). Antiserum and IF protocols provided by Dorrance lab. Device can process 600 liters of air/min. Multiple analytical protocols can be used. Very high capture efficiency. Can detect one spore using qpcr and IF protocols. U.S. and international patents pending

16 Interloper

17 Performance of Electrostatic Sampler Spores detected during first week of operation in 2009 (about 5 weeks before passive trap). Electrostatic sampler: 78,889 spores in 2 days Passive sampler: 11 spores in one week Spore detection concurrent with positive qpcr assays.

18 Summary and Conclusions A single fungicide application was sufficient to control rust. R1 application was most efficacious when latent infection began during V stages. R3 application was better when latent infection occurred during early R stages. Time of application would depend upon prevalence of other late season diseases, e.g. Cercospora leaf blight and frogeye leaf spot.

19 Summary and Conclusions, cont d There is a need to evaluate fungicides using this management strategy. Latent infection appears to increase in intensity long before symptoms develop (not shown). There appears to be a critical time during latency when fungicides lose efficacy.

20 Disclaimers and Exceptions These tests were conducted under very high disease pressure. Results may vary where inoculum arrives late in the season and conditions are not conducive for severe disease development. Experience will be required to optimize this strategy and to develop virtual models.

21 Conclusions and Recommendations Initiating fungicide applications after sentinel plots turn positive is risky, especially in northerly states. Monitoring spore deposition followed by qpcr assays of plants in the vicinity may be more reliable and less costly than current sentinel plot strategy.

22 Assessment of Spore Viability