SOYBEAN RUST Phakopsora pachyrhizi

1. SOYBEAN RUSTPhakopsora pachyrhizi G. L. Sciumbato, Plant Pathologist Delta Research and Extension Center Stoneville, MS

2. Facts about the rust fungus Obligate parasite-Cannot survive unless it is in a host. Over 100 alternative legume hosts- Can complete life cycle on many legumes. Hosts include kutzu, crimson clover, white clover, sesbania, beans, peas etc. Rust spores can survive for up to 30 days outside a host and can travel up to 400 miles.

3. Facts about the rust fungus Optimum growing temperatures 69-89O Fungal spores are sensitive to heat and die when temperatures are above 900 Fungus grows best under moist conditions. Long dew periods etc. Dry, hot weather inhibits growth of fungus. Spores built up on host plants and are blown by wind currents to infect soybean plants.

4. Facts about the disease on soybeans Can infect soybeans at most any growth stage Soybeans become more susceptible when they enter the reproductive stage (R1). No resistant varieties Causes premature defoliation, reduction in seed size and numbers Can cause up to 80% yield losses

5. Where we are-What we know! Rust has been in China since 1902 Rust a bigger problem in Southern China, much less of a problem in Northern China. (Spores travel from south to north each year) Rust found in Africa in 1996 and South America in 1998. In South America, susceptible hosts present year around.

6. Where we are-What we know! Rust has become a serious problem every year in parts of South America because susceptible hosts are present year around. Ninety percent plus of soybean acreage is treated with a foliar fungicide Rust carried by hurricane to the United States in November 2004. Rust found in late soybeans in most of the Southeastern United States. Also found in kitzu in Georgia and Florida.

7. What we have done to prepare Training sessions have been and are being conducted on rust identification and control. Numerous educational materials have been developed to train personnel how to identify rust Section 18 registrations are being obtained to register fungicides for the rust control.

8. What we have done to prepare A list of seven fungicides which have shown efficacy in controlling rust in South America are in the process of being approved for use in the United States. Other fungicides are being added to the list and are under the process of being registered. A program has been underway to breed soybeans for rust resistance. No resistant varieties are expected for 6-8 years.

9. Next year-2005 growing season We do not know to what extent rust has infected alternative hosts in areas such as South Florida and the Caribbean where it can over winter. We have been unable to detect rust in many alternative hosts from these areas. Therefore, we believe that rust may or may not be a problem in the U.S. in 2005.

10. Next year-2005 growing season Therefore, we are establishing Sentential plots. Sentential plots are small plantings of soybeans which are planted 2-3 weeks before the rest of the soybean crop is planted and monitored for rust. We hope to plant sentential plots along the Gulf Coast and up the Mississippi river. If rust is found in these plots, we will alert producers.

11. Now What? Several different scenarios as to what will happen next have been proposed

12. Scenario One-most probable Rust hosts die this winter in most of the United States. The fungus will over winter in hosts such as in South Florida or South Texas or in the Caribbean etc. This is similar to what happens in China and the fungus will have be carried by wind currents to the Southern United States and from then to the Northern soybean growing areas.

13. Scenario One If this scenario happens, the severity of the disease would depend on wind currents etc and the disease would have to built up. If this scenario happens, the disease would be more severe in the Southern United States and would be a problem 1 or 2 years out of 5 in the Midwest and Northern United States

14. Scenario Two-Unlikely The fungus is able to over winter in alternative hosts such as crimson clover, vetch in the United States. If this scenario happens, the disease would spread from the alternative hosts and rust would be a problem throughout the United States. This scenario is unlikely because the fungus does not over winter in China on alternative hosts.

15. Scenario Three- Unlikely The fungus does not over winter in alternative hosts such as crimson clover, vetch in the northern hemisphere. If this scenario happens, the disease would have to be carried back into the United States by Hurricanes etc.

16. Best Guess? Rust will probably not be severe in 2005 because the fungus has not built up in alternative hosts in areas where these hosts are not killed by winter. (South Florida, Caribbean, etc). Rust will built up in these areas and after 2005 or 2006 rust will be blown into the Southern United States every year.

17. Best Guess? Rust severity when this happens will depend on wind currents, temperature and moisture etc after the soybeans are planted. It will be possible to develop forecasting systems to predict rust severity etc.

18. Rust Control and Management No resistant varieties for 6-8 years Cultural practices such as row spacing, seeding rates etc have little effect. We will have to depend on sentential plots and forecasting systems to identify and predict rust severity. Foliar fungicides will have to be used to manage rust.

19. Foliar Fungicides to Control Rust Experience in Africa and South America has shown that 1-4 foliar fungicide applications beginning at the R1 growth stage are needed to manage rust. Fungicide labels will read that if you have 3-5% rust infection, it is too late to spray Two main types of fungicides 1. Preventative or Protectant 2. Curative

20. Foliar Fungicides to Control Rust Preventative fungicides such as Quadris and Headline have to be applied before rust infection. Curative fungicides such as Tilt, Folicur, Loredo etc. have some curative properties after rust infection. Mixtures of preventative and curative fungicides such as Stratego are also used.

21. What to do? We are proposing the following options to producers 1. Plan on applying a foliar fungicide at R1 and R3. If rust is present use a curative fungicide. 2. Monitor the sentential plots and apply a fungicide when rust is detected. If this method is used you run the risk of missing rust infections and not applying the fungicide soon enough.

22. What to do? 3. Wait until rust is detected and spray. This is very risky because rust is hard to detect. If you do not have to spray until R3, or for the R5 spraying, it is recommended that a fungicide such as Quadris, Headline, or the mixture Stratego be used. The reason for this is that these fungicides control other late season diseases and the control of these diseases will help defray fungicide costs.

23. STROBILURINS PREVENTATIVE ACTION ONLY-cannot be applied after disease is present. VERY EFFECTIVE IN PREVENTING DISEASE DEVELOPMENT. DEPENDING ON DOSAGE CAN PROVIDE LONG PERIODS OF DISEASE CONTROL CANOPY COVERAGE CRITICAL. CONTROL A NUMBER OF OTHER DISEASES.

24. QUADRIS (Syngenta) Common name AZOXYSTROBIN Preventative action only. Potential for resistance to develop. Depending on dosage, active for several weeks. Use rate 6.2 oz/A. Can be up to 15.4 oz/A. Cost per acre for each application=$12.89 for fungicide + $3.90 ground or 5.47 aerial applications costs.

25. HEADLINE (BASF) Common name Pyraclostrobin Recommended as a preventative, has some systemic activity. Potential for resistance to develop. Not quite as long lived as Quadris. Use rate 6.0 oz/A. Can be up to 12 oz/A Cost per acre for each application=$10.83 and up for fungicide + $3.90 ground or 5.47 aerial applications costs.

26. TRIAZOLES Primarily Preventative action but can have some curative activity. Some are very systemic and therefore spray coverage not as important. Some are short lived. No resistance to trizoles confirmed. Control some other diseases. Often mixed with other fungicides to manage fungicide resistance.

27. TILT, BUMPER, PROPIMAX(Syngenta, Dow, etc.) Common name PROPICONAZOLE. Has curative activity Short lived Often mixed with other fungicides. Use rate 4.0 oz/A. Can be up to 8 oz/A Cost per acre for each application=$10.16 and up for fungicide + $3.90 ground or 5.47 aerial applications costs.

28. FOLICUR (Bayer) Common name TEBUCONAZOLE. Has some curative activity. Looks good in trials in South America. Very systemic. Use rate 4.0 oz/A. Cost per acre for each application=$10.47 for fungicide + $3.90 ground or 5.47 aerial applications costs.

29. LOREDO, SYSTHANE (Dow) COMMON NAME MYCLOBUTANIL. Has some curative activity. Systemic. Use rate 4.0-8.0 oz/A. Cost per acre for each application=$5.75 and up for fungicide + $3.90 ground or 5.47 aerial applications costs.

30. DOMARK (Valent) Common name TETRACONAZOLE. Has some curative activity. Systemic. Looks good in South America. Use rate 10.0-13.0 oz/A. One of original seven to be granted a section 18 label when rust was found. Soybean registration pending. Cost per acre for each application=$12.42 and up for fungicide + $3.90 ground or 5.47 aerial applications costs.

31. CARAMBA (Bayer) Common name METCONAZOLE. Has some curative activity, systemic. Registration to be submitted in Feb. Use rate unknown. May also be premix with Headline Cost per acre for each application unknown + $3.90 ground or 5.47 aerial applications costs.

32. PUNCH (Dupont) Common name FLUSILAZOLE. Has some curative activity, systemic. Registration to be submitted in Feb. Use rate unknown. Also premix with famoxadone (Charisma) Cost per acre for each application unknown + $3.90 ground or 5.47 aerial applications costs.

33. IMPACT (CHEMINOVA) Common name FLUTRIAFOL. Has curative activity, systemic. Registration to be submitted in ?. Use rate unknown. Has looked good in South America Cost per acre for each application unknown + $3.90 ground or 5.47 aerial applications costs.

34. ALTO (SYNGENTA) Common name CYPROCONAZOLE. Has curative activity, systemic. Registration to be submitted in Feb. Use rate unknown. Has looked good in South America Also premix with Quadris = Quadris Extra Cost per acre for each application unknown + $3.90 ground or 5.47 aerial applications costs.

35. JAU6476 (BAYER) Common name is PROTHIOCANAZOLE. Has curative activity, systemic. Registration to be submitted in Feb. Use rate unknown. Also premix with Trifloxystobin Cost per acre for each application unknown + $3.90 ground or 5.47 aerial applications costs.

36. OTHER FUNGICIDES-BRAVO, EQUUS, ECHO (Syngenta, etc.) Common name CHLOROTHALONIL. Protectant activity only Short lived Not as effective as other fungicides Use rate 1 1/3 pt 2 � pt/A Cost per acre for each application = $7.20 and up for fungicide + $3.90 ground or 5.47 aerial application costs.

37. FUNGICIDE MIXES Two modes of action- reduces chances of resistance to fungicide building up. Broader spectrum of activity.

38. STRATEGO (Bayer) Mixture of trifloxystrobin + propiconazole Use rates of both fungicides are lower than when the fungicide is used alone.

39. PRISTINE (BASF) Mixture of pyraclostrobin + boscalid One of original seven to be granted a section 18 label when rust was found Boscalid has little activity on rust. Not registered on soybeans.

40. QUILT (Syngenta) Mixture of azoxystrobin + proponazole Use rates of both fungicides are lower than when the fungicide is used alone. Registration will be submitted in February.

41. Some Final thoughts It is an advantage to grow short season varieties (IV and early V) because fewer fungicide sprays are needed. It may be an advantage to plant early because the early planted beans are maturing in July and August when it is hot and weather conditions are not favorable for rust development.

42. Some Final thoughts Rust is manageable, however rust control will add $30-50 per acre to the cost of growing soybeans. Rust control must began before the disease is severe in your field. Rust has been managed in other areas where it is present and it can be managed in the United States.