CORN Newsletter: 2005-05, March 8, 2005

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C.O.R.N Newsletter 2005-05
March 8, 2005 - March 22, 2005

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Soybean Rust Update after the Brazil Trip
by Anne Dorrance


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Well, it appears that this rust fungus overwintered in Florida. Tests were started late last week to determine if the spores were still viable but from the appearance of the tissue in the picture, I would be surprised if they were not new lesions. It is still not time to panic. I learned a lot in Brazil and at the rust meetings in Arizona last week, and the take home messages at both meetings were:

1. THIS IS MANAGEABLE – we saw humungous fields in Brazil and the only place where we could find active rust lesions were in the check plots and in the skips of the sprayers. US producers will actually have more resources available than the Brazilians to assist in tracking and monitoring soybean rust in the US, and to assist in the best timing of fungicide applications. Production practices differ in Brazil for managing this disease based on latitude as well as disease pressure. One thing the farm managers all said that every year has been different and rainfall plays a key role in how the disease develops.

2. Fungicide timing is key to limiting losses – both strobilurin and triazole fungicide chemistries work best if applied prior to spore arrival. Not 2 weeks before – but just prior. Triazoles have the added benefit that if lesions have started they can stop or arrest development for the length of time the fungicide is in the leaf.

3. Coverage and canopy penetration are critical to the ability of the fungicides to limit development. This is a lower canopy disease. It is still not clear why, we heard conflicting information on this, but the bottom line is that this is where the fungicide needs to go.

4. The critical time to protect plants will be from beginning flowering (R1) to full seed (R6). This is where the greatest yield losses do occur. It is rare that infections can get established in the late V-stages. But this is one of those cases where we will have to monitor.

5. Rust is going to be challenge to diagnose. Early brown spot looks exactly the same as early rust lesions. Once the uredinia and spores are produced on these lesions – it’s a no brainer and then becomes easy to identify.

6. When to begin fungicide applications and what products to use will depend on two things – how much inoculum actually builds-up in the southern US. For example if this rust development is slow and does not spread to Arkansas until late June – this will delay all of our fungicide applications. If the rust develops quickly through the spring and Kentucky is reporting active lesions by mid-June, we should be applying fungicides much earlier.

7. We are still waiting for some final details to be worked out on the monitoring system. At this point, Ohio will have 30 plots (20 courtesy of United Soybean Board via check-off dollars and 10 USDA-APHIS and Ohio Dept. of Agriculture Plots). ALL suspect finds will go through the OSU C.Wayne Ellett Plant and Pest Diagnostic Clinic for verification prior to uploading into the national database. This national database is not launched just yet, but when it is – we will all have access to this map and can all monitor the development of rust.

One final thing – this is going to be a very dynamic situation. Companies are going to “tweak” their labels based on the data from this past year in South America. By soybean flowering time here – some of this should be settled as well as some additional Section 18s. This is the first time this disease will have developed in the US and we will learn the hard way what can be easily transferred from South America and what can not. But I think in the long run, with a little common sense and some cool heads, we can deal with this – even better than they have in South America.

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C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.

Information presented above and where trade names are used, they are supplied with the understanding that no discrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.

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Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.

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