For those that you have been following the recent storms there is some news related to soybean rust: From the Soybean Rust website (www.sbrusa.net), This is where the modelers ­ forecasters have been placing weather data.

This week they are predicting that soybean rust spores were picked up on tropical storm Erin and potentially deposited in Ohio. Don’t panic, don’t get excited and don’t get out the fungicide sprayers. These are predictions/speculations ­ and as part of this, the inoculum levels are very, very low­10 spores per 2.5 acres. To put this in a better perspective, when researchers inoculate in the greenhouse they need 1,000 spores ml and 2 to 3 mls are applied to each plant in order to get 1 to 2 pustules per leaf.

If the modelers were correct and soybean rust spores were deposited in Ohio over the past 2 days, and those spores were viable and they landed on a soybean leaf and did not end up in the river, it would take us a minimum of 10 days to find the first pustule and more likely 3 weeks to find the leaves/area where an infection occurred (due to the low inoculum) this would still be at very low incidence/severity for a field and well within anytime frame to make recommendations for our double crop. We will begin to increase our sampling following Labor day to determine a) if rust is present and b) if these model predictions are correct. Basically the ground-truthing can begin. In a case like this with spores from a hurricane or tropical storm, the inoculum is so diluted over the region that we can monitor the sentinel plots to make individual county/region fungicide predictions. Most of Ohio’s crop is well past any effect of this fungus on the crop.

This is a good time to remind everyone that our sentinel plot system has 2 purposes: 1) information for our own fungicide recommendations and 2) ground-truthing for these models. I’ve been on the phone today with several colleagues – the high temperatures are not expected to slow the fungus down – so next Tuesday would be the first day to find the first pustule – one on one leaf in 2.5 acres…..

I’m currently in negotiations on prizes if anyone finds it – however we will be running some markers on the soybean leaves to be sure it is a Ohio variety!

It will be interesting if this prediction proves to be true…we are not recommending any fungicides at this time and we still are required to go through the process of having USDA confirm a positive find. You are more than welcome to submit samples to our labs if in your scouting you find anything suspicious.

The map for the deposition looks like this:

Dr. Anne E. Dorrance
Associate Professor
Dept. of Plant Pathology
The Ohio State University, OARDC
1680 Madison Ave.
Wooster, OH 44691

web: www.oardc.ohio-state.edu/ohiofieldcropdisease/

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