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"Ten spores not enough" to determine, spread soybean rust
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7/11/2005 -- In her agronomic newsletter article this week, Anne Dorrance of Ohio State stated her bottom-line reaction to the news of rust-like spores being found in Kentucky: "Ten spores is not enough."
Here's her commentary from the Crop Observation and Recommendation Network newsletter for July 11-19, 2005:
The big news last week was that 10 spores, which look identical to soybean rust, were identified in a spore trap in Kentucky; two spores were found in Tennessee. NO SOYBEAN RUST HAS BEEN IDENTIFIED IN ANY GULF STATES – except a sentinel plot in Baldwin County, Ala. These spore traps were established throughout the south, courtesy of Syngenta, to assist in monitoring.
When spores are found, comparisons are made with the environment that occurred during that week. From the Kentucky reports, the environment was not very favorable. Scouting will intensify over the next two weeks in Kentucky to determine if any rust was established.
The inoculum in the United States is very, very, very low. With these hurricanes, the inoculum is being dispersed over a wide, wide area. Hurricane Ivan brought spores from northern South America -- it took from mid-September to early November before this rust could be detected. It appears at this point, based on inoculum levels in Alabama -– that Dennis will carry even lower levels of inoculum.
We will be monitoring fields the last week of July and first two weeks of August – to see if Dennis brought us any rust. It takes five to 10 days for lesions to form, but 10 days for spores to develop on these leaves. If it continues to stay hot and dry – it may take even longer.
One of the challenges of this past winter is that we only had information from Brazil to base guidelines and predictions. It is apparent now that one of the big differences between the two areas is the total inoculum. Brazil especially has very high levels of inoculum from a number of sources. Here in the United States this year (2005), this really has not developed.
It’s like starting a camp fire: you need a lot of small sticks and paper to get the fire going, we’ve only got a twig.
Fungicides are not recommended for Ohio for the next few weeks. In fact, with the number of fields with spider mites, adding fungicides may exacerbate another problem.
Source: C.O.R.N. newsletter, July 11-19, 2005, edition.
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