Soybean rust: time is on its side

In terms of Asian soybean rust development, Florida and Louisiana might as well be on 2 different continents.

One state - Louisiana - continues to receive rain. More fell across a wide part of the state yesterday and last night.

The other state - Florida - continues to suffer under a drought that actually started in 2006. Forest fires that began in south Georgia have since spread into northern Florida, forcing the state to temporarily close at least 2 interstates due to poor visibility caused by smoke.

These opposite weather conditions are giving rust plenty of running room into the central part of the continent but, so far, denying it entry into the Southeast and up the Atlantic Coast.

Rust was discovered on May 8 in Iberia Parish in south Louisiana, 53 days ahead of the first sighting in the state in 2006. Several factors now favor additional movement from that point:

• Plenty of rain. The Midsouth and lower Midwest have received ample showers to give rust places to propagate. That's in sharp contrast to 2006 when a spring and early summer drought created almost a "scorched earth" boundary between rust in south Louisiana and the rest of the Delta and regions farther north. Some growers in Mississippi made nearly their entire cotton crops with irrigation. In other words, there was no moist, humid climate to nurture spores.
  
• Later soybean plantings. Parts of the Delta have been pushing for earlier and earlier soybean plantings since the mid 1990s, but that hasn't been the case in 2007. Dry weather and a focus on planting corn held up most of the "ultra early" soybean seeding in Mississippi, south Arkansas and northeast Louisiana. By the time soybean rust got rolling last year, a large portion of the soybeans in these areas already had been cut, denying rust an easy stopover in its path north. While these areas will have fewer soybeans - one soybean seed salesman told us his territory in Louisiana and south Arkansas will be off 20% - there will still be plenty of locations for rust to lay over. And because of all the late planting, the welcome mat will be out longer.
• Louisiana missed most of the freeze. Yes, it got cold in southern Louisiana, but the region didn't experience any hard freezes. South Georgia and north Florida, on the other hand, saw a significant amount of dieback on kudzu, a main native host for soybean rust. That likely gave soybean rust more opportunity to establish itself in Louisiana's Acadian parishes, so the early find this year shouldn't be surprising.
• Time is on rust's side. Several plant pathologists who've followed rust development on other continents speculated that the disease probably wouldn't be much of a factor for at least the first couple of years after it made landfall in the U.S. It would take time for it to find niche areas to linger over the winter. Well, a couple of years have now passed.

Florida, in contrast, is dry, and so are most areas north of it into Alabama and Georgia. The drought has held up most dryland planting of any kind and delayed emergence where seed have gone into non-irrigated fields.

The following was posted on USDA's soybean rust web site by Florida Extension workers:

It is still very dry, and Florida is burning. If smoke, alone, could kill the rust, we probably would have eradicated it by now. We had some scattered rain, but the soil is very dry and leaf moisture from dew is still limiting. The forecast is for continuing dry weather. The kudzu is growing rapidly and in those sites that are infected the rust is progressing slowly. We have not had any sites become negative since the winter, but thus far we have found fewer positive sites than in previous years.