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Too late to do harm: Asian soybean rust found in southeast Texas

Although too late in the season to do much harm, Asian soybean rust has found its way to a Dayton-area kudzu patch in southeast Texas' Liberty County.

“Beyond seeing how late the rust can travel, I don't think this means much,” said Tom Isakeit on the day of the announcement. The Extension plant pathologist with Texas A&M University said producers are finishing up harvest all over the state.

“Liberty County is no exception. I looked at some of the few remaining soybean fields around there earlier this week. One producer told me he'd be harvesting his last beans in a week or so.”

While following the progression of soybean rust across the Southeast, Isakeit has been checking Texas soybeans and kudzu throughout the growing season. Several weeks ago, when Louisiana Extension specialists announced they'd found the disease east of Baton Rouge, La., Isakeit began to return to his search with new vigor. On Nov. 2, he found the disease in the sole patch of kudzu in Liberty County.

“In this particular region of Texas, there's hardly any kudzu. Actually, kudzu isn't widespread in Texas, period. The owner of the property where rust was found told me his kudzu patch dies back in the winter. Unless this winter is abnormally mild, the next freeze will likely mean the end of any major source of innoculum from that area.”

Despite long searches in soybean fields, kudzu patches and sentinel plots, no other rust infections have been reported in Texas. “I did find a sufficient amount of green leaves — although they were senescing quickly — on some of the plants so I could make some assessment of history. I was looking for any evidence of rust infections from several weeks ago. I found no signs of any infections.”

Still, it's possible there were beans infected in the state that weren't noticed. “I have no evidence of that, but it could have happened. If that occurred, though, it was after the crop was made — well past pod-fill.”

Isakeit allows that his finding could stoke concerns about the rust being closer to south Texas, a potential overwintering spot for the fungal disease. “There's little to no kudzu in the Rio Grande Valley, so I don't know what the rust would overwinter on. Maybe cowpeas are a possibility. Regardless, I see zero impact on Texas soybeans this year. If there's a threat, I don't believe it's from this particular kudzu patch. Any hedging I do is in case we don't see a freeze this winter.”

Isakeit believes the rust rode into Texas on Hurricane Rita.

“I'm not an epidemiologist or meteorological expert, so I'll leave it to them to say whether my belief about Rita being the carrier is a possibility or not. There are people who do modeling and could look at sources of spores — maybe from Florida or Georgia — and calculate whether or not winds could have moved it over here.

“My thinking in terms of risk to states further north of us is based on prevailing wind patterns. There's more risk if rust ever establishes in Mexico or Central America. If that happens, it is likely rust spores would follow the same wind paths that cereal rust does.”

Early every year, south Texas winter wheat is hit with cereal rust. As wheat is planted and grows further north, the rust travels up the country.

“That's a well-established pathway. I think soybean rust would follow a similar route.”

Texas soybean growers are concerned about the impact of Asian soybean rust because they don't typically get yields as high as those in the Midwest. With higher yields it's “easier to justify a fungicide application. Producers I speak with don't usually get much more than 35 bushels to the acre.

“We still don't know how the disease will act in Texas. But based on published information about temperature parameters the rust can handle, it's likely the Texas bean crop is at its most vulnerable at a time of the year that isn't favorable for the rust. It's maturing, flowering, and filling pods at a time when temperatures are normally too high for the fungus to do well.

“In other words, in most years we may escape any severe impact. That's my prediction, anyway.”


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