May 25, 2006
From: ProMED-mail<promed@promedmail.org>
Source: agriculture.com [edited]
<http://www.agriculture.com/ag/story.jhtml?storyid=/templatedata/ag/story/data/1148574163981.xml&catref=ag1001>


A bout of Asian soybean rust left more than 20 soybean seed growers near Tampico, Mexico, unexpectedly dealing with the disease. About 320 hectares, or 650 acres, were affected, resulting in defoliation and potential large yield losses.

ASR infections began in January 2006 but became increasingly noticeable in March and April. "It caught these particular growers by surprise, and it hit them pretty hard," said Dr. Marty Wiglesworth, Syngenta technical brand manager, fungicides.

Seed beans are generally harvested at the end of April into early May, so the majority of the affected acres should be out of the ground. Mexican growers will begin planting more soybeans closer to the Texas border in late May. According to Wiglesworth, the time gap between harvesting the seed beans and planting additional soybeans may be good news for U.S.
soybean growers.

"We cannot foresee whether the impact on the U.S. crop will be minimal. We don't know at this point," Wiglesworth said. "It depends on whether there are nearby patches of volunteer soybeans or kudzu for ASR to live on until the newly planted Mexican crop becomes susceptible at R1. Scouting fields is the prudent thing to do."

Potentially, Wiglesworth said ASR could be equated to the wheat rust that comes yearly out of Mexico and Texas into the Midwest. "If ASR establishes itself on a regular basis in Mexico, one possibility is that it could follow a very similar pathway as wheat rust. Overwintering ASR present in Florida and Georgia has a harder time moving directly into the Midwest unless there are unusual weather patterns, but Mexico could serve as a more consistent source into the Midwest. At this time, however, experts believe the current risk for rust in east Texas is low."

There are currently no effective fungicides labeled for use in Mexico for Asian Soybean Rust control, although Syngenta and other agrichemical companies are currently pursuing emergency exemptions for rust specific fungicides.

--
ProMED-mail
<promed@promedmail.org>

[The crop plant soybean, _Glycine max_, develops symptoms of the disease soybean rust (ASR), when infected by the fungus _Phakopsora pachyrhizi_, Asian strain.

ASR was found in Mexico for the 1st time on soybean leaves at the end of October 2005 in Tamuin, State of San Luis Potosi, and in Altamira, State of Tamaulipas, Mexico (20060219.0546). This new significant outbreak of ASR
in the 2006 soybean crop was found near the city of Tampico, which is east and south of these 2 previous locations, respectively. In previous updates on soybean rust in the USA (e.g. 20060226.0622) the possibility of Mexico becoming a major source of inoculum on an annual basis at the beginning of the ASR season has been voiced. Dr. Marty Wiglesworth mentions the same concern in this article. ASR has not been reported on newly planted soybeans in the USA to date (25 May 2006) in the 2006 crop season. Spores of the fungal pathogen were trapped in Texas this week but the question of the source was not addressed (see link). Any contribution of spores from the confirmed and other as yet unreported infections in Mexico may need to evaluated.

This article notes that the Mexican soybean crop nearest to the Texas border may escape infection from the infected plants in Tampico, which have now been harvested.

Earlier postings on ASR in 2006 in N. America are included in 20060518.1402 listed below.

Maps:
Mexico <http://go.hrw.com/atlas/norm_htm/mexico.htm>
Tampico <http://encarta.msn.com/map_701516937/Tampico.html>

Pictures: Pimple-like pustules on soybean leaves.
<http://www.plantpath.wisc.edu/soyhealth/rust/rustbrngh_small.jpg>

Links:
Spores in Texas: <http://www.stopsoybeanrust.com/viewStory.asp?StoryID=824>
<http://www.apsnet.org/online/feature/rust/ >
<http://www.usda.gov/soybeanrust/disease_info.shtml >
- Mod.JAD]

[see also in the archive:
Soybean rust, Asian strain update 2006 (04): USA 20060518.1402
Soybean rust - Mexico: 1st report 20060219.0546]