July 14, 2005
Source: stopsoybeanrust.com, 14 Jul 2005 [edited]
<http://www.stopsoybeanrust.com/viewStory.asp?StoryID=446>

Rust found in commercial soybean field in Baldwin County, Alabama

Asian soybean rust (ASR) was observed in a 60-acre commercial soybean field in Baldwin County, AL on 12 Jul 2005. The field is approximately 1 mile northeast of the soybean sentinel plots that were observed to have rust on 28 Jun and whose rust has progressed in the meantime.

According to Ed Sikora of Auburn University, ASR incidence within the field was estimated at 20 percent, with low disease severity. The field is estimated to be at the R4-R5 stage.

Sikora said that the field was sprayed with Stratego fungicide on 26 Jun, 2 days before it was detected at extremely low levels of ASR in our sentinel plots.

Sikora said that ASR has progressed in our sentinel plots. On 28 Jun, ASR symptoms were found on one plant in each of the 2 sentinel plots (planted side-by-side about 1 month apart). On 19 Jul, the older of the 2 plots had 100 percent disease incidence, and the younger plot had 75 percent incidence. No ASR was found on kudzu patches in the area, including patches located approximately half-way between the sentinel plots and the commercial field. Last week, he scouted 3 commercial soybean fields within 10 miles of the positive sentinel
plot; all 3 fields were at the V2 growth stage but no ASR was detected.

Soybeans are typically planted in late May or June in this county, Sikora said. The commercial field where ASR was detected is uncommon as far as its advanced growth stage for this area.

Growers in Alabama were told to consider spraying if the crop was between R1 and R6. Crops between bloom (R1) stage and pod fill (R6) stage should consider applying a premix or tank mix of a strobilurin and triazole-type fungicide. An application at the R3 growth stage, regardless if rust is reported in the immediate area, would provide about 3 weeks protection against ASR as well as reduce damage from Cercospora blight and frog-eye leaf spot.

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

[The first discovery of ASR in commercially grown soybeans in Alabama this season was recorded in Baldwin County, AL, on 12 Jul 2005. The field is mature for the area -- already at R4-R5 -- and had been treated with a fungicide 2 weeks prior to the finding. There are 8 growth stages for soybean: R1(1 flower at any node); R2 (flower at node immediately below the node with a completely unrolled leaf); R3 (pod is 1/2 cm long at 1 of the 4 uppermost nodes with a completely unrolled leaf); R4 (pod is 2 cm long at 1 of the 4 uppermost nodes with a
completely unrolled leaf); R5 (seeds beginning to develop [can be felt by squeezing or at least 1/8 inch long]) at 1 of the 4 uppermost nodes with a completely unrolled leaf); R6 (pod containing a green seed that fills the pod cavity at 1 of the 4 uppermost nodes with a completely unrolled leaf); R7 (Pods yellowing [1 normal pod on the main stem that has reached its mature pod color - brown or tan]); and R8 (95 percent of the pods have reached their mature pod color, approximately 5 to 10 days prior to harvest).

Control of ASR can be accomplished through utilization of fungicides and avoidance of very susceptible cultivars. Partial resistance or tolerance may be the most effective resistance strategies, especially when combined with stacked single genes or single genes with broad resistance.

Link:
<http://www.apsnet.org/online/feature/rust/>
- Mod.DH]

[see also in the archive:
Soybean rust, Asian strain - USA (FL): 1st report 2005 20050309.0693 Soybean rust, Asian strain - USA (GA) 20050429.1196 Soybean rust, Asian strain - Americas: alert 20050528.1476 Soybean rust, Asian strain - USA (GA) 20050505.1245 Soybean rust, Asian strain - USA (LA) 20050624.1769 Soybean rust, Asian strain - USA (FL) (02) 20050620.1731 Soybean rust, Asian strain - USA (LA) 20050624.1769 Soybean rust, Asian strain - USA (FL) (02) 20050620.1731 Soybean rust, Asian strain - USA (multistate)(03) 20050714.2005 Soybean rust, Asian strain - USA (multistate)(02): Florida 20050708.1938 Soybean rust, Asian strain - USA (multistate) 20050702.1868]