Soybean Rust Update: July 30, 2012

Soybean rust distribution in MS as of July 30, 2012.

Since last Thursday (7/26/12), additional soybean rust was detected in commercial soybean fields (Jefferson, Pike counties) as well as sentinel plots (Issaquena, Pearl River counties).  In all cases, soybean rust was detected at low levels in growth stages ranging from R5.2 to approximately R6.  The recent observations bring the total number of counties reporting soybean rust in MS to 5 (George, Issaquena, Jefferson, Pearl River, Pike).  Historically speaking, since November 2004, soybean rust has not been detected in 5 MS Counties in the month of July.  In addition, the observation in Issaquena County is the earliest that soybean rust has ever been detected in the Delta.  Prior to 2012, the earliest detection of soybean rust in the Delta was August 6, 2009 (Humphreys County).  Within our region, soybean rust continues to be detected in Louisiana in commercial soybean fields that border western MS.  At present, Issaquena County marks the farthest northern progression of the disease for the 2012 season.The effectiveness of the soybean sentinel plot program is highlighted by the recent soybean rust detections in 3 (George, Issaquena, Pearl River) of the 21 sentinel plots prior to commercial soybean fields in the area.  Early planted soybean plots, containing several different maturity groups to extend the period of reproductive growth stages, continues to provide protection for MS soybean farmers.  Soybean is most likely to become infected and a yield loss occur as a result of infection during early reproductive growth stages (R1-R4).  However, low levels of soybean rust in a field in the R5 growth stages will typically require several weeks to produce enough inoculum to injure yield.  Funds were provided to maintain the sentinel plot program throughout the state for the 2012 season by the Mississippi Soybean Promotion Board and the United Soybean Board.

Management alternatives

Soybean rust observed on the upper side of the leaf. However, the best way to detect the disease is based on the observance of the underside of the leaf.

Presently, based on the generally light nature of soybean rust at each location we are not suggesting that a large scale fungicide application be made.  We continue to believe that monitoring for the presence of the disease and then making a fungicide application when necessary is likely the best management alternative.  In addition, the environmental conditions we’ve experienced over the past 7 days are not considered to be conducive for the further development of soybean rust.  Generally speaking, environmental conditions with temperatures in the 90s during the day, and ample sunlight are not considered to be conducive for further spread and development.

Several different management scenarios were outlined in a previous blog posting.  At this time the management suggestions remain the same since the majority of the soybean crop in the general vicinity of the infected locations is beyond R5.5.  However, to look at the previous management suggestions follow the link:

https://www.mississippi-crops.com/2012/07/16/soybean-rust-detected-in-a-sentinel-plot-and-commercial-soybean-fields-in-george-county/

Environmental conditions and scouting situation

We will continue to scout soybean sentinel plots, commercial soybean fields, and to a lesser extent kudzu throughout the state.  A few kudzu patches will continue to be scouted simply because they have previously been determined to be susceptible to the fungus and they serve as an early warning in addition to soybean sentinel plots especially in counties where soybean is not grown.

At present, the Maturity Group III and IV in soybean sentinel plots have reached physiological maturity (R8).  The MG V and VII are presently between R5.8 and R6 depending on location.  The sentinel plots in Hinds and Jackson counties are not as far along as the rest of the sentinel plot locations since they were planted later.  The Hinds and Jackson county plots range from R4 (Jackson) to R5.4 (Hinds).  Additional sentinel plot locations are present in: Adams, Amite, Claiborne, Hancock, Monroe, Newton, Noxubee, Pike, Prentiss, Tippah, Tishomingo, Walthall, Warren, Washington, Wayne, and Wilkinson counties.

Stay tuned to the soybean rust public website (www.sbrusa.net) and the FREE telephone hotline (1-866-641-1847) that provides current information from AR, LA, and MS regarding the presence of soybean rust and any particular management alternatives.  The telephone hotline is sponsored in part by the Mississippi Soybean Promotion Board.