Asiatic Soybean Rust Update

Reprinted from North Carolina Pest News
Steve Koenning, Extension Plant Pathologist
Jim Dunphy, Extension Soybean Specialist

Asiatic soybean rust has been confirmed in Robeson and Johnston counties, North Carolina. Between this find, and the confirmation of rust in Robeson County, North Carolina, and in Union County, Georgia, this puts rust approximately 105 miles from Charlotte, 140 miles from Elizabeth City, 15 miles from Fayetteville, 15 miles from Murphy, 35 miles from Raleigh, 80 miles from Washington, 75 miles from Wilmington, and 80 miles from Winston-Salem, North Carolina.

We do not recommend spraying soybeans with a fungicide to control Asiatic soybean rust if they are not yet blooming, if they are blooming but rust has not been confirmed within 100 miles, or if full sized seeds are present in the top of the plant (stage R6). Such pre-bloom applications have seldom improved yields, and repeated applications will likely be needed to provide season-long protection against rust. The higher labeled rates tend to provide more days of prevention, and may thus require fewer applications. The triazole fungicides, alone or in combination with a strobilurin fungicide, will probably provide better prevention of rust than a strobilurin alone. Be sure to check the fungicide label to see how many times it may be used in a season.

An exception to the above recommendation is if Asiatic soybean rust is found on the farm before bloom, spraying a fungicide to the rest of the fields on the farm is recommended. Soybeans that have just reached full bloom (stage R2) typically have 65 days until they’re safe from rust or frost (stage R7) if they are full-season soybeans, or closer to 55 days if they are double-crop soybeans. If they have small pods in the top of the plants (stage R3), they have 55 and 47 days, respectively, to R7. With full sized pods in the top of the plants (stage R4), they have 45 and 38 days, respectively, until R7. From stage R5 (small seeds in the top of the plant) they typically have 35 and 30 days, respectively. From stage R6 (full sized seeds in the top of the plants), they typically have 20 and 17 days, respectively.

Rust will typically take 10 to 20 days from initial infection to develop to detectable levels. It will take another 7 to 14 days to spread to other leaves on the same plant, and another 10 days to cause significant defoliation.” This assumes optimal conditions for rust, “65 to 85 degrees, and either overcast or rainfall” through much of this period. This is not common in North Carolina in September and October but has and can occur.

The rust prediction models say there was a fair to good chance rust spores were deposited in North Carolina this weekend. If so, we expect to detect rust in about three weeks in sentinel plots, which would be about October 1. It will likely take another two weeks with optimal conditions for rust to increase to damaging levels.

The current status of soybean rust in the U.S. can always be found at http://sbr.ipmpipe.org/cgi-bin/sbr/public.cgi.

Alert: Soybean Rust Found in Georgia!

North Carolina State University and Cooperative Extension

Steve Koenning Extension, Soybean Pathology Specialist,

and Jim Dunphy Soybean Specialist, Crop Science

ASIATIC SOYBEAN RUST FOUND ON SOYBEAN IN DECATUR AND COLQUITT COUNTIES IN GEORGIA

 

Alert: Soybean Rust July 6, 2012:

“Conditions have been quite favorable for spread of soybean rust in Georgia; we now have confirmed soybean rust on kudzu in Decatur, Miller, Baker, Brooks, and Lowndes Counties; soybeans in Decatur and Colquitt Counties. Most soybean acreage along Georgia Coastal Plain will be sprayed with fungicides at bloom-early pod set for rust and anthracnose and insecticides added for kudzu bug.”

Weather has not been conducive to build up of rust with the high temperatures in North Carolina, thus it may be premature for North Carolina soybean producers to spray soybean for rust. Be prepared, however, and remember that applications for Southern Rust of Corn may compete with fungicide/insecticide applications on soybean in terms of the numbers of aerial applicators and amount of fungicide available.

The current status of Southern rust, Asiatic soybean rust, and various other spreading pests in the U.S. can found here  or here

More information is available here 

Domark 230me is not listed in the Ag Chem Manual for corn at this time but is labelled at a rate of 4-6 oz. per acre.

When deciding to spray a fungicide, consider these factors in decision making!

1. When will the corn reach maturity – early maturing corn may escape infection and you might want to concentrate on the later maturing hybrids.
2. Strobilurins provide excellent control of rust in general but their residual activity is short compared to the triazoles. Additionally, Strobilurins have limited systemic movement in plants compared to triazoles such as Tilt, Folicur, Domark, Caramba, and Proline, and are thus less forgiving of less than perfect application.
3. Application costs may actually be greater than fungicide costs in many instances, so consider using the higher fungicide rate which will provide more residual protection and increase the likelihood that you can get by with one application.

Vigilance is the key word for 2012! Most sentinel plots have been planted and we will have about 14 this year. Storms following a track similar to Beryl’s could bring rust to North Carolina later in the year.

Resources for Soybean Rust in 2012: 

Some sources for more detailed information on Asiatic soybean rust and Southern corn rust are listed below: 

The North Carolina Agricultural Chemical Manual

Soybean Rust Management in the Mid-Atlantic Region