The information and recommendations in this newsletter are applicable to North Carolina and may not apply in other areas.
The information and recommendations in this newsletter are applicable to North Carolina and may not apply in other areas.
From: Jim Dunphy and Steve Koenning, Extension Crop Science and Plant Pathology Specialists
Asiatic soybean rust was confirmed today at the Central Crops Research Station near Clayton, North Carolina in the sentinel plot located there. Four pustules on one leaf out of 100 leaves were positive for SBR and they were sporulating. This morning we checked samples from sentinel plots in Columbus, Carteret, Granville, Wayne, New Hanover, and Edgecombe Counties that were all negative for soybean rust. We will receive samples from the rest of the sentinel plots today thru Friday. Rust was found yesterday at the research station near Suffolk, Virginia, about 15 miles north of Gates County, North Carolina. Rust has now been confirmed on soybeans in Alabama, Arkansas, Florida, Georgia, Kentucky, Louisiana, Oklahoma, Missouri, Mississippi, South Carolina, Tennessee, Virginia, and North Carolina.
If no symptoms of rust are visible on the underneath side of the lower leaves yet, it will typically take four weeks or so before much serious defoliation takes place. In four weeks from now, probably 80% of our state’s soybeans will already be defoliated anyway.
That leaves no more than 20% of our state’s crop to worry about. If no symptoms of rust are visible, and the soybeans have one or more pods in the top four nodes of the main stem with full sized seeds (seeds touching each other in the pod), the field is not likely to suffer economic damage from rust, and would not need to be sprayed with a fungicide. If no symptoms are visible, and there are no full sized seeds in the top four nodes, growers should seriously consider spraying with a triazole fungicide, or a combination of a triazole and a strobulurin. If other foliar diseases are also present or considered likely to develop, our preference would be to spray with a strobulurin fungicide, or a combination of the two types of fungicides. The benefit of fungicide applications after plants enter growth stage 6 is highly questionable and not recommended at this time because of the general lack of a yield response this late in the season. Be aware that the use of fungicides pursuant to section 18 permits for control of soybean rust is not legal after plants enter growth stage 6. Fungicides with a soybean label for control of rust or other diseases may also have restrictions that forbid late season applications or requirements for lengthy pre-harvest periods, plant-back restrictions, or other restrictions.
North Carolina farmers should continue to check their soybeans that have not yet gotten full sized beans in the top of the plants, and to continue to monitor reliable reports of where else rust has been found. An up-to-date map of where rust has been found is at http://www.sbrusa.net. The current version of these North Carolina updates should also be available at our Teletip line at 800/662-7301.
Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age or disability. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.
Last modified on September 30, 2009 by Stephen J. Toth, Jr.