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Late-Season Issues in Midsouth Soybeans--2017

Midsouth soybean producers must continually monitor their crop from planting until harvest to ensure that factors that will limit yield and profit potential are managed effectively during the entire growing season. Two pests that should be watched closely during the latter part of the season are soybean rust and insects.

In Aug. 5, 2017 posts on the MCS blog site, MSU Extension Specialists Drs. Tom Allen and Trent Irby provide a Soybean Rust Update, and MSU Extension/Research Specialists Drs. Catchot, Cook, and Gore provide advice for late-season management of Redbanded stink bug [RBSB].

Soybean rust first appeared in the US in the fall of 2004. Since that time, there have been only isolated instances of rust infestations in Midsouth soybean fields. However, during the 13-year period since its first incursion into the country, there has always been concern that this disease could have a devastating effect on the US soybean crop; this has not happened.

In the rust update, the authors provide the following points/information related to soybean rust.

   Rust development is more likely to occur when weather conditions are cool and wet. Thus, the hotter and drier conditions in Miss. during July and August are not conducive to its development.

   In early August, soybean rust was found in variety trial plots located southwest of Jackson, Miss. and in Noxubee County, Miss. They surmise that these findings indicate that soybean rust likely moved through the state some time ago.

   Soybean plants at the R5.5 and later growth stages are considered to be beyond risk of yield loss from rust incursion.

   Strobilurin fungicides are not effective on rust if it is already present in a field. Therefore, fungicide products that are applied to soybean in the area of the state where rust has been detected should be a premix or tankmix of strobilurin + triazole products since the triazoles are active against the rust fungus if it is present.

   Fields of soybean that have already received a fungicide premix or tankmix product applied at the R3-R4 stage and that have reached R5 do not need a second fungicide application.

   Late-planted soybeans that are still in vegetative development stages should be monitored closely for rust incursion.

In the RBSB article, the authors provide the following information.

   RBSB thresholds are much lower than those for traditional stink bugs (southern green, green, and brown). LSU recommended threshold for treatment is 4 per 25 sweeps. This cannot be doubled at the R6 stage, and treatment sprays cannot be terminated at R6.5.

   RBSB damage to developing seed appears to be much greater and deeper into the season than that resulting from other stink bug species.

   As early-planted soybeans near maturity, RBSB numbers will increase in later-planted soybeans at an accelerated pace.

   RBSB preference is soybeans that are in the R5 to R6 stages of development.

   Since RBSB treatments will be applied closer to harvest, increased awareness is required for preharvest intervals of insecticides that target RBSB.

The RBSB issue has become such a hot topic this year that an Emergency RBSB Forum has been planned for Thursday, Aug. 17 at 2PM in the Capps Center on the DREC campus in Stoneville, Miss. The goal of this ArkLaMiss emergency forum is to provide and share all current data associated with RBSB damage potential and how to best manage this pest to minimize such damage. The meeting is free and open to all who want the latest information about this pest, and will be live-streamed for those who cannot attend. Check the MCS blog site early in the week of Aug. 14 for final details.

Composed by Larry G. Heatherly, Aug. 2017,