The 2017 soybean growing season promises to be one of the best ever in terms of yield potential. However, it has also provided producers in a wide geographical area a challenge presented by the redbanded stink bug [RBSB–Piezodorus guildinii].
The RBSB is not a new pest, but its incursion into the upper reaches of the Midsouth is a relatively new occurrence. It is touted as a more destructive stink bug pest than those of other stink bug species such as the green [GSB–Chinavia hilaris], southern green [SGSB–Nezara viridula], and the brown [BSB–Euschistus servus].
Researchers Depieri and Panizzi conducted laboratory studies [Neotropical Entomology 42:197-203, 2011]in Brazil to compare the damage caused by various stink bug species. Their study included the SGSB [Nezara viridula] and the RBSB [Piezodorus guildinii], plus the Neotropical brown stink bug [Euschistus heros–same genus as the BSB found in the US]. Important results from their research follow.
• Feeding time did not vary significantly between the SGSB and RBSB.
• Feeding by RBSB on mature soybean seeds resulted in the deepest seed damage.
• Histological damage by RBSB photographed by an electron transmission microscope was greater than that caused by the other species. This suggests that the deleterious effect of RBSB salivary enzymes to seed tissues is greatest for this species.
• The greater damage to seed caused by the RBSB is not related to the length of the stylets, since bugs of this species have shorter mouthparts than the other species, including SGSB, used in the study.
• Based on the above findings, the authors surmise from their data that the greater damage to soybean seed caused by the RBSB is due to the higher level of seed tissue damage caused by its saliva.
Click here to access the Aug. 5, 2017 MCS blog post by MSU researchers/extension specialists that contains up-to-date details about treatments that can be applied to prevent this insect pest from damaging developing seed late into the season. Important summary points from this post follow.
• With traditional stink bug species [SGSB, GSB, and BSB], the treatment threshold for soybeans is 9 per 25 sweeps until R6 stage. At R6, the recommended threshold is doubled until R6.5 stage when treatment can be terminated.
• Seed quality deductions [dockage] at the elevator resulting from traditional stink bug species [SBSB, GSB, and BSB] in Midsouth soybeans rarely occur after R6.
• With RBSB, the treatment threshold is 4 per 25 sweeps, which is roughly half that for the traditional stink bugs.
• The treatment threshold for RBSB cannot be doubled at R6 and insecticide treatments cannot be terminated at R6.5 as with the traditional stink bugs.
• RBSB infestations can damage soybean seed [reduced test weight, reduced oil, reduced protein, and elevator dockage] as late as R7 [one pod on main stem at mature pod color].
An Aug. 2017 RBSB Forum held in Stoneville, Miss. provided up-to-date information about the RBSB. Producers who did not attend this meeting are encouraged to view the video of this program, especially the presentation by Dr. Jeff Davis, LSU Assoc. Professor. The RBSB arrived in Louisiana in 2000, reached north Louisiana in 2006, and is a constant problem for Louisiana soybean producers.
Dr. Davis provides results from LSU research that was conducted to determine treatment thresholds for the RBSB, its overwintering capability that is dependent on the number of consecutive hours of below-freezing temperatures, and the efficacy of various insecticides against this pest.
Other important points from his presentation are:
• Weather injury and RBSB injury appear similar.
• Below-threshold numbers of RBSB can reduce yield if present over a long period.
• Soybean varieties differ in their susceptibility to RBSB.
• RBSB only feeds on legumes.
• RBSB movies into soybean from legumes where it overwinters, and will feed on stems of pre-reproductive soybeans.
• RBSB females must be controlled early to reduce the number of eggs; i.e., more eggs = more RBSB.
• The majority of RBSB is found in the lower portion of the soybean canopy. Thus, sweep net sampling may underestimate RBSB numbers, and insecticide effectiveness will depend on ground speed and volume of the spray solution [i.e., slower speed and greater volume will enhance control].
• Three insecticide applications should be budgeted for RBSB control in years when they are anticipated to occur.
• RBSB resistance to insecticides is developing, and will be permanent where it develops. Thus, rotation of insecticide chemistries is paramount.
• Soybean is still susceptible to RBSB damage even after harvest aids are applied. Control after this point is necessary to prevent seed weight loss, to prevent movement out of an infested field, and to reduce overwintering populations.
• Since legumes are the exclusive feeding source for RBSB, a cover crop mix that includes a legume will increase RBSB populations. This is especially so for a mix that includes crimson clover since it is the preferred overwintering host for this insect.
Again, producers should view the presentations made at this forum to get up-to-date information about the RBSB so that they will be prepared to manage this pest if/when it occurs.
Composed by Larry G. Heatherly, Aug. 2017, firstname.lastname@example.org. Thanks to Dr. Angus Catchot, MSU Extension Entomologist, for providing resources and review.