Stink Bugs and Redbanded Stink Bugs in Soybeans- What to do?
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Over the last few weeks we have been getting more and more calls about redbanded stink bug in soybeans. Redbanded stink bugs (RBSB) are voracious seed feeders, infest fields later, and are more difficult to control than greens, southern greens, or brown stink bugs. It appears that RBSB are very sensitive to cold winters which reduces their numbers dramatically in our area. The last year we had significant RBSB numbers was 2009, however, we have been finding them in the south delta for a couple of months and they are moving north. To date there have been several fields sprayed targeting RBSB. Ironically, greens, southern greens, and browns have been unusually light this year but numbers are starting to pick up in some places now.
Stink Bug Thresholds in MS:
For green, southern green, and brown stink bugs treat when populations reach 9 adults and or nymphs greater than 1/4 inch per 25 sweeps.
For redbanded stink bugs treat when populations reach 6 adults and or nymphs per 25 sweeps.
Terminating Stink Bug Sprays in Soybeans:
For green, southern green, and brown stink bugs use thresholds of 9 per 25 sweeps until R6. At R6 double to 18 per 25 sweeps and terminate sprays at R6.5.
For redbanded stink bugs use a threshold of 6 per 25 sweeps until R6. At R6 double to 12 per 25 sweeps and terminate at R7 instead of R6.5.
R6, R6.5, and R7 Growth Stages
R6 Growth Stage
We are referring to R6 when beans in the uppermost 4 nodes are “squared off” not just “barely touching”
R6.5 is when the beans begin to separated from the pod wall. If you correctly ID the R6 growth stage, R6.5 will be approximately 7-10 days later regardless of planting date or variety.
R7 is when you find one brown pod anywhere on the plant
Quality Loss in Soybeans from Stink Bugs:
Typically we manage stink bugs until near harvest but there are several things to consider before making an application to control stink bugs in beans beyond R6 growth stage.
1. Once all pods are R6, measurable yield loss from stink bugs is very low to none.
2. After R6 stink bug issues are mainly restricted to quality loss and possibly creating avenues for disease to set in if harvest is delayed.
3. Soybeans can tolerate many more stink bugs than “normal threshold” past R6 before quality deductions are measured.
4. Preharvest intervals for insecticides becomes a consideration.
5. Consider a desiccant soon as possible if RBSB numbers are increasing after R7.
Stink bugs cause yield loss typically by feeding on developing seed throughout the R5 growth stage. If seed are not fully developed in the pod, seed fed on by stink bugs are often aborted or shriveled up. Seed fed on at R6 stage and beyond typically do not shrivel or lose size but have a feeding legion on the seed. However, LSU has shown that redbanded stink bug and southern green stink bug do can reduce seed weight some but not green and brown stink bugs past R6. When elevators grade soybean seed, stink bug damage is only counted 1/4 percent compared to heat, mold or other grading factors. So stink bug damage carries 75% “less weight” than other forms of damage. This may be why we rarely receive deductions even when we high populations were in the field.
1. SB damage to developing seed. 2. Stink bug damage to seed that is filled out. Click to Enlarge
Stink bugs, weather, and disease probability:
Logically we have always assumed that a field of stink bug damaged pods may lead to greater incidence of disease and/or general seed rot if conditions were favorable for development and beans had to stay in the field for any prolonged period of time. We had a student that studied the incidence of fungi associated with soybeans as influenced by stink bug damage. The figure below shows fungal incidence from random soybeans that were collected from producer fields in the Delta region in 2010. Soybeans were shelled by hand and separated into three categories; stink bug damaged seed, seed that was damaged from other factors not including stink bugs, and seed that had no visible damage. Seed were then plated on a general microbiological growth medium and monitored for fungal development. Seed that were categorized as having stink bug damage did in fact have a significantly greater likelihood of fungi developing on the culture plates. It is not uncommon for tropical storms to develop this time of year and rain to set in on beans in the field and delay harvest beyond physiological maturity. While diseases such as Phomopsis seed decay can certainly be an issue in the absence of stink bugs, the likelihood of seed decay organisms leading to a loss of soybean seed quality may be greater if stink bugs are allowed to persist creating avenues (e.g., from wounding) for fungi to enter the seed.
Click to enlarge
Below is a decision aid we put together that addresses many of the questions we get everyday about late season stink bug applications. This will not fit every situation but can be used as a guideline for late season stink bug decisions.
Stink Bug Identification:
1, Green Stink Bug Adult, 2. Green Stink Bug Nymph, 3. Brown Stink Bug Adult, 4. Brown Stink Bug Nymph, 5. Southern Green Stink Bug Adult, 6. Southern Green Stink Bug Nymph, 7. Redshouldered Stink Bug Adult, 8. Redshouldered Stink Bug Nymph, 9. Redbanded Stink Bug Adult, 10. Redbanded “Spine” , 11. Redbanded Stink Bug Nymph, 12. Spined Soldier Bug, 13. Spined Soldier Bug Nymph
Redbanded Stink Bug Trial Data:
In 2009 Redbanded stink bugs were treated in numerous areas of the state but numbers crashed in 2010 and rebounded in 2013. This is the first year they have been an issue since then. Redbanded stinkbug are more aggressive feeders than our normal stink bug complex and re-infest fields much quicker after treatments. Because of this, the threshold is was reduced from 9/25 sweeps to 6/25 sweeps for this species. In fact, LA has even reduced their threshold further to 4/25 sweeps for Redbanded stink bugs.
Here are the results of some Redbanded Stink Bug trials from 2009 on insecticide performance. Click on any to enlarge.
Very informative and helpful. Pictures and descriptions were very clear and well done.