With the cool and drizzly weather, not too many people have bee looking at late maturing soybean. But it appears there are not any serious, widespread insect problems. There have been some reports of stink bug and soybean looper infestations, albeit mostly at sub-threshold levels. Having said that, the exception proves the rule. It remains very important to scout fields until they reach full seed (R6) plus another 7-10 days. Below are a few reminders about deciding when insecticide treatment is needed.
- Beginning at R6 – Double the threshold for green and brown stink bugs to 18 bugs per 25 sweeps, and after 7-10 days, treatment is no longer recommended.
- Do NOT double the threshold for redbanded stink bugs. It is recommended to make treatment for this pest using a threshold of 4 bugs per 25 sweep until at least R7. I expect some fields in the southern tier counties of Tennessee may encounter problems with redbanded stink bugs. Please refer to previous articles about this pest at http://news.utcrops.com/2017/09/soybean-insect-update-and-identifying-redbanded-stink-bugs/ and http://news.utcrops.com/2017/08/finishing-cotton-insects-but-not-soybean/.
- Increase the threshold for defoliation from 20-25% to 30-35% once a field reaches R6. After an additional 7-10 days, treatment for defoliating insects is not recommended. By this time, the field will begin naturally dropping leaves.
Use the guidelines below to help identify the late growth stages in soybean. These work for both determinate and indeterminate varieties.
- R6 – The “green bean” stage. Seed growth is rapid, and there are some full seed pods present in the top 4 nodes of the plant. Leaves on the lowest nodes may start yellowing, but the field is still green.
- R7 – Defined by the presence of 1 normal pod on the main stem that is mature in color (brown or tan). Green leaves are rapidly disappearing, and most seeds and pods appear yellow. Seeds are full-sized and at physiological maturity.
- R8 (full maturity) – 95% of the pods are mature in color. From this stage, it takes only 5 to 20 days of good drying weather to get soybeans below 15% moisture, ideal for harvest. Growers should harvest soon to avoid losses.