Battle for the Belt: Season 3, Episode 28 - Green Stem in Soybean

In Episode 28, we join Taylor Dill, PhD student, in the field at the Western Agriculture Research Station to discuss green stem in soybean: https://www.youtube.com/watch?v=46mOZFuRGZs

As soybean harvest ramps up throughout Ohio, there are some reports of green stem (Figure 1), including our Battle for the Belt plots at the Northwest and Western Agriculture Research Stations. Green stem is a disorder where the stems stay green and at times hold their leaves, while the pods have achieved their mature brown color (Figure 2).

Crop senescence and remobilization is the movement of nutrients from the leaves and stems to the pod and seeds; this is a source-sink relationship. If the “sinks” (pods and seeds) are aborted in response to crop stressors, the nutrients are not remobilized from the “source” (stems and leaves). When this happens, nutrients generally linger in the stem, causing them to stay green longer than normal. Plants with this condition can be individual plants, field edges, or almost an entire field.

Many stressors are associated with green stem, including:

Environmental stress can cause pod and seed abortion between R3-R6 stages, reducing sinks. Severity of green stem is dependent upon the stage that the stress occurred and can become more complex when considering contrasting planting dates.

Additionally, disease and insects can be a factor influencing green stem. Diseases can also decrease pod and seeds, decreasing sink strength. Diseases associated with green stem are bean pod mottle virus, tobacco ringspot virus, and phytoplasmas. Insects like stink bugs directly feed on pods and seeds and are most found in field edges. Bean leaf beetles also transmit bean pod mottle virus, so this insect has potential to influence green stem. Although disease and insects can influence green stem occurrence, we have not specifically identified any of these as factors affecting the green stem issue in our trials this season.

Some varieties show green stem more than others, so there can be a genetic predisposition with certain varieties producing underdeveloped pods. These plants look like male sterile plants that cannot make a viable seed and is often only seen in random individual plants in a field.

Lastly, fungicides can too be associated with green stem. However, this relationship is not well understood. Certain modes of action can have a “stay green” effect on soybean that can delay senescence and can be confused or contribute to green stem.

Management practices can reduce the chance of green stem, by mitigating abiotic and biotic stressors. Generally, green stem does not limit soybean yield. The main issue caused by green stem is harvest inefficiency, decreasing speed of the combine, plugging ups, and dockage of grain with lower quality.

A hard freeze can help resolve green stem, but delaying harvest until a hard freeze occurs may result in decreased yield and quality depending on the dry down of the field and the timeframe to the projected hard freeze date. A desiccant is usually not effective by the time that green stem is observed.

For more information on green stem, see the following science for Science for Success article: https://resources.ipmcenters.org/resource.cfm?rid=45225&vid=30376  

Updates from the field

Soybean harvest is almost finished at all three locations for the first planting dates; the fifth planting date is currently at R6 (full seed).  Nearly all planting dates of corn have reached physiological maturity (Figure 3), mainly leaving the fifth planting date at R5 (dent). Corn harvest has not yet started in our trials. A summary of weather conditions, planting dates, and crop stages can be found in Table 1.

Table 1. Precipitation, soil temperature, average air temperature, and cumulative GDDs at the Western Agricultural Research Station, the Northwest Agricultural Research Station, and Wooster Campus. Weather data retrieved from: https://weather.cfaes.osu.edu/. 

Keep following the ‘Battle for the Belt’ this growing season to learn more and get further updates! You can find the full video playlist of Battle for the Belt on the Ohio State Agronomy YouTube channel.