Update from the Field: Popping Pods
Posted by Dave Dyson, Agronomist on September 11, 2018
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We are in the home stretch with harvest just around the corner! The big question on every producer’s mind is, “How will my soybean plants yield?” In general, it can be fickle to predict soybean yield because there are many variables to consider.
The soybean plant is very adaptable. If the population is reduced, the plant will bush out to take advantage of the extra space in the field. The pod size can vary from two bean pods all the way up to five bean pods. This plays havoc on calculations involving number of seeds per plant per acre. The biggest variable for estimating soybean yield is the size of the bean itself. In the R6 stage, the soybean seed will completely fill the pod. Once this occurs the bean will start drying down and shrinking. The speed at which this happens ultimately determines the size of the seed.
The transition between R6 (a seed pod at full seed) to R7 (plant maturation) usually happens in August. This is why the old adage “August rain makes beans” rings very true. The more rain we have between R6 and R7, the slower the dry down process and the heavier the soybean seeds end up. The best rule of thumb that I have observed in my 25 years of trying to predict soybean yields is to multiply the amount of rain (in inches) you receive in August by 20 to equal an estimate of the bu/ac yield. This year, there are parts of The Andersons’ territory that have received more than nine inches of rain during August. This is not to say those areas are looking at 180 bu/ac yield in soybeans. Common sense overrides areas that receive an abnormal amount of rain in August.
Just because the soybeans have entered the R7 stage does not mean they are out of the woods yet. In the last week, I have seen an increase in insects feeding on soybean pods (figure 1 and 2). The three main insects that need to be on crop scouting radars are green stink bugs (figure 3), bean leaf beetles, and grasshoppers. These three insects not only do damage to the soybean plants and pods, but to the soybean seed, too. This directly equates to loss of yield! The economic thresholds for treatment for beetles and grasshoppers are that when approximately 5% or more of the marketable pods are damaged, and there are 10 or more beetles per foot of row or the grasshoppers are actively feeding, the producer needs to take action to protect his/her yield.
Figure 1: This picture shows pod feeding on a soybean plant. This picture was take outside of Wawpecong, Indiana, 2018.
Figure 2: This picture from Purdue University shows grasshopper feeding through the pod and into the soybean seed.
Figure 3: Most people know the stink bug as a shield shaped green insect, but Larry Byrne caught green stink bug nymphs hatching from eggs. This picture was taken around Oakley, Michigan, 2018.
In conclusion, continue scouting soybean fields. There can be fixable problems looming in the field. Insect pod feeding may not look like much damage, but as the pods dry down and shrink, the areas where feeding has occurred will be weak. Weakened pods may burst open, allowing soybean seeds to “pop” out of the pods. If the seed shatters to the ground, the yield reduction is 100% for that pod. Insecticide labels may help you decide if a pre-harvest application is warranted. The pre-harvest interval (PHI) for an application of products labeled to control bean leaf beetles and grasshoppers is typically 14 days or more. If you have any questions on your soybeans, don’t hesitate to contact me or someone on The Andersons’ agronomy team.
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Dave Dyson is a regional agronomist for The Andersons’ Farm Centers which are located throughout Ohio, Michigan, and Indiana. He is an Indiana native and grew up on a dairy farm in Miami County. A graduate of Purdue University with a degree in Crop & Soil Science, Dave has a deep knowledge of various agronomic topics and is committed to helping growers improve their crops. If you have any questions, Dave can be reached at david_dyson@andersonsinc.com.
