Agronomy Talk

LATE-SEASON SOYBEAN GRAIN QUALITY

Agronomy Brief

Published on Friday, May 6, 2022

 

Insect Damage

Stink bugs cause yield damage by feeding directly on the pod throughout the R5 growth stage. Seed that is fed on during this time can shrivel up or even be aborted in the pod. Beyond the R6 growth stage, actual yield loss from stink bugs is very low to nonexistent. At this growth stage, most of the damage done by these pests is isolated to quality loss and creates pathways for secondary pathogens to take hold if harvest becomes delayed. Grain injured by stink bugs typically carries 75% ‘less weight’ than other forms of damage when grading is completed at the elevator. Data from Mississippi State University states that stink bug thresholds should be at least double at the R7 growth stage. However, on average, the data shows that it takes much more than two times the threshold stink bug numbers to cause quality deductions at this growth stage.

 

Phomopsis Seed Decay (Phomopsis spp.)

Phomopsis seed decay is characterized by a white fungal growth on the outside of the seed within the pod. Diaporthe longicola is the fungus that causes Phomopsis. Seed coats can also appear split, mummified, or shriveled with the white fungal growth present on the individual seed. Phomopsis overwinters in soybean residue, and disease is favored by wet, warm temperatures during soybean maturation. A timely harvest will help reduce the risk of seed decay and preserve seed quality.

 

Purple Seed Stain (Cercospora kikuchii)

Seeds infected with Cercospora kikuchii can appear symptomless or, like the name states, having a purple coloration of the seed stretching from the hilum. This purple discoloration can completely cover the seed or affect a small portion of the seed around the hilum. Hilum is the visible ‘scar’ marking on the soybean where it was once attached to a soybean pod. Hilum is also referred to as the ‘eye’ and can be clear, yellow, brown, or black. Crop value may be lowered by dockage at the elevator, but the presence of purple seed stain (PSS) does not reduce the yield. There is no homogeneous relationship between the occurrence of Cercospora Leaf Blight (CLB) and PSS. Warm and wet conditions, and after soybean flowering, are environments that can heighten the occurrence of PSS.

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Shane Carver
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Shane Carver

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