Green stem disorder is likely a term that you have heard, but what does it really mean? By definition, green stem disorder is a condition in soybean plants where there is a delay in senescence (aging/ripening) of the plant’s stem, while the pods ripen and seeds mature normally. The cause of this abnormal effect is unknown, but the consequences to growers can be substantial. This disorder is a nuisance to producers because it complicates harvest by significantly increases the difficulty of cutting through the green stems. This slows down the harvest and also increases fuel and harvesting equipment maintenance costs.
Some may confuse this delayed senescence of the stem with the effects that many see from using a strobilurin fungicide; however, this is not the case. Strobilurin fungicides also delay plant senescence but this happens to the whole plant. The result of this delay is that the soybean plant has more time to assimilate the sun's energy into pod and seed development. This might result in harvesting a few days later than you would without a fungicide, but the plants are uniformly mature at harvest and the delay usually is worth the wait. Strobilurin fungicides have several positive effects on physiological processes within plants that allow them to stay green longer and therefore utilize the sun's energy through photosynthesis to produce larger beans, fuller pods and greater yields. Although green stem disorder may not impact yield, this malady may delay harvest and increase costs.
The photos below display the difference between green stem disorder and the greening effect of a strobilurin fungicide.
Green Stem Effect in Soybeans Strobilurin Greening Effect in Soybeans
In the first photo, the soybean plant that is displayed suffers from green stem disorder. Notice that the stem in this plant has a fluorescent green color, while the pods are brown and ready to be harvested. In the second photo, this fungicide-treated plant shows the greening effect that occurs with strobilurin fungicides. The overall plant appears green and healthier. By delaying the natural aging process in soybeans, strobilurin fungicides allow the plant to produce fuller pods and larger beans.