The development of the 2020 Louisiana soybean crop continues to be ahead of the five-year average with 96% of the crop blooming and 86% setting pods, compared to the five-year average of 95% and 85%, respectively. A total of 11% of the crop is beginning to mature. For the previous two weeks, the condition of the 2020 Louisiana soybean crop was rated as 89% good – excellent; however, the USDA reports the crop condition dropped to 85% good – excellent as of July 26. During the previous week, I walked fields that were showing stress due to dry and hot conditions.
Figure 1. For the previous two weeks, the condition of the 2020 Louisiana soybean crop was rated as 89% good – excellent; however, the USDA reports the crop rating dropped to 85% good – excellent as of July 26.
Recently, I was looking at a soybean field planted to a MG 5 determinate variety in Rapides Parish and the producer asked about flowers and pods that had fallen from the plant (Figure 2). Due to the structure of a soybean flower, almost all the flowers produced will be fertilized. Mainly, this is due to the proximity of the pollen to the ovaries within a single flower. In normal years, even in good environmental conditions, soybean plants will lose over half of the fertilized flowers or pods. On each node, multiple flowers will be positioned on pedicels that are connected to a single rachis (Figure 3). Normally, the first three pods on a rachis have the best chance of survival (Figure 4). If the plant is under stressful conditions, abscission of the lower flowers or pods can occur. Examples of stressful conditions leading to an increase in flower or pod abscission are drought, high temperatures, defoliation, and shade. If abscission occurs to older flowers or pods, soybean plants can compensate by the increased chance of survival of the flowers or pods towards the top of the rachis if the environmental conditions improve. Unfortunately, if the pod survives, any seed within the pod can be terminated at any time. To maximize yield, it is important to maintain as many best management practices as possible throughout the growing and harvest season.
Figure 2. Soybean flowers and pods that have fallen to the ground (Photo by David Moseley).
Figure 3. Multiple soybean flowers, of a MG 5 determinate variety, positioned on pedicels that are connected to a single rachis (Photo by David Moseley).
Figure 4. The first four flowers of a MG 5 determinate variety on a soybean rachis are retained. The remaining flowers or pods, except for the last two, are no longer connected to the rachis due to flower or pod abscission (Photo by David Moseley).
The LSU AgCenter and the LSU College of Agriculture