When it comes time to dig peanuts at the end of the growing season, many things influence how many pods make it into the basket. Research by Dan Anco and collaborators has documented two things which can decrease yield, over maturity and disease. Though slightly different, both have the potential to weaken pegs and increase pod loss, and both can be influenced by late season rains and delayed field access.
In the past, Virginia type peanuts have characteristically exhibited more of a tendency for pod loss due to over maturity than runner varieties. The same appears to be the case when looking at losses due to late or early leaf spot diseases. While late and early leaf spot have some differences, they both cause lesions and can defoliate canopies.
To reevaluate the role of leaf spot diseases and yield loss, researchers at the University of Florida teamed up with scientists across the southeast and in the Virginia-Carolina regions to pool together data and conditions from many years to look at two common questions:
- How much loss occurs with different amounts of leaf spot infection?,
- Is there a disease threshold where we might consider digging a field early?
Each situation can be somewhat unique, but based on their research, the team was able to develop some rough rules of thumb. Mature runner type losses became significant after approximately 30% of the canopy was defoliated due to disease, whereas mature Virginia type losses became significant when 25% or more of the canopy was shed.
For the second question, if a field is not yet at optimal maturity, it appears that when Virginia types pass 40% defoliation, they generally tend to increase losses (due to defoliation) faster than maturity is improving or yield is increasing in an otherwise healthy field. While it doesn’t look pretty, runner types appear to be able to sustain up to 50% defoliation while waiting on optimal maturity before losses increase more than the yield gains from additional maturity.
In other words, if the crop is not mature there is a critical threshold (40% for Virginia types and 50% for runner types) where yield losses due to defoliation will outweigh any further improvement in maturity.
As a reminder, if you are thinking about making a fungicide application to prevent end of season defoliation, and to help maintain the integrity of stems and pegs, be sure to check the preharvest interval (PHI) on the label of any fungicide you are considering to apply. Do not apply the fungicide if you are not able to wait until after the PHI has passed to harvest.
Digger operation and setup is important during every harvest, but is particularly important if field conditions include sizeable leaf spot defoliation or over maturity. In another set of studies, we have seen above ground digging losses to be significantly impacted by conveyor speed. To assist with digger conveyor speed setup, a calculator is available at the link below.