Following is some of the latest information from Dr. Bob Kemerait, UGA Extension Plant Pathologist, regarding peanut seeds and fungicide treatments for the 2020 season.
We have received many questions in recent days pertaining to the quality issues facing our peanut seed supply in 2020 and relative performance of seed treatments Dynasty PD and Rancona. Below is the information that you need to know now; as more information is developed we will pass it to you quickly. As you know, Rancona and Dynasty PD both contain several fungicides; however they do not contain the same fungicides. This is noteworthy in 2020 when Aspergillus flavus seems to be especially important.
- We have multiple years of data showing that Dynasty and Rancona are both very good seed treatments for peanuts.
- There has been a tendency for Rancona being stronger on Aspergillus than Dynasty. This was with Aspergillus niger (peanut crown rot) which has been our primary seed pathogen in recent years.
- UGA grad student Brian Jordan’s work showing that the mutation for high level resistance to QoI’s can occur in A. niger supports the clearly reduced efficacy of azoxystrobin (Abound) in furrow, and also on seed (although fludioxinil in Dynasty on seed would help moderate that effect).
- Those differences in control may or may not have been enough to make a difference in yield, although the pattern was there for that in some trials
The biggest issue we face with seed quality in 2020 is that this is a different scenario with Aspergillus flavus (a related, but different, pathogen).
Here is what we know now:
- Last season was extremely hot and dry. There is a much higher frequency of Aspergillus flavus in our peanut seed from last year than we usually see. A. flavus produces aflatoxin, but it can also be an important seedling pathogen.
- Culturing the pathogens from seed shows a huge difference in the efficacy of Dynasty and Rancona on this seed borne A. flavus, at least in some seed lots which were identified as being of lower germination.
- Rancona has considerably less incidence of A. flavus growth in these seed lots. The difference in seed treatments for inhibition of A. flavus is believed to help explain some of the differences in germination observed, with Rancona producing significantly higher germinations. Again, this is on some seed lots and not others. Preliminary evidence is that the later-harvested seeds, which were exposed to the most heat and drought, are the most likely to have high Aspergillus levels.
What does all of this mean? Are the differences observed this year due to A. flavus being resistant to QoI fungicides as sometimes occurs in A. niger? That issue is not known, but is being evaluated as quickly as possible. There is much we still need to learn, but for now we can say the following:
- Rancona and Dynasty have both been very good seed treatments. This year, with the emergence of A. flavus, Rancona will probably be more effective treatment on those lots with elevated A. flavus populations. (Elevated A. flavus populations seem to be linked to seed lots with lower germination).
- High quality seed with similar germinations on the Rancona and Dynasty will probably be fine with either product as the seed treatment.
- Either seed treatment will likely benefit from the addition of an in furrow spray. Proline and Velum Total have been the most consistent in recent years. Abound should not be paired with Dynasty, as it duplicates the chemistry most prone to resistance. Abound would add an additional chemical class where Rancona is being used, and may help with other seed pathogens other than QoI-resistant Aspergillus.
- If seed that is to be planted has (or is suspected to have lower germination rates), and the seed has been treated with Dynasty PD, then there is a greater need to consider use of additional in-furrow applications of Proline or Velum Total to protect stands.
NOTE: We cannot become too narrowly focused as many different pathogens can affect peanut seed!
Research (including grow out tests in the greenhouse) is seeking to answer more of these questions prior to planting season, and we will keep you updated as those results come in. It should be noted that these issues are being seen in commercial seed that have been produced, handled and stored with great care. Farmer saved seed are sometimes exposed to less than ideal conditions, and may have even more issues this season.