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Disease Management of Peanuts at 60 days and Beyond – Kemerait

Disease Management at 60 days and Beyond
By Bob Kemerait
Many of our peanut fields have reached, or are now beyond, 60 days after planting. During this
time of the season it is critical to protect a peanut crop from white mold and from leaf spot
diseases. Currently, rainfall has been abundant in many of our counties in Georgia. The rainfall
is beneficial to the growth and development of the peanut crop, but also creates near-perfect
condition for infection by leaf-spot pathogens and for the spread of fungal diseases. Moisture,
humidity, and warmer, hotter temperatures will flair white mold outbreaks. It has not been
particularly hot thus far in the season; however white mold is certainly active to one degree or
another in many fields. And hotter temperatures are what the month of August is all about.
Now is the time to stay the course, and sometimes becoming more aggressive, when deploying
a fungicide program that is effective against white mold and leaf spot diseases. Growers should
recognize that rain events are likely to flair disease and increase risk to losses unless adequate
control measures are implemented.
Many of the questions coming from Extension agents and consultants are in reference to
recommendations for “best” fungicide programs NOW for growers who are either late on the
current fungicide application or who have not sprayed the field at all, despite being 60 days (or
more) after planting. While there is not one single “best” program in these situations, there
are recommendations that UGA Extension can make to help the growers. It MUST be noted
that there is no “silver bullet” when a farmer gets behind in a fungicide program. The best
we can do is to suggest ways to minimize further development of disease and to reduce
losses.
Situation 1. Peanut crop is approaching 60 days after planting. Crop was sprayed for leaf spot
at 30 days after planting with chlorothalonil, but grower has been unable to get back in the field
since. What should we recommend to the grower for the next spray (hopefully around 60 day)?
Background: Given that field history, crop rotation, and variety all can have significant impact
on the amount of disease in a field, being 30 days since the last fungicide application may mean
different things to different growers, but it is not a good situation for anyone. Growers in this
situation can expect that some leaf spot and some white mold are active in the field. There will
likely be more leaf spot and white mold in some fields than in others, but all are threatened.
Recommended steps:

  1. Apply the next fungicide as quickly as possible.
  2. Applications made using tractor-mounted spray booms are likely to be more effective at
    this point than will be aerial applications (greater penetration of the canopy), but the
    important thing is to get a fungicide on the crop HOWEVER you can.
  3. Growers can expect that there is some leaf spot and white mold in their fields now,
    though hopefully no too much.
  4. Prior to 60 days after planting, the primary focus is on leaf spot; growers who can get in
    and spray at 60 days after planting hopefully have not lost too much on their white mold
    program.
  5. The decision to use Miravis should be made very carefully. Miravis is an excellent leaf
    spot material BUT does not perform nearly as well if leaf spot is active in a field prior to
    application. If there is the likelihood that leaf spot is already active, it is our
    understanding that Syngenta does not recommend use of Miravis in that specific
    situation.
  6. Leaf spot materials to be considered in this situation should be both curative and have
    protective activity. Examples would include chlorothalonil (1 pt) + Alto (5.5 fl oz),
    chlorothalonil (1 pt) + Domark (3.5 fl oz), Mazinga (2 pt/A) or chlorothalonil (1 pt) +
    Provysol ( 3 fl oz) tank-mixed with Excalia or Convoy. Absolute Max tank-mixed with
    chlorothalonil or use of Aproach Prima may also be effective. If a grower is using Elatus
    (especially at the lower 7.3 fl oz rate), I advise mixing additional leaf spot fungicide with
    it, likely Alto or Alto-Bravo. For use of Umbra, I would add chlorothalonil or other leaf
    spot material to reinforce the flutriafol component of Umbra. Use of Fontelis does not
    require addition of a leaf spot fungicide.
  7. Lucento and Priaxor have strong leaf spot activity and also some activity against white
    mold. Given the scenario outlined above, I believe if these products are to be used, it is
    best to follow an application of a more robust white mold material now at 60 days after
    planting.
  8. Perhaps the best “all round” leaf spot/white mold fungicide for this first scenario would
    be Provost Silver. As a “stand alone” product, Provost Silver offers a good combination
    of curative leaf spot activity and good white mold control.
  9. Propulse: for growers fighting nematodes and planning to make a “pegging-time”
    application of Propulse, now would be a very good time to do it. Propulse is effective
    not only against nematodes, but also quite good against leaf spot and white mold as
    well.
    Situation 2. Peanut crop is approaching 60 days after planting. Crop has not been sprayed at
    all and grower is looking for recommendations for the first, much delayed, fungicide
    application. What should we recommend to the grower for the first spray (hopefully around 60
    day). As in the above situation, even more here, there is no single best answer and there is no
    silver bullet.
    Background: Given that field history, crop rotation, and variety all can have significant impact
    on the amount of disease in a field, but it is not a good situation for anyone. Growers in this
    situation can expect that leaf spot and some white mold are active in the field. While the
    grower is still basically “on time” for white mold, he is late long overdue for a leaf spot
    application and threat to yield loss already exists. Fungicide application should be immediate
    and aggressive in choice of fungicide.
    Recommended steps:
  10. Apply the next fungicide program as quickly as possible.
  11. Applications made using tractor-mounted spray booms are likely to be more effective at
    this point than will be aerial applications (greater penetration of the canopy), but the
    important thing is to get a fungicide on the crop.
  12. Growers can expect that leaf spot is active in their field now, white mold could be as
    well.
  13. Prior to 60 days after planting, the primary focus is on leaf spot; growers who can get in
    and spray at 60 days after planting really have not lost too much on their white mold
    program.
  14. In this situation where no fungicide has been applied prior to 60 days after planting,
    growers are advised NOT to use Miraivs until it is clear that leaf spot has been
    controlled. They are also advised NOT to use Provysol with Convoy, Umbra, or EXCALIA
    UNLESS the tank mix also includes chlorothalonil.
  15. Leaf spot materials to be considered in this situation MUST be both curative and have
    protective activity. Examples would include chlorothalonil (1 pt) + Alto (5.5 fl oz),
    chlorothalonil (1 pt) + Domark (3.5 fl oz), Mazinga (2 pt/A), or chlorothalonil (1 pt) +
    Provysol ( 3 fl oz) in addition to Excalia or Convoy. If a grower is using Elatus he should
    use the higher rate of 9.5 fl oz/A. Also, I advise mixing additional leaf spot fungicide
    with the Elatus, likely Alto or Alto-Bravo. For use of Umbra, the grower must add
    chlorothalonil or other leaf spot material (preferable NOT another triazole fungicide
    alone) to reinforce the flutriafol component of Umbra. Use of Fontelis here does not
    require addition of a leaf spot fungicide. Fontelis will be good for white mold and does
    have good leaf spot activity, but more leaf spot activity may be needed.
  16. Lucento and Priaxor have strong leaf spot activity and also fair white mold activity.
    Given the scenario outlined above (60 days and no fungicide yet), I believe use of these
    products is best after following an application of a more robust white mold/leaf spot
    combination now at 60 days after planting.
  17. The best “all round” leaf spot/white mold fungicide for this scenario would be Provost
    Silver. As a “stand alone” product, Provost Silver seems to offer a good combination of
    curative leaf spot activity and good white mold control.
  18. Propulse: for growers fighting nematodes and planning to make a “pegging-time”
    application of Propulse, now would be a very good time to do it. Propulse is effective
    not only against nematodes, but also quite good against leaf spot and white mold as
    well.
    Again, delays in fungicide applications now could easily create disease management problems
    throughout the rest of the season. There are no “silver bullets”; however it is hoped that this
    information will be of benefit.
    The KEYS here are: 1) get a good fungicide or tank-mix of fungicides on as quickly as possible.
    2) Get as good coverages as you can. 3) Recognize disease is likely already active in the field, so
    be aggressive in your choice of fungicide and ensure there is both curative and protective
    activity.
    Subsequent questions:
  19. “Bob, you discouraged use of Miravis at 60 days after planting because you view this
    fungicide best used PRIOR to the development of leaf spot in a field. I was planning an
    Elatus+Miravis application at 60 days so now what? ANSWER: Excellent question.
    Miravis is an excellent leaf spot material best applied before disease appears in the
    field. Given early season delays in fungicide applications and the possibility for leaf spot
    to develop, even if undetected, I think it best not to use Miravis in the 60 day
    application. Use an aggressive and curative leafspot spray at 60 days, and if good
    scouting shows the disease is in check, begin the Elatus/Miravis program no more than
    14 days later. If an aggressive program is used (as noted in earlier recommendations)
    and leaf spot diseases are effectively managed, then it is certainly possible to use
    Miravis later in the season coupled with Elatus. Bottom line: Miravis + Elatus could be
    an outstanding application, IF leaf spot is “shut down” before that application.
  20. “Bob, you didn’t mention sulfur and I had planned to mix it with my Umbra. What is
    your recommendation on that?” ANSWER: Specific formulations of sulfur at 5 lb/A
    have been very effective in improving leaf spot control when tank-mixed with products
    like Umbra, Excalia, Abound, and Headline. Specific sulfur formulations offer the grower
    to better manage leaf spot diseases. Given Scenarios 1 and 2, I am hesitant to use sulfur
    ALONE when mixed with Umbra (or other products) at 60 days after planting, as
    CURATIVE activity is essential and sulfur is not curative. However, including sulfur in a
    mix with curative fungicides at 60 days after planting would be ok. Mixing sulfur with
    appropriate products at later dates would be appropriate, especially if leaf spot has
    been effectively managed bu earlier aggressive curative applications.