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Row Crop Disease Update – Kemerait

2021 Row Crop Disease Update 19 July

Greetings:

Peanut:  Many of our peanut fields have reached, or are rapidly approaching, 60 days after planting.  During this time of the season it is important to protect a peanut crop from white mold and from leaf spot diseases.  Currently, rainfall has been abundant in many of our counties.  The rainfall is beneficial to the growth and developments of the peanut crop, but also creates near-perfect condition for infection by leaf-spot pathogens and for the spread of the diseases.  Moisture, humidity, and warmer temperatures 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 other in many fields.

Now is the time to stay the course 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 agents 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 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 try 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:

  1. Apply the next fungicide program 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.
  3. Growers can expect that leaf spot is active in their field now, white mold could be as well.
  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 really have not lost too much on their white mold program.
  5. In this situation where no fungicide has been applied prior to 60 days after planting, growers are advised NOT to use Miraivs.  They are also advised NOT to use Provysol with Convoy, Umbra, or EXCALIA UNLESS the tank mix also includes chlorothalonil..
  6. 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.
  7. 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.
  8. 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. 
  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.

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.