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July and August are Critical Months for Disease Management in the Peanut Fields
Bob Kemerait
The 2020 season has been a difficult one for the peanut farmers even before they put the first seed in the ground. To a level I have not seen before, growers had to make early decisions about seed treatments and in-furrow fungicides at the same time they were trying to get the quality seed that they needed. Even after the fields were planted, many growers struggled with questions about replanting when their stands were less than they had hoped. For many peanut growers, the start of the 2020 season was filled with frustration and concern.

Now that we are in July and August is not too far away, most, but not all, of the concerns about Aspergillus crown rot are in the past. Aspergillus crown rot is primarily an early-season disease, though under drought-stressed conditions it may appear later as well. The lasting legacy of the problems with seed quality, reduced plant stands, and Aspergillus crown rot will be issues with Tomato spotted wilt this year. Already I am seeing spotted wilt in a number of fields, but there is nothing that can be done now.
Apart from efforts to fight tomato spotted wilt, nematodes, and seedling diseases earlier in the season, one of the most important periods for aggressive management of diseases occurs in July and in August.
Mistakes made now result in “getting behind in your disease control program”. This is a little like getting a lap down in a NASCAR race. No matter how hard a grower tries, and no matter how good his or her
fungicide program from this point forward is, it may be impossible to catch back up with the race leaders.
Why is disease management so critical in July and August? By this time of the season, three things have happened. In most fields and for most growers, the peanut plants have (or are closed to) lapping the row middles and have entered reproductive growth (the plants are blooming and setting pods). The growth of the peanut canopy increased leaf-wetness periods and
also traps humidity. The limbs and vines along the soil surface are in a perfect environment for attack by soilborne pathogens that cause white mold and Rhizoctonia limb rot. To make matters even more challenging, the growth of the plants not only increase the risk for leaf spot, white mold, and limb rot, but the dense foliage makes it difficult to get the fungicide to the target- the interior foliage and the crown of the plant. Secondly, by July, the amount of inoculum (often times fungal spores) is increasing in the field, which means that the plants are under increasing attack. Lastly, because of rains during July and August, it is easy for growers to be delayed in fungicide applications, which increases the opportunity for diseases to “get ahead of them”. What should growers be looking for? In addition to everything else that our growers must do in July and August, I STRONLY encourage them to put boot-prints in their fields. Whether the boots belong to them or to hired scouts does not matter to me. What is important is that someone if watching the crop for development of leaf spot, white mold, or any other disease, weed, or insect problem.

Diseases are BEST managed preventatively meaning that growers should NOT wait until white mold or leaf spot is present to begin treating with fungicides. However, careful scouting alerts the growers to problems in the field where the current fungicide program is not as effective as it could/needs to be. Deficiencies in a fungicide program do not necessarily mean that the fungicides themselves are not “working”. Disease problems in a field are often the results of late starts in a program, delays in making an application, or failure to get sufficient coverage on the plants. No matter what the cause of the problem, growers should quickly try to find a remedy for the issue.

What should growers be doing? Regardless of the fungicide program that growers are using, it is absolutely essential that they be on time (as much as they can) with their fungicide applications. When growers are delayed in a timely fungicide application, the diseases have the chance to not only get established, but to flourish as well. There are three things the growers must do for effective disease control.

1) The MUST be timely in their
fungicide applications.

2) They MUST apply fungicides appropriate for control of LEAF SPOT, WHITE MOLD, and RHIZOCTONIA LIMB ROT.

3) They MUST insure adequate coverage, which may mean irrigating within 8-12 hours after application, applying ahead of a rain event, or even spraying the fungicides at night when the leaves are folded. Successful fungicide programs incorporate all three of these considerations.

What if disease problems occur?
Problems with disease management occur frequently in peanut fields during July and August. These problems are almost inevitable, and, again, are typically less the result of fungicide choice and more often the result of application problem. However, I recommend the following steps to growers in these situations.

  1. Careful scouting allows a grower to address the problem quickly and effectively. Finding early stages of leaf spot or white mold while scouting is much better than seeing is as you drive by the field at 50 mph.
  2. Once the disease is identified in the field, take a deep breath and carefully decide if there is anything wrong with your program. Some disease in a field in inevitable, and not reason to panic. A little leaf spot or white mold simply is a reminder to keep on a good schedule with a good fungicide program.
  3. Where there is clearly and emerging problem with a disease or diseases in a field, growers should consider making another fungicide application more quickly than had been planned. For example, if the next application is scheduled for 10 days from now, the grower may make the application in 7 days.
  4. Growers should insure excellent coverage. Again, this could come from timing or irrigation, rainfall, spraying at night, increased spray volume, or increased pressure.
  5. Growers should consider if switching to another fungicide, for example one with greater curative activity or greater efficacy (often at a greater price) is warranted.
    Bottom Line
    Disease management is critical for all peanut growers at all times during the season. However, attention to effective management programs during July and August is absolutely essential. Falling behind could easily result in loss of disease control, loss of yield, and loss of profit. Make sure you stay on the lead lap.
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