Dr. Bob Kemeriat, UGA Extension Specialist
Late-season disease recommendations for a peanut crop are often confusing. Reasons for this include A) digging/harvest dates are not “set in stone”, B) the incidence of one disease versus another affects choice of fungicides, C) disease can be cryptic, as in the case of underground white mold, D) there are a number of fungicide options that can be deployed, and E) approaching rains can make it necessary to quickly change management plans. While there may not be a single “best” recommendation, some solutions are better than others. These solutions have three things in common: a) timeliness, b) use of the right products (emphasis that there is often more than one “right” product), and c) use of the right products at the right rates. Late-season management decisions are more important now than they ever have been as much of Georgia’s peanut crop remains in the ground for nearly 150 days. Our historic “spray every 14 days for a total of 7 sprays” may not go the distance anymore.
Growers often request advice on adjusting digging dates based upon disease in the field. Generally, it is best to wait until harvest maturity is reached in order to assure maximum grade, rather than digging the peanuts early. For example, though tomato spotted wilt may be severe in a field, I generally recommend waiting until harvest maturity to dig the peanuts, unless other diseases, like white mold or significant leaf spot, are “piggy-backing” on top of the plants already affected by the tomato spotted wilt. However, where defoliation from leaf spot is severe, then it may be critical to dig earlier than planned in order to protect yield. Georgia-06G can withstand defoliation of 50-60% IF digging is NOT delayed past maturity. Any unexpected delays in digging will result in yield losses. Where white mold is severe, for example greater than 40-50% incidence, the grower should consider digging early. Significant defoliation from leaf spot diseases and severe outbreaks of white mold will increase digging losses by weakening peg-strength.
NOTE: A critical consideration for choice of fungicides late in the season is that pre-harvest intervals (PHI) vary among fungicides. For example, Alto and Elatus have a 30-day PHI, and EXCALIA and Convoy have 40-day PHI, compared to 14-day PHI for other fungicides such as Provost Silver and Fontelis. Growers must always check the label to make sure of the PHI for a product Also, some consider “harvest” to be when the peanuts are dug. I personally believe that “harvest” is when the peanuts are picked.
Below are some typical situations that peanut growers may find themselves in and suggestions for control:
Grower is 4 or more weeks away from harvest and currently has excellent disease control.
Suggestion – I recommend the grower apply at least one more fungicide for leaf spot control with an inexpensive white mold material mixed with it, for good measure. It is generally helpful to use a mix of a protectant leaf spot fungicide (like chlorothalonil) mixed a leaf spot fungicide with some curative activity (e.g., Alto, Domark, Topsin) for best protection.
Suggestion – Given the low costs of tebuconazole and azoxystrobin, the grower may consider applying a tank-mix of tebuconazole + chlorothalonil or azoxystrobin + chlorothalonil for added insurance of white mold and leaf spot. If a grower has Georgia-12Y, azoxystrobin is probably a better choice than tebuconazole because of threat from Rhizoctonia limb rot.
Also, specific sulfur products may be appropriate replacements for the chlorothalonil.
NOTE 1: If white mold is not an issue, then the grower may stick with a leaf spot spray only.
Note 2: If grower has planted Georgia-06G or Georgia-12Y and the plants are leaf spot-free at 4 weeks prior to the anticipated digging date, an additional fungicide application for leaf spot may not be needed if grower is willing to watch/scout the field for other disease, for example peanut rust, and put a fungicide out if harvest is unexpectedly delayed, as with the approach of a hurricane.
Grower is 4 or more weeks away from harvest and has disease problems in the field.
If the problem is with leaf spot – Grower should ensure that any fungicide applied has systemic/curative activity. If a grower wants to use chlorothalonil, then they would mix a product like thiophanate methyl (Topsin M) or cyproconazole (Alto), with the chlorothalonil. Others may consider applying Priaxor, if they have not already applied Priaxor twice earlier in the season. Provost Silver from Bayer Crop Science has become a “go to” product for helping to protect peanuts from leaf spot diseases late in the season. Provost Silver is NOT a “silver bullet” but it has performed very well. A tank-mix of Provysol + tebuconazole may also be appropriate.
If the problem is white mold – Grower should continue with fungicide applications for management of white mold. If they have completed their regular white mold program, then they should extend the program, perhaps with a Fontelis, Provost Silver, tebuconazole/chlorothalonil or azoxystrobin/chlorothalonil mix. If the grower is unhappy with the level of control from their fungicide program, then we can offer alternative fungicides to apply. Where white mold AND leaf spot are late-season problem, then adding a extra fungicide to the Fontelis for additional leaf spot control may be beneficial.
Note: Why don’t I mention Convoy or Umbra or Excalia or Elatus? Pre-harvest interval may not matter to growers, but it DOES matter to UGA Extension. Elatus has a 30-day PHI, the others have a 40-day PHI. Many growers want to reach for a product like Convoy late in the season, but it is important to consider the time until harvest.
If the problem is underground white mold – Underground white mold is difficult to control. Applying a white mold fungicide ahead of irrigation or rain, or applying at night, can help to increase management of this disease.
Grower is no more than 3 weeks away from projected harvest and does not currently have a disease issue. Good news! This grower should be good-to-go for the remainder of the season and no more fungicides are required. SEE NOTE BELOW ABOUT HURRICANES
Grower is 3 or fewer weeks away from harvest and has a problem with disease.
If leaf spot is a problem and 2-3 weeks away from harvest, a last leaf spot fungicide application may be beneficial. If leaf spot is too severe (more than 25% defoliation already occurs), then a last application will not help. Tank mixing chlorothalonil with a systemic fungicide, like thiophanate methyl, Domark, or other appropriate systemic fungicide, could be beneficial.
If white mold is a problem and harvest is 3 weeks away, then it is likely beneficial to apply a final white mold fungicide. If harvest is 2 weeks or less away, then it is unlikely that a fungicide will be of any benefit.
NOTE: If harvest is likely to be delayed by threat from a hurricane or tropical storm, then the grower may reconsider recommendations for end-of-season fungicide applications.
Finishing “strong” in the 4th quarter of the 2024 peanut season is important. Finishing “strong” means timely applications, ahead of rains or storms if necessary,using the right fungicide combination at the right rate. Your yield depends on it.