Model Description

The Oklahoma Peanut Leafspot Model is a tool that has been developed to aid growers in proper timing of fungicide application for early leafspot, a foliar disease of peanuts. Using the Oklahoma Mesonet, the state's automated weather station network, the model calculates daily "infection hours" for each Mesonet site. An infection hour is defined as one hour with relative humidity greater than or equal to 90% and temperature between 60.5 and 86F. Beginning 30 days after planting or ten days since the last spray (whichever is later), the model accumulates infection hours and recommends a fungicide application when 36 such hours are met or exceeded.

Growers are encouraged to use the Site-Specific Interactive Model, which gives a spray or no spray recommendation. After the user clicks on a nearby Mesonet site, the model asks for the peanut plant date as well as the date of the last fungicide application for early leafspot (if one has occurred). This information is then entered and the model comes back with the recommendation (including the number of infection hours that have occurred since 30 days after planting or since 10 days after the last fungicide application, whichever is later). If a number of peanut fields are involved, each with various plant dates or fungicide application dates, the model should be run separately for each field. The grower can try various nearby Mesonet sites as well, as a conservative approach.

Rules for the early leafspot advisory are as follows:

1.It is recommended that growers wait until at least 30 days after planting before even considering spraying their peanuts for early leafspot. If a grower wishes to apply a first fungicide at 35 days after planting and then follow the advisory, that is acceptable; otherwise, the Model will not recommend a first spray until 36 infection hours have accumulated since 30 days after planting.

2.Once the peanuts are 30 days old, the Oklahoma Peanut Leafspot Model should be consulted on a regular, if not daily, basis. In addition, after a fungicide application, the model should be consulted regularly beginning 10 days after the spray date.

3.If a given field cannot be sprayed within 3 days of a model spray recommendation, then spray on a 14-day schedule.

4.Use only highly effective fungicides (Bravo, Folicur, or Tilt/Bravo). If another fungicide is used, spray on a 14-day schedule.

5.If levels of early leafspot exceed 25% infection (leaflets with spots or defoliated), revert to a 14-day schedule.

6.If late leafspot, web blotch, or pepper spot are identified, revert to a 14-day schedule.

7.Be alert to weather forecasts. Spray if rain is in the forecast and a field is close to reaching 36 infection hours.

8.Maintain the spray program until 14 days before the anticipated harvest.

Besides the Site-Specific Interactive Model section, the Oklahoma Peanut Leafspot Model web page features other sections. One can go to the Current Model Output section to see the latest model output for every Mesonet site. This includes the number of infection hours that occurred during the most recent 24-hour period (ending on 10 a.m. CDT of the date listed), the accumulation of infection hours since May 1, as well as the max/min temperature, max/min relative humidity, and rainfall during the 24-hour period. In addition, a "last effective spray date" (LSPDATE) is calculated.

This "last effective spray date" is an alternative method to use, but it is somewhat confusing and growers who have access to this web site are encouraged to use the much simpler interactive model, which makes the recommendation automatically. Using the LSPDATE method, a grower should apply a spray when (1) the LSPDATE first exceeds 20 days after planting, and, from then on, (2) once LSPDATE exceeds the date of the last fungicide application.

If one is interested in the time history of a specific Mesonet site, one can go to the Seasonal Model Output section to see daily model output since May 1 for that specific site. The Current Output section contains a color-coded map of Oklahoma showing accumulated infection hours since May 1, as well as images of peanut foliar diseases. Finally, Related Links contain links to publications about peanut diseases and other topics, as well as links to some web sites of possible interest.