Mildew Risk Models
To add either Mildew models to a site, follow the below steps:
Find your site in the sites list and select the spanner icon
Add sensor, search "Calculations & Agronomic Derivations" - select use
Go to the drop down in Select input type
Choose the appropriate Mildew Model
Map the temperature input and unit of measure
Select Add Sensor To Site
Gubler-Thomas powdery mildew model - UC Davis
The Gubler-Thomas Powdery Mildew Risk Index, developed at UC Davis, provides a useful tool to make smart decisions regarding preventative fungicide sprays based on the weather and optimum temperatures for conidial reproduction. The model uses these temperature thresholds to calculate a daily (0–100) risk index which can be used to adjust intervals between sprays.
An index of 0–30 indicates low risk of disease. Chemical fungicides may be used at intervals of 21 days, or label max, and sulfur may be used at 14–21 day intervals.
An index of 40–60 indicates moderate risk of disease.Chemical fungicides may be still be used at intervals of 21 days, or label maximum, at this risk index, but sulfur,if used, should have a reduced interval rate of 10–17 days.
Above 60 indicates high risk which should results in a 14 day interval, or label minimum, for chemical fungicides, and 7 days for sulfur.
Risk calculation:
If ( 70°F (21.1°C) <= Temperature < 85°F (29.4°C) ) for more than 6 h then Risk += 20, else Risk -= 10
If maximum temperature >= 95°F (35°C) then Risk -= 10
If risk > 100 then risk = 100
If risk < 0 then risk = 0
References:
https://blog.pestprophet.com/how-to-use-powdery-mildew-risk-index-model-on-grapes/
https://www.apsnet.org/edcenter/apsnetfeatures/Pages/UCDavisRisk.aspx
Gubler-Thomas strawberry powdery mildew model
Risk calculation:
If maximum temperature >= 32°C then reduce risk by 10, else
If ( 15°C <= Temperature < 25°C ) and humidity > 0.0 then increase risk by 20, else reduce risk by 10
If risk > 100 then risk = 100
If risk < 0 then risk = 0
Reference:
http://info.metos.at/tiki-index.php?page=Powdery+Mildew+Risk+Model+for+Strawberries